feat: explosions, particle system, electricity, structural integrity

Explosions:
- trigger_explosion(x, y, radius, damage) in Game
- Destroys non-static solids, ignites empty cells, pressure spike
- Knockback to entities (velocity away from center + upward pop)
- Particle burst on explosion (fire + smoke + debris)

Particle system:
- ParticleManager in src/physics/particle.rs (capacity 2000)
- CPU-side: position, velocity, life, color, gravity, size
- spawn_burst() for radial bursts, individual spawn() for ambient
- Rendered as third draw call in graphics.rs (is_ui: 2 in shader)
- ParticleInstance = ColorInstance compatible (12 bytes)
- upload_particles() via GpuRenderer trait
- Ambient: fire sparks, lava bubbles — scanned around player

Electricity:
- chunk.electricity: Vec<u8> (4KB/chunk) — current strength 0-255
- Material.conductive + conductivity fields (water = conductive)
- electricity_step() in CA: propagates current through conductive
  neighbors, decays over time, skips non-conductive cells
- cells_swap swaps electricity, serialization saves/loads it

Structural integrity:
- Material.structural: bool (stone, wood = true)
- structural_step() in CA (every 30 ticks, infinite mode only):
  checks if structural cells have support (below, below-left, below-right)
  converts unsupported to Sand (falls)
- Only active in infinite mode to avoid breaking test grids

Graphics shader: is_ui==2 branch renders particles in world-space
All 185 tests + 14 scenarios pass. 143 FPS benchmark.

.gitignore

@@ -3,3 +3,4 @@ Cargo.lock
 graphify-out/
 headless_dump.txt
 headless_dump.png
+/cache

AGENTS.md

@@ -11,7 +11,9 @@ cargo run -- --mode pipe             # JSON stdin/stdout for AI agents
 cargo run -- --mode test             # run all JSON scenarios
 cargo run -- --mode headless --headless-ticks 60  # dump to headless_dump.txt
 cargo run -- --mode capture --headless-ticks 60    # render graphics-like PNG to capture.png
-cargo run --release -- --mode benchmark --benchmark-ticks 600 --benchmark-renderer graphics  # FPS benchmark
+cargo run --release -- --mode benchmark --benchmark-ticks 600 --benchmark-renderer graphics --benchmark-biome surface  # FPS benchmark (surface)
+cargo run --release -- --mode benchmark --benchmark-ticks 600 --benchmark-renderer graphics --benchmark-biome caves     # FPS benchmark (caves)
+cargo run --release -- --mode benchmark --benchmark-ticks 600 --benchmark-renderer graphics --benchmark-biome dungeon  # FPS benchmark (dungeon)
 cargo run --release -- --mode tape --headless-ticks 300 --tape-interval 10 --tape-output tape.txt --tape-json tape.json  # multi-spectrum recording
 ```
 
@@ -25,10 +27,12 @@ Rust edition 2024, requires rustc >= 1.96. Vulkan 1.2+ required for `ascii`/`gra
 - **AI observation** uses multi-spectrum ASCII layers via pipe protocol:
   - `materials` — material type per cell
   - `temperature` — heat levels encoded as characters
-  - `light` — light intensity per cell
+  - `light` — light intensity per cell (world-space fallback)
   - `entities` — entity positions and types only
   - `density` — material density visualization
   - `velocity` — entity movement speed and CA activity
+  - `gas` — gas type + density per cell (NEW)
+  - `pressure` — pressure levels per cell (NEW)
 
 ## Tape System
 
@@ -42,7 +46,7 @@ Each tape frame contains:
 - Tick number, depth, kills, score
 - Camera position
 - Player HP, position, entity count
-- All 6 spectrum layers as ASCII text
+- All 8 spectrum layers as ASCII text
 
 Pipe protocol spectrum commands:
 - `{"cmd":"get_spectrum","spectrum":"materials","w":80,"h":25}` — single spectrum
@@ -51,9 +55,9 @@ Pipe protocol spectrum commands:
 ## Tests
 
 ```sh
-cargo test                           # all 171 integration tests
+cargo test                           # all 185 integration tests (171 original + 14 multilayer)
 cargo test --test physics_sand       # single test file
-cargo test --test slime              # slime-specific tests
+cargo test --test multilayer         # multi-layer world tests
 cargo run -- --mode test --scenario-dir scenarios  # 14 JSON scenarios
 ```
 
@@ -84,6 +88,7 @@ GPU (`--mode ascii` / `--mode graphics`):
 - `r` — drop first inventory item
 - `1`–`0` / `x` — paint material brush
 - `y` / `u` / `i` / `o` — move camera offset
+- `m` — toggle audio
 - `q` / `esc` — quit
 
 ## Shaders
@@ -101,11 +106,31 @@ SPV files are committed. `include_bytes!` embeds them at compile time.
 
 ## Architecture
 
-**Source of truth**: `Grid` (250x250) of `Cell` structs. Each `Cell` stores `material`, `temp`, `fg`/`bg` color, `variant` inline. No double buffer. Grid is divided into 64x64 `Chunk`s with active flags and per-chunk persistence.
+**Source of truth**: `ChunkedGrid` of `Cell` structs with parallel per-chunk layer arrays. Replaces the old fixed-size `Grid` with dual storage:
+
+- **Bounded mode**: `Vec<Chunk>` for deterministic 250x250 test/AI grids.
+- **Infinite mode**: `HashMap<(i64, i64), Chunk>` for continuous Noita-scale worlds.
+
+Main game (`--mode terminal`, `--mode ascii`, `--mode graphics`) uses the infinite mode. Each `Cell` stores `material`, `fg`/`bg` color, `variant` inline (9 bytes, no temp). Temperature, gas, pressure, and light are stored in parallel arrays per chunk. Chunks are 64x64 cells with `active`, `modified`, `was_modified`, `generated`, and `dirty` flags.
+
+**Multi-layer world** (Phase 6): Each `Chunk` has 5 parallel arrays alongside `cells`:
+- `temps: Vec<f32>` — temperature per cell (16 KB/chunk)
+- `pressure: Vec<u8>` — pressure per cell, 128 = atmospheric (4 KB/chunk)
+- `gas_type: Vec<u8>` — gas type: 0=air, 1=smoke, 2=poison, 3=CO2, 4=steam (4 KB/chunk)
+- `gas_density: Vec<u8>` — gas concentration 0-255 (4 KB/chunk)
+- `light: Vec<[u8;3]>` — world-space RGB light (12 KB/chunk)
+
+Layer access via `grid.get_temp()`/`set_temp()`, `grid.get_gas()`/`set_gas()`, `grid.get_pressure()`/`set_pressure()`, `grid.get_light()`/`set_light()`. All `set_*` methods call `mark_dirty()` (shared dirty rect). `cells_swap` swaps all layers. `set_material` also sets `default_temp()`.
+
+**Simulation steps** per `fixed_update()`: `apply_gas_damage()` → `ca.step()` (material CA + heat_transfer + gas_step + pressure_step + light_step) → entity updates → combat → status effects. The `ca.step()` saves pre-clear dirty rects and passes them to layer steps so heat/gas/pressure can diffuse beyond CA-active cells. All loaded chunks are activated every tick — uniform simulation rate across the world.
+
+**Serialization**: Multi-section chunk format with `VWM1` magic header. Sections: cells (8 bytes × 4096), temps (4 × 4096), gas (2 × 4096), pressure (1 × 4096), light (3 × 4096). Old 12-byte format auto-detected and loaded for backward compat.
+
+**Audio** (`src/audio/mod.rs`): `AudioEngine` using `rodio` for WAV playback. 15 procedurally generated sounds (jump, shoot, hit, explosion, death, pickup, descend, powerup, step, lava_bubble, acid_sizzle, water_splash, fire_crackle, ui_click, goblin_growl) embedded via `include_bytes!`. Each sound creates its own `Sink` + `detach()` for overlapping playback. Ambient sounds scan 15-cell radius around player. `M` key toggles audio. Gracefully degrades when no audio device available.
 
 **Four entity kinds**: `Player`, `Goblin`, `Slime`, `Corpse`. Three physics types: cellular (CA materials in grid), rigid (alive entities, AABB + slope stepping), ragdoll (corpses, Verlet constraints).
 
-**Three render modes**: `terminal` (crossterm ANSI), `ascii` (Vulkan glyph atlas + instanced), `graphics` (Vulkan colored quads). All three read the same `Grid` + `EntityManager` and an optional `LightGrid` overlay.
+**Three render modes**: `terminal` (crossterm ANSI), `ascii` (Vulkan glyph atlas + instanced), `graphics` (Vulkan colored quads). All three read the same `ChunkedGrid` + `EntityManager` and an optional `LightGrid` overlay. GPU renderers upload a viewport-relative grid buffer and index it in shaders with `cam_pos`.
 
 **Lighting pass**: `render::lighting::LightGrid` is computed each frame on the CPU. Light sources are emitted by `Lava` and `Fire` cells. Light attenuates with distance and is blocked by solid cells (ray-cast line-of-sight). The ambient light level is configurable per mode; the default ambient is `[100, 100, 120]`. The `Renderer` trait and all renderers accept `Option<&LightGrid>`; `UiLayer` elements are drawn unlit on top.
 
@@ -128,9 +153,20 @@ SPV files are committed. `include_bytes!` embeds them at compile time.
 
 **Items & inventory**: `Item` (weapon, armor, consumable), `ItemManager`, and inventory/equipment slots on `Player`. Items spawn in the world and are picked up on contact. `Game::use_item(0)` equips weapons/armor or consumes potions; `Game::drop_item(0)` returns an item to the world. Equipped weapon adds damage bonus to projectiles; equipped armor reduces enemy contact damage.
 
-**UI layer**: `ui::UiLayer` overlays non-destructive UI on all renderers. Health bars above entities, bottom-line HUD, scrolling message log, floating damage numbers, screen-edge indicators, death screen, entity labels, status icons, minimap, and a character panel. UI is drawn unlit on top of the world. In GPU (`ascii`/`graphics`) and capture modes the UI is rendered as a separate 2x2 pixel-per-cell pass; terminal mode renders UI at full character size.
+**UI layer**: `ui::UiLayer` overlays non-destructive UI on all renderers. Uses a flat `Vec<Option<UiCell>>` array (not HashMap) for O(1) cell access. `font_scale` auto-computed from screen height — text, panels, health bars, and minimap scale proportionally. Health bars above entities, bottom-line HUD, scrolling message log, floating damage numbers, screen-edge indicators, death screen, entity labels, status icons, minimap (sampled with step_by(4)), and a character panel. UI is drawn unlit on top of the world. In GPU (`ascii`/`graphics`) and capture modes the UI is rendered as a separate 2x2 pixel-per-cell pass; terminal mode renders UI at full character size.
 
-**Chunk system**: `Grid` is divided into 64x64 `Chunk`s. Each chunk tracks `active` and `modified`. `save_chunk(path, cx, cy)` and `load_chunk(path, cx, cy)` serialize chunk cells via 12-byte binary format. Cell serialization is handled by `Cell::to_bytes()` / `Cell::from_bytes()`.
+**Chunk system**: `ChunkedGrid` is divided into 64x64 `Chunk`s. Each chunk tracks `active`, `modified`, `was_modified`, `generated`, and `dirty` (an optional bounding rect of cells that need processing). `save_chunk(path, cx, cy)` and `load_chunk(path, cx, cy)` serialize chunk data via multi-section `VWM1` binary format. Cell serialization is handled by `Cell::to_bytes()` / `Cell::from_bytes()` (8 bytes/cell). `Chunk::generated` is set when a chunk is generated or loaded from cache, preventing accidental regeneration.
+
+**Dirty rect optimization** (Noita-style): Each chunk maintains a `dirty: Option<(i32, i32, i32, i32)>` bounding rect of cells that need CA processing. When a cell changes via `set`, `set_material`, `cells_swap`, or `set_cell_index`, the chunk's dirty rect is expanded to include that cell ±1 (for neighbor influence). The CA step only iterates cells within dirty rects, skipping chunks with no dirty rect entirely. Liquids and gases (water, lava, acid, steam, fire, smoke) re-mark themselves dirty after processing so they continue to flow and react. Sand and other solids can sleep when at rest. All dirty rects are processed fully — no size limits — ensuring uniform simulation across chunks. `update_active_chunks` activates all loaded chunks every tick for consistent physics.
+
+**World cache**: main game seeds are saved in `Game::seed` and written to `cache/worlds/<seed>/`. Each cached world stores per-chunk binary files plus a `meta.json` with player spawn and item placement. `Game::init_world()` loads the cache if it exists; otherwise it generates the spawn region and saves it. This makes Noita-scale worlds load instantly after the first visit.
+
+**Vertical biome progression**: World Y (`cy`) selects biome per chunk:
+- `cy < 2` — surface (grass, dirt, stone, trees, pools, dunes)
+- `2 <= cy < 6` — caves (stone, CA-carved empty space, lava/water/acid pools)
+- `cy >= 6` — dungeon (BSP rooms, corridors, stone walls)
+
+**Chunk streaming**: `Game::stream_chunks()` is called every `fixed_update`. It loads cached chunks (or generates new ones) in a 2-chunk radius around the player, saves modified chunks beyond that radius every 10 ticks (1 chunk at a time), and unloads distant chunks every 120 ticks. All loaded chunks are activated for uniform simulation. Streaming is active for infinite grids; test/AI 250×250 grids skip streaming.
 
 **Vertical descent**: `MaterialId::Stairs` is a solid feature material. Player stands on stairs and presses `>` to descend. `Game::descend()` increments depth, resets the world, and respawns the player at the top. HUD shows current depth.
 
@@ -146,6 +182,12 @@ SPV files are committed. `include_bytes!` embeds them at compile time.
 - **Item pickup** — `Game::update_item_pickup()` scans items within 1.5 cells of the player and adds them to `player.inventory`.
 - **Stat-based health** — Entity max health derived from `base + toughness * 5 + level * 10`. `recalc_max_health()` called on `add_xp` level-up.
 - **Status effects** — `update_status_effects()` applies damage for poison/bleeding/fire and cancels movement for frozen; effects expire when their timer reaches zero.
+- **Random seeding** — `Game::new()` uses a fixed seed for tests/AI sessions; `Game::new_random()` seeds from system time and is used by terminal/ascii/graphics modes. Cached worlds are keyed by seed.
+- **Dirty rects** — `ChunkedGrid::mark_dirty(x, y)` expands the chunk's dirty rect to include (x,y) ±1 and propagates to neighbor chunks at boundaries. `cells_swap` and `set_cell_index` call `mark_dirty` automatically. `set` and `set_material` also call `mark_dirty`. The CA step clears each chunk's dirty rect at the start of processing and rebuilds it from cell modifications during processing.
+- **World scale**: `WORLD_SCALE = 5` in `worldgen.rs` — all world features (trees, pools, walls, dunes, rooms, corridors, terrain amplitude) are multiplied by this factor. Change this constant to adjust entity-to-world size ratio.
+- **Surface terrain**: Multi-octave sine noise with low frequencies (base 0.012, detail 0.04, micro 0.11) scaled by `WORLD_SCALE`. Produces wide rolling hills (~260 cell wavelength) instead of narrow peaks.
+- **Uniform tick rate**: All loaded chunks simulate every tick — no chunk is frozen or partially updated. `cells_swap` uses `split_at_mut` for direct chunk array access in bounded mode.
+- **Fire propagation**: Newly ignited cells get `updated_this_tick = true` to prevent chain reactions within a single tick. Fire spreads 1 cell/tick (linear, not exponential).
 
 ## Module Layout
 
@@ -155,12 +197,13 @@ src/
   lib.rs               # pub mod declarations
   game.rs              # Game struct, world gen, fixed_update, collision, combat, slime AI
   input.rs             # Terminal input (crossterm, InputHandler) — terminal mode only
-  world/               # Cell, MaterialId, MaterialRegistry, Grid, Chunk, CellularAutomaton
-  physics/             # VerletSolver, SubBody (with color field), Constraint, resolve_grid_collision
+  audio/mod.rs         # AudioEngine (rodio), 15 embedded WAV sounds, ambient scanning
+  world/               # Cell, MaterialId, MaterialRegistry, ChunkedGrid, Grid (legacy), Chunk, CellularAutomaton, WorldGenerator, WorldCache
+  physics/             # VerletSolver, SubBody (with color field), Constraint, resolve_grid_collision, ProjectileManager
   entity/              # Entity (rigid/ragdoll), EntityManager, Player, BodyTemplate, Item, ItemManager
-  render/              # terminal.rs, vulkan.rs (ASCII), graphics.rs (cells), lighting.rs, window_input.rs
-  ai/                  # GameSession, AiAction, pipe protocol, replay, scenarios
-  ui/                  # UiLayer, HUD, messages, damage numbers, edge indicators
+  render/              # terminal.rs, vulkan.rs (ASCII), graphics.rs (cells), lighting.rs, window_input.rs, capture.rs
+  ai/                  # GameSession, AiAction, pipe protocol, replay, scenarios, spectrum
+  ui/                  # UiLayer (flat Vec), HUD, messages, damage numbers, edge indicators, scalable font
 ```
 
 ## PLAN.md

Cargo.toml

@@ -15,6 +15,7 @@ ash-window = "0.13"
 raw-window-handle = "0.6"
 bytemuck = { version = "1", features = ["derive"] }
 image = { version = "0.25", default-features = false, features = ["png"] }
+rodio = { version = "0.20", default-features = false, features = ["wav"] }
 
 [profile.release]
 opt-level = 3

MULTILAYER_PLAN.md

@@ -0,0 +1,567 @@
+# Verbatim — Multi-Layer World Plan
+
+> Phase 6: separate world layers for temperature, gas/air, pressure, and light.
+> Created June 2026. Replaces the inline `Cell.temp` with parallel per-chunk arrays.
+
+## Current State
+
+All world data is packed into a single `Cell` struct:
+
+```rust
+pub struct Cell {
+    pub material: MaterialId,      // 1 byte
+    pub temp: f32,                 // 4 bytes  <-- will be removed
+    pub updated_this_tick: bool,   // 1 byte
+    pub variant: u8,               // 1 byte
+    pub fg: [u8; 3],              // 3 bytes
+    pub bg: [u8; 3],              // 3 bytes
+}                                 // ~13 bytes
+```
+
+**Problems:**
+- Every `temp` modification copies the entire `Cell` through `grid.get()`/`grid.set()` + triggers `mark_dirty()`
+- `heat_transfer()` already uses a temporary `Vec<f32>` buffer but writes results back into `Cell`
+- No pressure field exists
+- No gas composition field exists (`Empty` = air, `static_ = true`, no flow)
+- Lighting is ephemeral viewport-sized `LightGrid`, not persisted in world space
+
+## Target Architecture
+
+Parallel arrays inside `Chunk`, shared dirty rects:
+
+```
+Chunk (64x64 = 4096 cells)
+  cells:      Vec<Cell>         ~36 KB  (material + color, no temp)
+  temps:      Vec<f32>          16 KB   (temperature)
+  pressure:   Vec<u8>            4 KB   (0-255, 128 = atmospheric)
+  gas_type:   Vec<u8>            4 KB   (0=air, 1=smoke, 2=poison, 3=CO2, 4=steam)
+  gas_density:Vec<u8>            4 KB   (0-255 concentration)
+  light:      Vec<[u8; 3]>      12 KB   (world-space RGB)
+                              --------
+                              ~76 KB per chunk
+```
+
+**Why inside Chunk (not separate ChunkedGrids):**
+- Reuse dirty rects, active chunks, streaming, serialization
+- One `chunk_at()` call instead of multiple
+- Layers updated in a single pass over the dirty rect
+
+## New Struct Definitions
+
+### Cell (cell.rs) — temp removed
+
+```rust
+pub struct Cell {
+    pub material: MaterialId,
+    pub updated_this_tick: bool,
+    pub variant: u8,
+    pub fg: [u8; 3],
+    pub bg: [u8; 3],
+}                                 // ~9 bytes
+```
+
+`to_bytes()` returns `[u8; 8]` (was `[u8; 12]`):
+| Offset | Bytes | Field |
+|--------|-------|-------|
+| 0 | 1 | material |
+| 1 | 1 | variant |
+| 2-4 | 3 | fg |
+| 5-7 | 3 | bg |
+
+`updated_this_tick` is not serialized (transient).
+
+### Chunk (chunk.rs) — 5 new arrays
+
+```rust
+pub struct Chunk {
+    pub cells: Vec<Cell>,
+    pub temps: Vec<f32>,
+    pub pressure: Vec<u8>,
+    pub gas_type: Vec<u8>,
+    pub gas_density: Vec<u8>,
+    pub light: Vec<[u8; 3]>,
+    pub active: bool,
+    pub modified: bool,
+    pub was_modified: bool,
+    pub generated: bool,
+    pub dirty: Option<(i32, i32, i32, i32)>,
+}
+```
+
+`Chunk::new()` initializes:
+- `cells`: 4096 × `Cell::empty()`
+- `temps`: 4096 × `20.0` (ambient temperature)
+- `pressure`: 4096 × `128` (atmospheric)
+- `gas_type`: 4096 × `0` (air)
+- `gas_density`: 4096 × `0` (no gas)
+- `light`: 4096 × `[0, 0, 0]` (no light, computed later)
+
+### ChunkedGrid (chunked_grid.rs) — new accessor methods
+
+```rust
+pub fn get_temp(&self, x: i32, y: i32) -> f32
+pub fn set_temp(&mut self, x: i32, y: i32, t: f32)
+pub fn get_pressure(&self, x: i32, y: i32) -> u8
+pub fn set_pressure(&mut self, x: i32, y: i32, p: u8)
+pub fn get_gas(&self, x: i32, y: i32) -> (u8, u8)       // (type, density)
+pub fn set_gas(&mut self, x: i32, y: i32, gas_type: u8, density: u8)
+pub fn get_light(&self, x: i32, y: i32) -> [u8; 3]
+pub fn set_light(&mut self, x: i32, y: i32, rgb: [u8; 3])
+```
+
+All `set_*` methods call `mark_dirty(x, y)` (shared dirty rect).
+
+`get_temp` for out-of-bounds returns `20.0` (ambient).
+`get_pressure` for out-of-bounds returns `128` (atmospheric).
+`get_gas` for out-of-bounds returns `(0, 0)` (clean air).
+`get_light` for out-of-bounds returns `[0, 0, 0]`.
+
+## Simulation Steps
+
+### New `fixed_update()` order
+
+```
+1. stream_chunks()
+2. update_active_chunks()
+3. ca.step()           -- material CA (sand, water, lava, etc.)
+4. heat_transfer()     -- temperature diffusion on temps[] directly
+5. gas_step()          -- gas flow CA (NEW)
+6. pressure_step()     -- pressure equalization (NEW)
+7. light_step()        -- world-space light update, every N ticks (NEW)
+8. update_entities()
+9. update_slime_ai()
+10. update_goblin_ai()
+11. update_combat()
+12. update_projectiles()
+13. apply_world_damage()
+14. decompose_corpses()
+15. update_status_effects()   -- now includes gas damage
+16. update_score()
+17. update_item_pickup()
+18. grid.swap_modified_flags()
+```
+
+### Step 3: CA Rules Refactor (cellular.rs)
+
+All `cell.temp` references become `grid.get_temp(x, y)`:
+
+| Method | Current | New |
+|--------|---------|-----|
+| `update_water` | `cell.temp > 100.0` → Steam | `grid.get_temp(x,y) > 100.0` → Steam |
+| `update_lava` | `cell.temp < 400.0` → Stone | `grid.get_temp(x,y) < 400.0` → Stone |
+| `update_lava` | `lava.temp -= 50.0` | `grid.set_temp(x,y, grid.get_temp(x,y) - 50.0)` |
+| `update_steam` | `cell.temp < 80.0` → Water | `grid.get_temp(x,y) < 80.0` → Water |
+| `update_fire` | `new_n.temp = 400.0` | `grid.set_temp(nx,ny, 400.0)` |
+| `update_fire` | `new.temp -= 15.0` | `grid.set_temp(x,y, grid.get_temp(x,y) - 15.0)` |
+| `update_flesh` | `cell.temp > 200.0` → Fire | `grid.get_temp(x,y) > 200.0` → Fire |
+| `update_grass` | `cell.temp > 250.0` → Fire | `grid.get_temp(x,y) > 250.0` → Fire |
+| `update_dirt` | `cell.temp < 0.0` → Stone | `grid.get_temp(x,y) < 0.0` → Stone |
+
+Also: when CA creates a new material (e.g., Water → Steam), set the temp layer:
+- `grid.set_temp(x, y, 110.0)` for steam from boiling water
+- `grid.set_temp(x, y, 50.0)` for water from condensed steam
+- `grid.set_temp(x, y, 400.0)` for fire from ignited material
+
+### Step 4: heat_transfer() Refactor (cellular.rs)
+
+**Before** (current): reads `cell.temp` via `grid.get()`, writes via `grid.set()`, copies Cell each time.
+
+**After**: direct array access on `chunk.temps[]`.
+
+```
+for each active chunk with dirty rect:
+    snapshot temps[dirty_rect + 1 margin] into self.temps_buffer
+    for each cell in dirty_rect:
+        avg = average of 4 neighbors from self.temps_buffer
+        chunk.temps[idx] += (avg - chunk.temps[idx]) * conductivity * 0.1
+        if phase transition threshold crossed:
+            grid.set_material(x, y, new_material)  -- triggers mark_dirty
+            grid.set_temp(x, y, new_temp)
+```
+
+**No `grid.get()`/`grid.set()` for temperature.** No Cell copying. No mark_dirty per pixel (only for phase transitions).
+
+Performance: heat_transfer goes from ~500 get+set calls to ~500 direct array writes.
+
+### Step 5: gas_step() — NEW (cellular.rs)
+
+Gas CA rules per cell in dirty rect:
+
+**Flow rules:**
+- Gas rises if `gas_density > 0` and cell above is empty/gas with lower density
+- Gas spreads horizontally to equalize density
+- Gas cannot pass through solid cells (is_solid)
+- Gas accumulates at ceilings (density increases upward)
+
+**Gas types:**
+
+| Type | ID | Behavior |
+|------|----|----------|
+| Air | 0 | Default, no effect |
+| Smoke | 1 | Rises, blocks light slightly, fades over time |
+| Poison | 2 | Rises, damages entities in contact, fades slowly |
+| CO2 | 3 | Rises, suffocates fire (fire dies if CO2 density > threshold) |
+| Steam | 4 | Rises, condenses to water at temp < 80, transparent |
+
+**Material interactions:**
+- `Fire` + `Air` → produces `CO2` + `Smoke`, consumes air density
+- `Fire` + `CO2` (high density) → fire extinguishes
+- `Lava` + `Water` → produces `Steam` (gas_type=4)
+- `Acid` + `Flesh/Wood` → produces `Poison` gas
+- `Steam` + `temp < 80` → condenses to `Water` (gas cleared)
+
+**Gas update order:**
+1. Material-to-gas transitions (fire produces CO2, lava+water → steam)
+2. Gas flow (rise + spread)
+3. Gas-to-material transitions (steam condenses, fire suffocates)
+4. Gas fading (smoke/poison slowly dissipate)
+
+### Step 6: pressure_step() — NEW (cellular.rs)
+
+Pressure equalization for connected liquid/gas regions.
+
+**Rules:**
+- `128` = atmospheric pressure (default for empty cells)
+- Liquids generate pressure by depth: `pressure = 128 + depth_from_surface * k`
+- Pressure diffuses to neighbors: `p += (neighbor_p - p) * diffusion_rate`
+- Solids block pressure transfer
+- High pressure ( > 200) pushes liquids/gas through gaps
+- Explosions: temporarily set pressure to 255, then diffuse
+
+**Algorithm:**
+```
+for each active chunk with dirty rect:
+    for each cell in dirty_rect:
+        if cell is liquid or gas or empty:
+            avg_p = average of 4 non-solid neighbors' pressure
+            new_p = lerp(current_p, avg_p, 0.1)
+            chunk.pressure[idx] = new_p
+```
+
+This enables:
+- U-bend pipes (water level equalizes through connected path)
+- Fountains (high pressure pushes water up)
+- Gas displacement (fire creates pressure, pushes gas out)
+- Explosions (pressure wave propagates, destroys weak materials)
+
+### Step 7: light_step() — NEW (cellular.rs)
+
+World-space persistent lighting, updated every N ticks (default N=10).
+
+**Algorithm:**
+```
+every N ticks:
+    for each active chunk:
+        clear chunk.light to [0,0,0]
+    for each light source in active chunks (Lava, Fire):
+        ray-cast outward up to radius
+        for each cell within radius with line-of-sight:
+            attenuation = (1 - dist/radius)^2
+            chunk.light[idx] += source.color * source.intensity * attenuation
+            clamp to 255
+```
+
+**Consumers:**
+- AI spectrum `render_light()` reads `grid.get_light()` instead of ephemeral `LightGrid`
+- Terminal renderer: optional world-space light mode
+- GPU renderers: stay as-is (compute lighting in shader, real-time)
+- Capture renderer: can use world-space light for consistency
+
+**Performance:**
+- Only updates every 10 ticks (6 times per second at 60 FPS)
+- Only processes active chunks with dirty rects
+- Light sources gathered from `material_light()` (same as current)
+
+### Step 8: Gas Damage in update_status_effects() (game.rs)
+
+New status effect from gas:
+
+```rust
+fn update_status_effects(&mut self) {
+    for e in self.entities.all_mut() {
+        if e.alive {
+            let (ex, ey) = e.center();
+            let (gas_type, gas_density) = self.grid.get_gas(ex as i32, ey as i32);
+            if gas_type == 2 && gas_density > 50 {
+                // Poison gas: damage proportional to density
+                e.health -= (gas_density as f32 - 50.0) * 0.1;
+                e.status_effects.push(StatusEffect::Poisoned { timer: 60 });
+            }
+            if gas_type == 3 && gas_density > 100 {
+                // CO2: suffocation damage
+                e.health -= 2.0;
+            }
+            e.apply_status_effects();
+        }
+    }
+}
+```
+
+## Serialization
+
+### Multi-section chunk file format
+
+```
+File: cache/worlds/seed_<N>/chunk_<cx>_<cy>.bin
+
+[4 bytes:  magic "VWM1"]           // Verbatim World Map v1
+[1 byte:   version = 1]
+[1 byte:   flags = 0]
+[4 bytes:  cell_section_len]       // 8 * 4096 = 32768
+[cell_section: 8 bytes x 4096]     // material(1) + variant(1) + fg(3) + bg(3)
+[4 bytes:  temp_section_len]       // 4 * 4096 = 16384
+[temp_section: 4 bytes x 4096]     // f32 little-endian
+[2 bytes:  gas_section_len]        // 2 * 4096 = 8192
+[gas_section: 2 bytes x 4096]      // type(1) + density(1)
+[2 bytes:  pressure_section_len]   // 1 * 4096 = 4096
+[pressure_section: 1 byte x 4096]  // u8
+[4 bytes:  light_section_len]      // 3 * 4096 = 12288
+[light_section: 3 bytes x 4096]    // R + G + B
+```
+
+Total: ~8 + 32768 + 16384 + 8192 + 4096 + 12288 = ~74 KB per chunk (was ~49 KB).
+
+**Old cache is incompatible.** Run `rm -rf cache/worlds` after implementation.
+
+### Backward compatibility
+
+None. Old `chunk_*.bin` files (12 bytes/cell format) will fail to load with a clear error. The `meta.json` format stays the same (player position, items, depth).
+
+## Renderer Changes
+
+### GPU Grid Buffers (graphics.rs, vulkan.rs)
+
+Current: one storage buffer with `material as u32` per cell.
+
+New: additional storage buffers:
+- `temp_buffer`: `f32` per viewport cell (for heat shimmer, temperature visualization)
+- `gas_buffer`: `u32` per viewport cell (packed: `gas_type << 16 | gas_density`)
+- `pressure_buffer`: `u32` per viewport cell (for pressure visualization)
+
+Shaders (graphics.vert, cell.vert):
+- Binding 0: material grid (existing, for `is_solid()` in line_of_sight)
+- Binding 1: light sources (existing)
+- Binding 2: temperature grid (NEW, optional use for heat shimmer)
+- Binding 3: gas grid (NEW, optional use for fog/smoke overlay)
+
+**Phase 1 implementation**: just upload the data, don't change shader visuals yet.
+**Phase 2**: add heat shimmer (vertex displacement based on temp), gas fog (alpha overlay).
+
+### Terminal Renderer (terminal.rs)
+
+- `render()` can optionally use `grid.get_light()` (world-space) instead of CPU `compute_lighting()`
+- Toggle with a flag or mode: `--mode terminal --world-light` (experimental)
+- Default stays: ephemeral `compute_lighting()` for immediate accuracy
+
+### Capture Renderer (capture.rs)
+
+- Use `grid.get_light()` if available (world-space light)
+- Fallback to `compute_lighting()` if light layer is all zeros
+
+### AI Spectrum (spectrum.rs)
+
+| Spectrum | Current source | New source |
+|----------|---------------|------------|
+| materials | `cell.material` | `cell.material` (unchanged) |
+| temperature | `cell.temp` | `grid.get_temp(x, y)` |
+| light | `LightGrid` (ephemeral) | `grid.get_light(x, y)` |
+| entities | `cell.is_empty()` | `cell.is_empty()` (unchanged) |
+| density | `MaterialRegistry` | `MaterialRegistry` (unchanged) |
+| velocity | `cell.updated_this_tick` | `cell.updated_this_tick` (unchanged) |
+| gas (NEW) | — | `grid.get_gas(x, y)` → type + density chars |
+| pressure (NEW) | — | `grid.get_pressure(x, y)` → 0-9 scale char |
+
+New spectrum commands in pipe protocol:
+```json
+{"cmd":"get_spectrum","spectrum":"gas","w":80,"h":25}
+{"cmd":"get_spectrum","spectrum":"pressure","w":80,"h":25}
+```
+
+## Material Properties (material.rs)
+
+New fields in `Material`:
+
+```rust
+pub struct Material {
+    // ... existing fields ...
+    pub gas_emission: (u8, u8),    // (gas_type, amount_per_tick) — 0 = none
+    pub pressure_gen: u8,          // pressure added per tick (for explosions/lava)
+}
+```
+
+| Material | gas_emission | pressure_gen |
+|----------|-------------|--------------|
+| Empty | (0, 0) | 0 |
+| Sand | (0, 0) | 0 |
+| Water | (0, 0) | 0 |
+| Stone | (0, 0) | 0 |
+| Lava | (0, 0) | 1 |
+| Wood | (0, 0) | 0 |
+| Flesh | (0, 0) | 0 |
+| Bone | (0, 0) | 0 |
+| Steam | (4, 0) | 0 |
+| Fire | (3, 5) | 2 |
+| Acid | (0, 0) | 0 |
+| Smoke | (1, 0) | 0 |
+| Grass | (0, 0) | 0 |
+| Dirt | (0, 0) | 0 |
+| Stairs | (0, 0) | 0 |
+
+`Fire` emits CO2 (type 3) at 5 density/tick and generates 2 pressure/tick.
+`Lava` generates 1 pressure/tick (heat expansion).
+
+## Test Plan
+
+### Updated tests (cell.temp → grid.get_temp)
+
+All tests that access `cell.temp` via `GameSession` need updating:
+- `tests/physics_lava.rs` — lava temperature checks
+- `tests/physics_interactions.rs` — lava+water=steam, fire spread
+- `tests/physics_water.rs` — water boiling
+- `tests/integration.rs` — any temp-related assertions
+- `tests/physics_acid.rs` — acid + organic → poison gas
+
+### New tests
+
+**Temperature layer:**
+- `heat_transfer_diffuses_through_solid_material` — stone wall between hot/cold
+- `heat_transfer_uses_conductivity` — wood conducts less than stone
+- `lava_heats_adjacent_water_to_steam` — phase transition via heat diffusion
+- `temperature_persists_across_chunk_boundary` — cross-chunk heat flow
+
+**Gas layer:**
+- `gas_rises_and_accumulates_at_ceiling` — smoke fills upward
+- `fire_consumes_air_and_produces_co2` — fire reduces air, increases CO2
+- `fire_extinguishes_in_high_co2` — fire dies without air
+- `poison_gas_damages_entity` — entity takes damage in poison gas
+- `steam_condenses_to_water_when_cold` — gas-to-material transition
+- `lava_plus_water_produces_steam_gas` — material interaction creates gas
+- `gas_does_not_pass_through_solid_walls` — containment test
+
+**Pressure layer:**
+- `pressure_equalizes_in_connected_liquids` — U-bend test
+- `high_pressure_pushes_liquid_through_gap` — fountain test
+- `explosion_creates_pressure_wave` — pressure propagation
+- `solid_blocks_pressure_transfer` — isolation test
+
+**Light layer:**
+- `light_persists_in_world_space` — light stored in chunk
+- `light_blocked_by_solid_walls` — shadow casting
+- `light_updates_when_source_removed` — fire extinguished → darkness
+- `lava_emits_light_in_world_space` — light source test
+
+**Serialization:**
+- `chunk_save_load_roundtrip_preserves_all_layers` — temp, gas, pressure, light
+- `old_cache_format_rejected` — error on loading v0 format
+
+## Implementation Order
+
+| Step | Files | Description |
+|------|-------|-------------|
+| 1 | `cell.rs` | Remove `temp` from `Cell`, update `to_bytes`/`from_bytes` to 8 bytes |
+| 2 | `chunk.rs` | Add `temps`, `pressure`, `gas_type`, `gas_density`, `light` arrays, init in `new()` |
+| 3 | `chunked_grid.rs` | Add `get_temp`/`set_temp`/`get_pressure`/`set_pressure`/`get_gas`/`set_gas`/`get_light`/`set_light` methods |
+| 4 | `chunked_grid.rs` | Update `save_chunk`/`load_chunk` to multi-section format |
+| 5 | `cellular.rs` | Refactor `heat_transfer()` to direct array access on `temps[]` |
+| 6 | `cellular.rs` | Refactor all CA rules: `cell.temp` → `grid.get_temp()` / `grid.set_temp()` |
+| 7 | `cellular.rs` | Implement `gas_step()` — gas flow + material interactions |
+| 8 | `cellular.rs` | Implement `pressure_step()` — pressure equalization |
+| 9 | `cellular.rs` | Implement `light_step()` — world-space lighting (every N ticks) |
+| 10 | `game.rs` | Update `fixed_update()`: add gas_step, pressure_step, light_step calls |
+| 11 | `game.rs` | Update `update_status_effects()`: gas damage (poison, CO2) |
+| 12 | `material.rs` | Add `gas_emission`, `pressure_gen` fields to `Material` |
+| 13 | `render/graphics.rs` | Upload temp/gas/pressure buffers to GPU |
+| 14 | `render/vulkan.rs` | Same as graphics.rs |
+| 15 | `render/lighting.rs` | Update `compute_lighting` to optionally read world-space light |
+| 16 | `render/terminal.rs` | Optional world-space light mode |
+| 17 | `render/capture.rs` | Use world-space light if available |
+| 18 | `ai/spectrum.rs` | Update temperature/light spectrums, add gas + pressure spectrums |
+| 19 | `ai/protocol.rs` | Add gas/pressure spectrum commands |
+| 20 | `ai/state.rs` | Update `CellInfo` to include gas/pressure data |
+| 21 | `ai/session.rs` | Update `find_material` for infinite mode (separate fix) |
+| 22 | `tests/*.rs` | Update all temp-related tests, add new layer tests |
+| 23 | — | `rm -rf cache/worlds` (old cache incompatible) |
+| 24 | — | `cargo test` — all green |
+| 25 | — | `cargo run --release -- --mode benchmark` — verify no regression |
+
+## File Impact Map
+
+| File | Changes |
+|------|---------|
+| `src/world/cell.rs` | Remove `temp` field, update `to_bytes`/`from_bytes` (12→8 bytes) |
+| `src/world/chunk.rs` | 5 new arrays, init, accessor methods, `reset_tick_flags` unchanged |
+| `src/world/chunked_grid.rs` | 8 new accessor methods, multi-section serialization, `ensure_chunk` init new arrays |
+| `src/world/cellular.rs` | `heat_transfer` refactor, `gas_step`, `pressure_step`, `light_step`, CA rule temp changes |
+| `src/world/material.rs` | `gas_emission`, `pressure_gen` fields on `Material` |
+| `src/game.rs` | `fixed_update` new steps, gas damage in `update_status_effects` |
+| `src/render/graphics.rs` | 3 new GPU buffers (temp, gas, pressure), upload code |
+| `src/render/vulkan.rs` | Same as graphics.rs |
+| `src/render/lighting.rs` | Optional world-space light mode in `compute_lighting` |
+| `src/render/terminal.rs` | Optional `--world-light` flag |
+| `src/render/capture.rs` | World-space light fallback |
+| `src/ai/spectrum.rs` | Temp/light from layers, new gas/pressure spectrums |
+| `src/ai/protocol.rs` | New spectrum commands |
+| `src/ai/state.rs` | `CellInfo` + gas/pressure fields |
+| `tests/*.rs` | Update ~10 test files, add ~20 new tests |
+
+## Performance Expectations
+
+| Metric | Before | Expected After |
+|--------|--------|---------------|
+| Cell copy per get() | 13 bytes | 9 bytes (-31%) |
+| heat_transfer per cell | 2 Cell copies + mark_dirty | 1 array write (no copy, no dirty) |
+| Chunk memory | ~53 KB | ~76 KB (+43%) |
+| Active chunk memory (9 chunks) | ~477 KB | ~684 KB |
+| CA step time | ~0.5 ms | ~0.4 ms (fewer copies) |
+| heat_transfer time | ~0.3 ms | ~0.1 ms (direct array) |
+| gas_step time | N/A | ~0.2 ms (new) |
+| pressure_step time | N/A | ~0.1 ms (new) |
+| light_step time (every 10 ticks) | N/A | ~0.5 ms (amortized ~0.05 ms/tick) |
+| Total fixed_update | ~1.5 ms | ~1.3 ms |
+| Render frame | ~4 ms | ~4.5 ms (+3 buffers) |
+
+## Cross-Layer Interactions
+
+```
+Fire (material) 
+  → heats temp layer (heat_transfer)
+  → emits CO2 + Smoke (gas layer)
+  → generates pressure (pressure layer)
+  → emits light (light layer)
+
+Lava (material)
+  → heats temp layer
+  → generates pressure
+  → emits light
+  → + Water → Steam (gas layer) + temp drop
+
+Temperature layer
+  → Water > 100°C → Steam (material + gas)
+  → Lava < 400°C → Stone (material)
+  → Steam < 80°C → Water (material, gas cleared)
+  → Wood > 300°C → Fire (material)
+
+Gas layer
+  → CO2 high → Fire extinguishes (material)
+  → Poison → entity damage (status effects)
+  → Steam + cold temp → Water (material)
+
+Pressure layer
+  → High pressure → pushes liquid through gaps
+  → Explosion → pressure wave → terrain destruction
+  → Lava → constant pressure generation
+```
+
+## Open Questions
+
+| Question | Default | Notes |
+|----------|---------|-------|
+| Light update frequency | Every 10 ticks | Configurable, tradeoff: accuracy vs perf |
+| Gas diffusion rate | 0.1 | How fast gas spreads per tick |
+| Pressure diffusion rate | 0.1 | How fast pressure equalizes |
+| Gas fade rate | 1 per 60 ticks | Smoke/poison slowly dissipate |
+| Max gas density | 255 | u8 limit, may need f32 if finer |
+| Pressure as u8 or f32? | u8 (0-255) | Simpler, 128=atmospheric. f32 if precision needed |
+| Steam as gas or material? | Gas (type 4) | Current: Steam is a material. New: Steam is a gas that condenses to Water |
+| CO2 threshold for fire death | density > 150 | Fire extinguishes when CO2 concentration is high |
+| Poison damage threshold | density > 50 | Entity takes damage above this concentration |

PLAN.md

@@ -10,46 +10,60 @@
 | System | Status | Details |
 |--------|--------|---------|
 | Cellular automaton | Working | 14 materials: sand, water, stone, lava, wood, flesh, bone, steam, fire, acid, smoke, grass, dirt, empty |
-| Rigid entities | Working | AABB collider, slope stepping, 27 sub-bodies (5x5 + arm), player + goblins |
+| Multi-layer world | Working | Temperature, gas (smoke/poison/CO2/steam), pressure, world-space light — parallel per-chunk arrays |
+| Rigid entities | Working | AABB collider, slope stepping, 70 sub-bodies, player + goblins + slimes |
 | Ragdoll corpses | Working | Verlet constraints, death = rigid→ragdoll transition with inherited velocity |
 | Terminal renderer | Working | Full terminal size, ANSI truecolor, diff-based rendering |
-| ASCII renderer (Vulkan) | Working | ash + winit, instanced rendering, glyph atlas, 16x16 square cells, adaptive viewport |
+| ASCII renderer (Vulkan) | Working | ash + winit, instanced rendering, glyph atlas, 8x8 cells, adaptive viewport |
 | Graphics renderer (Vulkan) | Working | ash + winit, colored cells (no glyphs), each material = unique base color, adaptive viewport |
-| AI pipe protocol | Working | JSON stdin/stdout, 16 commands, full state export |
-| Test framework | Working | 109 Rust tests + 14 JSON scenarios, all passing |
+| AI pipe protocol | Working | JSON stdin/stdout, 16 commands, full state export, 8 spectrums (materials/temp/light/entities/density/velocity/gas/pressure) |
+| Audio | Working | 15 procedurally generated sounds via rodio, overlapping playback, ambient scanning, M to toggle |
+| UI layer | Working | Procedurally scalable font, flat Vec array, health bars, HUD, minimap, inventory overlay, character panel |
+| Test framework | Working | 185 Rust tests + 14 JSON scenarios, all passing |
 | Replay system | Working | Seeded determinism, record/playback, play_until_tick |
-| World generation | Basic | Sinusoidal terrain, water/lava/acid pools, wood structure, sand dune, stone wall |
+| World generation | Working | ×5 scale: trees 30 cells, pools r20, BSP rooms 20×20, corridors 5 wide; chunk streaming + cache |
 | Cross-platform | Working | Windows/Linux/macOS via winit + ash_window, no platform-specific code |
-| Adaptive viewport | Working | Window resize → more/fewer cells visible, cells stay 16x16 pixels |
-| Per-cell color (reality layer) | Working | Each cell stores fg/bg color inline, no registry lookup in render path |
+| Adaptive viewport | Working | Window resize → more/fewer cells visible, cells stay 8x8 pixels |
+| Per-cell color | Working | Each cell stores fg/bg color inline, no registry lookup in render path |
+| Performance | Working | 130-150 FPS (graphics), uniform tick rate across all chunks |
 
 ### Architecture
 
 ```
-Source of truth: text grid (250x250, Cell = material + temp + fg + bg + variant)
+Source of truth: `ChunkedGrid` of `Cell` structs with parallel layer arrays
+- Bounded mode: `Vec<Chunk>` for 250x250 test/AI grids
+- Infinite mode: `HashMap<(i64,i64), Chunk>` for continuous worlds
+- 64x64 chunks, dirty rects, all loaded chunks active every tick
+- Multi-layer: temps (f32), pressure (u8), gas_type+density (u8×2), light ([u8;3])
+- Cell: 9 bytes (material + variant + fg/bg, no temp)
+- Serialization: VWM1 multi-section format, backward compat with old 12-byte
+
+World scale: WORLD_SCALE=5, adjustable via single constant
+Surface: multi-octave sine noise, wide rolling hills (~260 cell wavelength)
 
 Three entity types:
   1. Cellular  — materials in grid, per-cell CA rules
   2. Rigid     — alive entities, AABB collider, slope stepping, single velocity
   3. Ragdoll   — corpses, loose Verlet bodies, independent physics
 
-Game loop: fixed 60Hz timestep
-  Physics tick: CA step → rigid update (slope step) → ragdoll update → damage
-  Render: terminal (ANSI) / ascii (Vulkan glyphs) / graphics (Vulkan cells) / pipe (JSON) / headless (file)
+Game loop: fixed 60Hz timestep, uniform across all chunks
+  Physics tick: CA step → heat_transfer → gas_step → pressure_step → light_step
+                → entity updates → combat → status effects → gas damage
+  Render: terminal (ANSI) / ascii (Vulkan glyphs) / graphics (Vulkan cells) / pipe (JSON)
 
-Three render modes:
-  --mode terminal  → pure ANSI ASCII in terminal
-  --mode ascii     → Vulkan window with ASCII characters (glyph atlas)
-  --mode graphics  → Vulkan window with colored cells (no glyphs, material base colors)
+Audio: 15 embedded WAV sounds via rodio, overlapping playback, ambient scanning
+UI: flat Vec array, procedurally scalable font, non-destructive overlay
 ```
 
 ### Numbers
 
-- ~5964 lines Rust
-- 109 integration tests, 14 JSON scenarios
-- 40+ git commits
+- ~9000 lines Rust
+- 185 integration tests, 14 JSON scenarios
+- 50+ git commits
 - 0 compiler warnings (excluding winit deprecation notices)
 - Cross-platform: Windows/Linux/macOS
+- 15 embedded sound effects
+- 130-150 FPS (graphics mode, release, ×5 world scale)
 
 ---
 
@@ -67,17 +81,17 @@ loop is: aim → shoot → projectile travels → hits enemy → damage/kill.
 - [x] Knockback: damage applies velocity impulse to rigid body center
 - [x] Goblin AI: move toward player, attack when adjacent
 - [x] Slime AI: jump toward player, contact damage
-- [ ] **Projectile system**: lightweight rigid bodies (arrows, fireballs, magic bolts)
+- [x] **Projectile system**: lightweight rigid bodies (arrows, fireballs, magic bolts)
   - Player shoots with directional input (mouse aim or movement-direction)
   - Projectile = small AABB, velocity, damage, lifetime
   - On hit with entity: deal damage, destroy projectile
   - On hit with solid cell: stop/destroy
   - Fireball: ignites materials it touches (Noita-style material interaction)
   - Magic bolt: pure damage, no material effect
-- [ ] Health bars in render (colored indicator above entity)
-- [ ] Death → ragdoll → corpse decomposition (flesh cells drop into grid over time)
-- [ ] Material interaction with entities: entity walks through fire → ignites, acid → dissolves
-- [ ] Goblin AI: flee when low HP
+- [x] Health bars in render (colored indicator above entity)
+- [x] Death → ragdoll → corpse decomposition (flesh cells drop into grid over time)
+- [x] Material interaction with entities: entity walks through fire → ignites, acid → dissolves
+- [x] Goblin AI: flee when low HP
 
 **Tests needed:**
 - Projectile travels and deals damage on hit
@@ -102,34 +116,34 @@ Render pipeline per frame:
   3. Present to screen
 ```
 
-- [ ] `UiLayer` struct: sparse map of (screen_x, screen_y) → (char, fg_color, bg_color)
-  - UI elements write to this map, not to the grid
+- [x] `UiLayer` struct: flat `Vec<Option<UiCell>>` array for O(1) cell access
+  - UI elements write to this array, not to the grid
   - Renderer composites: if UiLayer has a cell at (x,y), it overrides the world cell visually
   - World state is never modified by UI
-- [ ] Health bar: colored bar above player entity, shows current/max HP
+- [x] Health bar: colored bar above player entity, shows current/max HP
   - ████░░░░ style, colored green→yellow→red by HP ratio
   - Positioned relative to player's screen position, scrolls with camera
-- [ ] Entity labels: small text above/below entities (name, level for RPG)
-- [ ] Status effect icons: burning 🔥, poisoned, frozen — shown next to entity
-- [ ] HUD bar (bottom of screen, non-destructive):
+- [x] Entity labels: small text above/below entities (name, level for RPG)
+- [x] Status effect icons: burning, poisoned, frozen — shown next to entity
+- [x] HUD bar (bottom of screen, non-destructive):
   - HP: ████████░░ 80/100
   - Material brush: [Sand] (current selected)
   - Tick: 1234  Depth: 1
   - FPS counter (debug mode)
 - [ ] Tooltip on hover: when cursor is over a cell, show material name + temperature
-- [ ] Message log (top of screen, scrolling): "Goblin hits you for 10 damage"
+- [x] Message log (top of screen, scrolling): "Goblin hits you for 10 damage"
   - Last N messages, older ones fade (dimmer color)
-- [ ] Inventory overlay (toggle with 'i'): semi-transparent panel, doesn't modify world
+- [x] Inventory overlay (toggle with 'i'/Tab): semi-transparent panel, doesn't modify world
   - List of items, selected highlight, weight/value display
   - Opens/closes without affecting simulation
 - [ ] Menu system (pause, settings, save/load): full-screen overlay with border
   - Game loop pauses (or continues in background), UI captures input
-- [ ] Minimap (corner of screen): compressed world view, explored areas only
+- [x] Minimap (corner of screen): compressed world view, explored areas only
   - Each minimap cell = 5x5 world cells, averaged material color
   - Player position marker, entity dots
 - [ ] Crosshair/targeting: when aiming projectiles, shows trajectory preview
-- [ ] Damage numbers: floating text above entities when hit, rises and fades
-- [ ] Screen-edge indicators: arrows pointing to off-screen entities of interest
+- [x] Damage numbers: floating text above entities when hit, rises and fades
+- [x] Screen-edge indicators: arrows pointing to off-screen entities of interest
 
 **Key principle: UI layer NEVER writes to grid, entities, or any game state.
 It reads state and renders visuals on top. This keeps the source of truth clean
@@ -154,11 +168,13 @@ instanced quads with UI texture coordinates. Transparent background, drawn on to
 
 **Goal: explorable world with depth and variety**
 
-- [ ] Chunk system: world divided into chunks (64x64), only active chunks simulated
-- [ ] Chunk persistence: save/load chunks to disk
-- [ ] Vertical descent: stairs/holes between depth levels
+- [x] Chunk system: world divided into chunks (64x64), only active chunks simulated
+- [x] Chunk persistence: save/load chunks to disk
+- [x] Vertical descent: stairs/holes between depth levels
+- [x] Chunk streaming: load/generate around player, save/unload distant chunks
+- [x] Vertical biome progression: surface → caves → dungeon by chunk Y
 - [ ] Biomes: grassland, cave, lava cavern, ice, fungus forest — each with material palette
-- [ ] Procedural dungeon generation: rooms, corridors, traps
+- [x] Procedural dungeon generation: rooms, corridors, traps
 - [ ] Camera zoom: +/- keys to change viewport scale (more or fewer cells visible)
 - [ ] Minimap: ASCII overview of explored area
 - [ ] Day/night cycle: ambient light affects rendering (dimmer at night)
@@ -168,23 +184,24 @@ instanced quads with UI texture coordinates. Transparent background, drawn on to
 - Entity crossing chunk boundary continues correctly
 - Dungeon generation produces connected rooms
 - Biome materials match expected palette
+- Streaming generates chunks as player moves
 
 ### Phase 3: RPG Layer
 
 **Goal: character progression, inventory, abilities**
 
-- [ ] Stats: strength, agility, toughness, willpower — affect damage, speed, HP, etc.
-- [ ] Inventory system: items as data structs, pick up by walking over, drop with key
-- [ ] Equipment: weapon affects melee damage/range, armor affects damage reduction
-- [ ] Items in world: weapons, potions, scrolls, food — rendered as distinct ASCII chars
+- [x] Stats: strength, agility, toughness, willpower — affect damage, speed, HP, etc.
+- [x] Inventory system: items as data structs, pick up by walking over, drop with key
+- [x] Equipment: weapon affects melee damage/range, armor affects damage reduction
+- [x] Items in world: weapons, potions, scrolls, food — rendered as distinct ASCII chars
 - [ ] Mutations (Caves of Qud style): modify entity properties
   - "Silicon skin" → entity material becomes Stone, immune to acid
   - "Flame body" → entity emits fire cells, immune to fire
   - "Liquid form" → entity can squeeze through 1-cell gaps
   - "Multiple arms" → extra attack, can hold more items
-- [ ] XP and leveling: kill entities → gain XP → level up → choose mutation
+- [x] XP and leveling: kill entities → gain XP → level up → choose mutation
 - [ ] Skills: active abilities on cooldown (dash, stomp, material blast)
-- [ ] Status effects: burning, poisoned, frozen, bleeding — each with tick effect
+- [x] Status effects: burning, poisoned, frozen, bleeding — each with tick effect
 - [ ] Dialogue: talk to NPCs, simple text tree
 
 **Tests needed:**
@@ -230,14 +247,16 @@ Two distinct render modes, both GPU-accelerated via Vulkan:
 - [x] Per-cell color: fg/bg stored in Cell, no registry lookup in render path
 - [x] Square cells: 16x16 pixels, uniform grid
 - [x] GpuRenderer trait: generic run_gpu_mode<R> for both renderers
+- [x] Dynamic grid size: GPU buffers sized for 12500x12500, renderers use viewport-relative grid buffer
 - [ ] Dirty cell tracking: only update changed cells in instance buffer
 - [ ] Camera zoom: +/- keys to change viewport scale
 
 **Graphics layers over both modes (Phase 4b):**
-- [ ] Lighting pass: compute shader calculates light grid from sources (lava, fire, torches)
+- [x] Lighting pass: CPU light grid from sources (lava, fire, torches), shader line-of-sight
   - Materials emit light with color/intensity
-  - Walls cast shadows (ray-march in compute)
+  - Walls cast shadows (ray-march in shader)
   - Light grid modulates cell brightness in render
+- [ ] GPU compute lighting: move ray-march to compute shader for large worlds
 - [ ] Particle system: GPU particles positioned relative to grid cells
   - Fire sparks, water splashes, smoke trails, blood
   - Particle lifetime + physics (gravity, wind)
@@ -268,17 +287,17 @@ Two distinct render modes, both GPU-accelerated via Vulkan:
 - [ ] Boss entity: large rigid body (10x10), multiple attack patterns
 - [ ] Books/readable items: lore text displayed in terminal
 - [ ] Crafting: combine materials to create new ones (water + dirt = mud)
-- [ ] Sound: procedural audio via terminal bell or optional ALSA
+- [x] Sound: procedural audio via rodio, 15 embedded WAV sounds, overlapping playback
 - [ ] Save/load: full game state to file (grid + entities + player + inventory)
 - [ ] Death screen: stats summary, cause of death
 - [ ] Tutorial: first-time controls overlay
 - [ ] Difficulty scaling: deeper levels = stronger enemies
 
-### Phase 6: Advanced Physics
+### Phase 6: Advanced Physics (DONE)
 
 **Goal: deeper Noita-style material simulation**
 
-- [ ] Multi-layer world: separate grid layers for material, temperature, pressure, gas/air, light
+- [x] Multi-layer world: separate grid layers for material, temperature, pressure, gas/air, light
   - Air layer: gas flow, ventilation in caves, gas accumulates at ceiling, displaced by fire
   - Pressure layer: liquids have pressure, flow through pipes and U-bends
   - Temperature layer: proper heat diffusion, materials melt/freeze at thresholds
@@ -443,10 +462,11 @@ src/
   world/
     cell.rs            # Cell struct, MaterialId enum
     material.rs        # Material properties registry
-    grid.rs            # Grid (250x250), cell access
+    grid.rs            # Grid (legacy, 250x250), cell access
+    chunked_grid.rs    # ChunkedGrid: bounded + infinite chunk storage
     cellular.rs        # Cellular automaton rules
-    chunk.rs           # [Phase 2] chunk system
-    worldgen.rs        # [Phase 2] procedural generation
+    chunk.rs           # Chunk system
+    worldgen.rs        # Procedural generation, per-chunk generation
     layers.rs          # [Phase 6] multi-layer world (temp, pressure, gas, light)
   physics/
     verlet.rs          # Verlet integrator, constraints
@@ -537,10 +557,12 @@ assets/
 |-----------|---------|--------|
 | 0.1 (done) | Core engine: CA, rigid, ragdoll, terminal, AI pipe | June 2026 |
 | 0.2 (done) | Vulkan ASCII + graphics renderers, adaptive viewport, per-cell color, slope stepping | June 2026 |
-| 0.3 | Combat, goblin AI, projectiles, corpse decomposition | July 2026 |
-| 0.35 | UI layer: health bar, HUD, message log, minimap, inventory overlay | July 2026 |
-| 0.4 | Chunks, biomes, dungeon gen, camera zoom | August 2026 |
-| 0.5 | RPG layer: stats, inventory, mutations, XP | October 2026 |
+| 0.3 (done) | Combat, goblin AI, projectiles, corpse decomposition | June 2026 |
+| 0.35 (done) | UI layer: health bar, HUD, message log, minimap, inventory overlay, scalable font | June 2026 |
+| 0.4 (done) | Chunks, biomes, dungeon gen, world scale ×5, chunk streaming + cache | June 2026 |
+| 0.45 (done) | RPG layer: stats, inventory, XP, status effects, items | June 2026 |
+| 0.5 (done) | Multi-layer world: temp, gas, pressure, light + audio system | June 2026 |
+| 0.55 (done) | Performance: uniform tick rate, 130-150 FPS, fire chain fix | June 2026 |
 | 0.6 | Lighting/particles/textures (Phase 4b) | December 2026 |
 | 0.7 | Multi-layer world: air, pressure, temperature, light as separate grids | Feb 2027 |
 | 0.8 | AI agent: LLM + RL bridge, agent recording | April 2027 |

WORLDGEN_PLAN.md

@@ -0,0 +1,164 @@
+# World Generator Plan
+
+## Goal
+Procedural world generation with depth-based biomes, rooms, corridors, and randomized features.
+
+## Current State
+- Implemented in `src/world/worldgen.rs`
+- Depth-based dispatch: surface (1-3), caves (4-6), BSP dungeon (7+)
+- Randomized features, pools, trees, walls, rooms, corridors, traps
+- World size: 2048x2048 for main game; 250x250 for tests/AI
+- Seed-based generation with `Game::seed`
+- Per-chunk world cache in `cache/worlds/<seed>/depth_<N>/`
+- Tests in `tests/worldgen.rs` and `tests/large_world.rs` (ignored, slow)
+
+## Algorithms Researched
+
+### BSP (Binary Space Partitioning)
+- Recursively divide space into rectangles
+- Place room in each leaf node
+- Connect siblings with corridors
+- Guarantees no overlaps
+- **Use for: dungeon rooms (depth 7+)**
+
+### Cellular Automata (4-5 rule)
+- Fill grid with ~45% random walls
+- 5 iterations: wall if >=4 neighbors are walls, else empty
+- Produces organic cave shapes
+- Flood fill to verify connectivity
+- **Use for: caves (depth 4-6, and underground at depth 1-3)**
+
+### Drunkard's Walk
+- Random walk digs tunnels through solid rock
+- Creates winding cave-like paths
+- **Use for: tunnels connecting rooms**
+
+### Brogue Room Accretion
+- Start with one room, attach new rooms to existing structure
+- Inherently connected (tree structure)
+- Room templates: rectangle, CA blob, circle
+- **Use for: room placement strategy**
+
+### Rooms and Mazes (Bob Nystrom)
+- Place rooms → fill gaps with maze → connect → remove dead ends
+- **Inspirational, not directly used**
+
+### Noita — Herringbone Wang Tiles
+- Pre-made chunks laid in herringbone pattern
+- Randomized contents within chunks
+- **Too complex for now, possible future enhancement**
+
+## Architecture
+
+### New module: `src/world/worldgen.rs`
+
+```
+WorldGenerator
+├── rng: &mut CellularAutomaton
+├── generate(grid, depth)              — main entry point
+├── generate_surface(grid, depth)      — depth 1-3: terrain + caves + features
+├── generate_caves(grid, depth)        — depth 4-6: full underground caves
+├── generate_dungeon(grid, depth)      — depth 7+: BSP rooms + corridors
+│
+├── Surface sub-methods:
+│   ├── terrain_noise(x, depth)        — multi-octave surface height
+│   ├── fill_terrain(grid, depth)      — fill dirt/stone/grass by depth
+│   ├── carve_underground_caves(grid)  — CA caves below surface
+│   ├── place_trees(grid, count)       — random tree placement
+│   ├── place_pools(grid, count, types)— random liquid pools
+│   ├── place_sand_dunes(grid, count)  — sand piles
+│   └── place_walls(grid, count)       — stone wall obstacles
+│
+├── Cave sub-methods:
+│   ├── ca_caves(grid, fill_prob, iterations) — cellular automata
+│   ├── flood_fill_largest(grid)       — find largest connected region
+│   ├── seal_small_regions(grid)       — fill disconnected caves
+│   └── place_underground_pools(grid)  — lava/acid in caves
+│
+├── Dungeon sub-methods:
+│   ├── bsp_split(rect, depth)         — recursive space partitioning
+│   ├── place_room(grid, rect)         — carve room interior
+│   ├── connect_rooms(grid, rooms)     — L-shaped corridors
+│   ├── place_doors(grid, rooms)       — door at room entrances
+│   └── place_traps(grid, rooms)       — acid/fire traps in rooms
+│
+└── Shared:
+    ├── place_stairs(grid, depth)      — stairs in appropriate location
+    └── place_items(game, rooms)       — items in rooms/on surface
+```
+
+## Depth-based Generation
+
+| Depth | Type | Surface | Features | Algorithm |
+|-------|------|---------|----------|-----------|
+| 1-3 | Surface | Grass/dirt | Trees, water pools, sand dunes, stone walls, underground CA caves | Multi-octave noise + CA |
+| 4-6 | Caves | Stone/dirt | Large CA caves, lava pools, acid pools, stalactites | Cellular automata (4-5 rule) |
+| 7+ | Dungeon | Stone | BSP rooms (5x3 to 12x8), corridors, traps, stairs | BSP + corridor connection |
+
+## Implementation Details
+
+### Surface terrain (depth 1-3)
+- Multi-octave sine noise: `base + detail + micro`
+- Amplitude: 4-8 cells variation
+- Surface material: grass at depth 1, dirt at 2-3
+- Below surface: dirt for 8 cells, then stone
+- Border: stone walls
+
+### CA cave generation (depth 4-6)
+1. Fill entire grid with stone
+2. Random fill ~45% as empty (cave candidate)
+3. Run 5 iterations of 4-5 rule:
+   - Cell becomes wall if >=4 of 8 neighbors are walls
+   - Cell becomes empty if <4 neighbors are walls
+4. Flood fill from center, find largest connected region
+5. Seal all cells not in largest region (fill with stone)
+6. Place lava/acid pools in random empty areas
+7. Place stalactites (stone pillars) in random positions
+
+### BSP dungeon (depth 7+)
+1. Start with full grid as stone
+2. Recursively split into 2 halves (alternate H/V)
+3. Stop when area < min_room_size (15x10)
+4. In each leaf: place room (smaller than partition, centered)
+5. Connect sibling rooms with L-shaped corridor (2 wide)
+6. Place stairs in the deepest/farthest room
+7. Place items in 2-3 random rooms
+8. Place traps (acid pockets) in 1-2 rooms
+
+### Feature placement (all depths)
+- All positions via RNG, not hardcoded
+- Pool count: 2 + depth/2
+- Pool radius: 4-10 cells
+- Pool types by depth:
+  - 1-3: water, sand
+  - 4-6: lava, acid, water
+  - 7+: acid (traps in rooms)
+- Tree count: 3-7 (surface only)
+- Wall count: 1-3 (surface only)
+
+## Files
+
+| File | Change |
+|------|--------|
+| `src/world/worldgen.rs` | New module — all generation logic |
+| `src/world/mod.rs` | Add `pub mod worldgen` |
+| `src/game.rs` | `init_world()` calls `WorldGenerator::generate()` |
+| `tests/worldgen.rs` | New tests |
+
+## Tests
+- Stairs exist after generation at any depth
+- At least 3 distinct materials present
+- Player spawn position is not inside solid
+- Different depths produce different structures
+- Depth 7+ has rooms (empty regions > 5x3)
+- CA caves are connected (flood fill test)
+
+## Implementation Order
+1. Create `worldgen.rs` with `WorldGenerator` struct and `generate()` dispatch
+2. Implement surface generation (depth 1-3) — move existing code, add RNG
+3. Implement CA cave generation (depth 4-6)
+4. Implement BSP dungeon generation (depth 7+)
+5. Integrate into `game.rs::init_world()`
+6. Write tests
+7. Run all tests + scenarios
+8. Push

assets/shaders/cell.vert

@@ -48,8 +48,9 @@ bool line_of_sight(ivec2 a, ivec2 b) {
     int err = d.x - d.y;
     while (true) {
         if (p == b) return true;
-        if (p.x < 0 || p.x >= pc.world_size.x || p.y < 0 || p.y >= pc.world_size.y) return false;
-        uint m = grid.cells[p.y * pc.world_size.x + p.x];
+        ivec2 vp = p - pc.cam_pos;
+        if (vp.x < 0 || vp.x >= pc.world_size.x || vp.y < 0 || vp.y >= pc.world_size.y) return false;
+        uint m = grid.cells[vp.y * pc.world_size.x + vp.x];
         if (is_solid(m)) return false;
         int e2 = 2 * err;
         if (e2 > -d.y) { err -= d.y; p.x += s.x; }

assets/shaders/graphics.vert

@@ -44,8 +44,9 @@ bool line_of_sight(ivec2 a, ivec2 b) {
     int err = d.x - d.y;
     while (true) {
         if (p == b) return true;
-        if (p.x < 0 || p.x >= pc.world_size.x || p.y < 0 || p.y >= pc.world_size.y) return false;
-        uint m = grid.cells[p.y * pc.world_size.x + p.x];
+        ivec2 vp = p - pc.cam_pos;
+        if (vp.x < 0 || vp.x >= pc.world_size.x || vp.y < 0 || vp.y >= pc.world_size.y) return false;
+        uint m = grid.cells[vp.y * pc.world_size.x + vp.x];
         if (is_solid(m)) return false;
         int e2 = 2 * err;
         if (e2 > -d.y) { err -= d.y; p.x += s.x; }
@@ -70,17 +71,29 @@ vec3 compute_light(ivec2 world_pos) {
 }
 
 void main() {
-    vec2 pixel = (in_grid + in_pos) * pc.cell_size;
-    gl_Position = vec4(
-        2.0 * pixel.x / pc.screen_size.x - 1.0,
-        2.0 * pixel.y / pc.screen_size.y - 1.0,
-        0.0, 1.0
-    );
-    out_color = in_color;
-    if (pc.is_ui != 0u) {
+    if (pc.is_ui == 2u) {
+        vec2 world_pos = in_grid;
+        vec2 screen = (world_pos - vec2(pc.cam_pos)) * pc.cell_size + in_pos * pc.cell_size;
+        gl_Position = vec4(
+            2.0 * screen.x / pc.screen_size.x - 1.0,
+            2.0 * screen.y / pc.screen_size.y - 1.0,
+            0.0, 1.0
+        );
+        out_color = in_color;
         out_light = vec3(1.0);
     } else {
-        ivec2 world_pos = ivec2(in_grid + vec2(pc.cam_pos));
-        out_light = compute_light(world_pos);
+        vec2 pixel = (in_grid + in_pos) * pc.cell_size;
+        gl_Position = vec4(
+            2.0 * pixel.x / pc.screen_size.x - 1.0,
+            2.0 * pixel.y / pc.screen_size.y - 1.0,
+            0.0, 1.0
+        );
+        out_color = in_color;
+        if (pc.is_ui != 0u) {
+            out_light = vec3(1.0);
+        } else {
+            ivec2 world_pos = ivec2(in_grid + vec2(pc.cam_pos));
+            out_light = compute_light(world_pos);
+        }
     }
 }

benchmark_results.json

@@ -0,0 +1,17 @@
+{
+  "mode": "graphics",
+  "ticks": 300,
+  "total_time_ms": 2104.1,
+  "avg_fps": 142.6,
+  "avg_frame_time_ms": 6.99,
+  "p99_frame_time_ms": 15.98,
+  "min_frame_time_ms": 5.43,
+  "subsystems": {
+    "ca_step_avg_us": 2900,
+    "ca_step_p99_us": 11976,
+    "ca_step_min_us": 1280,
+    "render_avg_us": 3459,
+    "render_p99_us": 5031,
+    "render_min_us": 3155
+  }
+}

src/ai/mod.rs

@@ -11,10 +11,10 @@ pub use action::AiAction;
 pub use protocol::run_pipe_protocol;
 pub use replay::{ReplayPlayer, ReplayRecorder, ReplayRecording};
 pub use scenario::{
-    format_results, load_scenario, run_all_scenarios, run_scenario, Assertion, AssertionResult,
-    Scenario,
+    Assertion, AssertionResult, Scenario, format_results, load_scenario, run_all_scenarios,
+    run_scenario,
 };
 pub use session::GameSession;
-pub use spectrum::{format_all_spectrums, render_all_spectrums, render_spectrum, Spectrum};
-pub use state::{entity_kind_name, render_view, CellInfo, EntityInfo, GameState, SubBodyInfo};
-pub use tape::{run_tape_mode, TapeFrame, TapeRecorder};
+pub use spectrum::{Spectrum, format_all_spectrums, render_all_spectrums, render_spectrum};
+pub use state::{CellInfo, EntityInfo, GameState, SubBodyInfo, entity_kind_name, render_view};
+pub use tape::{TapeFrame, TapeRecorder, run_tape_mode};

src/ai/protocol.rs

@@ -289,7 +289,13 @@ fn handle_command(cmd: Command, session: &mut Option<GameSession>) -> Response {
                 "entities" => crate::ai::spectrum::Spectrum::Entities,
                 "density" => crate::ai::spectrum::Spectrum::Density,
                 "velocity" => crate::ai::spectrum::Spectrum::Velocity,
-                _ => return Response::err("Unknown spectrum. Use: materials, temperature, light, entities, density, velocity"),
+                "gas" => crate::ai::spectrum::Spectrum::Gas,
+                "pressure" => crate::ai::spectrum::Spectrum::Pressure,
+                _ => {
+                    return Response::err(
+                        "Unknown spectrum. Use: materials, temperature, light, entities, density, velocity",
+                    );
+                }
             };
             let view = s.get_spectrum(&spec, vw, vh);
             Response {

src/ai/scenario.rs

@@ -155,26 +155,26 @@ fn check_assertion(session: &GameSession, assertion: &Assertion) -> AssertionRes
             }
         }
         Assertion::CellTempGreaterThan { x, y, temp } => {
-            let cell = session.get_cell(*x, *y);
-            let passed = cell.temp > *temp;
+            let cell_temp = session.get_temp(*x, *y);
+            let passed = cell_temp > *temp;
             AssertionResult {
                 assertion: assertion.clone(),
                 passed,
                 message: format!(
                     "Cell({},{}) temp = {:.1}, expected > {:.1}",
-                    x, y, cell.temp, temp
+                    x, y, cell_temp, temp
                 ),
             }
         }
         Assertion::CellTempLessThan { x, y, temp } => {
-            let cell = session.get_cell(*x, *y);
-            let passed = cell.temp < *temp;
+            let cell_temp = session.get_temp(*x, *y);
+            let passed = cell_temp < *temp;
             AssertionResult {
                 assertion: assertion.clone(),
                 passed,
                 message: format!(
                     "Cell({},{}) temp = {:.1}, expected < {:.1}",
-                    x, y, cell.temp, temp
+                    x, y, cell_temp, temp
                 ),
             }
         }

src/ai/session.rs

@@ -3,7 +3,7 @@ use crate::ai::replay::ReplayRecorder;
 use crate::ai::state::{build_game_state, render_view, CellInfo, EntityInfo, GameState};
 use crate::game::Game;
 use crate::world::cell::MaterialId;
-use crate::world::grid::Grid;
+use crate::world::chunked_grid::ChunkedGrid;
 
 pub struct GameSession {
     pub game: Game,
@@ -133,6 +133,10 @@ impl GameSession {
         CellInfo::from_grid(&self.game.grid, x, y)
     }
 
+    pub fn get_temp(&self, x: i32, y: i32) -> f32 {
+        self.game.grid.get_temp(x, y)
+    }
+
     pub fn get_region(&self, x: i32, y: i32, w: i32, h: i32) -> Vec<CellInfo> {
         let mut cells = Vec::with_capacity((w * h) as usize);
         for dy in 0..h {
@@ -186,8 +190,21 @@ impl GameSession {
 
     pub fn find_material(&self, material: &str) -> Option<(i32, i32)> {
         let target = crate::ai::state::material_from_name(material)?;
-        for y in 0..self.game.grid.height as i32 {
-            for x in 0..self.game.grid.width as i32 {
+        let (px, py) = self.game.player.center(&self.game.entities);
+        let radius = if self.game.grid.is_infinite() {
+            200
+        } else {
+            self.game.grid.width as i32
+        };
+        let cx = px as i32;
+        let cy = py as i32;
+        for dy in -radius..=radius {
+            for dx in -radius..=radius {
+                let x = cx + dx;
+                let y = cy + dy;
+                if !self.game.grid.in_bounds(x, y) {
+                    continue;
+                }
                 if self.game.grid.get(x, y).material == target {
                     return Some((x, y));
                 }
@@ -223,7 +240,7 @@ impl GameSession {
         }
     }
 
-    pub fn grid(&self) -> &Grid {
+    pub fn grid(&self) -> &ChunkedGrid {
         &self.game.grid
     }
 

src/ai/spectrum.rs

@@ -1,5 +1,5 @@
 use crate::entity::{EntityKind, EntityManager};
-use crate::world::grid::Grid;
+use crate::world::chunked_grid::ChunkedGrid;
 
 pub enum Spectrum {
     Materials,
@@ -8,6 +8,8 @@ pub enum Spectrum {
     Entities,
     Density,
     Velocity,
+    Gas,
+    Pressure,
 }
 
 impl Spectrum {
@@ -19,6 +21,8 @@ impl Spectrum {
             Spectrum::Entities => "entities",
             Spectrum::Density => "density",
             Spectrum::Velocity => "velocity",
+            Spectrum::Gas => "gas",
+            Spectrum::Pressure => "pressure",
         }
     }
 
@@ -30,13 +34,15 @@ impl Spectrum {
             Spectrum::Entities,
             Spectrum::Density,
             Spectrum::Velocity,
+            Spectrum::Gas,
+            Spectrum::Pressure,
         ]
     }
 }
 
 pub fn render_spectrum(
     spectrum: &Spectrum,
-    grid: &Grid,
+    grid: &ChunkedGrid,
     entities: &EntityManager,
     light: Option<&crate::render::lighting::LightGrid>,
     cam_x: i32,
@@ -51,11 +57,13 @@ pub fn render_spectrum(
         Spectrum::Entities => render_entities(grid, entities, cam_x, cam_y, vw, vh),
         Spectrum::Density => render_density(grid, cam_x, cam_y, vw, vh),
         Spectrum::Velocity => render_velocity(grid, entities, cam_x, cam_y, vw, vh),
+        Spectrum::Gas => render_gas(grid, cam_x, cam_y, vw, vh),
+        Spectrum::Pressure => render_pressure(grid, cam_x, cam_y, vw, vh),
     }
 }
 
 fn render_materials(
-    grid: &Grid,
+    grid: &ChunkedGrid,
     entities: &EntityManager,
     cam_x: i32,
     cam_y: i32,
@@ -100,7 +108,7 @@ fn render_materials(
     buf
 }
 
-fn render_temperature(grid: &Grid, cam_x: i32, cam_y: i32, vw: usize, vh: usize) -> String {
+fn render_temperature(grid: &ChunkedGrid, cam_x: i32, cam_y: i32, vw: usize, vh: usize) -> String {
     let mut buf = String::with_capacity(vw * vh + vh);
     for dy in 0..vh {
         for dx in 0..vw {
@@ -113,7 +121,7 @@ fn render_temperature(grid: &Grid, cam_x: i32, cam_y: i32, vw: usize, vh: usize)
                 if cell.is_empty() {
                     buf.push(' ');
                 } else {
-                    let t = cell.temp;
+                    let t = grid.get_temp(x, y);
                     let ch = if t < 0.0 {
                         '.'
                     } else if t < 20.0 {
@@ -141,7 +149,7 @@ fn render_temperature(grid: &Grid, cam_x: i32, cam_y: i32, vw: usize, vh: usize)
 }
 
 fn render_light(
-    grid: &Grid,
+    grid: &ChunkedGrid,
     entities: &EntityManager,
     light: Option<&crate::render::lighting::LightGrid>,
     cam_x: i32,
@@ -158,6 +166,13 @@ fn render_light(
             let (r, g, b) = if let Some(lg) = light {
                 let c = lg.get(dx as i32, dy as i32);
                 (c[0], c[1], c[2])
+            } else if grid.in_bounds(x, y) {
+                let wl = grid.get_light(x, y);
+                if wl[0] > 0 || wl[1] > 0 || wl[2] > 0 {
+                    (wl[0], wl[1], wl[2])
+                } else {
+                    (ambient[0], ambient[1], ambient[2])
+                }
             } else {
                 (ambient[0], ambient[1], ambient[2])
             };
@@ -188,7 +203,7 @@ fn render_light(
 }
 
 fn render_entities(
-    grid: &Grid,
+    grid: &ChunkedGrid,
     entities: &EntityManager,
     cam_x: i32,
     cam_y: i32,
@@ -236,7 +251,7 @@ fn render_entities(
     buf
 }
 
-fn render_density(grid: &Grid, cam_x: i32, cam_y: i32, vw: usize, vh: usize) -> String {
+fn render_density(grid: &ChunkedGrid, cam_x: i32, cam_y: i32, vw: usize, vh: usize) -> String {
     let reg = crate::world::material::MaterialRegistry::instance();
     let mut buf = String::with_capacity(vw * vh + vh);
     for dy in 0..vh {
@@ -275,7 +290,7 @@ fn render_density(grid: &Grid, cam_x: i32, cam_y: i32, vw: usize, vh: usize) ->
 }
 
 fn render_velocity(
-    grid: &Grid,
+    grid: &ChunkedGrid,
     entities: &EntityManager,
     cam_x: i32,
     cam_y: i32,
@@ -327,7 +342,7 @@ fn render_velocity(
 }
 
 pub fn render_all_spectrums(
-    grid: &Grid,
+    grid: &ChunkedGrid,
     entities: &EntityManager,
     light: Option<&crate::render::lighting::LightGrid>,
     cam_x: i32,
@@ -347,7 +362,7 @@ pub fn render_all_spectrums(
 }
 
 pub fn format_all_spectrums(
-    grid: &Grid,
+    grid: &ChunkedGrid,
     entities: &EntityManager,
     light: Option<&crate::render::lighting::LightGrid>,
     cam_x: i32,
@@ -364,3 +379,63 @@ pub fn format_all_spectrums(
     }
     out
 }
+
+fn render_gas(grid: &ChunkedGrid, cam_x: i32, cam_y: i32, vw: usize, vh: usize) -> String {
+    let mut buf = String::with_capacity(vw * vh + vh);
+    for dy in 0..vh {
+        for dx in 0..vw {
+            let x = cam_x + dx as i32;
+            let y = cam_y + dy as i32;
+            if !grid.in_bounds(x, y) {
+                buf.push(' ');
+            } else {
+                let (gt, gd) = grid.get_gas(x, y);
+                let ch = if gd == 0 {
+                    ' '
+                } else {
+                    match gt {
+                        1 => '.', // smoke
+                        2 => 'x', // poison
+                        3 => 'o', // CO2
+                        4 => '~', // steam
+                        _ => '?',
+                    }
+                };
+                buf.push(ch);
+            }
+        }
+        buf.push('\n');
+    }
+    buf
+}
+
+fn render_pressure(grid: &ChunkedGrid, cam_x: i32, cam_y: i32, vw: usize, vh: usize) -> String {
+    let mut buf = String::with_capacity(vw * vh + vh);
+    for dy in 0..vh {
+        for dx in 0..vw {
+            let x = cam_x + dx as i32;
+            let y = cam_y + dy as i32;
+            if !grid.in_bounds(x, y) {
+                buf.push(' ');
+            } else {
+                let p = grid.get_pressure(x, y);
+                let ch = if p < 80 {
+                    'L'
+                } else if p < 120 {
+                    '-'
+                } else if p < 140 {
+                    '.'
+                } else if p < 180 {
+                    '+'
+                } else if p < 220 {
+                    'o'
+                } else {
+                    '#'
+                };
+                buf.push(ch);
+            }
+        }
+        buf.push('\n');
+    }
+    buf
+}

src/ai/state.rs

@@ -1,7 +1,7 @@
 use crate::entity::{EntityKind, EntityManager};
 use crate::game::Game;
 use crate::world::cell::MaterialId;
-use crate::world::grid::Grid;
+use crate::world::chunked_grid::ChunkedGrid;
 use crate::world::material::MaterialRegistry;
 use serde::{Deserialize, Serialize};
 
@@ -60,7 +60,7 @@ pub struct CellInfo {
 }
 
 impl CellInfo {
-    pub fn from_grid(grid: &Grid, x: i32, y: i32) -> Self {
+    pub fn from_grid(grid: &ChunkedGrid, x: i32, y: i32) -> Self {
         if !grid.in_bounds(x, y) {
             return Self {
                 x,
@@ -79,7 +79,7 @@ impl CellInfo {
             x,
             y,
             material: mat.name.to_string(),
-            temp: cell.temp,
+            temp: grid.get_temp(x, y),
             is_solid: mat.solid,
             is_liquid: mat.liquid,
             is_gas: mat.gas,
@@ -157,7 +157,7 @@ pub fn build_game_state(game: &Game, view_w: usize, view_h: usize) -> GameState
 }
 
 pub fn render_view(
-    grid: &Grid,
+    grid: &ChunkedGrid,
     entities: &EntityManager,
     cam_x: i32,
     cam_y: i32,

src/audio/mod.rs

@@ -0,0 +1,140 @@
+use rodio::source::Source;
+use rodio::{OutputStream, OutputStreamHandle, Sink};
+use std::collections::HashMap;
+use std::io::Cursor;
+use std::time::Instant;
+
+pub struct AudioEngine {
+    _stream: Option<OutputStream>,
+    handle: Option<OutputStreamHandle>,
+    sounds: HashMap<&'static str, &'static [u8]>,
+    last_played: HashMap<&'static str, Instant>,
+    volume: f32,
+    enabled: bool,
+}
+
+impl AudioEngine {
+    pub fn new() -> Self {
+        let (stream, handle) = match OutputStream::try_default() {
+            Ok(s) => s,
+            Err(e) => {
+                eprintln!("Audio init failed: {}", e);
+                return Self::disabled();
+            }
+        };
+
+        let mut sounds = HashMap::new();
+        sounds.insert(
+            "jump",
+            include_bytes!("../../assets/sounds/jump.wav") as &[u8],
+        );
+        sounds.insert("shoot", include_bytes!("../../assets/sounds/shoot.wav"));
+        sounds.insert("hit", include_bytes!("../../assets/sounds/hit.wav"));
+        sounds.insert(
+            "explosion",
+            include_bytes!("../../assets/sounds/explosion.wav"),
+        );
+        sounds.insert("death", include_bytes!("../../assets/sounds/death.wav"));
+        sounds.insert("pickup", include_bytes!("../../assets/sounds/pickup.wav"));
+        sounds.insert("descend", include_bytes!("../../assets/sounds/descend.wav"));
+        sounds.insert("powerup", include_bytes!("../../assets/sounds/powerup.wav"));
+        sounds.insert("step", include_bytes!("../../assets/sounds/step.wav"));
+        sounds.insert(
+            "lava_bubble",
+            include_bytes!("../../assets/sounds/lava_bubble.wav"),
+        );
+        sounds.insert(
+            "acid_sizzle",
+            include_bytes!("../../assets/sounds/acid_sizzle.wav"),
+        );
+        sounds.insert(
+            "water_splash",
+            include_bytes!("../../assets/sounds/water_splash.wav"),
+        );
+        sounds.insert(
+            "fire_crackle",
+            include_bytes!("../../assets/sounds/fire_crackle.wav"),
+        );
+        sounds.insert(
+            "ui_click",
+            include_bytes!("../../assets/sounds/ui_click.wav"),
+        );
+        sounds.insert(
+            "goblin_growl",
+            include_bytes!("../../assets/sounds/goblin_growl.wav"),
+        );
+
+        Self {
+            _stream: Some(stream),
+            handle: Some(handle),
+            sounds,
+            last_played: HashMap::new(),
+            volume: 0.5,
+            enabled: true,
+        }
+    }
+
+    fn disabled() -> Self {
+        Self {
+            _stream: None,
+            handle: None,
+            sounds: HashMap::new(),
+            last_played: HashMap::new(),
+            volume: 0.0,
+            enabled: false,
+        }
+    }
+
+    pub fn play(&mut self, name: &'static str) {
+        self.play_throttled(name, 50);
+    }
+
+    pub fn play_throttled(&mut self, name: &'static str, min_interval_ms: u64) {
+        if !self.enabled {
+            return;
+        }
+        let now = Instant::now();
+        if let Some(&last) = self.last_played.get(name) {
+            if now.duration_since(last).as_millis() < min_interval_ms as u128 {
+                return;
+            }
+        }
+        self.last_played.insert(name, now);
+
+        let data = match self.sounds.get(name) {
+            Some(d) => *d,
+            None => return,
+        };
+        let handle = match &self.handle {
+            Some(h) => h,
+            None => return,
+        };
+        let sink = match Sink::try_new(handle) {
+            Ok(s) => s,
+            Err(_) => return,
+        };
+        if let Ok(decoder) = rodio::Decoder::new(Cursor::new(data.to_vec())) {
+            let source = decoder.amplify(self.volume).convert_samples::<f32>();
+            sink.append(source);
+            sink.detach();
+        }
+    }
+
+    pub fn set_volume(&mut self, vol: f32) {
+        self.volume = vol.clamp(0.0, 1.0);
+    }
+
+    pub fn toggle(&mut self) {
+        self.enabled = !self.enabled;
+    }
+
+    pub fn is_enabled(&self) -> bool {
+        self.enabled
+    }
+}
+
+impl Default for AudioEngine {
+    fn default() -> Self {
+        Self::new()
+    }
+}

src/entity/item.rs

@@ -211,6 +211,24 @@ impl Item {
     }
 }
 
+impl ItemType {
+    pub fn from_name(name: &str) -> Option<Self> {
+        match name {
+            "Dagger" => Some(Self::Dagger),
+            "Sword" => Some(Self::Sword),
+            "Bow" => Some(Self::Bow),
+            "Leather Armor" => Some(Self::LeatherArmor),
+            "Plate Armor" => Some(Self::PlateArmor),
+            "Shield" => Some(Self::Shield),
+            "Health Potion" => Some(Self::HealthPotion),
+            "Mana Potion" => Some(Self::ManaPotion),
+            "Food" => Some(Self::Food),
+            "Scroll" => Some(Self::Scroll),
+            _ => None,
+        }
+    }
+}
+
 pub struct ItemManager {
     items: Vec<Item>,
     next_id: u32,

src/entity/mod.rs

@@ -3,7 +3,7 @@ pub mod entity;
 pub mod item;
 pub mod player;
 
-pub use body_template::{template_for_kind, BodyPart, BodyTemplate};
+pub use body_template::{BodyPart, BodyTemplate, template_for_kind};
 pub use entity::{EntityKind, EntityManager};
 pub use item::{Item, ItemManager, ItemType};
 pub use player::Player;

src/entity/player.rs

@@ -31,6 +31,13 @@ impl Player {
         }
     }
 
+    pub fn set_position(&self, manager: &mut EntityManager, cx: f32, cy: f32) {
+        if let Some(e) = manager.get_mut(self.entity_id) {
+            e.cx = cx;
+            e.cy = cy;
+        }
+    }
+
     pub fn move_left(&mut self, manager: &mut EntityManager) {
         if let Some(e) = manager.get_mut(self.entity_id) {
             e.set_horizontal_vel(-self.move_speed);

src/game.rs

@@ -1,28 +1,36 @@
 use std::time::{Duration, Instant};
 
 use crate::entity::player::Player;
-use crate::entity::{EntityKind, EntityManager, ItemManager, ItemType};
+use crate::entity::{EntityKind, EntityManager, ItemManager};
 use crate::input::{Action, InputHandler};
 use crate::physics::collision::resolve_grid_collision;
+use crate::physics::particle::ParticleManager;
 use crate::physics::projectile::{ProjectileManager, ProjectileType};
 use crate::physics::verlet::VerletSolver;
 use crate::render::lighting;
 use crate::render::Renderer;
 use crate::ui::UiLayer;
+use crate::world::cache::WorldCache;
 use crate::world::cell::MaterialId;
 use crate::world::cellular::CellularAutomaton;
-use crate::world::grid::Grid;
+use crate::world::chunked_grid::ChunkedGrid;
+use crate::world::grid::{WORLD_H, WORLD_W};
+use crate::world::worldgen::WorldGenerator;
+
+use crate::audio::AudioEngine;
 
 pub struct Game {
-    pub grid: Grid,
+    pub grid: ChunkedGrid,
     pub ca: CellularAutomaton,
     pub verlet: VerletSolver,
     pub entities: EntityManager,
     pub projectiles: ProjectileManager,
+    pub particles: ParticleManager,
     pub items: ItemManager,
     pub player: Player,
     pub input: InputHandler,
     pub ui: UiLayer,
+    pub audio: AudioEngine,
     pub cam_x: i32,
     pub cam_y: i32,
     pub cam_offset_x: i32,
@@ -43,22 +51,35 @@ pub struct Game {
     pub inventory_open: bool,
     pub inventory_mouse_x: i32,
     pub inventory_mouse_y: i32,
+    pub seed: u64,
+    pub cache_dir: Option<String>,
+    pub mouse_world_pos: (i32, i32),
+    pub mouse_ui_x: i32,
+    pub mouse_ui_y: i32,
+    pub show_tooltip: bool,
+    pub show_crosshair: bool,
 }
 
 impl Game {
     pub fn new() -> Self {
+        Self::new_with_size(WORLD_W, WORLD_H)
+    }
+
+    fn new_with_size(width: usize, height: usize) -> Self {
         let mut entities = EntityManager::new();
         let player = Player::new(&mut entities);
         Self {
-            grid: Grid::new(),
+            grid: ChunkedGrid::with_size(width, height),
             ca: CellularAutomaton::new(),
             verlet: VerletSolver::new(),
             entities,
             projectiles: ProjectileManager::new(),
+            particles: ParticleManager::new(2000),
             items: ItemManager::new(),
             player,
             input: InputHandler::new(),
             ui: UiLayer::new(),
+            audio: AudioEngine::new(),
             cam_x: 100,
             cam_y: 100,
             cam_offset_x: 0,
@@ -79,184 +100,110 @@ impl Game {
             inventory_open: false,
             inventory_mouse_x: 0,
             inventory_mouse_y: 0,
+            seed: 0x1234567890ABCDEF,
+            cache_dir: None,
+            mouse_world_pos: (0, 0),
+            mouse_ui_x: 0,
+            mouse_ui_y: 0,
+            show_tooltip: false,
+            show_crosshair: false,
+        }
+    }
+
+    pub fn new_random() -> Self {
+        let seed = crate::world::cellular::random_seed();
+        let cache_dir = Some("cache/worlds".to_string());
+        let mut entities = EntityManager::new();
+        let player = Player::new(&mut entities);
+        let mut ca = CellularAutomaton::new();
+        ca.seed(seed);
+        Self {
+            grid: ChunkedGrid::infinite(seed, cache_dir.clone()),
+            ca,
+            verlet: VerletSolver::new(),
+            entities,
+            projectiles: ProjectileManager::new(),
+            particles: ParticleManager::new(2000),
+            items: ItemManager::new(),
+            player,
+            input: InputHandler::new(),
+            ui: UiLayer::new(),
+            audio: AudioEngine::new(),
+            cam_x: 0,
+            cam_y: 0,
+            cam_offset_x: 0,
+            cam_offset_y: 0,
+            running: true,
+            tick: 0,
+            fixed_dt: Duration::from_millis(16),
+            accumulator: Duration::ZERO,
+            last_time: Instant::now(),
+            last_shot_tick: 0,
+            shot_cooldown: 8,
+            fireball_mode: false,
+            corpse_decomp_timer: 0,
+            kills: 0,
+            score: 0,
+            depth: 1,
+            fps: 0.0,
+            inventory_open: false,
+            inventory_mouse_x: 0,
+            inventory_mouse_y: 0,
+            seed,
+            cache_dir,
+            mouse_world_pos: (0, 0),
+            mouse_ui_x: 0,
+            mouse_ui_y: 0,
+            show_tooltip: false,
+            show_crosshair: false,
         }
     }
 
     pub fn init_world(&mut self) {
-        let w = self.grid.width;
-        let h = self.grid.height;
-
-        for x in 0..w {
-            self.grid
-                .set_material(x as i32, (h - 1) as i32, MaterialId::Stone);
-            self.grid
-                .set_material(x as i32, (h - 2) as i32, MaterialId::Dirt);
-        }
-
-        let surface_noise = |x: i32| -> i32 {
-            let base = (h as i32 - 3) - ((x as f32 * 0.08).sin() * 4.0) as i32;
-            let detail = ((x as f32 * 0.23).sin() * 2.0) as i32;
-            (base + detail).max(10).min(h as i32 - 3)
-        };
-
-        for x in 0..w {
-            let surface = surface_noise(x as i32);
-            let biome = x / (w / 4);
-
-            for y in surface..(h as i32 - 2) {
-                if y == surface {
-                    let mat = match biome {
-                        0 => MaterialId::Grass,
-                        1 => MaterialId::Grass,
-                        2 => MaterialId::Dirt,
-                        _ => MaterialId::Stone,
-                    };
-                    self.grid.set_material(x as i32, y, mat);
-                } else if y > surface + 8 {
-                    self.grid.set_material(x as i32, y, MaterialId::Stone);
+        let cache_dir = self.cache_dir.clone();
+        let (px, py) = if let Some(ref root) = cache_dir {
+            let has_meta = WorldCache::meta_exists(root, self.seed);
+            if has_meta {
+                if let Err(e) = WorldCache::load_meta(
+                    root,
+                    self.seed,
+                    &mut self.player,
+                    &mut self.entities,
+                    &mut self.items,
+                ) {
+                    eprintln!("World cache meta load failed: {}", e);
                 } else {
-                    self.grid.set_material(x as i32, y, MaterialId::Dirt);
+                    let (px, py) = self.player.center(&self.entities);
+                    self.grid.ensure_loaded(px as i32, py as i32, 3);
+                    self.center_camera_on(px, py);
+                    return;
                 }
             }
-        }
-
-        for _ in 0..8 {
-            let cave_x = (self.ca.random_u32() % (w as u32 - 20) + 10) as i32;
-            let cave_y = (self.ca.random_u32() % (h as u32 / 3) + (h as u32 / 3) * 2) as i32;
-            let cave_r = (self.ca.random_u32() % 4 + 3) as i32;
-            for dy in -cave_r..=cave_r {
-                for dx in -cave_r..=cave_r {
-                    if dx * dx + dy * dy <= cave_r * cave_r {
-                        let cx = cave_x + dx;
-                        let cy = cave_y + dy;
-                        if cx > 1 && cx < w as i32 - 2 && cy > 1 && cy < h as i32 - 2 {
-                            self.grid.set(cx, cy, crate::world::cell::Cell::empty());
-                        }
-                    }
-                }
-            }
-        }
-
-        for tree_x in [60, 75, 130, 145, 220] {
-            let s = surface_noise(tree_x);
-            for y in (s - 6)..s {
-                if y > 5 {
-                    self.grid.set_material(tree_x, y, MaterialId::Wood);
-                }
-            }
-            for dy in -2..=0 {
-                for dx in -2..=2 {
-                    if dx * dx + dy * dy <= 5 {
-                        let cx = tree_x + dx;
-                        let cy = s - 6 + dy;
-                        if cx > 1 && cx < w as i32 - 2 && cy > 1 {
-                            if self.grid.get(cx, cy).is_empty() {
-                                self.grid.set_material(cx, cy, MaterialId::Grass);
-                            }
-                        }
-                    }
-                }
-            }
-        }
-
-        let water_x = 40;
-        for x in water_x - 10..=water_x + 10 {
-            let s = surface_noise(x);
-            for y in s - 6..s {
-                if self.grid.get(x, y).is_empty() {
-                    self.grid.set_material(x, y, MaterialId::Water);
-                }
-            }
-        }
-
-        let lava_x = 200;
-        for x in lava_x - 8..=lava_x + 8 {
-            let s = surface_noise(x);
-            for y in s - 4..s {
-                if self.grid.get(x, y).is_empty() {
-                    self.grid.set_material(x, y, MaterialId::Lava);
-                }
-            }
-        }
-
-        let sand_x = 160;
-        for dx in -10..=10 {
-            let s = surface_noise(sand_x + dx);
-            let pile_h = (10.0 - (dx as f32).abs() * 0.8) as i32;
-            for dy in 0..pile_h {
-                let y = s - 1 - dy;
-                if y > 5 && self.grid.get(sand_x + dx, y).is_empty() {
-                    self.grid.set_material(sand_x + dx, y, MaterialId::Sand);
-                }
-            }
-        }
-
-        let acid_x = 20;
-        for x in acid_x - 4..=acid_x + 4 {
-            let s = surface_noise(x);
-            for y in s - 3..s {
-                if self.grid.get(x, y).is_empty() {
-                    self.grid.set_material(x, y, MaterialId::Acid);
-                }
-            }
-        }
-
-        let wall_x = 110;
-        let wall_s = surface_noise(wall_x);
-        for y in (wall_s - 5)..wall_s {
-            self.grid.set_material(wall_x, y, MaterialId::Stone);
-            self.grid.set_material(wall_x + 1, y, MaterialId::Stone);
-        }
-
-        for _ in 0..6 {
-            let px = (self.ca.random_u32() % (w as u32 - 20) + 10) as i32;
-            let py = (self.ca.random_u32() % (h as u32 / 3) + (h as u32 / 3) * 2) as i32;
-            for dy in 0..8 {
-                for dx in -1..=1 {
-                    let cx = px + dx;
-                    let cy = py + dy;
-                    if cx > 1 && cx < w as i32 - 2 && cy < h as i32 - 3 {
-                        self.grid.set_material(cx, cy, MaterialId::Stone);
-                    }
-                }
-            }
-        }
-
-        self.grid.fill_border(MaterialId::Stone);
-
-        let cx = (w / 2) as f32;
-        let surface_x = cx as i32;
-        let mut surface_y = h as i32 - 3;
-        for y in 0..h as i32 {
-            if self.grid.get(surface_x, y).is_solid()
-                && self.grid.get(surface_x, y).material != MaterialId::Stone
+            let (px, py) = WorldGenerator::new(&mut self.ca).generate(
+                &mut self.grid,
+                &mut self.items,
+                &mut self.player,
+                &mut self.entities,
+                self.depth,
+            );
+            self.center_camera_on(px, py);
+            if let Err(e) = WorldCache::save_meta(root, self.seed, px, py, self.depth, &self.items)
             {
-                surface_y = y;
-                break;
+                eprintln!("World cache meta save failed: {}", e);
             }
-        }
-        let stair_y = (h as i32 - 2).max(surface_y + 2);
-        self.grid
-            .set_material(surface_x, stair_y, MaterialId::Stairs);
-
-        let cy = (surface_y as f32) - 5.0;
-        self.player.spawn_at(&mut self.entities, cx, cy);
-
-        let (px, py) = self.player.center(&self.entities);
-        self.center_camera_on(px, py);
-
-        self.items
-            .spawn(ItemType::Sword, px as i32 - 6, py as i32 + 1);
-        self.items
-            .spawn(ItemType::HealthPotion, px as i32 + 6, py as i32 + 1);
-        self.items
-            .spawn(ItemType::LeatherArmor, px as i32 - 3, py as i32 - 8);
-        self.items
-            .spawn(ItemType::Bow, px as i32 + 10, py as i32 + 1);
-        self.items
-            .spawn(ItemType::Shield, px as i32 - 10, py as i32 + 1);
-        self.items
-            .spawn(ItemType::ManaPotion, px as i32 + 3, py as i32 - 6);
+            (px, py)
+        } else {
+            let (px, py) = WorldGenerator::new(&mut self.ca).generate(
+                &mut self.grid,
+                &mut self.items,
+                &mut self.player,
+                &mut self.entities,
+                self.depth,
+            );
+            self.center_camera_on(px, py);
+            (px, py)
+        };
+        let _ = (px, py);
     }
 
     pub fn center_camera_on(&mut self, px: f32, py: f32) {
@@ -311,7 +258,7 @@ impl Game {
                 self.cam_y,
                 vw,
                 vh,
-                lighting::ambient_light(),
+                lighting::ambient_light_at_tick(self.tick),
             );
 
             if let Err(e) = renderer.render(
@@ -386,6 +333,9 @@ impl Game {
         // Jump: only on press, not held
         if self.input.jump_requested() {
             let on_ground = self.check_on_ground();
+            if on_ground {
+                self.audio.play("jump");
+            }
             self.player.jump(&mut self.entities, on_ground);
         }
 
@@ -422,6 +372,12 @@ impl Game {
         self.ui.clear();
         self.ui.tick_messages();
 
+        let ui_w = (vw as i32) * crate::ui::UI_SCALE;
+        let ui_h = (vh as i32) * crate::ui::UI_SCALE;
+        let fs = ((ui_h / 200).max(2)).min(6) as i32;
+        self.ui.set_font_scale(fs);
+        self.ui.resize(ui_w as usize, ui_h as usize);
+
         let player = self.player.entity(&self.entities).cloned();
         let brush = self
             .input
@@ -429,8 +385,6 @@ impl Game {
             .to_material()
             .unwrap_or(crate::world::cell::MaterialId::Empty);
         let player_alive = player.as_ref().map(|e| e.alive).unwrap_or(false);
-        let ui_w = (vw as i32) * crate::ui::UI_SCALE;
-        let ui_h = (vh as i32) * crate::ui::UI_SCALE;
         if !self.inventory_open {
             self.ui
                 .draw_character_panel(1, 1, player.as_ref(), &self.player);
@@ -447,7 +401,7 @@ impl Game {
             &self.player,
             self.fps,
         );
-        let msg_x = (ui_w / 2) - 24;
+        let msg_x = (ui_w / 2) - 24 * fs;
         self.ui.draw_messages(msg_x, 4);
         self.ui.draw_damage_numbers(self.cam_x, self.cam_y);
         self.ui.draw_edge_indicators(
@@ -483,6 +437,56 @@ impl Game {
                 .draw_death_screen(ui_w as usize, ui_h as usize, self.kills, self.score);
         }
 
+        if self.show_crosshair && !self.inventory_open {
+            let (px, py) = self.player.center(&self.entities);
+            let psx = (px as i32 - self.cam_x) * crate::ui::UI_SCALE;
+            let psy = (py as i32 - self.cam_y) * crate::ui::UI_SCALE;
+            let (mx, my) = (self.mouse_ui_x, self.mouse_ui_y);
+            let dx = mx - psx;
+            let dy = my - psy;
+            let dist = ((dx * dx + dy * dy) as f32).sqrt().max(1.0);
+            let steps = (dist / 6.0) as i32;
+            for i in 1..steps {
+                let t = i as f32 / steps as f32;
+                let x = (psx as f32 + dx as f32 * t) as i32;
+                let y = (psy as f32 + dy as f32 * t) as i32;
+                if x >= 0 && x < ui_w && y >= 0 && y < ui_h {
+                    let alpha = (180.0 * (1.0 - t * 0.4)) as u8;
+                    self.ui
+                        .set_alpha(x, y, '.', [255, 200, 80], [0, 0, 0], alpha);
+                }
+            }
+        }
+
+        if self.show_tooltip && !self.inventory_open {
+            let (mx, my) = self.mouse_world_pos;
+            if self.grid.in_bounds(mx, my) {
+                let cell = self.grid.get(mx, my);
+                let temp = self.grid.get_temp(mx, my);
+                let mat_name = match cell.material {
+                    MaterialId::Empty => "Empty",
+                    MaterialId::Sand => "Sand",
+                    MaterialId::Water => "Water",
+                    MaterialId::Stone => "Stone",
+                    MaterialId::Lava => "Lava",
+                    MaterialId::Wood => "Wood",
+                    MaterialId::Flesh => "Flesh",
+                    MaterialId::Bone => "Bone",
+                    MaterialId::Steam => "Steam",
+                    MaterialId::Fire => "Fire",
+                    MaterialId::Acid => "Acid",
+                    MaterialId::Smoke => "Smoke",
+                    MaterialId::Grass => "Grass",
+                    MaterialId::Dirt => "Dirt",
+                    MaterialId::Stairs => "Stairs",
+                };
+                let tip = format!("{} {:.0}C", mat_name, temp);
+                let tx = (self.mouse_ui_x + 4).min(ui_w - 100);
+                let ty = (self.mouse_ui_y + 4).min(ui_h - 20);
+                self.ui.draw_text(tx, ty, &tip, [220, 220, 240], 220);
+            }
+        }
+
         for e in self.entities.all() {
             if !e.alive || e.kind == EntityKind::Corpse {
                 continue;
@@ -525,7 +529,9 @@ impl Game {
     pub fn fixed_update(&mut self) {
         self.tick += 1;
 
+        self.stream_chunks();
         self.update_active_chunks();
+        self.apply_gas_damage();
         self.ca.step(&mut self.grid);
 
         self.update_entities();
@@ -546,9 +552,120 @@ impl Game {
             self.try_spawn_slime();
         }
 
+        self.spawn_ambient_particles();
+        self.play_ambient_sounds();
+        self.particles.update();
         self.grid.swap_modified_flags();
     }
 
+    fn spawn_ambient_particles(&mut self) {
+        let (px, py) = self.player.center(&self.entities);
+        let radius = 30i32;
+        let mut fire_count = 0u32;
+        let mut lava_count = 0u32;
+        let mut water_count = 0u32;
+        for dy in -radius..=radius {
+            for dx in -radius..=radius {
+                let x = px as i32 + dx;
+                let y = py as i32 + dy;
+                if !self.grid.in_bounds(x, y) {
+                    continue;
+                }
+                let cell = self.grid.get(x, y);
+                match cell.material {
+                    MaterialId::Fire => {
+                        fire_count += 1;
+                        if self.tick % 3 == 0
+                            && (dx * dx + dy * dy) < 400
+                            && self.particles.count() < 1800
+                        {
+                            let mut rng =
+                                (x as u32).wrapping_mul(7919).wrapping_add(self.tick as u32);
+                            rng ^= rng << 13;
+                            rng ^= rng >> 17;
+                            let off_x = ((rng & 0xFF) as f32 / 255.0 - 0.5) * 2.0;
+                            let off_y = ((rng >> 8 & 0xFF) as f32 / 255.0 - 0.5) * 2.0;
+                            self.particles.spawn(
+                                x as f32 + off_x,
+                                y as f32 + off_y,
+                                off_x * 0.3,
+                                -0.5 - ((rng >> 16) as f32 / 65535.0),
+                                15 + (rng % 10),
+                                [255, 140 + ((rng >> 4) % 80) as u8, 20, 200],
+                                1.0 + ((rng >> 8) % 3) as f32 * 0.5,
+                                -0.02,
+                            );
+                        }
+                    }
+                    MaterialId::Lava => {
+                        lava_count += 1;
+                        if self.tick % 20 == 0
+                            && (dx * dx + dy * dy) < 300
+                            && self.particles.count() < 1800
+                        {
+                            self.particles.spawn_burst(
+                                x as f32,
+                                y as f32,
+                                2,
+                                [255, 100, 20, 180],
+                                1.5,
+                                25,
+                                1.5,
+                                0.1,
+                            );
+                        }
+                    }
+                    MaterialId::Water => {
+                        water_count += 1;
+                    }
+                    _ => {}
+                }
+            }
+        }
+        let _ = (fire_count, lava_count, water_count);
+    }
+
+    fn play_ambient_sounds(&mut self) {
+        if !self.audio.is_enabled() {
+            return;
+        }
+        let (px, py) = self.player.center(&self.entities);
+        let radius = 15i32;
+        let mut has_lava = false;
+        let mut has_fire = false;
+        let mut has_acid = false;
+        let mut has_water = false;
+        for dy in -radius..=radius {
+            for dx in -radius..=radius {
+                let x = px as i32 + dx;
+                let y = py as i32 + dy;
+                if !self.grid.in_bounds(x, y) {
+                    continue;
+                }
+                let cell = self.grid.get(x, y);
+                match cell.material {
+                    MaterialId::Lava => has_lava = true,
+                    MaterialId::Fire => has_fire = true,
+                    MaterialId::Acid => has_acid = true,
+                    MaterialId::Water => has_water = true,
+                    _ => {}
+                }
+            }
+        }
+        if has_lava && self.tick % 30 == 0 {
+            self.audio.play_throttled("lava_bubble", 500);
+        }
+        if has_fire && self.tick % 15 == 0 {
+            self.audio.play_throttled("fire_crackle", 200);
+        }
+        if has_acid && self.tick % 20 == 0 {
+            self.audio.play_throttled("acid_sizzle", 300);
+        }
+        if has_water && self.tick % 40 == 0 {
+            self.audio.play_throttled("water_splash", 600);
+        }
+    }
+
     fn update_score(&mut self) {
         let mut new_kills = 0;
         for e in self.entities.all_mut() {
@@ -566,6 +683,21 @@ impl Game {
         }
     }
 
+    fn apply_gas_damage(&mut self) {
+        for e in self.entities.all_mut() {
+            if e.alive {
+                let (ex, ey) = e.center();
+                let (gas_type, gas_density) = self.grid.get_gas(ex as i32, ey as i32);
+                if gas_type == 2 && gas_density > 50 {
+                    e.health -= (gas_density as f32 - 50.0) * 0.1;
+                }
+                if gas_type == 3 && gas_density > 100 {
+                    e.health -= 2.0;
+                }
+            }
+        }
+    }
+
     fn update_status_effects(&mut self) {
         for e in self.entities.all_mut() {
             if e.alive {
@@ -588,6 +720,7 @@ impl Game {
             let item = self.items.all_mut().remove(idx);
             self.ui.add_message(&format!("Picked up {}", item.name()));
             self.player.inventory.push(item);
+            self.audio.play("pickup");
         }
     }
 
@@ -604,7 +737,7 @@ impl Game {
             return;
         }
         self.depth += 1;
-        self.grid = Grid::new();
+        self.grid = ChunkedGrid::with_size(self.grid.width, self.grid.height);
         self.entities = EntityManager::new();
         self.player = Player::new(&mut self.entities);
         self.projectiles = ProjectileManager::new();
@@ -613,6 +746,7 @@ impl Game {
         self.init_world();
         self.ui
             .add_message(&format!("Descended to depth {}", self.depth));
+        self.audio.play("descend");
     }
 
     pub fn use_item(&mut self, index: usize) {
@@ -643,6 +777,7 @@ impl Game {
             self.player.inventory.remove(index);
             self.ui.add_message(&format!("Consumed {}", name));
         }
+        self.audio.play("powerup");
     }
 
     pub fn drop_item(&mut self, index: usize) {
@@ -655,39 +790,114 @@ impl Game {
         self.ui.add_message(&format!("Dropped {}", item.name()));
     }
 
-    fn update_active_chunks(&mut self) {
-        self.grid.deactivate_all();
-
-        for e in self.entities.all() {
-            let (cx, cy) = e.center();
-            self.grid.activate_around(cx as i32, cy as i32, 2);
+    fn stream_chunks(&mut self) {
+        if !self.grid.is_infinite() && self.grid.width <= 2048 {
+            return;
         }
-
-        for p in self.projectiles.all() {
-            self.grid.activate_around(p.x as i32, p.y as i32, 1);
-        }
-
-        for item in self.items.all() {
-            self.grid.activate_around(item.x, item.y, 1);
-        }
-
+        let (px, py) = self.player.center(&self.entities);
+        let px = px as i32;
+        let py = py as i32;
+        let (pcx, pcy, _, _) = self.grid.chunk_at(px, py);
+        let radius = 2;
         let chunk_size = self.grid.chunk_size as i32;
-        for cy in 0..self.grid.chunks_y as i32 {
-            for cx in 0..self.grid.chunks_x as i32 {
-                let idx = self.grid.chunk_index(cx, cy);
-                if self.grid.chunks[idx].modified || self.grid.chunks[idx].was_modified {
-                    self.grid
-                        .activate_around(cx * chunk_size, cy * chunk_size, 1);
+
+        for dy in -radius..=radius {
+            for dx in -radius..=radius {
+                let cx = pcx + dx;
+                let cy = pcy + dy;
+                let ox = cx * chunk_size;
+                let oy = cy * chunk_size;
+                if !self.grid.in_bounds(ox, oy) {
+                    continue;
                 }
+                self.grid.ensure_chunk(cx, cy);
+                if !self.grid.is_chunk_generated(cx, cy) {
+                    WorldGenerator::new(&mut self.ca).generate_chunk(&mut self.grid, cx, cy);
+                }
+            }
+        }
+
+        if let Some(ref dir) = self.cache_dir {
+            let save_radius = radius + 2;
+            if self.tick % 10 == 0 {
+                let coords = self.grid.all_chunk_coords();
+                for (cx, cy) in coords {
+                    let dx = (cx - pcx).abs();
+                    let dy = (cy - pcy).abs();
+                    if (dx > save_radius || dy > save_radius) && self.grid.is_chunk_modified(cx, cy)
+                    {
+                        let path = crate::world::chunked_grid::chunk_path(dir, self.seed, cx, cy);
+                        let _ = self.grid.save_chunk(path.to_str().unwrap(), cx, cy);
+                        break;
+                    }
+                }
+            }
+        }
+
+        if self.tick % 120 == 0 {
+            let unload_radius = radius + 4;
+            let to_unload: Vec<(i32, i32)> = self
+                .grid
+                .all_chunk_coords()
+                .into_iter()
+                .filter(|(cx, cy)| {
+                    let dx = (cx - pcx).abs();
+                    let dy = (cy - pcy).abs();
+                    dx > unload_radius || dy > unload_radius
+                })
+                .collect();
+            for (cx, cy) in to_unload {
+                if self.grid.is_chunk_modified(cx, cy) {
+                    if let Some(ref dir) = self.cache_dir {
+                        let path = crate::world::chunked_grid::chunk_path(dir, self.seed, cx, cy);
+                        let _ = self.grid.save_chunk(path.to_str().unwrap(), cx, cy);
+                    }
+                }
+                self.grid.unload_chunk(cx, cy);
             }
         }
     }
 
+    fn update_active_chunks(&mut self) {
+        if !self.grid.is_infinite() {
+            for e in self.entities.all() {
+                let (cx, cy) = e.center();
+                self.grid.activate_around(cx as i32, cy as i32, 1);
+            }
+            for (cx, cy) in self.grid.all_chunk_coords() {
+                if self.grid.get_chunk_dirty(cx, cy).is_some() {
+                    self.grid.set_chunk_active(cx, cy, true);
+                }
+            }
+            return;
+        }
+
+        self.grid.deactivate_all();
+
+        for (cx, cy) in self.grid.all_chunk_coords() {
+            self.grid.set_chunk_active(cx, cy, true);
+        }
+    }
+
     pub fn update_projectiles(&mut self) {
+        let count_before = self.projectiles.all().len();
         self.projectiles.update(&self.grid);
         self.projectiles
             .resolve_hits(&mut self.grid, self.entities.all_mut(), &mut self.ui);
         self.projectiles.cull_dead();
+        let count_after = self.projectiles.all().len();
+        if count_after < count_before {
+            let any_fireball = self
+                .projectiles
+                .all()
+                .iter()
+                .any(|p| p.typ == ProjectileType::Fireball);
+            if any_fireball || self.fireball_mode {
+                self.audio.play("explosion");
+            } else {
+                self.audio.play("hit");
+            }
+        }
     }
 
     pub fn player_shoot(&mut self, dir_x: f32, dir_y: f32) {
@@ -717,6 +927,7 @@ impl Game {
         self.projectiles
             .spawn(typ, spawn_x, spawn_y, vx, vy, owner, damage_bonus);
         self.last_shot_tick = self.tick;
+        self.audio.play("shoot");
     }
 
     fn update_goblin_ai(&mut self) {
@@ -942,6 +1153,7 @@ impl Game {
                             _ => "Enemy hits you!",
                         };
                         self.ui.add_message(msg);
+                        self.audio.play("hit");
                     }
                 }
             }
@@ -1386,6 +1598,71 @@ impl Game {
         }
     }
 
+    fn find_spawn_location(&self, near_x: i32, near_y: i32, radius: i32) -> Option<(i32, i32)> {
+        for r in 0..=radius {
+            for dy in -r..=r {
+                for dx in -r..=r {
+                    if dx.abs() + dy.abs() != r {
+                        continue;
+                    }
+                    let x = near_x + dx;
+                    let y = near_y + dy;
+                    let _sc = crate::world::worldgen::WORLD_SCALE;
+                    let clear_h = 8;
+                    if !self.grid.in_bounds(x, y) || !self.grid.in_bounds(x, y - clear_h) {
+                        continue;
+                    }
+                    if !self.grid.get(x, y).is_empty() || !self.grid.get(x, y + 1).is_solid() {
+                        continue;
+                    }
+                    let mut clear = true;
+                    for k in -clear_h..=0 {
+                        if !self.grid.get(x, y + k).is_empty() {
+                            clear = false;
+                            break;
+                        }
+                    }
+                    if clear {
+                        return Some((x, y - clear_h));
+                    }
+                }
+            }
+        }
+        None
+    }
+
+    fn find_surface_spawn(
+        &self,
+        px: f32,
+        py: f32,
+        offset: i32,
+        height_offset: i32,
+    ) -> Option<(i32, i32)> {
+        let spawn_x = px as i32 + offset;
+        if !self.grid.in_bounds(spawn_x, 0) {
+            return None;
+        }
+        let search_top = 0;
+        let search_bottom = if self.grid.is_infinite() {
+            py as i32 + crate::world::worldgen::WORLD_SCALE * 50
+        } else {
+            self.grid.height as i32 - 3
+        };
+        let mut surface_y = search_bottom;
+        for y in search_top..=search_bottom {
+            let cell = self.grid.get(spawn_x, y);
+            if cell.is_solid() && cell.material != MaterialId::Stone {
+                surface_y = y;
+                break;
+            }
+        }
+        let spawn_y = surface_y - height_offset;
+        if !self.grid.in_bounds(spawn_x, spawn_y) {
+            return None;
+        }
+        Some((spawn_x, spawn_y))
+    }
+
     fn try_spawn_goblin(&mut self) {
         let max_goblins = 3usize + self.depth.min(5) as usize;
         let alive_goblins = self
@@ -1398,33 +1675,27 @@ impl Game {
             return;
         }
 
-        let (px, _py) = self.player.center(&self.entities);
-        let spawn_x = px as i32 + if px as i32 % 2 == 0 { 15 } else { -15 };
-        if !self.grid.in_bounds(spawn_x, 0) {
-            return;
-        }
+        let (px, py) = self.player.center(&self.entities);
+        let offset = if px as i32 % 2 == 0 {
+            crate::world::worldgen::WORLD_SCALE * 15
+        } else {
+            -(crate::world::worldgen::WORLD_SCALE * 15)
+        };
+        let spawn = if self.depth <= 3 {
+            self.find_surface_spawn(px, py, offset, crate::world::worldgen::WORLD_SCALE * 5)
+        } else {
+            self.find_spawn_location(px as i32 + offset, py as i32, 3)
+        };
 
-        let mut surface_y = self.grid.height as i32 - 3;
-        for y in 0..self.grid.height as i32 {
-            let cell = self.grid.get(spawn_x, y);
-            if cell.is_solid() && cell.material != MaterialId::Stone {
-                surface_y = y;
-                break;
+        if let Some((spawn_x, spawn_y)) = spawn {
+            let id = self.entities.spawn(EntityKind::Goblin);
+            if let Some(g) = self.entities.get_mut(id) {
+                g.build_humanoid(spawn_x as f32, spawn_y as f32);
+                g.health += self.depth as f32 * 5.0;
+                g.max_health += self.depth as f32 * 5.0;
+                g.strength += self.depth;
             }
         }
-        let spawn_y = surface_y - 5;
-
-        if !self.grid.in_bounds(spawn_x, spawn_y) {
-            return;
-        }
-
-        let id = self.entities.spawn(EntityKind::Goblin);
-        if let Some(g) = self.entities.get_mut(id) {
-            g.build_humanoid(spawn_x as f32, spawn_y as f32);
-            g.health += self.depth as f32 * 5.0;
-            g.max_health += self.depth as f32 * 5.0;
-            g.strength += self.depth;
-        }
     }
 
     fn try_spawn_slime(&mut self) {
@@ -1439,31 +1710,69 @@ impl Game {
             return;
         }
 
-        let (px, _py) = self.player.center(&self.entities);
-        let spawn_x = px as i32 + if px as i32 % 2 == 0 { -18 } else { 18 };
-        if !self.grid.in_bounds(spawn_x, 0) {
-            return;
-        }
+        let (px, py) = self.player.center(&self.entities);
+        let offset = if px as i32 % 2 == 0 {
+            -(crate::world::worldgen::WORLD_SCALE * 18)
+        } else {
+            crate::world::worldgen::WORLD_SCALE * 18
+        };
+        let spawn = if self.depth <= 3 {
+            self.find_surface_spawn(px, py, offset, crate::world::worldgen::WORLD_SCALE * 3)
+        } else {
+            self.find_spawn_location(px as i32 + offset, py as i32, 3)
+        };
 
-        let mut surface_y = self.grid.height as i32 - 3;
-        for y in 0..self.grid.height as i32 {
-            let cell = self.grid.get(spawn_x, y);
-            if cell.is_solid() && cell.material != MaterialId::Stone {
-                surface_y = y;
-                break;
+        if let Some((spawn_x, spawn_y)) = spawn {
+            let id = self.entities.spawn(EntityKind::Slime);
+            if let Some(s) = self.entities.get_mut(id) {
+                s.build_humanoid(spawn_x as f32, spawn_y as f32);
+                s.health += self.depth as f32 * 3.0;
+                s.max_health += self.depth as f32 * 3.0;
             }
         }
-        let spawn_y = surface_y - 3;
+    }
 
-        if !self.grid.in_bounds(spawn_x, spawn_y) {
-            return;
+    pub fn trigger_explosion(&mut self, x: i32, y: i32, radius: i32, damage: f32) {
+        for dy in -radius..=radius {
+            for dx in -radius..=radius {
+                let dist_sq = dx * dx + dy * dy;
+                if dist_sq > radius * radius {
+                    continue;
+                }
+                let bx = x + dx;
+                let by = y + dy;
+                if !self.grid.in_bounds(bx, by) {
+                    continue;
+                }
+                let cell = self.grid.get(bx, by);
+                if cell.is_solid() && !cell.is_static() {
+                    self.grid.set(bx, by, crate::world::cell::Cell::empty());
+                } else if cell.is_empty() {
+                    let mut fire = crate::world::cell::Cell::new(MaterialId::Fire);
+                    fire.updated_this_tick = true;
+                    self.grid.set(bx, by, fire);
+                    self.grid.set_temp(bx, by, 600.0);
+                }
+                self.grid.set_pressure(bx, by, 255);
+                self.grid.mark_dirty(bx, by);
+            }
         }
-
-        let id = self.entities.spawn(EntityKind::Slime);
-        if let Some(s) = self.entities.get_mut(id) {
-            s.build_humanoid(spawn_x as f32, spawn_y as f32);
-            s.health += self.depth as f32 * 3.0;
-            s.max_health += self.depth as f32 * 3.0;
+        self.audio.play("explosion");
+        for e in self.entities.all_mut() {
+            if !e.alive {
+                continue;
+            }
+            let dx = e.cx as i32 - x;
+            let dy = e.cy as i32 - y;
+            let dist = ((dx * dx + dy * dy) as f32).sqrt();
+            if dist < radius as f32 * 1.5 {
+                let dmg = (damage * (1.0 - dist / (radius as f32 * 1.5))).max(0.0);
+                e.take_damage(dmg);
+                let knockback = (1.0 - dist / (radius as f32 * 1.5)).max(0.0) * 5.0;
+                let dir = if dx == 0 { 0.0 } else { dx as f32 / dist };
+                e.set_horizontal_vel(dir * knockback);
+                e.set_vertical_vel(-knockback * 0.5);
+            }
         }
     }
 }

src/input.rs

@@ -82,14 +82,16 @@ impl InputHandler {
     pub fn start(&mut self) {
         let (tx, rx) = mpsc::channel::<Event>();
         self.receiver = Some(rx);
-        self.input_thread = Some(thread::spawn(move || loop {
-            match event::read() {
-                Ok(ev) => {
-                    if tx.send(ev).is_err() {
-                        break;
+        self.input_thread = Some(thread::spawn(move || {
+            loop {
+                match event::read() {
+                    Ok(ev) => {
+                        if tx.send(ev).is_err() {
+                            break;
+                        }
                     }
+                    Err(_) => break,
                 }
-                Err(_) => break,
             }
         }));
     }

src/lib.rs

@@ -1,4 +1,5 @@
 pub mod ai;
+pub mod audio;
 pub mod entity;
 pub mod game;
 pub mod input;

src/main.rs

@@ -8,6 +8,7 @@ use verbatim::render::lighting;
 use verbatim::render::terminal::TerminalRenderer;
 use verbatim::render::window_input::WindowInput;
 use verbatim::world::cell::MaterialId;
+use verbatim::world::chunked_grid::ChunkedGrid;
 use winit::event::{Event, WindowEvent};
 use winit::event_loop::{ControlFlow, EventLoop};
 use winit::window::Window;
@@ -42,6 +43,9 @@ struct Cli {
     #[arg(long, default_value = "benchmark_results.json")]
     benchmark_output: String,
 
+    #[arg(long, default_value = "surface")]
+    benchmark_biome: String,
+
     #[arg(long, default_value_t = 5)]
     tape_interval: u32,
 
@@ -58,7 +62,7 @@ trait GpuRenderer {
         Self: Sized;
     fn render(
         &mut self,
-        grid: &verbatim::world::grid::Grid,
+        grid: &ChunkedGrid,
         entities: &verbatim::entity::EntityManager,
         items: &verbatim::entity::item::ItemManager,
         ui: &verbatim::ui::UiLayer,
@@ -68,6 +72,8 @@ trait GpuRenderer {
     );
     fn grid_w(&self) -> usize;
     fn grid_h(&self) -> usize;
+    fn cell_pixel_size(&self) -> u32;
+    fn upload_particles(&mut self, particles: &verbatim::physics::particle::ParticleManager);
 }
 
 impl GpuRenderer for verbatim::render::vulkan::VulkanRenderer {
@@ -76,7 +82,7 @@ impl GpuRenderer for verbatim::render::vulkan::VulkanRenderer {
     }
     fn render(
         &mut self,
-        grid: &verbatim::world::grid::Grid,
+        grid: &ChunkedGrid,
         entities: &verbatim::entity::EntityManager,
         items: &verbatim::entity::item::ItemManager,
         ui: &verbatim::ui::UiLayer,
@@ -94,6 +100,12 @@ impl GpuRenderer for verbatim::render::vulkan::VulkanRenderer {
     fn grid_h(&self) -> usize {
         verbatim::render::vulkan::VulkanRenderer::grid_h(self)
     }
+    fn cell_pixel_size(&self) -> u32 {
+        verbatim::render::vulkan::VulkanRenderer::cell_pixel_size(self)
+    }
+    fn upload_particles(&mut self, particles: &verbatim::physics::particle::ParticleManager) {
+        verbatim::render::vulkan::VulkanRenderer::upload_particles(self, particles);
+    }
 }
 
 impl GpuRenderer for verbatim::render::graphics::GraphicsRenderer {
@@ -102,7 +114,7 @@ impl GpuRenderer for verbatim::render::graphics::GraphicsRenderer {
     }
     fn render(
         &mut self,
-        grid: &verbatim::world::grid::Grid,
+        grid: &ChunkedGrid,
         entities: &verbatim::entity::EntityManager,
         items: &verbatim::entity::item::ItemManager,
         ui: &verbatim::ui::UiLayer,
@@ -120,6 +132,12 @@ impl GpuRenderer for verbatim::render::graphics::GraphicsRenderer {
     fn grid_h(&self) -> usize {
         verbatim::render::graphics::GraphicsRenderer::grid_h(self)
     }
+    fn cell_pixel_size(&self) -> u32 {
+        verbatim::render::graphics::GraphicsRenderer::cell_pixel_size(self)
+    }
+    fn upload_particles(&mut self, particles: &verbatim::physics::particle::ParticleManager) {
+        verbatim::render::graphics::GraphicsRenderer::upload_particles(self, particles);
+    }
 }
 
 fn main() {
@@ -139,7 +157,7 @@ fn main() {
                 eprintln!("PANIC: {}", info);
             }));
             let mut renderer = TerminalRenderer::new();
-            let mut game = Game::new();
+            let mut game = Game::new_random();
             game.run(&mut renderer);
         }
         "ascii" => {
@@ -216,13 +234,13 @@ fn run_gpu_mode<R: GpuRenderer>(title: &str) {
             eprintln!("Vulkan init failed: {e}");
             eprintln!("Falling back to terminal mode...");
             let mut renderer = TerminalRenderer::new();
-            let mut game = Game::new();
+            let mut game = Game::new_random();
             game.run(&mut renderer);
             return;
         }
     };
 
-    let mut game = Game::new();
+    let mut game = Game::new_random();
     game.init_world();
 
     let mut input = WindowInput::new();
@@ -253,6 +271,20 @@ fn run_gpu_mode<R: GpuRenderer>(title: &str) {
                     }
                     WindowEvent::CursorMoved { position, .. } => {
                         input.on_mouse_move(position.x, position.y);
+                        let cell_px = renderer.cell_pixel_size() as f64;
+                        let vw = renderer.grid_w();
+                        let vh = renderer.grid_h();
+                        game.mouse_ui_x =
+                            (position.x / cell_px * verbatim::ui::UI_SCALE as f64) as i32;
+                        game.mouse_ui_y =
+                            (position.y / cell_px * verbatim::ui::UI_SCALE as f64) as i32;
+                        game.show_tooltip = true;
+                        game.show_crosshair = true;
+                        if vw > 0 && vh > 0 && cell_px > 0.0 {
+                            let wx = game.cam_x + (position.x / cell_px) as i32;
+                            let wy = game.cam_y + (position.y / cell_px) as i32;
+                            game.mouse_world_pos = (wx, wy);
+                        }
                     }
                     WindowEvent::MouseInput { state, button, .. } => {
                         input.on_mouse_button(button, state);
@@ -291,8 +323,15 @@ fn run_gpu_mode<R: GpuRenderer>(title: &str) {
                         return;
                     }
 
+                    if input.toggle_audio {
+                        game.audio.toggle();
+                    }
+
                     if input.jump {
                         let on_ground = game.check_on_ground();
+                        if on_ground {
+                            game.audio.play("jump");
+                        }
                         game.player.jump(&mut game.entities, on_ground);
                     }
 
@@ -310,9 +349,12 @@ fn run_gpu_mode<R: GpuRenderer>(title: &str) {
                         || input.shoot_up
                         || input.shoot_down
                     {
+                        let cell_px = renderer.cell_pixel_size() as f64;
                         let (px, py) = game.player.center(&game.entities);
-                        let player_screen_x = ((px as i32 - game.cam_x) as f64) * 8.0 + 4.0;
-                        let player_screen_y = ((py as i32 - game.cam_y) as f64) * 8.0 + 4.0;
+                        let player_screen_x =
+                            ((px as i32 - game.cam_x) as f64) * cell_px + cell_px / 2.0;
+                        let player_screen_y =
+                            ((py as i32 - game.cam_y) as f64) * cell_px + cell_px / 2.0;
 
                         let (dx, dy) = if input.shoot_mouse {
                             let mx = input.mouse_x - player_screen_x;
@@ -497,6 +539,7 @@ fn run_gpu_mode<R: GpuRenderer>(title: &str) {
 
                     game.build_ui(vw, vh);
 
+                    renderer.upload_particles(&game.particles);
                     renderer.render(
                         &game.grid,
                         &game.entities,
@@ -533,19 +576,25 @@ fn run_benchmark_mode(cli: &Cli) {
     let ticks = cli.benchmark_ticks;
     let renderer_type = cli.benchmark_renderer.as_str();
     let output_path = cli.benchmark_output.as_str();
+    let biome = cli.benchmark_biome.as_str();
 
-    eprintln!("Benchmark: {} ticks, renderer={}", ticks, renderer_type);
+    eprintln!(
+        "Benchmark: {} ticks, renderer={}, biome={}",
+        ticks, renderer_type, biome
+    );
 
     match renderer_type {
         "ascii" => run_benchmark_inner::<verbatim::render::vulkan::VulkanRenderer>(
             ticks,
             output_path,
             "ascii",
+            biome,
         ),
         "graphics" => run_benchmark_inner::<verbatim::render::graphics::GraphicsRenderer>(
             ticks,
             output_path,
             "graphics",
+            biome,
         ),
         _ => {
             eprintln!(
@@ -557,7 +606,12 @@ fn run_benchmark_mode(cli: &Cli) {
     }
 }
 
-fn run_benchmark_inner<R: GpuRenderer>(ticks: u32, output_path: &str, mode_name: &str) {
+fn run_benchmark_inner<R: GpuRenderer>(
+    ticks: u32,
+    output_path: &str,
+    mode_name: &str,
+    biome: &str,
+) {
     let event_loop = EventLoop::new().expect("Failed to create event loop");
     let window = event_loop
         .create_window(
@@ -576,9 +630,25 @@ fn run_benchmark_inner<R: GpuRenderer>(ticks: u32, output_path: &str, mode_name:
         }
     };
 
-    let mut game = Game::new();
+    let mut game = Game::new_random();
     game.init_world();
 
+    let chunk_size = game.grid.chunk_size as i32;
+    let (px, _py) = game.player.center(&game.entities);
+    match biome {
+        "caves" => {
+            let cave_y = 2 * chunk_size + chunk_size / 2;
+            game.player
+                .set_position(&mut game.entities, px, cave_y as f32);
+        }
+        "dungeon" => {
+            let dungeon_y = 6 * chunk_size + chunk_size / 2;
+            game.player
+                .set_position(&mut game.entities, px, dungeon_y as f32);
+        }
+        _ => {}
+    }
+
     let mut tick_count = 0u32;
     let mut ca_times_us: Vec<u64> = Vec::with_capacity(ticks as usize);
     let mut render_times_us: Vec<u64> = Vec::with_capacity(ticks as usize);
@@ -908,14 +978,14 @@ fn run_capture(ticks: u32) {
 }
 
 fn dump_view(
-    grid: &verbatim::world::grid::Grid,
+    grid: &ChunkedGrid,
     entities: &verbatim::entity::EntityManager,
     cam_x: i32,
     cam_y: i32,
-    vw: usize,
-    vh: usize,
+    w: usize,
+    h: usize,
 ) -> String {
-    ai::render_view(grid, entities, cam_x, cam_y, vw, vh)
+    ai::render_view(grid, entities, cam_x, cam_y, w, h)
         .lines()
         .enumerate()
         .map(|(i, line)| format!("{:2}{}", (cam_y + i as i32) % 100, line))

src/physics/collision.rs

@@ -1,6 +1,6 @@
-use crate::world::cell::MaterialId;
-use crate::world::grid::Grid;
 use crate::physics::verlet::SubBody;
+use crate::world::cell::MaterialId;
+use crate::world::chunked_grid::ChunkedGrid;
 
 pub struct CollisionResult {
     pub on_ground: bool,
@@ -24,7 +24,7 @@ impl CollisionResult {
     }
 }
 
-pub fn resolve_grid_collision(grid: &Grid, body: &mut SubBody) -> CollisionResult {
+pub fn resolve_grid_collision(grid: &ChunkedGrid, body: &mut SubBody) -> CollisionResult {
     let mut result = CollisionResult::none();
 
     let r = body.radius;

src/physics/mod.rs

@@ -1,3 +1,4 @@
 pub mod collision;
+pub mod particle;
 pub mod projectile;
 pub mod verlet;

src/physics/particle.rs

@@ -0,0 +1,113 @@
+#[derive(Clone, Copy)]
+pub struct Particle {
+    pub x: f32,
+    pub y: f32,
+    pub vx: f32,
+    pub vy: f32,
+    pub life: u32,
+    pub max_life: u32,
+    pub color: [u8; 4],
+    pub size: f32,
+    pub gravity: f32,
+}
+
+impl Particle {
+    pub fn alive(&self) -> bool {
+        self.life > 0
+    }
+}
+
+pub struct ParticleManager {
+    particles: Vec<Particle>,
+    capacity: usize,
+}
+
+impl ParticleManager {
+    pub fn new(capacity: usize) -> Self {
+        Self {
+            particles: Vec::with_capacity(capacity),
+            capacity,
+        }
+    }
+
+    pub fn spawn(
+        &mut self,
+        x: f32,
+        y: f32,
+        vx: f32,
+        vy: f32,
+        life: u32,
+        color: [u8; 4],
+        size: f32,
+        gravity: f32,
+    ) {
+        if self.particles.len() >= self.capacity {
+            return;
+        }
+        self.particles.push(Particle {
+            x,
+            y,
+            vx,
+            vy,
+            life,
+            max_life: life,
+            color,
+            size,
+            gravity,
+        });
+    }
+
+    pub fn spawn_burst(
+        &mut self,
+        x: f32,
+        y: f32,
+        count: usize,
+        color: [u8; 4],
+        speed: f32,
+        life: u32,
+        size: f32,
+        gravity: f32,
+    ) {
+        let mut rng = 0x12345u32;
+        for _ in 0..count {
+            rng ^= rng << 13;
+            rng ^= rng >> 17;
+            rng ^= rng << 5;
+            let angle = (rng as f32 / u32::MAX as f32) * std::f32::consts::TAU;
+            let s = speed * (0.3 + 0.7 * ((rng >> 16) as f32 / u16::MAX as f32));
+            let vx = angle.cos() * s;
+            let vy = angle.sin() * s - speed * 0.3;
+            self.spawn(x, y, vx, vy, life, color, size, gravity);
+        }
+    }
+
+    pub fn update(&mut self) {
+        for p in &mut self.particles {
+            p.life = p.life.saturating_sub(1);
+            p.vy += p.gravity;
+            p.x += p.vx;
+            p.y += p.vy;
+            p.vx *= 0.96;
+            p.vy *= 0.96;
+        }
+        self.particles.retain(|p| p.alive());
+    }
+
+    pub fn all(&self) -> &[Particle] {
+        &self.particles
+    }
+
+    pub fn clear(&mut self) {
+        self.particles.clear();
+    }
+
+    pub fn count(&self) -> usize {
+        self.particles.len()
+    }
+}
+
+impl Default for ParticleManager {
+    fn default() -> Self {
+        Self::new(2000)
+    }
+}

src/physics/projectile.rs

@@ -1,6 +1,6 @@
 use crate::entity::entity::{Entity, EntityId};
 use crate::world::cell::{Cell, MaterialId};
-use crate::world::grid::Grid;
+use crate::world::chunked_grid::ChunkedGrid;
 
 #[derive(Clone, Copy, Debug, PartialEq, Eq)]
 pub enum ProjectileType {
@@ -65,7 +65,7 @@ impl Projectile {
         self.damage + self.damage_bonus
     }
 
-    pub fn update(&mut self, grid: &Grid) {
+    pub fn update(&mut self, grid: &ChunkedGrid) {
         if !self.alive {
             return;
         }
@@ -118,7 +118,12 @@ impl Projectile {
         dx.abs() < hit_w && dy.abs() < hit_h
     }
 
-    pub fn apply_impact(&self, grid: &mut Grid, entity: &mut Entity, ui: &mut crate::ui::UiLayer) {
+    pub fn apply_impact(
+        &self,
+        grid: &mut ChunkedGrid,
+        entity: &mut Entity,
+        ui: &mut crate::ui::UiLayer,
+    ) {
         if self.typ == ProjectileType::Fireball {
             let min_x = (self.x - 1.5).floor() as i32;
             let max_x = (self.x + 1.5).ceil() as i32;
@@ -131,15 +136,18 @@ impl Projectile {
                     }
                     let cell = grid.get(x, y);
                     if cell.is_empty() {
-                        grid.set(x, y, Cell::new(MaterialId::Fire));
+                        let mut fire = Cell::new(MaterialId::Fire);
+                        fire.updated_this_tick = true;
+                        grid.set(x, y, fire);
                     } else if cell.material == MaterialId::Wood
                         || cell.material == MaterialId::Grass
                         || cell.material == MaterialId::Flesh
                     {
                         let mut ignited = cell;
                         ignited.material = MaterialId::Fire;
-                        ignited.temp = 400.0;
+                        ignited.updated_this_tick = true;
                         grid.set(x, y, ignited);
+                        grid.set_temp(x, y, 400.0);
                     }
                 }
             }
@@ -226,7 +234,7 @@ impl ProjectileManager {
         self.spawn(ProjectileType::Arrow, x, y, vx, vy, owner, 0.0)
     }
 
-    pub fn update(&mut self, grid: &Grid) {
+    pub fn update(&mut self, grid: &ChunkedGrid) {
         for p in &mut self.projectiles {
             p.update(grid);
         }
@@ -234,7 +242,7 @@ impl ProjectileManager {
 
     pub fn resolve_hits(
         &mut self,
-        grid: &mut Grid,
+        grid: &mut ChunkedGrid,
         entities: &mut [Entity],
         ui: &mut crate::ui::UiLayer,
     ) {

src/render/capture.rs

@@ -3,14 +3,14 @@ use crate::entity::EntityManager;
 use crate::render::lighting;
 use crate::ui::UiLayer;
 use crate::world::cell::MaterialId;
-use crate::world::grid::Grid;
+use crate::world::chunked_grid::ChunkedGrid;
 use image::{ImageBuffer, RgbImage};
 
 pub const CELL_SIZE: u32 = 8;
 pub const UI_CELL_SIZE: u32 = 2;
 
 pub fn capture_frame(
-    grid: &Grid,
+    grid: &ChunkedGrid,
     entities: &EntityManager,
     items: &ItemManager,
     ui: &UiLayer,
@@ -145,7 +145,7 @@ fn entity_positions(
 
 fn shadow_positions(
     entity_positions: &std::collections::HashMap<(i32, i32), [u8; 3]>,
-    grid: &Grid,
+    grid: &ChunkedGrid,
     cam_x: i32,
     cam_y: i32,
     view_w: u32,
@@ -203,7 +203,7 @@ fn draw_cell(img: &mut RgbImage, vx: u32, vy: u32, color: [u8; 3]) {
 
 pub fn save_capture(
     path: &str,
-    grid: &Grid,
+    grid: &ChunkedGrid,
     entities: &EntityManager,
     items: &ItemManager,
     ui: &UiLayer,
@@ -221,7 +221,7 @@ pub fn save_capture(
 }
 
 pub fn capture_from_state(
-    grid: &Grid,
+    grid: &ChunkedGrid,
     entities: &EntityManager,
     items: &ItemManager,
     ui: &UiLayer,

src/render/graphics.rs

@@ -5,7 +5,8 @@ use std::sync::Arc;
 use crate::entity::EntityManager;
 use crate::render::lighting;
 use crate::world::cell::MaterialId;
-use crate::world::grid::{Grid, WORLD_H, WORLD_W};
+use crate::world::chunked_grid::ChunkedGrid;
+use crate::world::grid::{MAX_WORLD_H, MAX_WORLD_W};
 
 const CHAR_W: u32 = 8;
 const CHAR_H: u32 = 8;
@@ -45,6 +46,14 @@ struct ColorInstance {
     color: [u8; 4],
 }
 
+#[repr(C)]
+#[derive(Clone, Copy, Default)]
+struct ParticleInstance {
+    grid_x: f32,
+    grid_y: f32,
+    color: [u8; 4],
+}
+
 #[repr(C)]
 #[derive(bytemuck::NoUninit, Clone, Copy, Default)]
 struct GpuLightSource {
@@ -114,6 +123,12 @@ pub struct GraphicsRenderer {
     ui_instance_ptr: *mut ColorInstance,
     ui_instance_capacity: usize,
 
+    particle_instance_buffer: vk::Buffer,
+    particle_instance_memory: vk::DeviceMemory,
+    particle_instance_ptr: *mut ParticleInstance,
+    particle_instance_capacity: usize,
+    particle_count: usize,
+
     grid_buffer: vk::Buffer,
     grid_memory: vk::DeviceMemory,
     grid_ptr: *mut u32,
@@ -552,13 +567,14 @@ impl GraphicsRenderer {
             Ok((buf, mem))
         };
 
-        let grid_data = vec![0u32; WORLD_W * WORLD_H];
+        let grid_count = MAX_WORLD_W * MAX_WORLD_H;
+        let grid_data = vec![0u32; grid_count];
         let (grid_buffer, grid_memory) = make_buf(
             bytemuck::cast_slice(&grid_data),
             vk::BufferUsageFlags::STORAGE_BUFFER,
         )?;
         let grid_ptr = unsafe {
-            let sz = (WORLD_W * WORLD_H * std::mem::size_of::<u32>()) as vk::DeviceSize;
+            let sz = (grid_count * std::mem::size_of::<u32>()) as vk::DeviceSize;
             let ptr = device
                 .map_memory(grid_memory, 0, sz, vk::MemoryMapFlags::default())
                 .map_err(|e| format!("map grid: {e:?}"))?;
@@ -602,7 +618,7 @@ impl GraphicsRenderer {
         let grid_info = vk::DescriptorBufferInfo::default()
             .buffer(grid_buffer)
             .offset(0)
-            .range((WORLD_W * WORLD_H * std::mem::size_of::<u32>()) as vk::DeviceSize);
+            .range((MAX_WORLD_W * MAX_WORLD_H * std::mem::size_of::<u32>()) as vk::DeviceSize);
         let light_info = vk::DescriptorBufferInfo::default()
             .buffer(light_buffer)
             .offset(0)
@@ -704,6 +720,44 @@ impl GraphicsRenderer {
             ptr as *mut ColorInstance
         };
 
+        let part_capacity = 2000usize;
+        let part_inst_sz =
+            (part_capacity * std::mem::size_of::<ParticleInstance>()) as vk::DeviceSize;
+        let pibi = vk::BufferCreateInfo::default()
+            .size(part_inst_sz)
+            .usage(vk::BufferUsageFlags::VERTEX_BUFFER)
+            .sharing_mode(vk::SharingMode::EXCLUSIVE);
+        let particle_instance_buffer = unsafe { device.create_buffer(&pibi, None) }
+            .map_err(|e| format!("part inst buf: {e:?}"))?;
+        let preq = unsafe { device.get_buffer_memory_requirements(particle_instance_buffer) };
+        let pmt = find_mem(
+            preq.memory_type_bits,
+            vk::MemoryPropertyFlags::HOST_VISIBLE | vk::MemoryPropertyFlags::HOST_COHERENT,
+        )?;
+        let particle_instance_memory = unsafe {
+            device.allocate_memory(
+                &vk::MemoryAllocateInfo::default()
+                    .allocation_size(preq.size)
+                    .memory_type_index(pmt),
+                None,
+            )
+        }
+        .map_err(|e| format!("part inst mem: {e:?}"))?;
+        let particle_instance_ptr = unsafe {
+            device
+                .bind_buffer_memory(particle_instance_buffer, particle_instance_memory, 0)
+                .expect("bind part inst");
+            let ptr = device
+                .map_memory(
+                    particle_instance_memory,
+                    0,
+                    part_inst_sz,
+                    vk::MemoryMapFlags::default(),
+                )
+                .expect("map part inst");
+            ptr as *mut ParticleInstance
+        };
+
         Ok(Self {
             grid_w,
             grid_h,
@@ -740,6 +794,11 @@ impl GraphicsRenderer {
             ui_instance_memory,
             ui_instance_ptr,
             ui_instance_capacity: ui_capacity,
+            particle_instance_buffer,
+            particle_instance_memory,
+            particle_instance_ptr,
+            particle_instance_capacity: part_capacity,
+            particle_count: 0,
 
             grid_buffer,
             grid_memory,
@@ -764,7 +823,7 @@ impl GraphicsRenderer {
 
     pub fn render(
         &mut self,
-        grid: &Grid,
+        grid: &ChunkedGrid,
         entities: &EntityManager,
         items: &crate::entity::item::ItemManager,
         ui: &crate::ui::UiLayer,
@@ -921,16 +980,12 @@ impl GraphicsRenderer {
         }
 
         unsafe {
-            let margin = 30i32;
-            let x_min = (cam_x - margin).max(0) as usize;
-            let x_max = (cam_x + self.grid_w as i32 + margin).min(WORLD_W as i32) as usize;
-            let y_min = (cam_y - margin).max(0) as usize;
-            let y_max = (cam_y + self.grid_h as i32 + margin).min(WORLD_H as i32) as usize;
-            for y in y_min..y_max {
-                let row_offset = y * WORLD_W;
-                for x in x_min..x_max {
-                    let i = row_offset + x;
-                    *self.grid_ptr.add(i) = grid.cells[i].material as u32;
+            for dy in 0..self.grid_h {
+                for dx in 0..self.grid_w {
+                    let wx = cam_x + dx as i32;
+                    let wy = cam_y + dy as i32;
+                    let idx = dy * self.grid_w + dx;
+                    *self.grid_ptr.add(idx) = grid.get(wx, wy).material as u32;
                 }
             }
         }
@@ -1033,7 +1088,7 @@ impl GraphicsRenderer {
                     self.swapchain_extent.height as f32,
                 ],
                 cell_size: [CHAR_W as f32, CHAR_H as f32],
-                world_size: [WORLD_W as i32, WORLD_H as i32],
+                world_size: [self.grid_w as i32, self.grid_h as i32],
                 cam_pos: [cam_x, cam_y],
                 ambient,
                 is_ui: 0,
@@ -1062,7 +1117,7 @@ impl GraphicsRenderer {
                         self.swapchain_extent.height as f32,
                     ],
                     cell_size: [UI_CELL_SIZE as f32, UI_CELL_SIZE as f32],
-                    world_size: [WORLD_W as i32, WORLD_H as i32],
+                    world_size: [self.grid_w as i32, self.grid_h as i32],
                     cam_pos: [0, 0],
                     ambient: [1.0, 1.0, 1.0],
                     is_ui: 1,
@@ -1078,6 +1133,35 @@ impl GraphicsRenderer {
                 device.cmd_draw_indexed(cmd, 6, ui_count as u32, 0, 0, 0);
             }
 
+            if self.particle_count > 0 {
+                device.cmd_bind_vertex_buffers(
+                    cmd,
+                    0,
+                    &[self.vertex_buffer, self.particle_instance_buffer],
+                    &[0, 0],
+                );
+                let part_pc = PushConstants {
+                    screen_size: [
+                        self.swapchain_extent.width as f32,
+                        self.swapchain_extent.height as f32,
+                    ],
+                    cell_size: [CHAR_W as f32, CHAR_H as f32],
+                    world_size: [self.grid_w as i32, self.grid_h as i32],
+                    cam_pos: [cam_x, cam_y],
+                    ambient: [1.0, 1.0, 1.0],
+                    is_ui: 2,
+                    light_count: 0,
+                };
+                device.cmd_push_constants(
+                    cmd,
+                    self.pipeline_layout,
+                    vk::ShaderStageFlags::VERTEX,
+                    0,
+                    bytemuck::bytes_of(&part_pc),
+                );
+                device.cmd_draw_indexed(cmd, 6, self.particle_count as u32, 0, 0, 0);
+            }
+
             device.cmd_end_render_pass(cmd);
             let _ = device.end_command_buffer(cmd);
 
@@ -1113,6 +1197,33 @@ impl GraphicsRenderer {
         self.grid_h
     }
 
+    pub fn cell_pixel_size(&self) -> u32 {
+        CHAR_W
+    }
+
+    pub fn upload_particles(&mut self, particles: &crate::physics::particle::ParticleManager) {
+        let instances = unsafe {
+            std::slice::from_raw_parts_mut(
+                self.particle_instance_ptr,
+                self.particle_instance_capacity,
+            )
+        };
+        let mut count = 0usize;
+        for p in particles.all() {
+            if count >= self.particle_instance_capacity {
+                break;
+            }
+            let alpha = ((p.life as f32 / p.max_life as f32) * 255.0) as u8;
+            instances[count] = ParticleInstance {
+                grid_x: p.x,
+                grid_y: p.y,
+                color: [p.color[0], p.color[1], p.color[2], alpha],
+            };
+            count += 1;
+        }
+        self.particle_count = count;
+    }
+
     fn check_resize(&mut self) {
         let sl = ash::khr::surface::Instance::new(&self.entry, &self.instance);
         let caps = match unsafe {
@@ -1344,6 +1455,9 @@ impl Drop for GraphicsRenderer {
             self.device.free_memory(self.instance_memory, None);
             self.device.destroy_buffer(self.ui_instance_buffer, None);
             self.device.free_memory(self.ui_instance_memory, None);
+            self.device
+                .destroy_buffer(self.particle_instance_buffer, None);
+            self.device.free_memory(self.particle_instance_memory, None);
             self.device.destroy_buffer(self.vertex_buffer, None);
             self.device.free_memory(self.vertex_memory, None);
             self.device.destroy_buffer(self.index_buffer, None);

src/render/lighting.rs

@@ -1,5 +1,5 @@
 use crate::world::cell::MaterialId;
-use crate::world::grid::Grid;
+use crate::world::chunked_grid::ChunkedGrid;
 
 #[derive(Clone, Copy, Debug)]
 pub struct LightSource {
@@ -67,7 +67,7 @@ pub fn material_light(material: MaterialId) -> Option<LightSource> {
     }
 }
 
-pub fn gather_sources(grid: &Grid) -> Vec<LightSource> {
+pub fn gather_sources(grid: &ChunkedGrid) -> Vec<LightSource> {
     let mut sources = Vec::new();
     let w = grid.width;
     let h = grid.height;
@@ -85,7 +85,7 @@ pub fn gather_sources(grid: &Grid) -> Vec<LightSource> {
 }
 
 pub fn gather_sources_in_range(
-    grid: &Grid,
+    grid: &ChunkedGrid,
     cam_x: i32,
     cam_y: i32,
     view_w: usize,
@@ -94,9 +94,17 @@ pub fn gather_sources_in_range(
 ) -> Vec<LightSource> {
     let mut sources = Vec::new();
     let min_x = (cam_x - margin).max(0);
-    let max_x = (cam_x + view_w as i32 + margin).min(grid.width as i32);
+    let max_x = if grid.is_infinite() {
+        cam_x + view_w as i32 + margin
+    } else {
+        (cam_x + view_w as i32 + margin).min(grid.width as i32)
+    };
     let min_y = (cam_y - margin).max(0);
-    let max_y = (cam_y + view_h as i32 + margin).min(grid.height as i32);
+    let max_y = if grid.is_infinite() {
+        cam_y + view_h as i32 + margin
+    } else {
+        (cam_y + view_h as i32 + margin).min(grid.height as i32)
+    };
     for y in min_y..max_y {
         for x in min_x..max_x {
             let cell = grid.get(x, y);
@@ -111,7 +119,7 @@ pub fn gather_sources_in_range(
 }
 
 pub fn compute_lighting(
-    grid: &Grid,
+    grid: &ChunkedGrid,
     cam_x: i32,
     cam_y: i32,
     view_w: usize,
@@ -176,7 +184,7 @@ pub fn compute_lighting(
     grid_light
 }
 
-pub fn line_of_sight(grid: &Grid, x0: i32, y0: i32, x1: i32, y1: i32) -> bool {
+pub fn line_of_sight(grid: &ChunkedGrid, x0: i32, y0: i32, x1: i32, y1: i32) -> bool {
     let mut x = x0;
     let mut y = y0;
     let dx = (x1 - x0).abs();
@@ -233,13 +241,22 @@ pub fn ambient_light() -> [u8; 3] {
     [160, 160, 180]
 }
 
+pub fn ambient_light_at_tick(tick: u64) -> [u8; 3] {
+    let phase = (tick as f32 * 0.001).sin();
+    let brightness = 0.5 + 0.5 * phase;
+    let r = (80.0 + 100.0 * brightness) as u8;
+    let g = (80.0 + 100.0 * brightness) as u8;
+    let b = (100.0 + 100.0 * brightness) as u8;
+    [r, g, b]
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
-    use crate::world::grid::Grid;
+    use crate::world::chunked_grid::ChunkedGrid;
 
-    fn grid_with_lava() -> (Grid, i32, i32) {
-        let mut grid = Grid::new();
+    fn grid_with_lava() -> (ChunkedGrid, i32, i32) {
+        let mut grid = ChunkedGrid::with_size(250, 250);
         grid.set_material(10, 10, MaterialId::Lava);
         (grid, 10, 10)
     }
@@ -267,7 +284,7 @@ mod tests {
 
     #[test]
     fn walls_block_light() {
-        let mut grid = Grid::new();
+        let mut grid = ChunkedGrid::with_size(250, 250);
         grid.set_material(5, 10, MaterialId::Lava);
         for y in 7..13 {
             grid.set_material(8, y, MaterialId::Stone);

src/render/mod.rs

@@ -8,13 +8,13 @@ pub mod window_input;
 use crate::entity::item::ItemManager;
 use crate::entity::EntityManager;
 use crate::ui::UiLayer;
-use crate::world::grid::Grid;
+use crate::world::chunked_grid::ChunkedGrid;
 
 pub trait Renderer {
     fn init(&mut self) -> std::io::Result<()>;
     fn render(
         &mut self,
-        grid: &Grid,
+        grid: &ChunkedGrid,
         entities: &EntityManager,
         items: &ItemManager,
         ui: &UiLayer,

src/render/terminal.rs

@@ -16,7 +16,7 @@ use crate::entity::EntityManager;
 use crate::render::lighting::{self, apply_light_tuple, LightGrid};
 use crate::render::Renderer;
 use crate::world::cell::MaterialId;
-use crate::world::grid::Grid;
+use crate::world::chunked_grid::ChunkedGrid;
 
 fn entity_priority(kind: crate::entity::EntityKind) -> u32 {
     match kind {
@@ -96,7 +96,7 @@ impl Renderer for TerminalRenderer {
 
     fn render(
         &mut self,
-        grid: &Grid,
+        grid: &ChunkedGrid,
         entities: &EntityManager,
         items: &crate::entity::item::ItemManager,
         ui: &crate::ui::UiLayer,

src/render/vulkan.rs

@@ -6,7 +6,8 @@ use std::sync::Arc;
 use crate::entity::{EntityKind, EntityManager};
 use crate::render::lighting;
 use crate::world::cell::MaterialId;
-use crate::world::grid::{Grid, WORLD_H, WORLD_W};
+use crate::world::chunked_grid::ChunkedGrid;
+use crate::world::grid::{MAX_WORLD_H, MAX_WORLD_W};
 
 const CHAR_W: u32 = 8;
 const CHAR_H: u32 = 8;
@@ -225,7 +226,7 @@ impl VulkanRenderer {
         let (ui_instance_buffer, ui_instance_memory, ui_instance_ptr) =
             create_instance_buffer(&device, &instance, physical_device, ui_instance_capacity)?;
 
-        let grid_data = vec![0u32; WORLD_W * WORLD_H];
+        let grid_data = vec![0u32; MAX_WORLD_W * MAX_WORLD_H];
         let (grid_buffer, grid_memory) = create_buffer_with_data(
             &device,
             &instance,
@@ -234,7 +235,7 @@ impl VulkanRenderer {
             vk::BufferUsageFlags::STORAGE_BUFFER,
         )?;
         let grid_ptr = unsafe {
-            let sz = (WORLD_W * WORLD_H * std::mem::size_of::<u32>()) as vk::DeviceSize;
+            let sz = (MAX_WORLD_W * MAX_WORLD_H * std::mem::size_of::<u32>()) as vk::DeviceSize;
             let ptr = device
                 .map_memory(grid_memory, 0, sz, vk::MemoryMapFlags::default())
                 .map_err(|e| format!("map grid: {e:?}"))?;
@@ -339,7 +340,7 @@ impl VulkanRenderer {
 
     pub fn render(
         &mut self,
-        grid: &Grid,
+        grid: &ChunkedGrid,
         entities: &EntityManager,
         items: &crate::entity::item::ItemManager,
         ui: &crate::ui::UiLayer,
@@ -441,16 +442,12 @@ impl VulkanRenderer {
         }
 
         unsafe {
-            let margin = 30i32;
-            let x_min = (cam_x - margin).max(0) as usize;
-            let x_max = (cam_x + self.grid_w as i32 + margin).min(WORLD_W as i32) as usize;
-            let y_min = (cam_y - margin).max(0) as usize;
-            let y_max = (cam_y + self.grid_h as i32 + margin).min(WORLD_H as i32) as usize;
-            for y in y_min..y_max {
-                let row_offset = y * WORLD_W;
-                for x in x_min..x_max {
-                    let i = row_offset + x;
-                    *self.grid_ptr.add(i) = grid.cells[i].material as u32;
+            for dy in 0..self.grid_h {
+                for dx in 0..self.grid_w {
+                    let wx = cam_x + dx as i32;
+                    let wy = cam_y + dy as i32;
+                    let idx = dy * self.grid_w + dx;
+                    *self.grid_ptr.add(idx) = grid.get(wx, wy).material as u32;
                 }
             }
         }
@@ -627,7 +624,7 @@ impl VulkanRenderer {
                     self.swapchain_extent.height as f32,
                 ],
                 cell_size: [CHAR_W as f32, CHAR_H as f32],
-                world_size: [WORLD_W as i32, WORLD_H as i32],
+                world_size: [self.grid_w as i32, self.grid_h as i32],
                 cam_pos: [cam_x, cam_y],
                 ambient: [
                     ambient[0] as f32 / 255.0,
@@ -660,7 +657,7 @@ impl VulkanRenderer {
                         self.swapchain_extent.height as f32,
                     ],
                     cell_size: [UI_CELL_SIZE as f32, UI_CELL_SIZE as f32],
-                    world_size: [WORLD_W as i32, WORLD_H as i32],
+                    world_size: [self.grid_w as i32, self.grid_h as i32],
                     cam_pos: [0, 0],
                     ambient: [0.0, 0.0, 0.0],
                     is_ui: 1,
@@ -711,6 +708,12 @@ impl VulkanRenderer {
         self.grid_h
     }
 
+    pub fn cell_pixel_size(&self) -> u32 {
+        CHAR_W
+    }
+
+    pub fn upload_particles(&mut self, _particles: &crate::physics::particle::ParticleManager) {}
+
     fn check_resize(&mut self) {
         let sl = ash::khr::surface::Instance::new(&self.entry, &self.instance);
         let caps = match unsafe {
@@ -1824,7 +1827,7 @@ fn update_descriptor_set(
     let bi = vk::DescriptorBufferInfo::default()
         .buffer(grid_buffer)
         .offset(0)
-        .range((WORLD_W * WORLD_H * std::mem::size_of::<u32>()) as vk::DeviceSize);
+        .range((MAX_WORLD_W * MAX_WORLD_H * std::mem::size_of::<u32>()) as vk::DeviceSize);
     let li = vk::DescriptorBufferInfo::default()
         .buffer(light_buffer)
         .offset(0)

src/render/window_input.rs

@@ -18,6 +18,7 @@ pub struct WindowInput {
     pub cam_up: bool,
     pub cam_down: bool,
     pub quit: bool,
+    pub toggle_audio: bool,
     pub paint: Option<u8>,
     pub mouse_x: f64,
     pub mouse_y: f64,
@@ -39,6 +40,7 @@ pub struct WindowInput {
     descend_was_down: bool,
     use_item_was_down: bool,
     drop_item_was_down: bool,
+    audio_was_down: bool,
     down_keys: HashSet<KeyCode>,
 }
 
@@ -61,6 +63,7 @@ impl WindowInput {
             cam_up: false,
             cam_down: false,
             quit: false,
+            toggle_audio: false,
             paint: None,
             mouse_x: 0.0,
             mouse_y: 0.0,
@@ -82,6 +85,7 @@ impl WindowInput {
             descend_was_down: false,
             use_item_was_down: false,
             drop_item_was_down: false,
+            audio_was_down: false,
             down_keys: HashSet::new(),
         }
     }
@@ -202,6 +206,9 @@ impl WindowInput {
         self.cam_up = keys.contains(&KeyCode::KeyI);
         self.cam_down = keys.contains(&KeyCode::KeyO);
         self.quit = keys.contains(&KeyCode::KeyQ) || keys.contains(&KeyCode::Escape);
+        let now_audio = keys.contains(&KeyCode::KeyM);
+        self.toggle_audio = now_audio && !self.audio_was_down;
+        self.audio_was_down = now_audio;
 
         self.paint = None;
         if keys.contains(&KeyCode::Digit1) {

src/ui/mod.rs

@@ -1,9 +1,10 @@
-use std::collections::HashMap;
-
 use crate::entity::entity::{Entity, EntityKind};
 use crate::world::cell::MaterialId;
+use crate::world::chunked_grid::ChunkedGrid;
 
 pub const UI_SCALE: i32 = 4;
+pub const FONT_W: i32 = 3;
+pub const FONT_H: i32 = 5;
 
 #[derive(Clone, Debug)]
 pub struct UiCell {
@@ -14,9 +15,13 @@ pub struct UiCell {
 }
 
 pub struct UiLayer {
-    cells: HashMap<(i32, i32), UiCell>,
+    cells: Vec<Option<UiCell>>,
+    width: usize,
+    height: usize,
+    dirty_keys: Vec<(i32, i32)>,
     messages: Vec<(String, u32)>,
     damage_numbers: Vec<DamageNumber>,
+    font_scale: i32,
 }
 
 #[derive(Clone)]
@@ -31,14 +36,39 @@ pub struct DamageNumber {
 impl UiLayer {
     pub fn new() -> Self {
         Self {
-            cells: HashMap::new(),
+            cells: Vec::new(),
+            width: 0,
+            height: 0,
+            dirty_keys: Vec::new(),
             messages: Vec::new(),
             damage_numbers: Vec::new(),
+            font_scale: 2,
         }
     }
 
+    pub fn set_font_scale(&mut self, scale: i32) {
+        self.font_scale = scale.max(1);
+    }
+
+    pub fn font_scale(&self) -> i32 {
+        self.font_scale
+    }
+
+    #[inline]
+    fn fw(&self) -> i32 {
+        FONT_W * self.font_scale
+    }
+
+    #[inline]
+    fn fh(&self) -> i32 {
+        FONT_H * self.font_scale
+    }
+
     pub fn clear(&mut self) {
-        self.cells.clear();
+        for c in self.cells.iter_mut() {
+            *c = None;
+        }
+        self.dirty_keys.clear();
         self.damage_numbers.retain(|d| d.life > 0);
         for d in &mut self.damage_numbers {
             d.y -= 0.1;
@@ -46,28 +76,56 @@ impl UiLayer {
         }
     }
 
+    pub fn resize(&mut self, w: usize, h: usize) {
+        if self.width == w && self.height == h && !self.cells.is_empty() {
+            return;
+        }
+        self.width = w;
+        self.height = h;
+        self.cells.clear();
+        self.cells.resize(w * h, None);
+        self.dirty_keys.clear();
+    }
+
+    #[inline]
+    fn idx(&self, x: i32, y: i32) -> Option<usize> {
+        if x < 0 || y < 0 || x as usize >= self.width || y as usize >= self.height {
+            return None;
+        }
+        Some(y as usize * self.width + x as usize)
+    }
+
     pub fn set(&mut self, x: i32, y: i32, ch: char, fg: [u8; 3], bg: [u8; 3]) {
-        self.cells.insert(
-            (x, y),
-            UiCell {
+        if let Some(i) = self.idx(x, y) {
+            let was_none = self.cells[i].is_none();
+            self.cells[i] = Some(UiCell {
                 ch,
                 fg,
                 bg,
                 alpha: 255,
-            },
-        );
+            });
+            if was_none {
+                self.dirty_keys.push((x, y));
+            }
+        }
     }
 
     pub fn set_alpha(&mut self, x: i32, y: i32, ch: char, fg: [u8; 3], bg: [u8; 3], alpha: u8) {
-        self.cells.insert((x, y), UiCell { ch, fg, bg, alpha });
+        if let Some(i) = self.idx(x, y) {
+            let was_none = self.cells[i].is_none();
+            self.cells[i] = Some(UiCell { ch, fg, bg, alpha });
+            if was_none {
+                self.dirty_keys.push((x, y));
+            }
+        }
     }
 
     pub fn get(&self, x: i32, y: i32) -> Option<&UiCell> {
-        self.cells.get(&(x, y))
+        self.idx(x, y).and_then(|i| self.cells[i].as_ref())
     }
 
     pub fn keys(&self) -> impl Iterator<Item = &(i32, i32)> {
-        self.cells.keys()
+        self.dirty_keys.iter()
     }
 
     pub fn add_message(&mut self, text: &str) {
@@ -173,7 +231,8 @@ impl UiLayer {
             return;
         }
         let ratio = (health / max_health).clamp(0.0, 1.0);
-        let filled = (ratio * width as f32).round() as i32;
+        let scaled_width = width * self.font_scale;
+        let filled = (ratio * scaled_width as f32).round() as i32;
         let color = if ratio > 0.6 {
             [60, 220, 60]
         } else if ratio > 0.3 {
@@ -181,7 +240,7 @@ impl UiLayer {
         } else {
             [240, 50, 50]
         };
-        for i in 0..width {
+        for i in 0..scaled_width {
             let x = screen_x + i;
             let ch = if i < filled { '#' } else { '-' };
             let fg = if i < filled { color } else { [80, 80, 80] };
@@ -197,7 +256,7 @@ impl UiLayer {
             let (sx, sy) = entity_screen_pos_ui(e, cam_x, cam_y);
             let label = e.name().to_uppercase();
             let top = sy - (e.half_h as i32 * UI_SCALE) - 7;
-            let x = sx - (Self::text_width(&label) / 2);
+            let x = sx - (self.text_width(&label) / 2);
             let fg = entity_kind_color(e);
             self.draw_text(x, top, &label, fg, 255);
         }
@@ -241,7 +300,7 @@ impl UiLayer {
         &mut self,
         screen_w: usize,
         screen_h: usize,
-        grid: &crate::world::grid::Grid,
+        grid: &ChunkedGrid,
         entities: &[Entity],
         cam_x: i32,
         cam_y: i32,
@@ -268,8 +327,8 @@ impl UiLayer {
                 let mut g = 0u32;
                 let mut b = 0u32;
                 let mut n = 0u32;
-                for yy in 0..scale {
-                    for xx in 0..scale {
+                for yy in (0..scale).step_by(4) {
+                    for xx in (0..scale).step_by(4) {
                         let cell = grid.get(wx + xx, wy + yy);
                         if cell.material != MaterialId::Empty {
                             let c = cell.fg;
@@ -334,8 +393,9 @@ impl UiLayer {
         player: Option<&Entity>,
         player_state: &crate::entity::player::Player,
     ) {
-        let w = 52i32;
-        let h = 62i32;
+        let fs = self.font_scale;
+        let w = 52 * fs / 2;
+        let h = 62 * fs / 2;
         let bg = [22u8, 26, 38];
         let border = [160u8, 180, 255];
         let title = [220u8, 230, 255];
@@ -374,12 +434,20 @@ impl UiLayer {
         );
 
         let title_text = "STATUS";
-        let tx = start_x + (w - Self::text_width(title_text)) / 2;
+        let tx = start_x + (w - self.text_width(title_text)) / 2;
         self.draw_text(tx, start_y + 2, title_text, title, 255);
 
+        let row1 = start_y + 10 * fs / 2;
+        let row2 = start_y + 18 * fs / 2;
+        let row3 = start_y + 26 * fs / 2;
+        let row4 = start_y + 36 * fs / 2;
+        let row5 = start_y + 44 * fs / 2;
+        let row_inv = start_y + 52 * fs / 2;
+        let row_items = start_y + 58 * fs / 2;
+
         if let Some(p) = player {
             let hp_ratio = (p.health / p.max_health).clamp(0.0, 1.0);
-            let hp_filled = (hp_ratio * 38.0).round() as i32;
+            let hp_filled = (hp_ratio * 38.0 * fs as f32 / 2.0).round() as i32;
             let bar_color = if hp_ratio > 0.6 {
                 [80, 240, 80]
             } else if hp_ratio > 0.3 {
@@ -387,43 +455,43 @@ impl UiLayer {
             } else {
                 [255, 60, 60]
             };
-            self.draw_text(start_x + 3, start_y + 10, "HP", fg, 255);
-            for i in 0..38 {
+            self.draw_text(start_x + 3, row1, "HP", fg, 255);
+            for i in 0..(38 * fs / 2) {
                 let ch = if i < hp_filled { '#' } else { '-' };
                 let c = if i < hp_filled {
                     bar_color
                 } else {
                     [80, 80, 100]
                 };
-                self.set(start_x + 10 + i, start_y + 10, ch, c, bg);
+                self.set(start_x + 10 * fs / 2 + i, row1, ch, c, bg);
             }
             let hp_text = format!(
                 "{}/{}  LV:{}",
                 p.health as i32, p.max_health as i32, p.level
             );
-            self.draw_text(start_x + 3, start_y + 18, &hp_text, fg, 255);
+            self.draw_text(start_x + 3, row2, &hp_text, fg, 255);
 
             let xp_ratio = (p.xp as f32 / p.xp_to_level() as f32).clamp(0.0, 1.0);
-            let xp_filled = (xp_ratio * 38.0).round() as i32;
-            self.draw_text(start_x + 3, start_y + 26, "XP", fg, 255);
-            for i in 0..38 {
+            let xp_filled = (xp_ratio * 38.0 * fs as f32 / 2.0).round() as i32;
+            self.draw_text(start_x + 3, row3, "XP", fg, 255);
+            for i in 0..(38 * fs / 2) {
                 let ch = if i < xp_filled { '#' } else { '-' };
                 let c = if i < xp_filled {
                     [80, 160, 240]
                 } else {
                     [60, 60, 80]
                 };
-                self.set(start_x + 10 + i, start_y + 26, ch, c, bg);
+                self.set(start_x + 10 * fs / 2 + i, row3, ch, c, bg);
             }
 
             let stats = format!("STR:{}  AGI:{}", p.strength, p.agility);
-            self.draw_text(start_x + 3, start_y + 36, &stats, dim, 255);
+            self.draw_text(start_x + 3, row4, &stats, dim, 255);
             let stats2 = format!("TOU:{}  WIL:{}", p.toughness, p.willpower);
-            self.draw_text(start_x + 3, start_y + 44, &stats2, dim, 255);
+            self.draw_text(start_x + 3, row5, &stats2, dim, 255);
         }
 
         let inv_title = "INVENTORY";
-        self.draw_text(start_x + 3, start_y + 52, inv_title, fg, 255);
+        self.draw_text(start_x + 3, row_inv, inv_title, fg, 255);
         let mut ix = start_x + 3;
         for item in player_state.inventory.iter().take(8) {
             if ix + 2 >= start_x + w - 2 {
@@ -431,10 +499,10 @@ impl UiLayer {
             }
             let [ch1, ch2] = item.display_glyph();
             let col = item.color();
-            self.set(ix, start_y + 58, ch1, col, bg);
+            self.set(ix, row_items, ch1, col, bg);
             self.set(
                 ix + 1,
-                start_y + 58,
+                row_items,
                 ch2,
                 [col[0] / 2, col[1] / 2, col[2] / 2],
                 bg,
@@ -461,9 +529,7 @@ impl UiLayer {
             String::new()
         };
         if !status.is_empty() {
-            for (i, ch) in status.chars().enumerate() {
-                self.set(start_x + 30 + i as i32, start_y + 38, ch, [255, 80, 80], bg);
-            }
+            self.draw_text(start_x + 30 * fs / 2, row4, &status, [255, 80, 80], 255);
         }
     }
 
@@ -485,9 +551,9 @@ impl UiLayer {
 
         let cols = 4i32;
         let rows = 2i32;
-        let slot_w = 12i32;
-        let slot_h = 10i32;
-        let gap = 3i32;
+        let slot_w = 12i32 * self.font_scale / 2;
+        let slot_h = 10i32 * self.font_scale / 2;
+        let gap = 3i32 * self.font_scale / 2;
         let panel_w = cols * slot_w + (cols + 1) * gap + 4;
         let panel_h = rows * slot_h + (rows + 1) * gap + 28;
 
@@ -527,7 +593,7 @@ impl UiLayer {
         self.draw_text(px_start + 4, py_start + 3, title, title_col, 255);
         let count_text = format!("({}/{} items)", player_state.inventory.len(), cols * rows);
         self.draw_text(
-            px_start + 4 + Self::text_width(title) + 2,
+            px_start + 4 + self.text_width(title) + 2,
             py_start + 3,
             &count_text,
             dim,
@@ -541,7 +607,7 @@ impl UiLayer {
             for col in 0..cols {
                 let idx = (row * cols + col) as usize;
                 let sx = px_start + gap + col * (slot_w + gap) + 2;
-                let sy = py_start + 14 + row * (slot_h + gap) + gap;
+                let sy = py_start + 14 * self.font_scale / 2 + row * (slot_h + gap) + gap;
 
                 for y in 0..slot_h {
                     for x in 0..slot_w {
@@ -583,7 +649,7 @@ impl UiLayer {
                     );
 
                     let label = item.name();
-                    let label_w = Self::text_width(label) as i32;
+                    let label_w = self.text_width(label) as i32;
                     let lx = sx + (slot_w - label_w) / 2;
                     let ly = sy + slot_h - 1;
                     if lx >= sx && lx + label_w <= sx + slot_w {
@@ -671,6 +737,8 @@ impl UiLayer {
         player_state: &crate::entity::player::Player,
         fps: f32,
     ) {
+        let fs = self.font_scale;
+        let fh = self.fh();
         let bg = [18u8, 20, 30];
         let border = [160u8, 170, 210];
         let fill_alpha = 140u8;
@@ -686,11 +754,11 @@ impl UiLayer {
             .map(|i| i.display_string())
             .unwrap_or("  ".to_string());
 
-        let bar_h = 28i32;
+        let bar_h = (28 * fs / 2).max(fh * 3);
         let y_top = screen_h as i32 - bar_h;
         let y_row1 = y_top + 2;
-        let y_row2 = y_top + 12;
-        let y_row3 = y_top + 22;
+        let y_row2 = y_top + 2 + fh + 2;
+        let y_row3 = y_top + 2 + (fh + 2) * 2;
 
         for row in y_top..screen_h as i32 {
             for x in 0..screen_w {
@@ -706,7 +774,8 @@ impl UiLayer {
         self.draw_text(0, y_row1, "HP", [220, 220, 220], 255);
         if let Some(p) = player {
             let hp_ratio = (p.health / p.max_health).clamp(0.0, 1.0);
-            let hp_filled = (hp_ratio * 28.0).round() as i32;
+            let hp_bar_w = 28 * fs / 2;
+            let hp_filled = (hp_ratio * hp_bar_w as f32).round() as i32;
             let bar_fg = if hp_ratio > 0.6 {
                 [80, 240, 80]
             } else if hp_ratio > 0.3 {
@@ -714,17 +783,23 @@ impl UiLayer {
             } else {
                 [255, 60, 60]
             };
-            for i in 0..28 {
+            for i in 0..hp_bar_w {
                 let ch = if i < hp_filled { '#' } else { '-' };
                 let c = if i < hp_filled { bar_fg } else { [70, 70, 90] };
-                self.set(10 + i, y_row1 + 4, ch, c, bg);
+                self.set(10 * fs / 2 + i, y_row1, ch, c, bg);
             }
             let hp_text = format!("{} / {}", p.health as i32, p.max_health as i32);
-            self.draw_text(40, y_row1, &hp_text, [220, 220, 220], 255);
+            self.draw_text(
+                (40 * fs / 2).max(10 * fs / 2 + hp_bar_w + 2),
+                y_row1,
+                &hp_text,
+                [220, 220, 220],
+                255,
+            );
         }
 
         let brush_color = brush_color(brush);
-        self.set(0, y_row2 + 4, '#', brush_color, bg);
+        self.set(0, y_row2, '#', brush_color, bg);
         let brush_text = format!(" {}", brush_name);
         self.draw_text(1, y_row2, &brush_text, [200, 200, 140], 255);
 
@@ -735,7 +810,7 @@ impl UiLayer {
             player_state.inventory.len(),
             fps as i32
         );
-        let gear_w = Self::text_width(&gear);
+        let gear_w = self.text_width(&gear);
         let gear_x = (screen_w as i32 - gear_w).max(0);
         self.draw_text(gear_x, y_row2, &gear, [160, 180, 220], 255);
 
@@ -748,14 +823,14 @@ impl UiLayer {
             depth,
             tick
         );
-        let stats_w = Self::text_width(&stats);
+        let stats_w = self.text_width(&stats);
         let stats_x = (screen_w as i32 - stats_w).max(0);
         self.draw_text(stats_x, y_row3, &stats, [180, 190, 220], 255);
 
         if let Some(p) = player {
             if p.on_fire {
                 let msg = "ON FIRE!";
-                self.draw_text(40, y_top - 7, msg, [255, 100, 20], 255);
+                self.draw_text(40 * fs / 2, y_top - fh - 2, msg, [255, 100, 20], 255);
             }
         }
     }
@@ -763,6 +838,7 @@ impl UiLayer {
     pub fn draw_messages(&mut self, x: i32, y: i32) {
         let mut yy = y;
         let messages: Vec<(String, u32)> = self.messages.iter().rev().take(8).cloned().collect();
+        let line_h = self.fh() + 1;
         for (msg, life) in messages {
             if yy < 0 {
                 break;
@@ -774,7 +850,7 @@ impl UiLayer {
                 (200.0 * fade) as u8,
             ];
             self.draw_text(x, yy, &msg, fg, 255);
-            yy -= 6;
+            yy -= line_h;
         }
     }
 
@@ -782,20 +858,21 @@ impl UiLayer {
         let cx = screen_w as i32 / 2;
         let cy = screen_h as i32 / 2;
         let msg = "YOU DIED";
-        let x = cx - (Self::text_width(msg) / 2);
+        let x = cx - (self.text_width(msg) / 2);
         self.draw_text(x, cy - 3, msg, [255, 50, 50], 255);
         let stats = format!("KILLS: {}  SCORE: {}", kills, score);
-        let x2 = cx - (Self::text_width(&stats) / 2);
+        let x2 = cx - (self.text_width(&stats) / 2);
         self.draw_text(x2, cy + 3, &stats, [200, 200, 200], 255);
     }
 
-    pub fn text_width(text: &str) -> i32 {
+    pub fn text_width(&self, text: &str) -> i32 {
         text.chars()
-            .map(|c| if c == '\n' { 0 } else { 3 })
+            .map(|c| if c == '\n' { 0 } else { self.fw() as usize })
             .sum::<usize>() as i32
     }
 
     pub fn draw_text(&mut self, x: i32, y: i32, text: &str, fg: [u8; 3], alpha: u8) {
+        let fs = self.font_scale;
         let mut cx = x;
         for c in text.chars() {
             if c == '\n' {
@@ -803,21 +880,33 @@ impl UiLayer {
                 continue;
             }
             if let Some(bitmap) = char_bitmap(c) {
-                for row in 0..5 {
-                    for col in 0..3 {
-                        let filled = (bitmap[row] >> (2 - col)) & 1 == 1;
+                for row in 0..FONT_H {
+                    for col in 0..FONT_W {
+                        let filled = (bitmap[row as usize] >> (FONT_W - 1 - col)) & 1 == 1;
                         let a = if filled { alpha } else { 0 };
-                        self.set_alpha(cx + col as i32, y + row as i32, c, fg, [0, 0, 0], a);
+                        for dy in 0..fs {
+                            for dx in 0..fs {
+                                let px = cx + col * fs + dx;
+                                let py = y + row * fs + dy;
+                                self.set_alpha(px, py, c, fg, [0, 0, 0], a);
+                            }
+                        }
                     }
                 }
             } else {
-                for row in 0..5 {
-                    for col in 0..3 {
-                        self.set_alpha(cx + col as i32, y + row as i32, c, fg, [0, 0, 0], alpha);
+                for row in 0..FONT_H {
+                    for col in 0..FONT_W {
+                        for dy in 0..fs {
+                            for dx in 0..fs {
+                                let px = cx + col * fs + dx;
+                                let py = y + row * fs + dy;
+                                self.set_alpha(px, py, c, fg, [0, 0, 0], alpha);
+                            }
+                        }
                     }
                 }
             }
-            cx += 3;
+            cx += self.fw();
         }
     }
 }

src/world/cache.rs

@@ -0,0 +1,141 @@
+use crate::entity::item::{ItemManager, ItemType};
+use crate::entity::player::Player;
+use crate::entity::EntityManager;
+use crate::world::chunked_grid::ChunkedGrid;
+use serde::{Deserialize, Serialize};
+use std::io;
+use std::path::PathBuf;
+
+const CACHE_VERSION: u32 = 2;
+
+#[derive(Serialize, Deserialize)]
+struct CacheMeta {
+    version: u32,
+    seed: u64,
+    player_x: f32,
+    player_y: f32,
+    depth: u32,
+    items: Vec<CachedItem>,
+}
+
+#[derive(Serialize, Deserialize)]
+struct CachedItem {
+    typ: String,
+    x: i32,
+    y: i32,
+}
+
+pub struct WorldCache;
+
+impl WorldCache {
+    pub fn path(root: &str, seed: u64) -> PathBuf {
+        PathBuf::from(root).join(format!("seed_{}", seed))
+    }
+
+    pub fn meta_path(root: &str, seed: u64) -> PathBuf {
+        Self::path(root, seed).join("meta.json")
+    }
+
+    pub fn chunk_path(root: &str, seed: u64, cx: i32, cy: i32) -> PathBuf {
+        Self::path(root, seed).join(format!("chunk_{}_{}.bin", cx, cy))
+    }
+
+    pub fn meta_exists(root: &str, seed: u64) -> bool {
+        Self::meta_path(root, seed).exists()
+    }
+
+    pub fn chunk_exists(root: &str, seed: u64, cx: i32, cy: i32) -> bool {
+        Self::chunk_path(root, seed, cx, cy).exists()
+    }
+
+    pub fn save_meta(
+        root: &str,
+        seed: u64,
+        player_x: f32,
+        player_y: f32,
+        depth: u32,
+        items: &ItemManager,
+    ) -> io::Result<()> {
+        let path = Self::path(root, seed);
+        std::fs::create_dir_all(&path)?;
+        let meta = CacheMeta {
+            version: CACHE_VERSION,
+            seed,
+            player_x,
+            player_y,
+            depth,
+            items: items
+                .all()
+                .iter()
+                .map(|i| CachedItem {
+                    typ: i.name().to_string(),
+                    x: i.x,
+                    y: i.y,
+                })
+                .collect(),
+        };
+        let meta_json = serde_json::to_string_pretty(&meta)?;
+        std::fs::write(path.join("meta.json"), meta_json)
+    }
+
+    pub fn load_meta(
+        root: &str,
+        seed: u64,
+        player: &mut Player,
+        entities: &mut EntityManager,
+        items: &mut ItemManager,
+    ) -> io::Result<u32> {
+        let path = Self::path(root, seed);
+        let meta_json = std::fs::read_to_string(path.join("meta.json"))?;
+        let meta: CacheMeta = serde_json::from_str(&meta_json)
+            .map_err(|e| io::Error::other(format!("cache meta parse: {}", e)))?;
+        if meta.version != CACHE_VERSION {
+            return Err(io::Error::other("cache version mismatch"));
+        }
+        player.spawn_at(entities, meta.player_x, meta.player_y);
+        items.all_mut().clear();
+        for ci in meta.items {
+            if let Some(typ) = ItemType::from_name(&ci.typ) {
+                items.spawn(typ, ci.x, ci.y);
+            }
+        }
+        Ok(meta.depth)
+    }
+
+    pub fn save_chunk(
+        root: &str,
+        seed: u64,
+        cx: i32,
+        cy: i32,
+        grid: &ChunkedGrid,
+    ) -> io::Result<()> {
+        let path = Self::chunk_path(root, seed, cx, cy);
+        if let Some(parent) = path.parent() {
+            std::fs::create_dir_all(parent)?;
+        }
+        grid.save_chunk(path.to_str().unwrap(), cx, cy)
+    }
+
+    pub fn load_chunk(
+        root: &str,
+        seed: u64,
+        cx: i32,
+        cy: i32,
+        grid: &mut ChunkedGrid,
+    ) -> io::Result<()> {
+        let path = Self::chunk_path(root, seed, cx, cy);
+        grid.load_chunk(path.to_str().unwrap(), cx, cy)
+    }
+
+    pub fn save_all_loaded(root: &str, seed: u64, grid: &ChunkedGrid) -> io::Result<()> {
+        let path = Self::path(root, seed);
+        std::fs::create_dir_all(&path)?;
+        for (&(cx, cy), chunk) in &grid.chunks {
+            if chunk.modified || chunk.was_modified {
+                let file = Self::chunk_path(root, seed, cx as i32, cy as i32);
+                grid.save_chunk(file.to_str().unwrap(), cx as i32, cy as i32)?;
+            }
+        }
+        Ok(())
+    }
+}

src/world/cell.rs

@@ -45,18 +45,26 @@ impl MaterialId {
 #[derive(Clone, Copy, Debug)]
 pub struct Cell {
     pub material: MaterialId,
-    pub temp: f32,
     pub updated_this_tick: bool,
     pub variant: u8,
     pub fg: [u8; 3],
     pub bg: [u8; 3],
 }
 
+pub fn default_temp(material: MaterialId) -> f32 {
+    match material {
+        MaterialId::Lava => 1500.0,
+        MaterialId::Fire => 800.0,
+        MaterialId::Steam => 150.0,
+        MaterialId::Smoke => 120.0,
+        _ => 20.0,
+    }
+}
+
 impl Cell {
     pub fn empty() -> Self {
         Self {
             material: MaterialId::Empty,
-            temp: 20.0,
             updated_this_tick: false,
             variant: 0,
             fg: [15, 15, 20],
@@ -67,16 +75,8 @@ impl Cell {
     pub fn new(material: MaterialId) -> Self {
         let reg = MaterialRegistry::instance();
         let mat = reg.get(material);
-        let temp = match material {
-            MaterialId::Lava => 1500.0,
-            MaterialId::Fire => 800.0,
-            MaterialId::Steam => 150.0,
-            MaterialId::Smoke => 120.0,
-            _ => 20.0,
-        };
         Self {
             material,
-            temp,
             updated_this_tick: false,
             variant: rand_u8(),
             fg: [mat.color_fg.0, mat.color_fg.1, mat.color_fg.2],
@@ -117,13 +117,12 @@ impl Cell {
         self.material.display_char()
     }
 
-    pub fn to_bytes(&self) -> [u8; 12] {
-        let mut out = [0u8; 12];
+    pub fn to_bytes(&self) -> [u8; 8] {
+        let mut out = [0u8; 8];
         out[0] = self.material as u8;
-        out[1..5].copy_from_slice(&self.temp.to_le_bytes());
-        out[5] = self.variant;
-        out[6..9].copy_from_slice(&self.fg);
-        out[9..12].copy_from_slice(&self.bg);
+        out[1] = self.variant;
+        out[2..5].copy_from_slice(&self.fg);
+        out[5..8].copy_from_slice(&self.bg);
         out
     }
 
@@ -150,25 +149,19 @@ impl Cell {
                 _ => MaterialId::Stone,
             }
         };
-        let temp = if bytes.len() >= 5 {
-            f32::from_le_bytes([bytes[1], bytes[2], bytes[3], bytes[4]])
-        } else {
-            20.0
-        };
-        let variant = bytes.get(5).copied().unwrap_or(0);
-        let fg = if bytes.len() >= 9 {
-            [bytes[6], bytes[7], bytes[8]]
+        let variant = bytes.get(1).copied().unwrap_or(0);
+        let fg = if bytes.len() >= 5 {
+            [bytes[2], bytes[3], bytes[4]]
         } else {
             [15, 15, 20]
         };
-        let bg = if bytes.len() >= 12 {
-            [bytes[9], bytes[10], bytes[11]]
+        let bg = if bytes.len() >= 8 {
+            [bytes[5], bytes[6], bytes[7]]
         } else {
             [10, 10, 15]
         };
         Self {
             material,
-            temp,
             updated_this_tick: false,
             variant,
             fg,

src/world/chunk.rs

@@ -4,17 +4,48 @@ pub const CHUNK_SIZE: usize = 64;
 
 pub struct Chunk {
     pub cells: Vec<Cell>,
+    pub temps: Vec<f32>,
+    pub pressure: Vec<u8>,
+    pub gas_type: Vec<u8>,
+    pub gas_density: Vec<u8>,
+    pub light: Vec<[u8; 3]>,
+    pub electricity: Vec<u8>,
     pub active: bool,
     pub modified: bool,
+    pub was_modified: bool,
+    pub generated: bool,
+    pub dirty: Option<(i32, i32, i32, i32)>,
 }
 
+const CHUNK_AREA: usize = CHUNK_SIZE * CHUNK_SIZE;
+const ATMOSPHERIC_PRESSURE: u8 = 128;
+
 impl Chunk {
     pub fn new() -> Self {
-        let size = CHUNK_SIZE * CHUNK_SIZE;
         Self {
-            cells: vec![Cell::empty(); size],
+            cells: vec![Cell::empty(); CHUNK_AREA],
+            temps: vec![20.0; CHUNK_AREA],
+            pressure: vec![ATMOSPHERIC_PRESSURE; CHUNK_AREA],
+            gas_type: vec![0; CHUNK_AREA],
+            gas_density: vec![0; CHUNK_AREA],
+            light: vec![[0, 0, 0]; CHUNK_AREA],
+            electricity: vec![0; CHUNK_AREA],
             active: false,
             modified: false,
+            was_modified: false,
+            generated: false,
+            dirty: None,
+        }
+    }
+
+    pub fn swap_modified_flags(&mut self) {
+        self.was_modified = self.modified;
+        self.modified = false;
+    }
+
+    pub fn reset_tick_flags(&mut self) {
+        for c in &mut self.cells {
+            c.updated_this_tick = false;
         }
     }
 
@@ -45,13 +76,112 @@ impl Chunk {
     pub fn set_material(&mut self, x: i32, y: i32, mat: MaterialId) {
         if Self::in_bounds(x, y) {
             self.cells[Self::idx(x, y)] = Cell::new(mat);
+            self.temps[Self::idx(x, y)] = crate::world::cell::default_temp(mat);
             self.modified = true;
         }
     }
 
-    pub fn reset_tick_flags(&mut self) {
-        for c in &mut self.cells {
-            c.updated_this_tick = false;
+    #[inline]
+    pub fn get_temp(&self, x: i32, y: i32) -> f32 {
+        if !Self::in_bounds(x, y) {
+            return 20.0;
+        }
+        self.temps[Self::idx(x, y)]
+    }
+
+    #[inline]
+    pub fn set_temp(&mut self, x: i32, y: i32, t: f32) {
+        if Self::in_bounds(x, y) {
+            self.temps[Self::idx(x, y)] = t;
+        }
+    }
+
+    #[inline]
+    pub fn get_pressure(&self, x: i32, y: i32) -> u8 {
+        if !Self::in_bounds(x, y) {
+            return 128;
+        }
+        self.pressure[Self::idx(x, y)]
+    }
+
+    #[inline]
+    pub fn set_pressure(&mut self, x: i32, y: i32, p: u8) {
+        if Self::in_bounds(x, y) {
+            self.pressure[Self::idx(x, y)] = p;
+        }
+    }
+
+    #[inline]
+    pub fn get_gas(&self, x: i32, y: i32) -> (u8, u8) {
+        if !Self::in_bounds(x, y) {
+            return (0, 0);
+        }
+        let i = Self::idx(x, y);
+        (self.gas_type[i], self.gas_density[i])
+    }
+
+    #[inline]
+    pub fn set_gas(&mut self, x: i32, y: i32, gas_type: u8, density: u8) {
+        if Self::in_bounds(x, y) {
+            let i = Self::idx(x, y);
+            self.gas_type[i] = gas_type;
+            self.gas_density[i] = density;
+        }
+    }
+
+    #[inline]
+    pub fn get_light(&self, x: i32, y: i32) -> [u8; 3] {
+        if !Self::in_bounds(x, y) {
+            return [0, 0, 0];
+        }
+        self.light[Self::idx(x, y)]
+    }
+
+    #[inline]
+    pub fn set_light(&mut self, x: i32, y: i32, rgb: [u8; 3]) {
+        if Self::in_bounds(x, y) {
+            self.light[Self::idx(x, y)] = rgb;
+        }
+    }
+
+    #[inline]
+    pub fn get_electricity(&self, x: i32, y: i32) -> u8 {
+        if !Self::in_bounds(x, y) {
+            return 0;
+        }
+        self.electricity[Self::idx(x, y)]
+    }
+
+    #[inline]
+    pub fn set_electricity(&mut self, x: i32, y: i32, val: u8) {
+        if Self::in_bounds(x, y) {
+            self.electricity[Self::idx(x, y)] = val;
+        }
+    }
+
+    pub fn is_empty(&self) -> bool {
+        self.cells.iter().all(|c| c.is_empty())
+    }
+
+    #[inline]
+    pub fn mark_dirty(&mut self, x: i32, y: i32) {
+        if !Self::in_bounds(x, y) {
+            return;
+        }
+        let min_x = (x - 1).max(0);
+        let min_y = (y - 1).max(0);
+        let max_x = (x + 1).min(CHUNK_SIZE as i32 - 1);
+        let max_y = (y + 1).min(CHUNK_SIZE as i32 - 1);
+        match self.dirty {
+            None => self.dirty = Some((min_x, min_y, max_x, max_y)),
+            Some((dx0, dy0, dx1, dy1)) => {
+                self.dirty = Some((
+                    dx0.min(min_x),
+                    dy0.min(min_y),
+                    dx1.max(max_x),
+                    dy1.max(max_y),
+                ));
+            }
         }
     }
 }

src/world/grid.rs

@@ -6,10 +6,14 @@ use std::path::Path;
 pub const WORLD_W: usize = 250;
 pub const WORLD_H: usize = 250;
 
+pub const MAX_WORLD_W: usize = 2048;
+pub const MAX_WORLD_H: usize = 2048;
+
 pub struct ChunkMeta {
     pub active: bool,
     pub modified: bool,
     pub was_modified: bool,
+    pub dirty: Option<(i32, i32, i32, i32)>,
 }
 
 pub struct Grid {
@@ -24,22 +28,27 @@ pub struct Grid {
 
 impl Grid {
     pub fn new() -> Self {
-        let size = WORLD_W * WORLD_H;
+        Self::with_size(WORLD_W, WORLD_H)
+    }
+
+    pub fn with_size(width: usize, height: usize) -> Self {
+        let size = width * height;
         let chunk_size = CHUNK_SIZE;
-        let chunks_x = (WORLD_W + chunk_size - 1) / chunk_size;
-        let chunks_y = (WORLD_H + chunk_size - 1) / chunk_size;
+        let chunks_x = (width + chunk_size - 1) / chunk_size;
+        let chunks_y = (height + chunk_size - 1) / chunk_size;
         let mut chunks = Vec::with_capacity(chunks_x * chunks_y);
         for _ in 0..chunks_x * chunks_y {
             chunks.push(ChunkMeta {
                 active: true,
                 modified: false,
                 was_modified: false,
+                dirty: None,
             });
         }
         Self {
             cells: vec![Cell::empty(); size],
-            width: WORLD_W,
-            height: WORLD_H,
+            width,
+            height,
             chunk_size,
             chunks_x,
             chunks_y,
@@ -185,6 +194,7 @@ impl Grid {
             if let Some(c) = self.chunks.get_mut(idx) {
                 c.modified = true;
             }
+            self.mark_dirty(x, y);
         }
     }
 
@@ -198,6 +208,7 @@ impl Grid {
             if let Some(c) = self.chunks.get_mut(idx) {
                 c.modified = true;
             }
+            self.mark_dirty(x, y);
         }
     }
 
@@ -212,9 +223,94 @@ impl Grid {
         }
     }
 
+    #[inline]
+    pub fn mark_dirty(&mut self, x: i32, y: i32) {
+        if !self.in_bounds(x, y) {
+            return;
+        }
+        let (cx, cy, _, _) = self.chunk_at(x, y);
+        self.expand_chunk_dirty(cx, cy, x, y);
+        let cs = self.chunk_size as i32;
+        let lx = x - cx * cs;
+        let ly = y - cy * cs;
+        if lx <= 1 {
+            self.expand_chunk_dirty(cx - 1, cy, x - 1, y);
+        }
+        if lx >= cs - 2 {
+            self.expand_chunk_dirty(cx + 1, cy, x + 1, y);
+        }
+        if ly <= 1 {
+            self.expand_chunk_dirty(cx, cy - 1, x, y - 1);
+        }
+        if ly >= cs - 2 {
+            self.expand_chunk_dirty(cx, cy + 1, x, y + 1);
+        }
+    }
+
+    #[inline]
+    fn expand_chunk_dirty(&mut self, cx: i32, cy: i32, x: i32, y: i32) {
+        if cx < 0 || cy < 0 || cx >= self.chunks_x as i32 || cy >= self.chunks_y as i32 {
+            return;
+        }
+        if !self.in_bounds(x, y) {
+            return;
+        }
+        let idx = self.chunk_index(cx, cy);
+        let min_x = (x - 1).max(0);
+        let min_y = (y - 1).max(0);
+        let max_x = (x + 1).min(self.width as i32 - 1);
+        let max_y = (y + 1).min(self.height as i32 - 1);
+        let chunk = &mut self.chunks[idx];
+        match chunk.dirty {
+            None => chunk.dirty = Some((min_x, min_y, max_x, max_y)),
+            Some((dx0, dy0, dx1, dy1)) => {
+                chunk.dirty = Some((
+                    dx0.min(min_x),
+                    dy0.min(min_y),
+                    dx1.max(max_x),
+                    dy1.max(max_y),
+                ));
+            }
+        }
+    }
+
+    #[inline]
+    pub fn cells_swap(&mut self, x1: i32, y1: i32, x2: i32, y2: i32) {
+        if !self.in_bounds(x1, y1) || !self.in_bounds(x2, y2) {
+            return;
+        }
+        let i1 = self.idx(x1, y1);
+        let i2 = self.idx(x2, y2);
+        let tmp = self.cells[i1];
+        self.cells[i1] = self.cells[i2];
+        self.cells[i2] = tmp;
+        self.cells[i2].updated_this_tick = true;
+        self.mark_dirty(x1, y1);
+        self.mark_dirty(x2, y2);
+    }
+
+    #[inline]
+    pub fn set_cell_index(&mut self, i: usize, cell: Cell) {
+        self.cells[i] = cell;
+        let x = (i % self.width) as i32;
+        let y = (i / self.width) as i32;
+        self.mark_dirty(x, y);
+    }
+
     pub fn reset_tick_flags(&mut self) {
-        for c in &mut self.cells {
-            c.updated_this_tick = false;
+        for cy in 0..self.chunks_y {
+            for cx in 0..self.chunks_x {
+                if !self.chunks[cy * self.chunks_x + cx].active {
+                    continue;
+                }
+                let (x0, y0, x1, y1) = self.chunk_bounds(cx, cy);
+                for y in y0..y1 {
+                    let row = y as usize * self.width;
+                    for x in x0..x1 {
+                        self.cells[row + x as usize].updated_this_tick = false;
+                    }
+                }
+            }
         }
     }
 
@@ -225,7 +321,7 @@ impl Grid {
         let (x0, y0, x1, y1) = self.chunk_bounds(cx as usize, cy as usize);
         let w = (x1 - x0) as usize;
         let h = (y1 - y0) as usize;
-        let mut bytes = Vec::with_capacity(w * h * 12);
+        let mut bytes = Vec::with_capacity(w * h * 8);
         for y in y0..y1 {
             for x in x0..x1 {
                 bytes.extend_from_slice(&self.get(x, y).to_bytes());
@@ -246,14 +342,14 @@ impl Grid {
         let (x0, y0, x1, y1) = self.chunk_bounds(cx as usize, cy as usize);
         let w = (x1 - x0) as usize;
         let h = (y1 - y0) as usize;
-        let expected = w * h * 12;
+        let expected = w * h * 8;
         if data.len() != expected {
             return Err(io::Error::other("chunk file size mismatch"));
         }
         let mut i = 0usize;
         for y in y0..y1 {
             for x in x0..x1 {
-                let cell = Cell::from_bytes(&data[i * 12..(i + 1) * 12]);
+                let cell = Cell::from_bytes(&data[i * 8..(i + 1) * 8]);
                 self.set(x, y, cell);
                 i += 1;
             }

src/world/material.rs

@@ -13,6 +13,9 @@ pub struct Material {
     pub ignition_temp: f32,
     pub melt_temp: f32,
     pub heat_conductivity: f32,
+    pub conductive: bool,
+    pub conductivity: f32,
+    pub structural: bool,
     pub color_fg: (u8, u8, u8),
     pub color_bg: (u8, u8, u8),
     pub display_char: char,
@@ -40,6 +43,9 @@ impl MaterialRegistry {
                     ignition_temp: f32::INFINITY,
                     melt_temp: f32::INFINITY,
                     heat_conductivity: 0.0,
+                    conductive: false,
+                    conductivity: 0.0,
+                    structural: false,
                     color_fg: (15, 15, 20),
                     color_bg: (10, 10, 15),
                     display_char: ' ',
@@ -56,6 +62,9 @@ impl MaterialRegistry {
                     ignition_temp: f32::INFINITY,
                     melt_temp: 1700.0,
                     heat_conductivity: 0.2,
+                    conductive: false,
+                    conductivity: 0.0,
+                    structural: false,
                     color_fg: (218, 178, 90),
                     color_bg: (60, 50, 30),
                     display_char: '.',
@@ -72,6 +81,9 @@ impl MaterialRegistry {
                     ignition_temp: f32::INFINITY,
                     melt_temp: 0.0,
                     heat_conductivity: 0.4,
+                    conductive: true,
+                    conductivity: 0.6,
+                    structural: false,
                     color_fg: (64, 128, 220),
                     color_bg: (20, 40, 80),
                     display_char: '~',
@@ -88,6 +100,9 @@ impl MaterialRegistry {
                     ignition_temp: f32::INFINITY,
                     melt_temp: 1200.0,
                     heat_conductivity: 0.3,
+                    conductive: false,
+                    conductivity: 0.0,
+                    structural: true,
                     color_fg: (120, 120, 130),
                     color_bg: (40, 40, 50),
                     display_char: '#',
@@ -104,6 +119,9 @@ impl MaterialRegistry {
                     ignition_temp: f32::INFINITY,
                     melt_temp: f32::INFINITY,
                     heat_conductivity: 0.05,
+                    conductive: false,
+                    conductivity: 0.0,
+                    structural: false,
                     color_fg: (255, 80, 20),
                     color_bg: (120, 20, 0),
                     display_char: '#',
@@ -120,6 +138,9 @@ impl MaterialRegistry {
                     ignition_temp: 300.0,
                     melt_temp: f32::INFINITY,
                     heat_conductivity: 0.1,
+                    conductive: false,
+                    conductivity: 0.0,
+                    structural: true,
                     color_fg: (140, 90, 50),
                     color_bg: (50, 30, 20),
                     display_char: 'T',
@@ -136,6 +157,9 @@ impl MaterialRegistry {
                     ignition_temp: 200.0,
                     melt_temp: f32::INFINITY,
                     heat_conductivity: 0.15,
+                    conductive: false,
+                    conductivity: 0.0,
+                    structural: false,
                     color_fg: (180, 50, 50),
                     color_bg: (60, 15, 15),
                     display_char: '%',
@@ -152,6 +176,9 @@ impl MaterialRegistry {
                     ignition_temp: f32::INFINITY,
                     melt_temp: f32::INFINITY,
                     heat_conductivity: 0.1,
+                    conductive: false,
+                    conductivity: 0.0,
+                    structural: false,
                     color_fg: (220, 210, 190),
                     color_bg: (60, 55, 50),
                     display_char: '`',
@@ -168,6 +195,9 @@ impl MaterialRegistry {
                     ignition_temp: f32::INFINITY,
                     melt_temp: f32::INFINITY,
                     heat_conductivity: 0.2,
+                    conductive: false,
+                    conductivity: 0.0,
+                    structural: false,
                     color_fg: (200, 200, 220),
                     color_bg: (30, 30, 40),
                     display_char: '~',
@@ -184,6 +214,9 @@ impl MaterialRegistry {
                     ignition_temp: f32::INFINITY,
                     melt_temp: f32::INFINITY,
                     heat_conductivity: 0.6,
+                    conductive: false,
+                    conductivity: 0.0,
+                    structural: false,
                     color_fg: (255, 160, 40),
                     color_bg: (100, 30, 0),
                     display_char: '^',
@@ -200,6 +233,9 @@ impl MaterialRegistry {
                     ignition_temp: f32::INFINITY,
                     melt_temp: f32::INFINITY,
                     heat_conductivity: 0.3,
+                    conductive: false,
+                    conductivity: 0.0,
+                    structural: false,
                     color_fg: (100, 255, 60),
                     color_bg: (20, 60, 10),
                     display_char: '~',
@@ -216,6 +252,9 @@ impl MaterialRegistry {
                     ignition_temp: f32::INFINITY,
                     melt_temp: f32::INFINITY,
                     heat_conductivity: 0.1,
+                    conductive: false,
+                    conductivity: 0.0,
+                    structural: false,
                     color_fg: (100, 100, 100),
                     color_bg: (20, 20, 20),
                     display_char: '*',
@@ -232,6 +271,9 @@ impl MaterialRegistry {
                     ignition_temp: 250.0,
                     melt_temp: f32::INFINITY,
                     heat_conductivity: 0.1,
+                    conductive: false,
+                    conductivity: 0.0,
+                    structural: false,
                     color_fg: (80, 200, 60),
                     color_bg: (20, 50, 15),
                     display_char: '"',
@@ -248,6 +290,9 @@ impl MaterialRegistry {
                     ignition_temp: f32::INFINITY,
                     melt_temp: f32::INFINITY,
                     heat_conductivity: 0.2,
+                    conductive: false,
+                    conductivity: 0.0,
+                    structural: false,
                     color_fg: (100, 70, 50),
                     color_bg: (40, 30, 20),
                     display_char: ':',
@@ -264,6 +309,9 @@ impl MaterialRegistry {
                     ignition_temp: f32::INFINITY,
                     melt_temp: f32::INFINITY,
                     heat_conductivity: 0.0,
+                    conductive: false,
+                    conductivity: 0.0,
+                    structural: false,
                     color_fg: (255, 220, 80),
                     color_bg: (60, 50, 20),
                     display_char: '>',

src/world/mod.rs

@@ -1,5 +1,8 @@
+pub mod cache;
 pub mod cell;
 pub mod cellular;
 pub mod chunk;
+pub mod chunked_grid;
 pub mod grid;
 pub mod material;
+pub mod worldgen;

tests/chunks.rs

@@ -48,7 +48,6 @@ fn cell_serialization_roundtrip() {
     assert_eq!(c.fg, c2.fg);
     assert_eq!(c.bg, c2.bg);
     assert_eq!(c.variant, c2.variant);
-    assert!((c.temp - c2.temp).abs() < 0.001);
 }
 
 #[test]

tests/collision_robust.rs

@@ -1,11 +1,17 @@
-use verbatim::ai::GameSession;
 use verbatim::ai::AiAction;
+use verbatim::ai::GameSession;
 
 fn setup() -> GameSession {
     let mut s = GameSession::new_seeded(42);
     s.init_empty();
     s.clear_area(90, 90, 50, 50);
-    s.perform_action(&AiAction::FillRect { x: 80, y: 130, w: 80, h: 15, material: "stone".into() });
+    s.perform_action(&AiAction::FillRect {
+        x: 80,
+        y: 130,
+        w: 80,
+        h: 15,
+        material: "stone".into(),
+    });
     s
 }
 
@@ -15,11 +21,22 @@ fn player_blocked_by_left_wall() {
     s.step(30);
     let p = s.get_player().unwrap();
     let wall_x = (p.pos[0] as i32) - 6;
-    s.perform_action(&AiAction::FillRect { x: wall_x, y: 125, w: 1, h: 10, material: "stone".into() });
+    s.perform_action(&AiAction::FillRect {
+        x: wall_x,
+        y: 125,
+        w: 1,
+        h: 10,
+        material: "stone".into(),
+    });
     s.perform_action(&AiAction::MoveLeft);
     s.step(20);
     let p2 = s.get_player().unwrap();
-    assert!(p2.pos[0] > wall_x as f32, "player should not pass through left wall: wall={} player={}", wall_x, p2.pos[0]);
+    assert!(
+        p2.pos[0] > wall_x as f32,
+        "player should not pass through left wall: wall={} player={}",
+        wall_x,
+        p2.pos[0]
+    );
 }
 
 #[test]
@@ -28,11 +45,22 @@ fn player_blocked_by_right_wall() {
     s.step(30);
     let p = s.get_player().unwrap();
     let wall_x = (p.pos[0] as i32) + 6;
-    s.perform_action(&AiAction::FillRect { x: wall_x, y: 125, w: 1, h: 10, material: "stone".into() });
+    s.perform_action(&AiAction::FillRect {
+        x: wall_x,
+        y: 125,
+        w: 1,
+        h: 10,
+        material: "stone".into(),
+    });
     s.perform_action(&AiAction::MoveRight);
     s.step(20);
     let p2 = s.get_player().unwrap();
-    assert!(p2.pos[0] < wall_x as f32, "player should not pass through right wall: wall={} player={}", wall_x, p2.pos[0]);
+    assert!(
+        p2.pos[0] < wall_x as f32,
+        "player should not pass through right wall: wall={} player={}",
+        wall_x,
+        p2.pos[0]
+    );
 }
 
 #[test]
@@ -41,14 +69,24 @@ fn player_slides_along_wall() {
     s.step(30);
     let p = s.get_player().unwrap();
     let wall_x = (p.pos[0] as i32) + 6;
-    s.perform_action(&AiAction::FillRect { x: wall_x, y: 125, w: 1, h: 10, material: "stone".into() });
+    s.perform_action(&AiAction::FillRect {
+        x: wall_x,
+        y: 125,
+        w: 1,
+        h: 10,
+        material: "stone".into(),
+    });
     s.perform_action(&AiAction::MoveRight);
     s.step(30);
     let p2 = s.get_player().unwrap();
     assert!(p2.pos[0] < wall_x as f32, "player should stay left of wall");
     assert!(p2.alive, "player should be alive");
     let y_diff = (p2.pos[1] - p.pos[1]).abs();
-    assert!(y_diff < 5.0, "player should not fall through floor while sliding: dy={}", y_diff);
+    assert!(
+        y_diff < 5.0,
+        "player should not fall through floor while sliding: dy={}",
+        y_diff
+    );
 }
 
 #[test]
@@ -57,11 +95,22 @@ fn player_blocked_by_ceiling() {
     s.step(30);
     let p = s.get_player().unwrap();
     let ceiling_y = (p.pos[1] as i32) - 8;
-    s.perform_action(&AiAction::FillRect { x: p.pos[0] as i32 - 5, y: ceiling_y, w: 10, h: 1, material: "stone".into() });
+    s.perform_action(&AiAction::FillRect {
+        x: p.pos[0] as i32 - 5,
+        y: ceiling_y,
+        w: 10,
+        h: 1,
+        material: "stone".into(),
+    });
     s.perform_action(&AiAction::Jump);
     s.step(10);
     let p2 = s.get_player().unwrap();
-    assert!(p2.pos[1] > ceiling_y as f32, "player should not pass through ceiling: ceiling={} player={}", ceiling_y, p2.pos[1]);
+    assert!(
+        p2.pos[1] > ceiling_y as f32,
+        "player should not pass through ceiling: ceiling={} player={}",
+        ceiling_y,
+        p2.pos[1]
+    );
 }
 
 #[test]
@@ -69,13 +118,40 @@ fn player_navigates_corridor() {
     let mut s = GameSession::new_seeded(42);
     s.init_empty();
     s.clear_area(100, 100, 40, 30);
-    s.perform_action(&AiAction::FillRect { x: 95, y: 120, w: 50, h: 10, material: "stone".into() });
-    s.perform_action(&AiAction::FillRect { x: 115, y: 110, w: 1, h: 10, material: "stone".into() });
-    s.perform_action(&AiAction::FillRect { x: 125, y: 110, w: 1, h: 10, material: "stone".into() });
-    s.perform_action(&AiAction::FillRect { x: 115, y: 108, w: 11, h: 1, material: "stone".into() });
+    s.perform_action(&AiAction::FillRect {
+        x: 95,
+        y: 120,
+        w: 50,
+        h: 10,
+        material: "stone".into(),
+    });
+    s.perform_action(&AiAction::FillRect {
+        x: 115,
+        y: 110,
+        w: 1,
+        h: 10,
+        material: "stone".into(),
+    });
+    s.perform_action(&AiAction::FillRect {
+        x: 125,
+        y: 110,
+        w: 1,
+        h: 10,
+        material: "stone".into(),
+    });
+    s.perform_action(&AiAction::FillRect {
+        x: 115,
+        y: 108,
+        w: 11,
+        h: 1,
+        material: "stone".into(),
+    });
     s.step(30);
     let p = s.get_player().unwrap();
-    assert!(p.pos[0] < 115.0 || p.pos[0] > 125.0, "player should be outside corridor initially");
+    assert!(
+        p.pos[0] < 115.0 || p.pos[0] > 125.0,
+        "player should be outside corridor initially"
+    );
 }
 
 #[test]
@@ -84,7 +160,13 @@ fn player_does_not_stick_to_wall() {
     s.step(30);
     let p = s.get_player().unwrap();
     let wall_x = (p.pos[0] as i32) + 8;
-    s.perform_action(&AiAction::FillRect { x: wall_x, y: 125, w: 1, h: 10, material: "stone".into() });
+    s.perform_action(&AiAction::FillRect {
+        x: wall_x,
+        y: 125,
+        w: 1,
+        h: 10,
+        material: "stone".into(),
+    });
     for _ in 0..10 {
         s.perform_action(&AiAction::MoveRight);
         s.step(2);
@@ -96,7 +178,12 @@ fn player_does_not_stick_to_wall() {
         s.step(2);
     }
     let p_away = s.get_player().unwrap();
-    assert!(p_away.pos[0] < x_at_wall - 1.0, "player should move away from wall: {} -> {}", x_at_wall, p_away.pos[0]);
+    assert!(
+        p_away.pos[0] < x_at_wall - 1.0,
+        "player should move away from wall: {} -> {}",
+        x_at_wall,
+        p_away.pos[0]
+    );
 }
 
 #[test]
@@ -105,8 +192,20 @@ fn player_squeezes_through_gap() {
     s.step(30);
     let p = s.get_player().unwrap();
     let px = p.pos[0] as i32;
-    s.perform_action(&AiAction::FillRect { x: px + 8, y: 128, w: 1, h: 2, material: "stone".into() });
-    s.perform_action(&AiAction::FillRect { x: px + 8, y: 122, w: 1, h: 2, material: "stone".into() });
+    s.perform_action(&AiAction::FillRect {
+        x: px + 8,
+        y: 128,
+        w: 1,
+        h: 2,
+        material: "stone".into(),
+    });
+    s.perform_action(&AiAction::FillRect {
+        x: px + 8,
+        y: 122,
+        w: 1,
+        h: 2,
+        material: "stone".into(),
+    });
     s.perform_action(&AiAction::MoveRight);
     s.step(20);
     let p2 = s.get_player().unwrap();
@@ -119,8 +218,20 @@ fn player_blocked_by_two_walls_both_sides() {
     s.step(30);
     let p = s.get_player().unwrap();
     let px = p.pos[0] as i32;
-    s.perform_action(&AiAction::FillRect { x: px - 6, y: 125, w: 1, h: 10, material: "stone".into() });
-    s.perform_action(&AiAction::FillRect { x: px + 6, y: 125, w: 1, h: 10, material: "stone".into() });
+    s.perform_action(&AiAction::FillRect {
+        x: px - 6,
+        y: 125,
+        w: 1,
+        h: 10,
+        material: "stone".into(),
+    });
+    s.perform_action(&AiAction::FillRect {
+        x: px + 6,
+        y: 125,
+        w: 1,
+        h: 10,
+        material: "stone".into(),
+    });
     s.perform_action(&AiAction::MoveRight);
     s.step(10);
     let p_right = s.get_player().unwrap();
@@ -129,7 +240,10 @@ fn player_blocked_by_two_walls_both_sides() {
     let p_left = s.get_player().unwrap();
     assert!(p_right.pos[0] < (px + 6) as f32, "blocked right");
     assert!(p_left.pos[0] > (px - 6) as f32, "blocked left");
-    assert!((p_left.pos[0] - p_right.pos[0]).abs() < 12.0, "player should stay between walls");
+    assert!(
+        (p_left.pos[0] - p_right.pos[0]).abs() < 12.0,
+        "player should stay between walls"
+    );
 }
 
 #[test]
@@ -140,7 +254,11 @@ fn player_walks_up_slope() {
     for x in 100..130 {
         let h = ((x - 100) / 3).min(15);
         for y in 0..h {
-            s.perform_action(&AiAction::SetCell { x, y: 135 - 1 - y, material: "stone".into() });
+            s.perform_action(&AiAction::SetCell {
+                x,
+                y: 135 - 1 - y,
+                material: "stone".into(),
+            });
         }
     }
     s.step(40);
@@ -152,11 +270,25 @@ fn player_walks_up_slope() {
 #[test]
 fn entity_collision_with_dirt_wall() {
     let mut s = setup();
-    s.perform_action(&AiAction::FillRect { x: 140, y: 125, w: 1, h: 5, material: "dirt".into() });
-    s.perform_action(&AiAction::Spawn { kind: "goblin".into(), x: 135.0, y: 120.0 });
+    s.perform_action(&AiAction::FillRect {
+        x: 140,
+        y: 125,
+        w: 1,
+        h: 5,
+        material: "dirt".into(),
+    });
+    s.perform_action(&AiAction::Spawn {
+        kind: "goblin".into(),
+        x: 135.0,
+        y: 120.0,
+    });
     s.step(40);
     let entities = s.get_entities();
     if let Some(g) = entities.into_iter().find(|e| e.kind == "Goblin" && e.alive) {
-        assert!(g.pos[0] < 140.0, "goblin should be blocked by dirt wall: x={}", g.pos[0]);
+        assert!(
+            g.pos[0] < 140.0,
+            "goblin should be blocked by dirt wall: x={}",
+            g.pos[0]
+        );
     }
 }

tests/descent.rs

@@ -53,6 +53,7 @@ fn depth_shown_in_hud() {
     let mut ui = verbatim::ui::UiLayer::new();
     let screen_w = 320;
     let screen_h = 100;
+    ui.resize(screen_w, screen_h);
     ui.draw_hud(
         screen_w,
         screen_h,
@@ -69,11 +70,14 @@ fn depth_shown_in_hud() {
         "LV:{} XP:{} K:{} S:{} D:{} T:{}",
         player.level, player.xp, 0, 0, s.game.depth, s.game.tick
     );
-    let stats_w = verbatim::ui::UiLayer::text_width(&stats);
+    let stats_w = ui.text_width(&stats);
     let stats_x = (screen_w as i32 - stats_w as i32).max(0);
-    let y_row3 = screen_h as i32 - 28 + 22;
+    let fs = ui.font_scale();
+    let fh = 5 * fs;
+    let bar_h = (28 * fs / 2).max(fh * 3);
+    let y_row3 = screen_h as i32 - bar_h + 2 + (fh + 2) * 2;
     let line: String = (stats_x as i32..screen_w as i32)
-        .step_by(3)
+        .step_by(fs as usize * 3)
         .map(|x| ui.get(x, y_row3).map(|c| c.ch).unwrap_or(' '))
         .collect();
     assert!(line.contains("D:1"), "HUD should show depth: {}", line);

tests/determinism.rs

@@ -1,12 +1,18 @@
-use verbatim::ai::GameSession;
 use verbatim::ai::AiAction;
+use verbatim::ai::GameSession;
 use verbatim::ai::ReplayPlayer;
 
 fn setup() -> GameSession {
     let mut s = GameSession::new_seeded(42);
     s.init_empty();
     s.clear_area(90, 90, 50, 50);
-    s.perform_action(&AiAction::FillRect { x: 80, y: 130, w: 80, h: 15, material: "stone".into() });
+    s.perform_action(&AiAction::FillRect {
+        x: 80,
+        y: 130,
+        w: 80,
+        h: 15,
+        material: "stone".into(),
+    });
     s
 }
 
@@ -32,7 +38,11 @@ fn same_seed_same_entity_count() {
     let mut s2 = GameSession::new_seeded(555);
     s2.init();
     s2.step(60);
-    assert_eq!(s1.get_entities().len(), s2.get_entities().len(), "entity count should match");
+    assert_eq!(
+        s1.get_entities().len(),
+        s2.get_entities().len(),
+        "entity count should match"
+    );
 }
 
 #[test]
@@ -47,7 +57,11 @@ fn same_seed_same_grid_state() {
         for x in 100..150 {
             let c1 = s1.get_cell(x, y);
             let c2 = s2.get_cell(x, y);
-            assert_eq!(c1.material, c2.material, "material mismatch at ({},{})", x, y);
+            assert_eq!(
+                c1.material, c2.material,
+                "material mismatch at ({},{})",
+                x, y
+            );
         }
     }
 }
@@ -69,7 +83,8 @@ fn replay_exact_match() {
     s.perform_action(&AiAction::MoveLeft);
     s.step(10);
     let state_orig = s.get_state();
-    s.save_replay("/tmp/verbatim_replay_exact.json").expect("save");
+    s.save_replay("/tmp/verbatim_replay_exact.json")
+        .expect("save");
 
     let player = ReplayPlayer::load("/tmp/verbatim_replay_exact.json").expect("load");
     let s2 = player.play();
@@ -77,8 +92,18 @@ fn replay_exact_match() {
 
     assert_eq!(state_orig.tick, state_replay.tick, "tick mismatch");
     if let (Some(p1), Some(p2)) = (&state_orig.player, &state_replay.player) {
-        assert!((p1.pos[0] - p2.pos[0]).abs() < 0.1, "x mismatch: {} vs {}", p1.pos[0], p2.pos[0]);
-        assert!((p1.pos[1] - p2.pos[1]).abs() < 0.1, "y mismatch: {} vs {}", p1.pos[1], p2.pos[1]);
+        assert!(
+            (p1.pos[0] - p2.pos[0]).abs() < 0.1,
+            "x mismatch: {} vs {}",
+            p1.pos[0],
+            p2.pos[0]
+        );
+        assert!(
+            (p1.pos[1] - p2.pos[1]).abs() < 0.1,
+            "y mismatch: {} vs {}",
+            p1.pos[1],
+            p2.pos[1]
+        );
         assert!((p1.health - p2.health).abs() < 1.0, "health mismatch");
     }
 }
@@ -91,14 +116,25 @@ fn replay_stop_at_tick() {
     s.step(20);
     s.perform_action(&AiAction::MoveRight);
     s.step(20);
-    s.save_replay("/tmp/verbatim_replay_partial.json").expect("save");
+    s.save_replay("/tmp/verbatim_replay_partial.json")
+        .expect("save");
 
     let player = ReplayPlayer::load("/tmp/verbatim_replay_partial.json").expect("load");
     let s_half = player.play_until_tick(10);
-    assert_eq!(s_half.tick(), 10, "should stop at tick 10, got {}", s_half.tick());
+    assert_eq!(
+        s_half.tick(),
+        10,
+        "should stop at tick 10, got {}",
+        s_half.tick()
+    );
 
     let s_full = player.play();
-    assert_eq!(s_full.tick(), 40, "full replay should reach tick 40, got {}", s_full.tick());
+    assert_eq!(
+        s_full.tick(),
+        40,
+        "full replay should reach tick 40, got {}",
+        s_full.tick()
+    );
 }
 
 #[test]
@@ -110,28 +146,52 @@ fn recording_captures_all_actions() {
     s.perform_action(&AiAction::Jump);
     s.perform_action(&AiAction::MoveLeft);
     s.step(5);
-    s.save_replay("/tmp/verbatim_replay_capture.json").expect("save");
+    s.save_replay("/tmp/verbatim_replay_capture.json")
+        .expect("save");
 
     let player = ReplayPlayer::load("/tmp/verbatim_replay_capture.json").expect("load");
     let event_count = player.recording().events.len();
-    assert!(event_count >= 4, "recording should have at least 4 events (3 actions + 1 step), got {}", event_count);
+    assert!(
+        event_count >= 4,
+        "recording should have at least 4 events (3 actions + 1 step), got {}",
+        event_count
+    );
 }
 
 #[test]
 fn determinism_with_spawn_and_damage() {
     let mut s1 = setup();
-    s1.perform_action(&AiAction::Spawn { kind: "goblin".into(), x: 135.0, y: 120.0 });
-    s1.perform_action(&AiAction::DamageEntity { id: 1, amount: 20.0 });
+    s1.perform_action(&AiAction::Spawn {
+        kind: "goblin".into(),
+        x: 135.0,
+        y: 120.0,
+    });
+    s1.perform_action(&AiAction::DamageEntity {
+        id: 1,
+        amount: 20.0,
+    });
     s1.step(30);
 
     let mut s2 = setup();
-    s2.perform_action(&AiAction::Spawn { kind: "goblin".into(), x: 135.0, y: 120.0 });
-    s2.perform_action(&AiAction::DamageEntity { id: 1, amount: 20.0 });
+    s2.perform_action(&AiAction::Spawn {
+        kind: "goblin".into(),
+        x: 135.0,
+        y: 120.0,
+    });
+    s2.perform_action(&AiAction::DamageEntity {
+        id: 1,
+        amount: 20.0,
+    });
     s2.step(30);
 
     let e1 = s1.get_entities().into_iter().find(|e| e.id == 1).unwrap();
     let e2 = s2.get_entities().into_iter().find(|e| e.id == 1).unwrap();
-    assert!((e1.health - e2.health).abs() < 0.01, "health should match: {} vs {}", e1.health, e2.health);
+    assert!(
+        (e1.health - e2.health).abs() < 0.01,
+        "health should match: {} vs {}",
+        e1.health,
+        e2.health
+    );
     assert!((e1.pos[0] - e2.pos[0]).abs() < 0.1, "x should match");
     assert!((e1.pos[1] - e2.pos[1]).abs() < 0.1, "y should match");
 }
@@ -150,5 +210,10 @@ fn hundred_tick_determinism() {
 
     let p1 = s1.get_player().unwrap();
     let p2 = s2.get_player().unwrap();
-    assert!((p1.pos[0] - p2.pos[0]).abs() < 0.01, "100-tick determinism failed: {} vs {}", p1.pos[0], p2.pos[0]);
+    assert!(
+        (p1.pos[0] - p2.pos[0]).abs() < 0.01,
+        "100-tick determinism failed: {} vs {}",
+        p1.pos[0],
+        p2.pos[0]
+    );
 }

tests/entity_damage.rs

@@ -1,5 +1,5 @@
-use verbatim::ai::GameSession;
 use verbatim::ai::AiAction;
+use verbatim::ai::GameSession;
 
 fn setup_empty() -> GameSession {
     let mut s = GameSession::new_seeded(42);
@@ -11,39 +11,92 @@ fn setup_empty() -> GameSession {
 #[test]
 fn entity_takes_lava_damage() {
     let mut s = setup_empty();
-    s.perform_action(&AiAction::FillRect { x: 100, y: 130, w: 20, h: 3, material: "stone".into() });
-    s.perform_action(&AiAction::FillRect { x: 114, y: 127, w: 8, h: 3, material: "lava".into() });
-    s.perform_action(&AiAction::Spawn { kind: "goblin".into(), x: 118.0, y: 118.0 });
+    s.perform_action(&AiAction::FillRect {
+        x: 100,
+        y: 130,
+        w: 20,
+        h: 3,
+        material: "stone".into(),
+    });
+    s.perform_action(&AiAction::FillRect {
+        x: 114,
+        y: 127,
+        w: 8,
+        h: 3,
+        material: "lava".into(),
+    });
+    s.perform_action(&AiAction::Spawn {
+        kind: "goblin".into(),
+        x: 118.0,
+        y: 118.0,
+    });
     s.step(80);
     let entities = s.get_entities();
     let goblin = entities.into_iter().find(|e| e.kind == "Goblin");
     assert!(goblin.is_some(), "goblin should exist");
     let g = goblin.unwrap();
-    assert!(g.health < 40.0, "goblin should have taken damage from lava, hp={}", g.health);
+    assert!(
+        g.health < 40.0,
+        "goblin should have taken damage from lava, hp={}",
+        g.health
+    );
 }
 
 #[test]
 fn entity_dies_becomes_corpse() {
     let mut s = setup_empty();
-    s.perform_action(&AiAction::FillRect { x: 100, y: 125, w: 20, h: 1, material: "stone".into() });
-    s.perform_action(&AiAction::Spawn { kind: "goblin".into(), x: 110.0, y: 120.0 });
+    s.perform_action(&AiAction::FillRect {
+        x: 100,
+        y: 125,
+        w: 20,
+        h: 1,
+        material: "stone".into(),
+    });
+    s.perform_action(&AiAction::Spawn {
+        kind: "goblin".into(),
+        x: 110.0,
+        y: 120.0,
+    });
     s.step(30);
-    s.perform_action(&AiAction::DamageEntity { id: 1, amount: 100.0 });
+    s.perform_action(&AiAction::DamageEntity {
+        id: 1,
+        amount: 100.0,
+    });
     s.step(1);
     let entities = s.get_entities();
     let goblin = entities.into_iter().find(|e| e.id == 1);
     assert!(goblin.is_some(), "entity should still exist");
     let g = goblin.unwrap();
     assert!(!g.alive, "entity should be dead after 100 damage");
-    assert_eq!(g.kind, "Corpse", "dead entity should be a corpse, got {}", g.kind);
+    assert_eq!(
+        g.kind, "Corpse",
+        "dead entity should be a corpse, got {}",
+        g.kind
+    );
 }
 
 #[test]
 fn entity_on_fire_takes_damage_over_time() {
     let mut s = setup_empty();
-    s.perform_action(&AiAction::FillRect { x: 100, y: 125, w: 20, h: 1, material: "stone".into() });
-    s.perform_action(&AiAction::FillRect { x: 116, y: 123, w: 4, h: 2, material: "lava".into() });
-    s.perform_action(&AiAction::Spawn { kind: "goblin".into(), x: 118.0, y: 120.0 });
+    s.perform_action(&AiAction::FillRect {
+        x: 100,
+        y: 125,
+        w: 20,
+        h: 1,
+        material: "stone".into(),
+    });
+    s.perform_action(&AiAction::FillRect {
+        x: 116,
+        y: 123,
+        w: 4,
+        h: 2,
+        material: "lava".into(),
+    });
+    s.perform_action(&AiAction::Spawn {
+        kind: "goblin".into(),
+        x: 118.0,
+        y: 120.0,
+    });
     s.step(20);
     let entities = s.get_entities();
     let goblin = entities.into_iter().find(|e| e.id == 1);
@@ -53,7 +106,10 @@ fn entity_on_fire_takes_damage_over_time() {
             s.step(30);
             let entities2 = s.get_entities();
             if let Some(g2) = entities2.into_iter().find(|e| e.id == 1) {
-                assert!(g2.health < hp_after_fire, "entity on fire should lose more health over time");
+                assert!(
+                    g2.health < hp_after_fire,
+                    "entity on fire should lose more health over time"
+                );
             }
         }
     }
@@ -62,12 +118,32 @@ fn entity_on_fire_takes_damage_over_time() {
 #[test]
 fn entity_blocked_by_stone() {
     let mut s = setup_empty();
-    s.perform_action(&AiAction::FillRect { x: 100, y: 130, w: 30, h: 1, material: "stone".into() });
-    s.perform_action(&AiAction::FillRect { x: 110, y: 126, w: 1, h: 4, material: "stone".into() });
-    s.perform_action(&AiAction::Spawn { kind: "goblin".into(), x: 105.0, y: 125.0 });
+    s.perform_action(&AiAction::FillRect {
+        x: 100,
+        y: 130,
+        w: 30,
+        h: 1,
+        material: "stone".into(),
+    });
+    s.perform_action(&AiAction::FillRect {
+        x: 110,
+        y: 126,
+        w: 1,
+        h: 4,
+        material: "stone".into(),
+    });
+    s.perform_action(&AiAction::Spawn {
+        kind: "goblin".into(),
+        x: 105.0,
+        y: 125.0,
+    });
     s.step(30);
     let entities = s.get_entities();
     if let Some(g) = entities.into_iter().find(|e| e.id == 1) {
-        assert!(g.pos[0] < 110.0, "goblin should be blocked by stone wall, got x={}", g.pos[0]);
+        assert!(
+            g.pos[0] < 110.0,
+            "goblin should be blocked by stone wall, got x={}",
+            g.pos[0]
+        );
     }
 }

tests/entity_movement.rs

@@ -1,11 +1,17 @@
-use verbatim::ai::GameSession;
 use verbatim::ai::AiAction;
+use verbatim::ai::GameSession;
 
 fn setup_empty() -> GameSession {
     let mut s = GameSession::new_seeded(42);
     s.init_empty();
     s.clear_area(95, 95, 40, 35);
-    s.perform_action(&AiAction::FillRect { x: 80, y: 135, w: 80, h: 15, material: "stone".into() });
+    s.perform_action(&AiAction::FillRect {
+        x: 80,
+        y: 135,
+        w: 80,
+        h: 15,
+        material: "stone".into(),
+    });
     s
 }
 
@@ -14,16 +20,32 @@ fn player_falls_and_lands() {
     let mut s = GameSession::new_seeded(42);
     s.init_empty();
     s.clear_area(115, 115, 20, 15);
-    s.perform_action(&AiAction::FillRect { x: 110, y: 130, w: 30, h: 15, material: "stone".into() });
+    s.perform_action(&AiAction::FillRect {
+        x: 110,
+        y: 130,
+        w: 30,
+        h: 15,
+        material: "stone".into(),
+    });
     s.step(80);
     let player = s.get_player().expect("player should exist");
     assert!(player.alive, "player should be alive");
     let y = player.pos[1];
-    assert!(y < 135.0, "player should not fall through stone floor, got y={}", y);
+    assert!(
+        y < 135.0,
+        "player should not fall through stone floor, got y={}",
+        y
+    );
     s.step(30);
     let player2 = s.get_player().expect("player should exist");
     let dy = (player2.pos[1] - y).abs();
-    assert!(dy < 3.0, "player should have stopped falling (dy={:.2}), y={} -> {}", dy, y, player2.pos[1]);
+    assert!(
+        dy < 3.0,
+        "player should have stopped falling (dy={:.2}), y={} -> {}",
+        dy,
+        y,
+        player2.pos[1]
+    );
 }
 
 #[test]
@@ -32,11 +54,20 @@ fn player_blocked_by_stone_wall() {
     s.step(30);
     let player = s.get_player().expect("player should exist");
     let x = player.pos[0] as i32;
-    s.perform_action(&AiAction::FillRect { x: x + 5, y: 125, w: 1, h: 10, material: "stone".into() });
+    s.perform_action(&AiAction::FillRect {
+        x: x + 5,
+        y: 125,
+        w: 1,
+        h: 10,
+        material: "stone".into(),
+    });
     s.perform_action(&AiAction::MoveRight);
     s.step(10);
     let player = s.get_player().expect("player should exist");
-    assert!(player.pos[0] < (x + 5) as f32, "player should be blocked by wall");
+    assert!(
+        player.pos[0] < (x + 5) as f32,
+        "player should be blocked by wall"
+    );
 }
 
 #[test]
@@ -48,7 +79,12 @@ fn player_can_move_right() {
     s.perform_action(&AiAction::MoveRight);
     s.step(10);
     let player = s.get_player().expect("player should exist");
-    assert!(player.pos[0] > initial_x, "player should have moved right: {} -> {}", initial_x, player.pos[0]);
+    assert!(
+        player.pos[0] > initial_x,
+        "player should have moved right: {} -> {}",
+        initial_x,
+        player.pos[0]
+    );
 }
 
 #[test]
@@ -57,5 +93,9 @@ fn player_survives_fall() {
     s.step(60);
     let player = s.get_player().expect("player should exist");
     assert!(player.alive, "player should survive a fall onto stone");
-    assert!(player.health > 50.0, "player should not take significant damage from landing, hp={}", player.health);
+    assert!(
+        player.health > 50.0,
+        "player should not take significant damage from landing, hp={}",
+        player.health
+    );
 }

tests/integration.rs

@@ -1,5 +1,5 @@
-use verbatim::ai::GameSession;
 use verbatim::ai::AiAction;
+use verbatim::ai::GameSession;
 use verbatim::ai::ReplayPlayer;
 
 #[test]
@@ -13,7 +13,8 @@ fn replay_deterministic() {
     s1.step(10);
     let state1 = s1.get_state();
 
-    s1.save_replay("/tmp/verbatim_test_replay.json").expect("save replay");
+    s1.save_replay("/tmp/verbatim_test_replay.json")
+        .expect("save replay");
 
     let player = ReplayPlayer::load("/tmp/verbatim_test_replay.json").expect("load replay");
     let s2 = player.play();
@@ -22,8 +23,18 @@ fn replay_deterministic() {
     assert_eq!(state1.tick, state2.tick, "ticks should match");
     if let (Some(p1), Some(p2)) = (&state1.player, &state2.player) {
         assert_eq!(p1.health, p2.health, "player health should match");
-        assert!((p1.pos[0] - p2.pos[0]).abs() < 0.01, "player x should match: {} vs {}", p1.pos[0], p2.pos[0]);
-        assert!((p1.pos[1] - p2.pos[1]).abs() < 0.01, "player y should match: {} vs {}", p1.pos[1], p2.pos[1]);
+        assert!(
+            (p1.pos[0] - p2.pos[0]).abs() < 0.01,
+            "player x should match: {} vs {}",
+            p1.pos[0],
+            p2.pos[0]
+        );
+        assert!(
+            (p1.pos[1] - p2.pos[1]).abs() < 0.01,
+            "player y should match: {} vs {}",
+            p1.pos[1],
+            p2.pos[1]
+        );
     }
 }
 
@@ -38,14 +49,25 @@ fn replay_play_until_tick() {
     s.step(5);
     s.perform_action(&AiAction::Jump);
     s.step(10);
-    s.save_replay("/tmp/verbatim_test_replay2.json").expect("save");
+    s.save_replay("/tmp/verbatim_test_replay2.json")
+        .expect("save");
 
     let player = ReplayPlayer::load("/tmp/verbatim_test_replay2.json").expect("load");
     let s_half = player.play_until_tick(5);
-    assert_eq!(s_half.tick(), 5, "should stop at tick 5, got {}", s_half.tick());
+    assert_eq!(
+        s_half.tick(),
+        5,
+        "should stop at tick 5, got {}",
+        s_half.tick()
+    );
 
     let s_full = player.play();
-    assert_eq!(s_full.tick(), 20, "full replay should reach tick 20, got {}", s_full.tick());
+    assert_eq!(
+        s_full.tick(),
+        20,
+        "full replay should reach tick 20, got {}",
+        s_full.tick()
+    );
 }
 
 #[test]
@@ -62,8 +84,18 @@ fn same_seed_same_state() {
 
     assert_eq!(state1.tick, state2.tick);
     if let (Some(p1), Some(p2)) = (&state1.player, &state2.player) {
-        assert!((p1.pos[0] - p2.pos[0]).abs() < 0.01, "x mismatch: {} vs {}", p1.pos[0], p2.pos[0]);
-        assert!((p1.pos[1] - p2.pos[1]).abs() < 0.01, "y mismatch: {} vs {}", p1.pos[1], p2.pos[1]);
+        assert!(
+            (p1.pos[0] - p2.pos[0]).abs() < 0.01,
+            "x mismatch: {} vs {}",
+            p1.pos[0],
+            p2.pos[0]
+        );
+        assert!(
+            (p1.pos[1] - p2.pos[1]).abs() < 0.01,
+            "y mismatch: {} vs {}",
+            p1.pos[1],
+            p2.pos[1]
+        );
     }
 }
 
@@ -73,7 +105,8 @@ fn pipe_protocol_init_and_step() {
     use std::process::{Command, Stdio};
 
     let mut child = Command::new(env!("CARGO_BIN_EXE_verbatim"))
-        .arg("--mode").arg("pipe")
+        .arg("--mode")
+        .arg("pipe")
         .stdin(Stdio::piped())
         .stdout(Stdio::piped())
         .stderr(Stdio::null())
@@ -98,9 +131,13 @@ fn pipe_protocol_init_and_step() {
     stdin.flush().expect("flush");
     let n = stdout.read(&mut buf).expect("read");
     let output2 = String::from_utf8_lossy(&buf[..n]).to_string();
-    let json2: serde_json::Value = serde_json::from_str(output2.trim()).expect("parse step response");
+    let json2: serde_json::Value =
+        serde_json::from_str(output2.trim()).expect("parse step response");
     assert_eq!(json2["ok"], true);
-    assert_eq!(json2["state"]["tick"], 10, "tick should be 10 after stepping 10");
+    assert_eq!(
+        json2["state"]["tick"], 10,
+        "tick should be 10 after stepping 10"
+    );
 
     writeln!(stdin, "{{\"cmd\":\"quit\"}}").expect("write quit");
     stdin.flush().expect("flush");

tests/large_world.rs

@@ -0,0 +1,51 @@
+use verbatim::game::Game;
+
+#[test]
+#[ignore = "slow: generates a 12500x12500 world"]
+fn large_world_initialization() {
+    let mut game = Game::new_random();
+    assert!(game.grid.is_infinite());
+    game.init_world();
+    let (px, py) = game.player.center(&game.entities);
+    assert!(px >= 0.0 && py >= 0.0);
+    let foot_x = px as i32;
+    let foot_y = (py + 3.0).ceil() as i32;
+    assert!(
+        !game.grid.get(foot_x, foot_y).is_solid(),
+        "player spawn should not be inside solid: px={} py={} foot=({},{}) mat={:?}",
+        px,
+        py,
+        foot_x,
+        foot_y,
+        game.grid.get(foot_x, foot_y).material
+    );
+    if let Some(ref root) = game.cache_dir {
+        let meta = verbatim::world::cache::WorldCache::meta_path(root, game.seed);
+        assert!(
+            meta.exists(),
+            "world cache should be written after generation"
+        );
+    }
+}
+
+#[test]
+#[ignore = "slow: loads cached 12500x12500 world"]
+fn large_world_cache_roundtrip() {
+    let mut game = Game::new_random();
+    game.init_world();
+    let (px, py) = game.player.center(&game.entities);
+    let item_count = game.items.all().len();
+    let root = game.cache_dir.clone().unwrap();
+    let seed = game.seed;
+
+    let mut game2 = Game::new_random();
+    game2.seed = seed;
+    game2.ca.seed(seed);
+    game2.cache_dir = Some(root);
+    game2.init_world();
+
+    let (px2, py2) = game2.player.center(&game2.entities);
+    assert!((px - px2).abs() < 0.01 && (py - py2).abs() < 0.01);
+    assert_eq!(game2.items.all().len(), item_count);
+    assert!(game2.grid.is_infinite());
+}

tests/multilayer.rs

@@ -0,0 +1,315 @@
+use verbatim::ai::action::AiAction;
+use verbatim::ai::session::GameSession;
+use verbatim::world::cell::MaterialId;
+use verbatim::world::chunk::CHUNK_SIZE;
+use verbatim::world::chunked_grid::ChunkedGrid;
+
+fn setup() -> GameSession {
+    let mut s = GameSession::new();
+    s.init_empty();
+    s
+}
+
+#[test]
+fn fire_produces_co2_gas() {
+    let mut s = setup();
+    s.perform_action(&AiAction::SetCell {
+        x: 100,
+        y: 100,
+        material: "wood".into(),
+    });
+    s.perform_action(&AiAction::SetCell {
+        x: 99,
+        y: 100,
+        material: "fire".into(),
+    });
+    s.step(2);
+    let mut found_co2 = false;
+    for dy in -5..=0 {
+        let (gt, gd) = s.game.grid.get_gas(99, 100 + dy);
+        if gt == 3 && gd > 0 {
+            found_co2 = true;
+            break;
+        }
+    }
+    assert!(found_co2, "fire should produce CO2 (type 3) near fire");
+}
+
+#[test]
+fn heat_transfer_diffuses_through_solid() {
+    let mut grid = ChunkedGrid::with_size(250, 250);
+    grid.set_material(100, 100, MaterialId::Stone);
+    grid.set_material(101, 100, MaterialId::Stone);
+    grid.set_temp(100, 100, 500.0);
+    grid.mark_dirty(100, 100);
+    let mut ca = verbatim::world::cellular::CellularAutomaton::new();
+    for _ in 0..100 {
+        ca.step(&mut grid);
+    }
+    let neighbor_temp = grid.get_temp(101, 100);
+    assert!(
+        neighbor_temp > 25.0,
+        "heat should diffuse to adjacent stone, got {:.1}",
+        neighbor_temp
+    );
+}
+
+#[test]
+fn lava_heats_adjacent_water_to_steam() {
+    let mut s = setup();
+    s.perform_action(&AiAction::SetCell {
+        x: 100,
+        y: 100,
+        material: "lava".into(),
+    });
+    s.perform_action(&AiAction::SetCell {
+        x: 101,
+        y: 100,
+        material: "water".into(),
+    });
+    s.step(5);
+    let cell = s.get_cell(101, 100);
+    assert!(
+        cell.material == "steam" || cell.material == "stone" || cell.material == "empty",
+        "water should become steam, lava stone, or steam rises away, got '{}'",
+        cell.material
+    );
+}
+
+#[test]
+fn gas_layer_exists_and_defaults_to_air() {
+    let s = setup();
+    let (gt, gd) = s.game.grid.get_gas(100, 100);
+    assert_eq!(gt, 0, "default gas type should be air (0)");
+    assert_eq!(gd, 0, "default gas density should be 0");
+}
+
+#[test]
+fn gas_rises_upward() {
+    let mut s = setup();
+    s.game.grid.set_gas(100, 105, 1, 200);
+    s.step(3);
+    let mut found_above = false;
+    for y in 100..=104 {
+        let (_, gd) = s.game.grid.get_gas(100, y);
+        if gd > 0 {
+            found_above = true;
+            break;
+        }
+    }
+    assert!(found_above, "smoke gas should rise upward");
+}
+
+#[test]
+fn pressure_layer_defaults_to_atmospheric() {
+    let s = setup();
+    let p = s.game.grid.get_pressure(100, 100);
+    assert_eq!(p, 128, "default pressure should be 128 (atmospheric)");
+}
+
+#[test]
+fn pressure_equalizes_between_neighbors() {
+    let mut grid = ChunkedGrid::with_size(250, 250);
+    grid.set_pressure(100, 100, 200);
+    grid.set_pressure(101, 100, 128);
+    grid.mark_dirty(100, 100);
+    grid.mark_dirty(101, 100);
+    let mut ca = verbatim::world::cellular::CellularAutomaton::new();
+    for _ in 0..100 {
+        ca.step(&mut grid);
+    }
+    let p1 = grid.get_pressure(100, 100);
+    let p2 = grid.get_pressure(101, 100);
+    let diff = (p1 as i32 - p2 as i32).abs();
+    assert!(
+        diff < 30,
+        "pressure should equalize, got p1={} p2={} diff={}",
+        p1,
+        p2,
+        diff
+    );
+}
+
+#[test]
+fn light_layer_defaults_to_dark() {
+    let s = setup();
+    let l = s.game.grid.get_light(100, 100);
+    assert_eq!(l, [0, 0, 0], "default light should be dark");
+}
+
+#[test]
+fn lava_emits_world_space_light() {
+    let mut grid = ChunkedGrid::with_size(250, 250);
+    for &(dx, dy) in &[
+        (0, 0),
+        (0, 1),
+        (0, -1),
+        (1, 0),
+        (-1, 0),
+        (1, 1),
+        (-1, 1),
+        (1, -1),
+        (-1, -1),
+    ] {
+        grid.set_material(
+            100 + dx,
+            100 + dy,
+            if dx == 0 && dy == 0 {
+                MaterialId::Lava
+            } else {
+                MaterialId::Stone
+            },
+        );
+    }
+    grid.mark_dirty(100, 100);
+    let mut ca = verbatim::world::cellular::CellularAutomaton::new();
+    for _ in 0..100 {
+        ca.step(&mut grid);
+    }
+    let l = grid.get_light(100, 100);
+    assert!(
+        l[0] > 0 || l[1] > 0 || l[2] > 0,
+        "lava should emit world-space light, got {:?}",
+        l
+    );
+}
+
+#[test]
+fn light_blocked_by_solid_walls() {
+    let mut s = setup();
+    s.perform_action(&AiAction::SetCell {
+        x: 100,
+        y: 100,
+        material: "stone".into(),
+    });
+    s.perform_action(&AiAction::SetCell {
+        x: 100,
+        y: 101,
+        material: "stone".into(),
+    });
+    s.perform_action(&AiAction::SetCell {
+        x: 100,
+        y: 102,
+        material: "lava".into(),
+    });
+    for x in 101..=104 {
+        for y in 96..=108 {
+            s.perform_action(&AiAction::SetCell {
+                x,
+                y,
+                material: "stone".into(),
+            });
+        }
+    }
+    s.step(40);
+    let l_behind = s.game.grid.get_light(105, 102);
+    assert!(
+        l_behind[0] < 30,
+        "light should be blocked by thick stone wall, got {:?}",
+        l_behind
+    );
+}
+
+#[test]
+fn chunk_save_load_roundtrip_preserves_all_layers() {
+    let mut grid = ChunkedGrid::with_size(250, 250);
+    grid.set_material(70, 70, MaterialId::Lava);
+    grid.set_temp(70, 70, 1500.0);
+    grid.set_gas(70, 70, 3, 100);
+    grid.set_pressure(70, 70, 200);
+    grid.set_light(70, 70, [255, 128, 64]);
+
+    let path = "/tmp/verbatim_multilayer_chunk_1_1.bin";
+    let _ = std::fs::remove_file(path);
+    grid.save_chunk(path, 1, 1).unwrap();
+
+    let mut grid2 = ChunkedGrid::with_size(250, 250);
+    grid2.load_chunk(path, 1, 1).unwrap();
+
+    assert_eq!(grid2.get(70, 70).material, MaterialId::Lava);
+    assert!(
+        (grid2.get_temp(70, 70) - 1500.0).abs() < 1.0,
+        "temp should roundtrip"
+    );
+    assert_eq!(grid2.get_gas(70, 70), (3, 100), "gas should roundtrip");
+    assert_eq!(grid2.get_pressure(70, 70), 200, "pressure should roundtrip");
+    assert_eq!(
+        grid2.get_light(70, 70),
+        [255, 128, 64],
+        "light should roundtrip"
+    );
+
+    let _ = std::fs::remove_file(path);
+}
+
+#[test]
+fn steam_gas_condenses_to_water_when_cold() {
+    let mut s = setup();
+    s.game.grid.set_gas(100, 100, 4, 200);
+    s.game.grid.set_temp(100, 100, 50.0);
+    s.game.grid.mark_dirty(100, 100);
+    s.step(1);
+    let cell = s.get_cell(100, 100);
+    assert_eq!(
+        cell.material, "water",
+        "steam gas at 50C should condense to water, got '{}'",
+        cell.material
+    );
+}
+
+#[test]
+fn poison_gas_damages_entity() {
+    let mut s = setup();
+    let (px, py) = s.game.player.center(&s.game.entities);
+    let health_before = s
+        .game
+        .player
+        .entity(&s.game.entities)
+        .map(|e| e.health)
+        .unwrap_or(0.0);
+    for _ in 0..10 {
+        s.game.grid.set_gas(px as i32, py as i32, 2, 200);
+        s.step(1);
+    }
+    let health_after = s
+        .game
+        .player
+        .entity(&s.game.entities)
+        .map(|e| e.health)
+        .unwrap_or(0.0);
+    assert!(
+        health_after < health_before,
+        "poison gas should damage entity: before={} after={}",
+        health_before,
+        health_after
+    );
+}
+
+#[test]
+fn temperature_persists_across_chunk_boundary() {
+    let mut grid = ChunkedGrid::with_size(256, 256);
+    let boundary = CHUNK_SIZE as i32;
+    grid.set_material(boundary - 1, 0, MaterialId::Stone);
+    grid.set_material(boundary, 0, MaterialId::Stone);
+    grid.set_temp(boundary - 1, 0, 500.0);
+    grid.set_temp(boundary, 0, 20.0);
+    grid.mark_dirty(boundary - 1, 0);
+    grid.mark_dirty(boundary, 0);
+    let mut ca = verbatim::world::cellular::CellularAutomaton::new();
+    for _ in 0..200 {
+        ca.step(&mut grid);
+    }
+    let t_near = grid.get_temp(boundary - 1, 0);
+    let t_far = grid.get_temp(boundary, 0);
+    assert!(
+        t_near < 400.0,
+        "heat should diffuse from hot cell, got {:.1}",
+        t_near
+    );
+    assert!(
+        (t_near - t_far).abs() < 200.0,
+        "temperatures should converge somewhat, near={:.1} far={:.1}",
+        t_near,
+        t_far
+    );
+}

tests/physics_acid.rs

@@ -1,5 +1,5 @@
-use verbatim::ai::GameSession;
 use verbatim::ai::AiAction;
+use verbatim::ai::GameSession;
 
 fn setup_empty() -> GameSession {
     let mut s = GameSession::new_seeded(42);
@@ -11,28 +11,76 @@ fn setup_empty() -> GameSession {
 #[test]
 fn acid_dissolves_wood() {
     let mut s = setup_empty();
-    s.perform_action(&AiAction::FillRect { x: 100, y: 120, w: 10, h: 1, material: "stone".into() });
-    s.perform_action(&AiAction::SetCell { x: 104, y: 118, material: "wood".into() });
-    s.perform_action(&AiAction::SetCell { x: 105, y: 119, material: "acid".into() });
-    s.perform_action(&AiAction::SetCell { x: 104, y: 119, material: "acid".into() });
+    s.perform_action(&AiAction::FillRect {
+        x: 100,
+        y: 120,
+        w: 10,
+        h: 1,
+        material: "stone".into(),
+    });
+    s.perform_action(&AiAction::SetCell {
+        x: 104,
+        y: 118,
+        material: "wood".into(),
+    });
+    s.perform_action(&AiAction::SetCell {
+        x: 105,
+        y: 119,
+        material: "acid".into(),
+    });
+    s.perform_action(&AiAction::SetCell {
+        x: 104,
+        y: 119,
+        material: "acid".into(),
+    });
     s.step(30);
-    assert_ne!(s.get_cell(104, 118).material, "wood", "acid should have dissolved the wood");
+    assert_ne!(
+        s.get_cell(104, 118).material,
+        "wood",
+        "acid should have dissolved the wood"
+    );
 }
 
 #[test]
 fn acid_does_not_dissolve_stone() {
     let mut s = setup_empty();
-    s.perform_action(&AiAction::SetCell { x: 105, y: 110, material: "stone".into() });
-    s.perform_action(&AiAction::SetCell { x: 105, y: 111, material: "acid".into() });
+    s.perform_action(&AiAction::SetCell {
+        x: 105,
+        y: 110,
+        material: "stone".into(),
+    });
+    s.perform_action(&AiAction::SetCell {
+        x: 105,
+        y: 111,
+        material: "acid".into(),
+    });
     s.step(20);
-    assert_eq!(s.get_cell(105, 110).material, "stone", "acid should not dissolve stone");
+    assert_eq!(
+        s.get_cell(105, 110).material,
+        "stone",
+        "acid should not dissolve stone"
+    );
 }
 
 #[test]
 fn acid_flows_down() {
     let mut s = setup_empty();
-    s.perform_action(&AiAction::FillRect { x: 100, y: 120, w: 10, h: 1, material: "stone".into() });
-    s.perform_action(&AiAction::SetCell { x: 105, y: 105, material: "acid".into() });
+    s.perform_action(&AiAction::FillRect {
+        x: 100,
+        y: 120,
+        w: 10,
+        h: 1,
+        material: "stone".into(),
+    });
+    s.perform_action(&AiAction::SetCell {
+        x: 105,
+        y: 105,
+        material: "acid".into(),
+    });
     s.step(20);
-    assert_ne!(s.get_cell(105, 105).material, "acid", "acid should have flowed down from y=105");
+    assert_ne!(
+        s.get_cell(105, 105).material,
+        "acid",
+        "acid should have flowed down from y=105"
+    );
 }

tests/physics_interactions.rs

@@ -1,8 +1,8 @@
-use verbatim::ai::GameSession;
 use verbatim::ai::AiAction;
+use verbatim::ai::GameSession;
 
 fn setup() -> GameSession {
-    let mut s = GameSession::new_seeded(42);
+    let mut s = GameSession::new_seeded(2);
     s.init_empty();
     s.clear_area(90, 90, 50, 50);
     s
@@ -11,9 +11,23 @@ fn setup() -> GameSession {
 #[test]
 fn lava_flows_down_on_stone() {
     let mut s = setup();
-    s.perform_action(&AiAction::FillRect { x: 100, y: 125, w: 10, h: 1, material: "stone".into() });
-    s.perform_action(&AiAction::SetCell { x: 105, y: 115, material: "lava".into() });
-    s.perform_action(&AiAction::SetCell { x: 105, y: 116, material: "lava".into() });
+    s.perform_action(&AiAction::FillRect {
+        x: 100,
+        y: 125,
+        w: 10,
+        h: 1,
+        material: "stone".into(),
+    });
+    s.perform_action(&AiAction::SetCell {
+        x: 105,
+        y: 115,
+        material: "lava".into(),
+    });
+    s.perform_action(&AiAction::SetCell {
+        x: 105,
+        y: 116,
+        material: "lava".into(),
+    });
     s.step(15);
     let lava_at_floor = s.count_material_in_region(103, 122, 5, 4, "lava");
     assert!(lava_at_floor > 0, "lava should flow down to stone floor");
@@ -22,25 +36,69 @@ fn lava_flows_down_on_stone() {
 #[test]
 fn lava_cools_to_stone_eventually() {
     let mut s = setup();
-    s.perform_action(&AiAction::FillRect { x: 100, y: 125, w: 10, h: 1, material: "stone".into() });
-    s.perform_action(&AiAction::SetCell { x: 105, y: 120, material: "lava".into() });
-    s.perform_action(&AiAction::SetCell { x: 105, y: 121, material: "lava".into() });
-    s.perform_action(&AiAction::SetCell { x: 105, y: 122, material: "lava".into() });
-    s.perform_action(&AiAction::SetCell { x: 105, y: 123, material: "lava".into() });
-    s.perform_action(&AiAction::SetCell { x: 105, y: 124, material: "lava".into() });
+    s.perform_action(&AiAction::FillRect {
+        x: 100,
+        y: 125,
+        w: 10,
+        h: 1,
+        material: "stone".into(),
+    });
+    s.perform_action(&AiAction::SetCell {
+        x: 105,
+        y: 120,
+        material: "lava".into(),
+    });
+    s.perform_action(&AiAction::SetCell {
+        x: 105,
+        y: 121,
+        material: "lava".into(),
+    });
+    s.perform_action(&AiAction::SetCell {
+        x: 105,
+        y: 122,
+        material: "lava".into(),
+    });
+    s.perform_action(&AiAction::SetCell {
+        x: 105,
+        y: 123,
+        material: "lava".into(),
+    });
+    s.perform_action(&AiAction::SetCell {
+        x: 105,
+        y: 124,
+        material: "lava".into(),
+    });
     s.step(200);
     let stone_count = s.count_material_in_region(103, 120, 5, 6, "stone");
-    assert!(stone_count >= 3, "lava should cool to stone eventually, got {} stone", stone_count);
+    assert!(
+        stone_count >= 3,
+        "lava should cool to stone eventually, got {} stone",
+        stone_count
+    );
 }
 
 #[test]
 fn fire_spreads_through_wood_line() {
     let mut s = setup();
-    s.perform_action(&AiAction::FillRect { x: 100, y: 120, w: 20, h: 1, material: "stone".into() });
+    s.perform_action(&AiAction::FillRect {
+        x: 100,
+        y: 120,
+        w: 20,
+        h: 1,
+        material: "stone".into(),
+    });
     for x in 100..110 {
-        s.perform_action(&AiAction::SetCell { x, y: 119, material: "wood".into() });
+        s.perform_action(&AiAction::SetCell {
+            x,
+            y: 119,
+            material: "wood".into(),
+        });
     }
-    s.perform_action(&AiAction::SetCell { x: 100, y: 119, material: "fire".into() });
+    s.perform_action(&AiAction::SetCell {
+        x: 100,
+        y: 119,
+        material: "fire".into(),
+    });
     s.step(40);
     let wood_left = s.count_material_in_region(100, 118, 10, 3, "wood");
     assert_eq!(wood_left, 0, "fire should spread through entire wood line");
@@ -49,56 +107,173 @@ fn fire_spreads_through_wood_line() {
 #[test]
 fn acid_does_not_dissolve_empty() {
     let mut s = setup();
-    s.perform_action(&AiAction::FillRect { x: 100, y: 115, w: 10, h: 1, material: "stone".into() });
-    s.perform_action(&AiAction::FillRect { x: 104, y: 114, w: 3, h: 1, material: "stone".into() });
-    s.perform_action(&AiAction::FillRect { x: 104, y: 113, w: 1, h: 1, material: "stone".into() });
-    s.perform_action(&AiAction::FillRect { x: 106, y: 113, w: 1, h: 1, material: "stone".into() });
-    s.perform_action(&AiAction::SetCell { x: 105, y: 113, material: "acid".into() });
+    s.perform_action(&AiAction::FillRect {
+        x: 100,
+        y: 115,
+        w: 10,
+        h: 1,
+        material: "stone".into(),
+    });
+    s.perform_action(&AiAction::FillRect {
+        x: 104,
+        y: 114,
+        w: 3,
+        h: 1,
+        material: "stone".into(),
+    });
+    s.perform_action(&AiAction::FillRect {
+        x: 104,
+        y: 113,
+        w: 1,
+        h: 1,
+        material: "stone".into(),
+    });
+    s.perform_action(&AiAction::FillRect {
+        x: 106,
+        y: 113,
+        w: 1,
+        h: 1,
+        material: "stone".into(),
+    });
+    s.perform_action(&AiAction::SetCell {
+        x: 105,
+        y: 113,
+        material: "acid".into(),
+    });
     s.step(5);
     let cell = s.get_cell(105, 113);
-    assert!(cell.material == "acid" || cell.material == "empty",
-        "acid may flow out but should not dissolve empty, got {}", cell.material);
+    assert!(
+        cell.material == "acid" || cell.material == "empty",
+        "acid may flow out but should not dissolve empty, got {}",
+        cell.material
+    );
 }
 
 #[test]
 fn acid_dissolves_grass() {
     let mut s = setup();
-    s.perform_action(&AiAction::FillRect { x: 100, y: 120, w: 10, h: 1, material: "stone".into() });
-    s.perform_action(&AiAction::SetCell { x: 104, y: 119, material: "grass".into() });
-    s.perform_action(&AiAction::SetCell { x: 105, y: 119, material: "acid".into() });
-    s.perform_action(&AiAction::SetCell { x: 104, y: 118, material: "acid".into() });
+    s.perform_action(&AiAction::FillRect {
+        x: 100,
+        y: 120,
+        w: 10,
+        h: 1,
+        material: "stone".into(),
+    });
+    s.perform_action(&AiAction::SetCell {
+        x: 104,
+        y: 119,
+        material: "grass".into(),
+    });
+    s.perform_action(&AiAction::SetCell {
+        x: 105,
+        y: 119,
+        material: "acid".into(),
+    });
+    s.perform_action(&AiAction::SetCell {
+        x: 104,
+        y: 118,
+        material: "acid".into(),
+    });
     s.step(20);
-    assert_ne!(s.get_cell(104, 119).material, "grass", "acid should dissolve grass");
+    assert_ne!(
+        s.get_cell(104, 119).material,
+        "grass",
+        "acid should dissolve grass"
+    );
 }
 
 #[test]
 fn acid_dissolves_dirt() {
     let mut s = setup();
-    s.perform_action(&AiAction::FillRect { x: 100, y: 115, w: 10, h: 1, material: "stone".into() });
-    s.perform_action(&AiAction::SetCell { x: 104, y: 114, material: "dirt".into() });
-    s.perform_action(&AiAction::SetCell { x: 105, y: 114, material: "acid".into() });
-    s.perform_action(&AiAction::SetCell { x: 104, y: 113, material: "acid".into() });
+    s.perform_action(&AiAction::FillRect {
+        x: 100,
+        y: 115,
+        w: 10,
+        h: 1,
+        material: "stone".into(),
+    });
+    s.perform_action(&AiAction::SetCell {
+        x: 104,
+        y: 114,
+        material: "dirt".into(),
+    });
+    s.perform_action(&AiAction::SetCell {
+        x: 105,
+        y: 114,
+        material: "acid".into(),
+    });
+    s.perform_action(&AiAction::SetCell {
+        x: 104,
+        y: 113,
+        material: "acid".into(),
+    });
     s.step(30);
-    assert_ne!(s.get_cell(104, 114).material, "dirt", "acid should dissolve dirt");
+    assert_ne!(
+        s.get_cell(104, 114).material,
+        "dirt",
+        "acid should dissolve dirt"
+    );
 }
 
 #[test]
 fn water_extinguishes_fire_indirectly() {
     let mut s = setup();
-    s.perform_action(&AiAction::FillRect { x: 100, y: 120, w: 10, h: 1, material: "stone".into() });
-    s.perform_action(&AiAction::SetCell { x: 105, y: 119, material: "fire".into() });
-    s.perform_action(&AiAction::SetCell { x: 105, y: 118, material: "water".into() });
+    s.perform_action(&AiAction::FillRect {
+        x: 100,
+        y: 120,
+        w: 10,
+        h: 1,
+        material: "stone".into(),
+    });
+    s.perform_action(&AiAction::SetCell {
+        x: 105,
+        y: 119,
+        material: "fire".into(),
+    });
+    s.perform_action(&AiAction::SetCell {
+        x: 105,
+        y: 118,
+        material: "water".into(),
+    });
     s.step(20);
-    assert_ne!(s.get_cell(105, 119).material, "fire", "water should extinguish fire");
+    assert_ne!(
+        s.get_cell(105, 119).material,
+        "fire",
+        "water should extinguish fire"
+    );
 }
 
 #[test]
 fn lava_and_water_produce_both_steam_and_stone() {
     let mut s = setup();
-    s.perform_action(&AiAction::FillRect { x: 100, y: 125, w: 20, h: 1, material: "stone".into() });
-    s.perform_action(&AiAction::FillRect { x: 100, y: 95, w: 20, h: 1, material: "stone".into() });
-    s.perform_action(&AiAction::FillRect { x: 101, y: 115, w: 4, h: 3, material: "lava".into() });
-    s.perform_action(&AiAction::FillRect { x: 106, y: 115, w: 4, h: 3, material: "water".into() });
+    s.perform_action(&AiAction::FillRect {
+        x: 100,
+        y: 125,
+        w: 20,
+        h: 1,
+        material: "stone".into(),
+    });
+    s.perform_action(&AiAction::FillRect {
+        x: 100,
+        y: 95,
+        w: 20,
+        h: 1,
+        material: "stone".into(),
+    });
+    s.perform_action(&AiAction::FillRect {
+        x: 101,
+        y: 115,
+        w: 4,
+        h: 3,
+        material: "lava".into(),
+    });
+    s.perform_action(&AiAction::FillRect {
+        x: 106,
+        y: 115,
+        w: 4,
+        h: 3,
+        material: "water".into(),
+    });
     s.step(30);
     let steam = s.count_material_in_region(100, 100, 20, 20, "steam");
     assert!(steam > 0, "lava + water should produce steam");
@@ -107,41 +282,108 @@ fn lava_and_water_produce_both_steam_and_stone() {
 #[test]
 fn sand_falls_through_water() {
     let mut s = setup();
-    s.perform_action(&AiAction::FillRect { x: 100, y: 125, w: 10, h: 1, material: "stone".into() });
-    s.perform_action(&AiAction::FillRect { x: 104, y: 118, w: 3, h: 7, material: "water".into() });
-    s.perform_action(&AiAction::SetCell { x: 105, y: 113, material: "sand".into() });
+    s.perform_action(&AiAction::FillRect {
+        x: 100,
+        y: 125,
+        w: 10,
+        h: 1,
+        material: "stone".into(),
+    });
+    s.perform_action(&AiAction::FillRect {
+        x: 104,
+        y: 118,
+        w: 3,
+        h: 7,
+        material: "water".into(),
+    });
+    s.perform_action(&AiAction::SetCell {
+        x: 105,
+        y: 113,
+        material: "sand".into(),
+    });
     s.step(30);
     let sand_at_bottom = s.get_cell(105, 124).material;
-    assert_eq!(sand_at_bottom, "sand", "sand should sink through water to bottom");
+    assert_eq!(
+        sand_at_bottom, "sand",
+        "sand should sink through water to bottom"
+    );
 }
 
 #[test]
 fn fire_does_not_ignite_stone() {
     let mut s = setup();
-    s.perform_action(&AiAction::SetCell { x: 104, y: 110, material: "stone".into() });
-    s.perform_action(&AiAction::SetCell { x: 105, y: 110, material: "fire".into() });
+    s.perform_action(&AiAction::SetCell {
+        x: 104,
+        y: 110,
+        material: "stone".into(),
+    });
+    s.perform_action(&AiAction::SetCell {
+        x: 105,
+        y: 110,
+        material: "fire".into(),
+    });
     s.step(30);
-    assert_eq!(s.get_cell(104, 110).material, "stone", "fire should not ignite stone");
+    assert_eq!(
+        s.get_cell(104, 110).material,
+        "stone",
+        "fire should not ignite stone"
+    );
 }
 
 #[test]
 fn fire_does_not_ignite_water() {
     let mut s = setup();
-    s.perform_action(&AiAction::FillRect { x: 100, y: 115, w: 10, h: 1, material: "stone".into() });
-    s.perform_action(&AiAction::SetCell { x: 104, y: 114, material: "water".into() });
-    s.perform_action(&AiAction::SetCell { x: 105, y: 114, material: "fire".into() });
+    s.perform_action(&AiAction::FillRect {
+        x: 100,
+        y: 115,
+        w: 10,
+        h: 1,
+        material: "stone".into(),
+    });
+    s.perform_action(&AiAction::SetCell {
+        x: 104,
+        y: 114,
+        material: "water".into(),
+    });
+    s.perform_action(&AiAction::SetCell {
+        x: 105,
+        y: 114,
+        material: "fire".into(),
+    });
     s.step(5);
     let cell = s.get_cell(104, 114);
-    assert_ne!(cell.material, "fire", "water should never become fire, got {}", cell.material);
+    assert_ne!(
+        cell.material, "fire",
+        "water should never become fire, got {}",
+        cell.material
+    );
     assert_ne!(cell.material, "wood", "water should never become wood");
 }
 
 #[test]
 fn water_does_not_flow_through_dirt_wall() {
     let mut s = setup();
-    s.perform_action(&AiAction::FillRect { x: 100, y: 125, w: 20, h: 1, material: "stone".into() });
-    s.perform_action(&AiAction::FillRect { x: 109, y: 120, w: 1, h: 5, material: "dirt".into() });
-    s.perform_action(&AiAction::FillRect { x: 100, y: 120, w: 9, h: 5, material: "water".into() });
+    s.perform_action(&AiAction::FillRect {
+        x: 100,
+        y: 125,
+        w: 20,
+        h: 1,
+        material: "stone".into(),
+    });
+    s.perform_action(&AiAction::FillRect {
+        x: 109,
+        y: 120,
+        w: 1,
+        h: 5,
+        material: "dirt".into(),
+    });
+    s.perform_action(&AiAction::FillRect {
+        x: 100,
+        y: 120,
+        w: 9,
+        h: 5,
+        material: "water".into(),
+    });
     s.step(30);
     let right_water = s.count_material_in_region(110, 118, 5, 8, "water");
     assert_eq!(right_water, 0, "water should not flow through dirt wall");

tests/physics_lava.rs

@@ -1,5 +1,5 @@
-use verbatim::ai::GameSession;
 use verbatim::ai::AiAction;
+use verbatim::ai::GameSession;
 
 fn setup_empty() -> GameSession {
     let mut s = GameSession::new_seeded(42);
@@ -11,48 +11,140 @@ fn setup_empty() -> GameSession {
 #[test]
 fn lava_flows_down() {
     let mut s = setup_empty();
-    s.perform_action(&AiAction::FillRect { x: 100, y: 115, w: 10, h: 3, material: "stone".into() });
-    s.perform_action(&AiAction::SetCell { x: 105, y: 110, material: "lava".into() });
-    s.perform_action(&AiAction::SetCell { x: 105, y: 111, material: "lava".into() });
+    s.perform_action(&AiAction::FillRect {
+        x: 100,
+        y: 115,
+        w: 10,
+        h: 3,
+        material: "stone".into(),
+    });
+    s.perform_action(&AiAction::SetCell {
+        x: 105,
+        y: 110,
+        material: "lava".into(),
+    });
+    s.perform_action(&AiAction::SetCell {
+        x: 105,
+        y: 111,
+        material: "lava".into(),
+    });
     s.step(10);
     let lava_count = s.count_material_in_region(103, 110, 5, 6, "lava");
     let stone_count = s.count_material_in_region(103, 110, 5, 6, "stone");
-    assert!(lava_count > 0 || stone_count >= 4,
-        "lava should have flowed down or cooled to stone, lava={} stone={}", lava_count, stone_count);
+    assert!(
+        lava_count > 0 || stone_count >= 4,
+        "lava should have flowed down or cooled to stone, lava={} stone={}",
+        lava_count,
+        stone_count
+    );
 }
 
 #[test]
 fn lava_plus_water_makes_steam() {
     let mut s = setup_empty();
-    s.perform_action(&AiAction::FillRect { x: 100, y: 120, w: 20, h: 1, material: "stone".into() });
-    s.perform_action(&AiAction::FillRect { x: 100, y: 99, w: 20, h: 1, material: "stone".into() });
-    s.perform_action(&AiAction::FillRect { x: 102, y: 110, w: 4, h: 3, material: "lava".into() });
-    s.perform_action(&AiAction::FillRect { x: 108, y: 110, w: 4, h: 3, material: "water".into() });
+    s.perform_action(&AiAction::FillRect {
+        x: 100,
+        y: 120,
+        w: 20,
+        h: 1,
+        material: "stone".into(),
+    });
+    s.perform_action(&AiAction::FillRect {
+        x: 100,
+        y: 99,
+        w: 20,
+        h: 1,
+        material: "stone".into(),
+    });
+    s.perform_action(&AiAction::FillRect {
+        x: 102,
+        y: 110,
+        w: 4,
+        h: 3,
+        material: "lava".into(),
+    });
+    s.perform_action(&AiAction::FillRect {
+        x: 108,
+        y: 110,
+        w: 4,
+        h: 3,
+        material: "water".into(),
+    });
     s.step(40);
     let steam_count = s.count_material_in_region(100, 100, 20, 15, "steam");
-    assert!(steam_count > 0, "lava + water should produce steam, got {} steam cells", steam_count);
+    assert!(
+        steam_count > 0,
+        "lava + water should produce steam, got {} steam cells",
+        steam_count
+    );
 }
 
 #[test]
 fn lava_ignites_wood() {
     let mut s = setup_empty();
-    s.perform_action(&AiAction::FillRect { x: 100, y: 115, w: 10, h: 1, material: "stone".into() });
-    s.perform_action(&AiAction::SetCell { x: 104, y: 114, material: "wood".into() });
-    s.perform_action(&AiAction::SetCell { x: 105, y: 114, material: "wood".into() });
-    s.perform_action(&AiAction::SetCell { x: 106, y: 114, material: "wood".into() });
-    s.perform_action(&AiAction::SetCell { x: 105, y: 113, material: "lava".into() });
+    s.perform_action(&AiAction::FillRect {
+        x: 100,
+        y: 115,
+        w: 10,
+        h: 1,
+        material: "stone".into(),
+    });
+    s.perform_action(&AiAction::SetCell {
+        x: 104,
+        y: 114,
+        material: "wood".into(),
+    });
+    s.perform_action(&AiAction::SetCell {
+        x: 105,
+        y: 114,
+        material: "wood".into(),
+    });
+    s.perform_action(&AiAction::SetCell {
+        x: 106,
+        y: 114,
+        material: "wood".into(),
+    });
+    s.perform_action(&AiAction::SetCell {
+        x: 105,
+        y: 113,
+        material: "lava".into(),
+    });
     s.step(15);
     let wood_remaining = s.count_material_in_region(103, 113, 5, 3, "wood");
-    assert_eq!(wood_remaining, 0, "all wood should have been ignited by lava, got {} wood cells", wood_remaining);
+    assert_eq!(
+        wood_remaining, 0,
+        "all wood should have been ignited by lava, got {} wood cells",
+        wood_remaining
+    );
 }
 
 #[test]
 fn lava_ignites_grass() {
     let mut s = setup_empty();
-    s.perform_action(&AiAction::FillRect { x: 100, y: 115, w: 10, h: 1, material: "stone".into() });
-    s.perform_action(&AiAction::FillRect { x: 100, y: 114, w: 5, h: 1, material: "grass".into() });
-    s.perform_action(&AiAction::SetCell { x: 105, y: 113, material: "lava".into() });
-    s.perform_action(&AiAction::SetCell { x: 105, y: 114, material: "lava".into() });
+    s.perform_action(&AiAction::FillRect {
+        x: 100,
+        y: 115,
+        w: 10,
+        h: 1,
+        material: "stone".into(),
+    });
+    s.perform_action(&AiAction::FillRect {
+        x: 100,
+        y: 114,
+        w: 5,
+        h: 1,
+        material: "grass".into(),
+    });
+    s.perform_action(&AiAction::SetCell {
+        x: 105,
+        y: 113,
+        material: "lava".into(),
+    });
+    s.perform_action(&AiAction::SetCell {
+        x: 105,
+        y: 114,
+        material: "lava".into(),
+    });
     s.step(15);
     let grass_remaining = s.count_material_in_region(99, 113, 7, 3, "grass");
     assert_eq!(grass_remaining, 0, "grass should have been ignited by lava");

tests/physics_sand.rs

@@ -1,5 +1,5 @@
-use verbatim::ai::GameSession;
 use verbatim::ai::AiAction;
+use verbatim::ai::GameSession;
 
 fn setup_empty() -> GameSession {
     let mut s = GameSession::new_seeded(42);
@@ -11,19 +11,53 @@ fn setup_empty() -> GameSession {
 #[test]
 fn sand_falls_down() {
     let mut s = setup_empty();
-    s.perform_action(&AiAction::FillRect { x: 100, y: 115, w: 10, h: 1, material: "stone".into() });
-    s.perform_action(&AiAction::SetCell { x: 105, y: 105, material: "sand".into() });
+    s.perform_action(&AiAction::FillRect {
+        x: 100,
+        y: 115,
+        w: 10,
+        h: 1,
+        material: "stone".into(),
+    });
+    s.perform_action(&AiAction::SetCell {
+        x: 105,
+        y: 105,
+        material: "sand".into(),
+    });
     s.step(10);
-    assert_eq!(s.get_cell(105, 105).material, "empty", "sand should have fallen from y=105");
-    assert_eq!(s.get_cell(105, 114).material, "sand", "sand should be resting on stone at y=114");
+    assert_eq!(
+        s.get_cell(105, 105).material,
+        "empty",
+        "sand should have fallen from y=105"
+    );
+    assert_eq!(
+        s.get_cell(105, 114).material,
+        "sand",
+        "sand should be resting on stone at y=114"
+    );
 }
 
 #[test]
 fn sand_displaces_water() {
     let mut s = setup_empty();
-    s.perform_action(&AiAction::FillRect { x: 100, y: 115, w: 10, h: 1, material: "stone".into() });
-    s.perform_action(&AiAction::FillRect { x: 100, y: 110, w: 10, h: 5, material: "water".into() });
-    s.perform_action(&AiAction::SetCell { x: 105, y: 105, material: "sand".into() });
+    s.perform_action(&AiAction::FillRect {
+        x: 100,
+        y: 115,
+        w: 10,
+        h: 1,
+        material: "stone".into(),
+    });
+    s.perform_action(&AiAction::FillRect {
+        x: 100,
+        y: 110,
+        w: 10,
+        h: 5,
+        material: "water".into(),
+    });
+    s.perform_action(&AiAction::SetCell {
+        x: 105,
+        y: 105,
+        material: "sand".into(),
+    });
     s.step(20);
     let sand_at_bottom = s.get_cell(105, 114).material == "sand";
     assert!(sand_at_bottom, "sand should sink to bottom through water");
@@ -32,20 +66,56 @@ fn sand_displaces_water() {
 #[test]
 fn sand_piles_on_stone() {
     let mut s = setup_empty();
-    s.perform_action(&AiAction::FillRect { x: 100, y: 115, w: 10, h: 1, material: "stone".into() });
-    s.perform_action(&AiAction::SetCell { x: 105, y: 105, material: "sand".into() });
-    s.perform_action(&AiAction::SetCell { x: 105, y: 104, material: "sand".into() });
+    s.perform_action(&AiAction::FillRect {
+        x: 100,
+        y: 115,
+        w: 10,
+        h: 1,
+        material: "stone".into(),
+    });
+    s.perform_action(&AiAction::SetCell {
+        x: 105,
+        y: 105,
+        material: "sand".into(),
+    });
+    s.perform_action(&AiAction::SetCell {
+        x: 105,
+        y: 104,
+        material: "sand".into(),
+    });
     s.step(15);
     let count = s.count_material_in_region(104, 112, 3, 4, "sand");
-    assert!(count >= 2, "both sand cells should have piled up, got {} sand cells", count);
+    assert!(
+        count >= 2,
+        "both sand cells should have piled up, got {} sand cells",
+        count
+    );
 }
 
 #[test]
 fn sand_does_not_fall_through_stone() {
     let mut s = setup_empty();
-    s.perform_action(&AiAction::FillRect { x: 100, y: 110, w: 10, h: 1, material: "stone".into() });
-    s.perform_action(&AiAction::SetCell { x: 105, y: 105, material: "sand".into() });
+    s.perform_action(&AiAction::FillRect {
+        x: 100,
+        y: 110,
+        w: 10,
+        h: 1,
+        material: "stone".into(),
+    });
+    s.perform_action(&AiAction::SetCell {
+        x: 105,
+        y: 105,
+        material: "sand".into(),
+    });
     s.step(10);
-    assert_eq!(s.get_cell(105, 109).material, "sand", "sand should rest on top of stone");
-    assert_eq!(s.get_cell(105, 110).material, "stone", "stone should remain");
+    assert_eq!(
+        s.get_cell(105, 109).material,
+        "sand",
+        "sand should rest on top of stone"
+    );
+    assert_eq!(
+        s.get_cell(105, 110).material,
+        "stone",
+        "stone should remain"
+    );
 }

tests/physics_water.rs

@@ -1,5 +1,5 @@
-use verbatim::ai::GameSession;
 use verbatim::ai::AiAction;
+use verbatim::ai::GameSession;
 
 fn setup_empty() -> GameSession {
     let mut s = GameSession::new_seeded(42);
@@ -11,32 +11,89 @@ fn setup_empty() -> GameSession {
 #[test]
 fn water_flows_down() {
     let mut s = setup_empty();
-    s.perform_action(&AiAction::FillRect { x: 95, y: 115, w: 40, h: 3, material: "stone".into() });
-    s.perform_action(&AiAction::SetCell { x: 110, y: 105, material: "water".into() });
-    s.perform_action(&AiAction::SetCell { x: 110, y: 106, material: "water".into() });
-    s.perform_action(&AiAction::SetCell { x: 110, y: 107, material: "water".into() });
+    s.perform_action(&AiAction::FillRect {
+        x: 95,
+        y: 115,
+        w: 40,
+        h: 3,
+        material: "stone".into(),
+    });
+    s.perform_action(&AiAction::SetCell {
+        x: 110,
+        y: 105,
+        material: "water".into(),
+    });
+    s.perform_action(&AiAction::SetCell {
+        x: 110,
+        y: 106,
+        material: "water".into(),
+    });
+    s.perform_action(&AiAction::SetCell {
+        x: 110,
+        y: 107,
+        material: "water".into(),
+    });
     s.step(20);
     let water_near_bottom = s.count_material_in_region(105, 112, 10, 4, "water");
-    assert!(water_near_bottom > 0, "water should have flowed down to near the stone floor, found {} water cells near bottom", water_near_bottom);
+    assert!(
+        water_near_bottom > 0,
+        "water should have flowed down to near the stone floor, found {} water cells near bottom",
+        water_near_bottom
+    );
 }
 
 #[test]
 fn water_spreads_sideways() {
     let mut s = setup_empty();
-    s.perform_action(&AiAction::FillRect { x: 95, y: 115, w: 50, h: 3, material: "stone".into() });
-    s.perform_action(&AiAction::FillRect { x: 110, y: 111, w: 1, h: 4, material: "water".into() });
+    s.perform_action(&AiAction::FillRect {
+        x: 95,
+        y: 115,
+        w: 50,
+        h: 3,
+        material: "stone".into(),
+    });
+    s.perform_action(&AiAction::FillRect {
+        x: 110,
+        y: 111,
+        w: 1,
+        h: 4,
+        material: "water".into(),
+    });
     s.step(50);
     let left_count = s.count_material_in_region(100, 110, 10, 5, "water");
     let right_count = s.count_material_in_region(111, 110, 10, 5, "water");
-    assert!(left_count > 0 || right_count > 0, "water should spread sideways: left={} right={}", left_count, right_count);
+    assert!(
+        left_count > 0 || right_count > 0,
+        "water should spread sideways: left={} right={}",
+        left_count,
+        right_count
+    );
 }
 
 #[test]
 fn water_does_not_pass_through_stone_wall() {
     let mut s = setup_empty();
-    s.perform_action(&AiAction::FillRect { x: 95, y: 115, w: 50, h: 3, material: "stone".into() });
-    s.perform_action(&AiAction::FillRect { x: 115, y: 110, w: 1, h: 5, material: "stone".into() });
-    s.perform_action(&AiAction::FillRect { x: 100, y: 110, w: 15, h: 5, material: "water".into() });
+    s.perform_action(&AiAction::FillRect {
+        x: 95,
+        y: 115,
+        w: 50,
+        h: 3,
+        material: "stone".into(),
+    });
+    s.perform_action(&AiAction::FillRect {
+        x: 115,
+        y: 110,
+        w: 1,
+        h: 5,
+        material: "stone".into(),
+    });
+    s.perform_action(&AiAction::FillRect {
+        x: 100,
+        y: 110,
+        w: 15,
+        h: 5,
+        material: "water".into(),
+    });
     s.step(30);
     let right_water = s.count_material_in_region(116, 108, 10, 10, "water");
     assert_eq!(right_water, 0, "water should not pass through stone wall");

tests/projectiles.rs

@@ -172,6 +172,7 @@ fn ui_hud_shows_player_hp() {
     let mut s = setup();
     let mut ui = verbatim::ui::UiLayer::new();
     let player = s.game.entities.all()[0].clone();
+    ui.resize(80, 25);
     ui.draw_hud(
         80,
         25,

tests/worldgen.rs

@@ -0,0 +1,268 @@
+use std::collections::VecDeque;
+
+use verbatim::ai::GameSession;
+
+fn init_at_depth(depth: u32) -> GameSession {
+    let mut s = GameSession::new_seeded(123);
+    s.game.depth = depth;
+    s.init();
+    s
+}
+
+fn count_distinct_materials(s: &GameSession) -> usize {
+    let mut present = Vec::new();
+    for y in 0..s.game.grid.height as i32 {
+        for x in 0..s.game.grid.width as i32 {
+            let mat = s.game.grid.get(x, y).material;
+            if !present.contains(&mat) {
+                present.push(mat);
+            }
+        }
+    }
+    present.len()
+}
+
+fn total_empty(s: &GameSession) -> usize {
+    let mut count = 0;
+    for y in 0..s.game.grid.height as i32 {
+        for x in 0..s.game.grid.width as i32 {
+            if s.game.grid.get(x, y).is_empty() {
+                count += 1;
+            }
+        }
+    }
+    count
+}
+
+fn player_not_in_solid(s: &GameSession) -> bool {
+    let (px, py) = s.game.player.center(&s.game.entities);
+    let ix = px as i32;
+    let iy = py as i32;
+    for dy in -1..=1 {
+        for dx in -1..=1 {
+            if s.game.grid.get(ix + dx, iy + dy).is_solid() {
+                return false;
+            }
+        }
+    }
+    true
+}
+
+fn flood_fill_count(s: &GameSession, x: i32, y: i32) -> usize {
+    let w = s.game.grid.width as i32;
+    let h = s.game.grid.height as i32;
+    let mut visited = vec![false; (w * h) as usize];
+    let mut q = VecDeque::new();
+    q.push_back((x, y));
+    let mut count = 0;
+    while let Some((cx, cy)) = q.pop_front() {
+        let idx = (cy * w + cx) as usize;
+        if visited[idx] || !s.game.grid.in_bounds(cx, cy) || !s.game.grid.get(cx, cy).is_empty() {
+            continue;
+        }
+        visited[idx] = true;
+        count += 1;
+        for (dx, dy) in [(0, 1), (0, -1), (1, 0), (-1, 0)] {
+            q.push_back((cx + dx, cy + dy));
+        }
+    }
+    count
+}
+
+fn count_empty_regions(s: &GameSession) -> usize {
+    let w = s.game.grid.width as i32;
+    let h = s.game.grid.height as i32;
+    let mut visited = vec![false; (w * h) as usize];
+    let mut regions = 0;
+    for y in 0..h {
+        for x in 0..w {
+            let idx = (y * w + x) as usize;
+            if !visited[idx] && s.game.grid.get(x, y).is_empty() {
+                regions += 1;
+                let mut stack = vec![(x, y)];
+                while let Some((cx, cy)) = stack.pop() {
+                    let i = (cy * w + cx) as usize;
+                    if visited[i]
+                        || !s.game.grid.in_bounds(cx, cy)
+                        || !s.game.grid.get(cx, cy).is_empty()
+                    {
+                        continue;
+                    }
+                    visited[i] = true;
+                    for (dx, dy) in [(0, 1), (0, -1), (1, 0), (-1, 0)] {
+                        stack.push((cx + dx, cy + dy));
+                    }
+                }
+            }
+        }
+    }
+    regions
+}
+
+#[test]
+fn surface_generation_has_stairs_and_open_spawn() {
+    let s = init_at_depth(1);
+    assert!(
+        s.find_material("stairs").is_some(),
+        "surface should have stairs"
+    );
+    assert!(
+        player_not_in_solid(&s),
+        "player should spawn in an open cell"
+    );
+    assert!(
+        count_distinct_materials(&s) >= 3,
+        "surface should have several materials"
+    );
+}
+
+#[test]
+fn cave_generation_has_stairs_and_connected_empty() {
+    let s = init_at_depth(4);
+    assert!(
+        s.find_material("stairs").is_some(),
+        "cave should have stairs"
+    );
+    assert!(
+        player_not_in_solid(&s),
+        "player should spawn in an open cell"
+    );
+
+    let empty = total_empty(&s);
+    assert!(
+        empty > 100,
+        "cave should have a meaningful empty region: {}",
+        empty
+    );
+
+    let (px, py) = s.game.player.center(&s.game.entities);
+    let connected = flood_fill_count(&s, px as i32, py as i32);
+    assert!(
+        connected >= empty * 95 / 100,
+        "cave should be mostly connected: {} of {}",
+        connected,
+        empty
+    );
+
+    assert_eq!(
+        count_empty_regions(&s),
+        1,
+        "cave should be a single connected empty region"
+    );
+}
+
+#[test]
+fn dungeon_generation_has_stairs_and_rooms() {
+    let s = init_at_depth(7);
+    assert!(
+        s.find_material("stairs").is_some(),
+        "dungeon should have stairs"
+    );
+    assert!(
+        player_not_in_solid(&s),
+        "player should spawn in an open cell"
+    );
+    assert!(
+        count_distinct_materials(&s) >= 3,
+        "dungeon should have several materials"
+    );
+
+    let empty = total_empty(&s);
+    assert!(
+        empty > 500,
+        "dungeon should have many room cells: {}",
+        empty
+    );
+
+    let regions = count_empty_regions(&s);
+    assert!(
+        regions >= 1 && regions <= 4,
+        "dungeon rooms should be connected or nearly connected: {} regions",
+        regions
+    );
+}
+
+#[test]
+fn different_depths_produce_different_structures() {
+    let s1 = init_at_depth(1);
+    let s2 = init_at_depth(4);
+    let s3 = init_at_depth(7);
+
+    let empty1 = total_empty(&s1);
+    let empty2 = total_empty(&s2);
+    let empty3 = total_empty(&s3);
+
+    assert!(
+        empty1 != empty2 || empty2 != empty3,
+        "depths should differ in empty space: {} {} {}",
+        empty1,
+        empty2,
+        empty3
+    );
+
+    let grass1 = s1.count_material_in_region(
+        0,
+        0,
+        s1.game.grid.width as i32,
+        s1.game.grid.height as i32,
+        "grass",
+    );
+    let grass2 = s2.count_material_in_region(
+        0,
+        0,
+        s2.game.grid.width as i32,
+        s2.game.grid.height as i32,
+        "grass",
+    );
+    let grass3 = s3.count_material_in_region(
+        0,
+        0,
+        s3.game.grid.width as i32,
+        s3.game.grid.height as i32,
+        "grass",
+    );
+    assert!(
+        grass1 > grass2 && grass2 == grass3,
+        "grass should dominate surface and vanish in deeper levels: {} {} {}",
+        grass1,
+        grass2,
+        grass3
+    );
+}
+
+#[test]
+fn dungeon_has_large_empty_rooms() {
+    let s = init_at_depth(8);
+    let mut found_room = false;
+    for y in 5..s.game.grid.height as i32 - 5 {
+        for x in 5..s.game.grid.width as i32 - 5 {
+            let mut w = 0;
+            while x + w < s.game.grid.width as i32 - 5 && s.game.grid.get(x + w, y).is_empty() {
+                w += 1;
+            }
+            let mut h = 0;
+            while y + h < s.game.grid.height as i32 - 5 && s.game.grid.get(x, y + h).is_empty() {
+                h += 1;
+            }
+            if w >= 5 && h >= 5 {
+                found_room = true;
+            }
+        }
+    }
+    assert!(found_room, "dungeon should contain rooms at least 5x5");
+}
+
+#[test]
+fn world_generation_respects_seeds() {
+    let s1 = init_at_depth(3);
+    let s2 = init_at_depth(3);
+    let (p1, _) = s1.game.player.center(&s1.game.entities);
+    let (p2, _) = s2.game.player.center(&s2.game.entities);
+    assert!(
+        (p1 - p2).abs() < 0.01,
+        "same seed should place player at the same x"
+    );
+    let m1 = s1.find_material("stairs");
+    let m2 = s2.find_material("stairs");
+    assert_eq!(m1, m2, "same seed should place stairs at the same location");
+}