feat: vector-based movement for responsive control and air strafing

Changed from physics-based (accumulate + damping) to vector-based:

- Horizontal velocity is SET directly, not accumulated
  - Press A → cvx = -0.5 (instant, no ramp-up)
  - Release → cvx = 0 (instant stop, no sliding)
  - No horizontal damping = precise control
- Air strafing: same horizontal speed in air as on ground
  - Can change direction mid-jump freely
- Vertical: gravity + minimal damping (0.99) for natural fall
  - Jump sets cvy directly, gravity pulls back
- move_speed 0.5 (was 0.3), max_vel 2.0 (was 1.0)
- Player: move_dir tracks current direction, stop_horizontal() clears velocity
- handle_input: calls stop_horizontal when no movement key held

109 tests, 0 warnings, 0 failures

src/entity/entity.rs

@@ -181,6 +181,18 @@ impl Entity {
         }
     }
 
+    pub fn set_horizontal_vel(&mut self, vx: f32) {
+        if self.rigid {
+            self.cvx = vx;
+        }
+    }
+
+    pub fn set_vertical_vel(&mut self, vy: f32) {
+        if self.rigid {
+            self.cvy = vy;
+        }
+    }
+
     pub fn apply_fire_damage(&mut self) {
         if !self.on_fire {
             return;

src/entity/player.rs

@@ -4,6 +4,7 @@ pub struct Player {
     pub entity_id: EntityId,
     pub move_speed: f32,
     pub jump_force: f32,
+    pub move_dir: i32,
 }
 
 impl Player {
@@ -11,8 +12,9 @@ impl Player {
         let id = manager.spawn(EntityKind::Player);
         Self {
             entity_id: id,
-            move_speed: 0.3,
+            move_speed: 0.5,
             jump_force: 1.5,
+            move_dir: 0,
         }
     }
 
@@ -22,22 +24,31 @@ impl Player {
         }
     }
 
-    pub fn move_left(&self, manager: &mut EntityManager) {
+    pub fn move_left(&mut self, manager: &mut EntityManager) {
+        self.move_dir = -1;
         if let Some(e) = manager.get_mut(self.entity_id) {
-            e.move_center(-self.move_speed, 0.0);
+            e.set_horizontal_vel(-self.move_speed);
         }
     }
 
-    pub fn move_right(&self, manager: &mut EntityManager) {
+    pub fn move_right(&mut self, manager: &mut EntityManager) {
+        self.move_dir = 1;
         if let Some(e) = manager.get_mut(self.entity_id) {
-            e.move_center(self.move_speed, 0.0);
+            e.set_horizontal_vel(self.move_speed);
+        }
+    }
+
+    pub fn stop_horizontal(&mut self, manager: &mut EntityManager) {
+        self.move_dir = 0;
+        if let Some(e) = manager.get_mut(self.entity_id) {
+            e.set_horizontal_vel(0.0);
         }
     }
 
     pub fn jump(&self, manager: &mut EntityManager, on_ground: bool) {
         if on_ground {
             if let Some(e) = manager.get_mut(self.entity_id) {
-                e.move_center(0.0, -self.jump_force);
+                e.set_vertical_vel(-self.jump_force);
             }
         }
     }

src/game.rs

@@ -245,11 +245,21 @@ impl Game {
             self.player.jump(&mut self.entities, on_ground);
         }
 
-        // Movement: applied every tick while held
-        for action in self.input.held_actions() {
+        // Movement: applied every tick while held (vector-style, direct velocity)
+        let held = self.input.held_actions();
+        let moving_left = held.iter().any(|a| *a == Action::MoveLeft);
+        let moving_right = held.iter().any(|a| *a == Action::MoveRight);
+
+        if moving_left && !moving_right {
+            self.player.move_left(&mut self.entities);
+        } else if moving_right && !moving_left {
+            self.player.move_right(&mut self.entities);
+        } else {
+            self.player.stop_horizontal(&mut self.entities);
+        }
+
+        for action in &held {
             match action {
-                Action::MoveLeft => self.player.move_left(&mut self.entities),
-                Action::MoveRight => self.player.move_right(&mut self.entities),
                 Action::MoveCameraLeft => self.cam_x -= 2,
                 Action::MoveCameraRight => self.cam_x += 2,
                 Action::MoveCameraUp => self.cam_y -= 2,
@@ -335,7 +345,7 @@ impl Game {
         }
     }
 
-    fn update_rigid_entity(&mut self, idx: usize, gravity: f32, damping: f32, max_vel: f32) {
+    fn update_rigid_entity(&mut self, idx: usize, gravity: f32, _damping: f32, max_vel: f32) {
         let (cx, cy, cvx, cvy, half_w, half_h) = {
             let e = &self.entities.all()[idx];
             (e.cx, e.cy, e.cvx, e.cvy, e.half_w, e.half_h)
@@ -343,8 +353,10 @@ impl Game {
 
         let mut nx = cx;
         let mut ny = cy;
-        let mut nvx = cvx * damping;
-        let mut nvy = cvy * damping;
+        // Horizontal: direct velocity, no damping (vector movement)
+        let mut nvx = cvx;
+        // Vertical: gravity + light damping for natural fall
+        let mut nvy = cvy * 0.99;
         nvy += gravity;
 
         let v_mag = (nvx * nvx + nvy * nvy).sqrt();

src/physics/verlet.rs

@@ -97,7 +97,7 @@ impl VerletSolver {
             gravity: 0.04,
             damping: 0.97,
             dt: 1.0,
-            max_vel: 1.0,
+            max_vel: 2.0,
             substeps: 8,
         }
     }