Add temporal history and jitter policy

include/faset/render/temporal.hpp

@@ -0,0 +1,76 @@
+#pragma once
+#include <array>
+#include <cstdint>
+#include <optional>
+#include <string>
+
+namespace faset::render {
+
+enum class TemporalMode { Off, TAA, Upscale };
+
+struct TemporalCapabilities {
+    bool compute{};
+    bool formats{};
+    bool extent{};
+};
+
+enum class TemporalFallbackReason {
+    None,
+    ComputeUnavailable,
+    FormatUnavailable,
+    ExtentUnsupported
+};
+
+TemporalFallbackReason temporal_fallback_reason(TemporalMode requested,
+                                                TemporalCapabilities available) noexcept;
+TemporalMode select_effective_temporal_mode(TemporalMode requested,
+                                            TemporalCapabilities available) noexcept;
+
+enum class TemporalResetReason {
+    None,
+    FirstFrame,
+    CameraCut,
+    CameraDiscontinuity,
+    ViewChanged,
+    ViewportChanged,
+    ProjectionChanged,
+    Resize,
+    ModeChanged,
+    ScaleChanged,
+    ShaderReload,
+    Unsupported
+};
+
+// Snapshot matrices/rect stay unjittered. This is independent of HZB history:
+// Direct rendering and GPU frustum mode can still accumulate temporal color.
+// A missing previous key means no completed frame is available to reuse.
+struct TemporalHistoryKey {
+    std::string view_id;
+    std::uint32_t output_width{}, output_height{};
+    std::uint32_t internal_width{}, internal_height{};
+    std::array<float, 4> scene_rect{};
+    std::array<float, 16> projection{}, view_projection{};
+    std::array<float, 3> camera_eye{};
+    TemporalMode mode{TemporalMode::Off};
+    float render_scale{1};
+    std::uint64_t shader_generation{};
+    bool camera_cut{};
+};
+
+struct TemporalHistoryDecision {
+    bool valid{};
+    TemporalResetReason reason{TemporalResetReason::FirstFrame};
+};
+
+TemporalHistoryDecision
+evaluate_temporal_history(const std::optional<TemporalHistoryKey>& previous,
+                          const TemporalHistoryKey& current) noexcept;
+
+// Sixteen-phase Halton(2,3) offset in clip-space units, for the scene raster
+// projection only. UI, picking, culling, and history keys use unjittered space.
+// A zero viewport extent throws std::invalid_argument.
+std::array<float, 2> temporal_jitter(std::uint64_t frame_index,
+                                     std::uint32_t viewport_width,
+                                     std::uint32_t viewport_height);
+
+} // namespace faset::render