EN-022 engine half: real previous-frame transforms for material draws

native/shared/shaders/material_abi.wgsl

@@ -215,6 +215,22 @@ struct JointMatrices {
 @group(3) @binding(0) var<uniform> draw:   PerDraw;
 @group(3) @binding(1) var<uniform> joints: JointMatrices;
 
+// EN-022 — standard motion vector from current/previous clip positions.
+// Matches the core path's convention exactly (NDC delta × 0.5). Vertex
+// shaders pass their clip position plus a previous-frame clip position:
+// static geometry uses `draw.prev_mvp * local` (or
+// `view.prev_view_proj * world` — for static models the two agree);
+// procedurally displaced geometry (wind sway) re-evaluates the
+// displacement at `frame.time - frame.delta_time` and projects with
+// `view.prev_view_proj`. Write the result to OpaqueOut.velocity — a
+// zero write disables TAA's motion-adaptive clamp for that surface
+// (the round-2 audit's primary TSR-shimmer mechanism, F8).
+fn abi_motion_vector(curr_clip: vec4<f32>, prev_clip: vec4<f32>) -> vec2<f32> {
+  let c = curr_clip.xy / curr_clip.w;
+  let p = prev_clip.xy / prev_clip.w;
+  return (c - p) * 0.5;
+}
+
 // =====================================================================
 // Group 4 — SceneInputs (optional; `reads_scene = true` materials only)
 // =====================================================================

native/shared/src/renderer/material_system.rs

@@ -294,6 +294,19 @@ pub struct MaterialSystem {
     pub translucent_commands:  Vec<MaterialDrawCommand>,  // Transparent + Refractive + Additive
     next_draw_slot: usize,
 
+    /// EN-022 — per-slot model matrices from the PREVIOUS frame, keyed
+    /// by draw slot (= submission order, which is stable frame-to-frame
+    /// for immediate-mode games; the cached-model path relies on the
+    /// same convention). `submit_draw` composes prev_vp × prev_model
+    /// into PerDraw.prev_mvp so materials can output real motion
+    /// vectors — the ABI field existed since day one but was filled
+    /// with the CURRENT mvp, making world velocity identically zero
+    /// (round-2 audit F8).
+    prev_models: Vec<[[f32; 4]; 4]>,
+    cur_models:  Vec<[[f32; 4]; 4]>,
+    /// Previous frame's view-projection (set in reset_draw_slot).
+    prev_vp: [[f32; 4]; 4],
+
     /// EN-001 — instance buffers, indexed by InstanceBufferHandle
     /// (1-based; 0 = invalid). Each entry owns a wgpu Buffer + element
     /// count. Created via `create_instance_buffer`, consumed by
@@ -622,6 +635,9 @@ impl MaterialSystem {
             commands: Vec::new(),
             translucent_commands: Vec::new(),
             next_draw_slot: 0,
+            prev_models: Vec::new(),
+            cur_models: Vec::new(),
+            prev_vp: super::IDENTITY_MAT4,
             instance_buffers: Vec::new(),
             texture_arrays: Vec::new(),
             material_texture_arrays: Vec::new(),
@@ -694,8 +710,15 @@ impl MaterialSystem {
     /// Reset the per-draw slot cursor. Commands lists are cleared by
     /// the Renderer from its own `begin_frame` so the order of reset
     /// vs. submit is deterministic.
-    pub fn reset_draw_slot(&mut self) {
+    ///
+    /// EN-022 — also rotates the per-slot model history: this frame's
+    /// models become the previous frame's, and `prev_vp` is set to the
+    /// VP that was current when those models were submitted.
+    pub fn reset_draw_slot(&mut self, prev_vp: [[f32; 4]; 4]) {
         self.next_draw_slot = 0;
+        std::mem::swap(&mut self.prev_models, &mut self.cur_models);
+        self.cur_models.clear();
+        self.prev_vp = prev_vp;
     }
 
     /// Phase 5 — set/replace `user_params` for a specific material. The
@@ -1393,7 +1416,10 @@ impl MaterialSystem {
         mesh_idx: usize,
         mvp: [[f32; 4]; 4],
         model: [[f32; 4]; 4],
-        prev_mvp: [[f32; 4]; 4],
+        // EN-022: ignored — callers historically passed the CURRENT mvp
+        // here, zeroing every motion vector. The real previous-frame
+        // transform is reconstructed from the per-slot model history.
+        _legacy_prev_mvp: [[f32; 4]; 4],
         tint: [f32; 4],
         skin_info: [u32; 4],
     ) {
@@ -1408,6 +1434,17 @@ impl MaterialSystem {
         self.next_draw_slot += 1;
         self.ensure_draw_slot(device, joint_buffer, slot);
 
+        // EN-022 — draw identity is the submission slot (stable order
+        // frame-to-frame, same convention the cached-model path uses).
+        // A fresh slot (first frame, or the frame after a draw-count
+        // change) falls back to the current model = zero object motion.
+        let prev_model = self.prev_models.get(slot).copied().unwrap_or(model);
+        let prev_mvp = super::mat4_multiply(self.prev_vp, prev_model);
+        if self.cur_models.len() <= slot {
+            self.cur_models.resize(slot + 1, model);
+        }
+        self.cur_models[slot] = model;
+
         let per_draw = PerDrawUniforms { mvp, model, prev_mvp, model_tint: tint, skin_info };
         queue.write_buffer(&self.per_draw_buffers[slot], 0, bytemuck::bytes_of(&per_draw));
 
@@ -1447,7 +1484,8 @@ impl MaterialSystem {
         instance_count: u32,
         mvp: [[f32; 4]; 4],
         model: [[f32; 4]; 4],
-        prev_mvp: [[f32; 4]; 4],
+        // EN-022: ignored — see submit_draw.
+        _legacy_prev_mvp: [[f32; 4]; 4],
         tint: [f32; 4],
         skin_info: [u32; 4],
     ) {
@@ -1462,6 +1500,18 @@ impl MaterialSystem {
         self.next_draw_slot += 1;
         self.ensure_draw_slot(device, joint_buffer, slot);
 
+        // EN-022 — same slot-history reconstruction as submit_draw.
+        // Instance transforms live in the (static) instance buffer, so
+        // prev vs current only differ by the fallback model + camera;
+        // per-instance wind sway derives its own previous position in
+        // the vertex shader from frame.time - frame.delta_time.
+        let prev_model = self.prev_models.get(slot).copied().unwrap_or(model);
+        let prev_mvp = super::mat4_multiply(self.prev_vp, prev_model);
+        if self.cur_models.len() <= slot {
+            self.cur_models.resize(slot + 1, model);
+        }
+        self.cur_models[slot] = model;
+
         let per_draw = PerDrawUniforms { mvp, model, prev_mvp, model_tint: tint, skin_info };
         queue.write_buffer(&self.per_draw_buffers[slot], 0, bytemuck::bytes_of(&per_draw));
 

native/shared/src/renderer/material_system_tests.rs

@@ -171,7 +171,7 @@ fn fs_main(_in: VsOut) -> TranslucentOut {
         };
         let pv = bytemuck::Zeroable::zeroed();
         sys.update_frame_uniforms(&queue, &pf, &pv);
-        sys.reset_draw_slot();
+        sys.reset_draw_slot(crate::renderer::IDENTITY_MAT4);
 
         // MVP = identity so the fullscreen tri stays in NDC.
         let identity = [

native/shared/src/renderer/mod.rs

@@ -8885,10 +8885,12 @@ impl Renderer {
         self.uniform_slot_count = 0;
         self.render_mode = RenderMode::ScreenSpace;
         // Phase 1c — clear last frame's material draws so the new
-        // frame's submissions start from an empty list.
+        // frame's submissions start from an empty list. EN-022: the
+        // reset also rotates the per-slot model history and pins the
+        // previous frame's VP for motion-vector reconstruction.
         self.material_system.commands.clear();
         self.material_system.translucent_commands.clear();
-        self.material_system.reset_draw_slot();
+        self.material_system.reset_draw_slot(self.prev_vp_matrix);
 
         // Write identity uniforms to slot 0 (2D uses logical points,
         // not physical pixels — see Renderer::new).