Fix motion vector computation after #17688.

crates/bevy_pbr/src/render/gpu_preprocess.rs

@@ -626,12 +626,10 @@ impl Node for EarlyGpuPreprocessNode {
                     continue;
                 };
 
-                // If we're drawing indirectly, make sure the mesh preprocessing
-                // shader has access to the view info it needs to do culling.
-                let mut dynamic_offsets: SmallVec<[u32; 1]> = smallvec![];
-                if !no_indirect_drawing {
-                    dynamic_offsets.push(view_uniform_offset.offset);
-                }
+                // Make sure the mesh preprocessing shader has access to the
+                // view info it needs to do culling and motion vector
+                // computation.
+                let dynamic_offsets = [view_uniform_offset.offset];
 
                 // Are we drawing directly or indirectly?
                 match *phase_bind_groups {
@@ -1317,6 +1315,11 @@ fn preprocess_direct_bind_group_layout_entries() -> DynamicBindGroupLayoutEntrie
     DynamicBindGroupLayoutEntries::new_with_indices(
         ShaderStages::COMPUTE,
         (
+            // `view`
+            (
+                0,
+                uniform_buffer::<ViewUniform>(/* has_dynamic_offset= */ true),
+            ),
             // `current_input`
             (3, storage_buffer_read_only::<MeshInputUniform>(false)),
             // `previous_input`
@@ -1361,11 +1364,6 @@ fn gpu_culling_bind_group_layout_entries() -> DynamicBindGroupLayoutEntries {
             8,
             storage_buffer_read_only::<MeshCullingData>(/* has_dynamic_offset= */ false),
         ),
-        // `view`
-        (
-            0,
-            uniform_buffer::<ViewUniform>(/* has_dynamic_offset= */ true),
-        ),
     ))
 }
 
@@ -1802,11 +1800,14 @@ impl<'a> PreprocessBindGroupBuilder<'a> {
         )
         .ok();
 
+        let view_uniforms_binding = self.view_uniforms.uniforms.binding()?;
+
         Some(PhasePreprocessBindGroups::Direct(
             self.render_device.create_bind_group(
                 "preprocess_direct_bind_group",
                 &self.pipelines.direct_preprocess.bind_group_layout,
                 &BindGroupEntries::with_indices((
+                    (0, view_uniforms_binding),
                     (3, self.current_input_buffer.as_entire_binding()),
                     (4, self.previous_input_buffer.as_entire_binding()),
                     (

crates/bevy_pbr/src/render/mesh.rs

@@ -478,13 +478,13 @@ pub struct MeshUniform {
     pub first_vertex_index: u32,
     /// The current skin index, or `u32::MAX` if there's no skin.
     pub current_skin_index: u32,
-    /// The previous skin index, or `u32::MAX` if there's no previous skin.
-    pub previous_skin_index: u32,
     /// The material and lightmap indices, packed into 32 bits.
     ///
     /// Low 16 bits: index of the material inside the bind group data.
     /// High 16 bits: index of the lightmap in the binding array.
     pub material_and_lightmap_bind_group_slot: u32,
+    /// Padding.
+    pub pad: u32,
 }
 
 /// Information that has to be transferred from CPU to GPU in order to produce
@@ -515,6 +515,11 @@ pub struct MeshInputUniform {
     ///
     /// This is used for TAA. If not present, this will be `u32::MAX`.
     pub previous_input_index: u32,
+    /// The frame number of the previous frame.
+    ///
+    /// The shader compared this field to the current frame number in order to
+    /// determine whether [`Self::previous_input_index`] is valid.
+    pub previous_input_frame_number: u32,
     /// The index of this mesh's first vertex in the vertex buffer.
     ///
     /// Multiple meshes can be packed into a single vertex buffer (see
@@ -534,8 +539,6 @@ pub struct MeshInputUniform {
     pub index_count: u32,
     /// The current skin index, or `u32::MAX` if there's no skin.
     pub current_skin_index: u32,
-    /// The previous skin index, or `u32::MAX` if there's no previous skin.
-    pub previous_skin_index: u32,
     /// The material and lightmap indices, packed into 32 bits.
     ///
     /// Low 16 bits: index of the material inside the bind group data.
@@ -577,7 +580,6 @@ impl MeshUniform {
         material_bind_group_slot: MaterialBindGroupSlot,
         maybe_lightmap: Option<(LightmapSlotIndex, Rect)>,
         current_skin_index: Option<u32>,
-        previous_skin_index: Option<u32>,
     ) -> Self {
         let (local_from_world_transpose_a, local_from_world_transpose_b) =
             mesh_transforms.world_from_local.inverse_transpose_3x3();
@@ -595,9 +597,9 @@ impl MeshUniform {
             flags: mesh_transforms.flags,
             first_vertex_index,
             current_skin_index: current_skin_index.unwrap_or(u32::MAX),
-            previous_skin_index: previous_skin_index.unwrap_or(u32::MAX),
             material_and_lightmap_bind_group_slot: u32::from(material_bind_group_slot)
                 | ((lightmap_bind_group_slot as u32) << 16),
+            pad: 0,
         }
     }
 }
@@ -1115,11 +1117,7 @@ impl RenderMeshInstanceGpuBuilder {
                 None => (false, 0, 0),
             };
 
-        let current_skin_index = match skin_indices.current.get(&entity) {
-            Some(skin_indices) => skin_indices.index(),
-            None => u32::MAX,
-        };
-        let previous_skin_index = match skin_indices.prev.get(&entity) {
+        let current_skin_index = match skin_indices.get(&entity) {
             Some(skin_indices) => skin_indices.index(),
             None => u32::MAX,
         };
@@ -1148,6 +1146,7 @@ impl RenderMeshInstanceGpuBuilder {
             lightmap_uv_rect: self.lightmap_uv_rect,
             flags: self.mesh_flags.bits(),
             previous_input_index: u32::MAX,
+            previous_input_frame_number: u32::MAX,
             first_vertex_index,
             first_index_index,
             index_count: if mesh_is_indexed {
@@ -1156,7 +1155,6 @@ impl RenderMeshInstanceGpuBuilder {
                 vertex_count
             },
             current_skin_index,
-            previous_skin_index,
             material_and_lightmap_bind_group_slot: u32::from(
                 self.shared.material_bindings_index.slot,
             ) | ((lightmap_slot as u32) << 16),
@@ -1557,7 +1555,7 @@ fn set_mesh_motion_vector_flags(
     skin_indices: Res<SkinIndices>,
     morph_indices: Res<MorphIndices>,
 ) {
-    for &entity in skin_indices.prev.keys() {
+    for &entity in skin_indices.keys() {
         render_mesh_instances
             .insert_mesh_instance_flags(entity, RenderMeshInstanceFlags::HAS_PREVIOUS_SKIN);
     }
@@ -1827,9 +1825,7 @@ impl GetBatchData for MeshPipeline {
             };
         let maybe_lightmap = lightmaps.render_lightmaps.get(&main_entity);
 
-        let current_skin_index = skin_indices.current.get(&main_entity).map(SkinIndex::index);
-        let previous_skin_index = skin_indices.prev.get(&main_entity).map(SkinIndex::index);
-
+        let current_skin_index = skin_indices.get(&main_entity).map(SkinIndex::index);
         let material_bind_group_index = mesh_instance.material_bindings_index;
 
         Some((
@@ -1839,7 +1835,6 @@ impl GetBatchData for MeshPipeline {
                 material_bind_group_index.slot,
                 maybe_lightmap.map(|lightmap| (lightmap.slot_index, lightmap.uv_rect)),
                 current_skin_index,
-                previous_skin_index,
             ),
             mesh_instance.should_batch().then_some((
                 material_bind_group_index.group,
@@ -1897,16 +1892,14 @@ impl GetFullBatchData for MeshPipeline {
             };
         let maybe_lightmap = lightmaps.render_lightmaps.get(&main_entity);
 
-        let current_skin_index = skin_indices.current.get(&main_entity).map(SkinIndex::index);
-        let previous_skin_index = skin_indices.prev.get(&main_entity).map(SkinIndex::index);
+        let current_skin_index = skin_indices.get(&main_entity).map(SkinIndex::index);
 
         Some(MeshUniform::new(
             &mesh_instance.transforms,
             first_vertex_index,
             mesh_instance.material_bindings_index.slot,
             maybe_lightmap.map(|lightmap| (lightmap.slot_index, lightmap.uv_rect)),
             current_skin_index,
-            previous_skin_index,
         ))
     }
 
@@ -2793,8 +2786,7 @@ impl<P: PhaseItem, const I: usize> RenderCommand<P> for SetMeshBindGroup<I> {
             return RenderCommandResult::Success;
         };
 
-        let current_skin_index = skin_indices.current.get(entity);
-        let prev_skin_index = skin_indices.prev.get(entity);
+        let current_skin_index = skin_indices.get(entity);
         let current_morph_index = morph_indices.current.get(entity);
         let prev_morph_index = morph_indices.prev.get(entity);
 
@@ -2841,14 +2833,11 @@ impl<P: PhaseItem, const I: usize> RenderCommand<P> for SetMeshBindGroup<I> {
         if has_motion_vector_prepass {
             // Attach the previous skin index for motion vector computation. If
             // there isn't one, just use zero as the shader will ignore it.
-            if current_skin_index.is_some() && skin::skins_use_uniform_buffers(&render_device) {
-                match prev_skin_index {
-                    Some(prev_skin_index) => {
-                        dynamic_offsets[offset_count] = prev_skin_index.byte_offset;
-                    }
-                    None => dynamic_offsets[offset_count] = 0,
+            if skin::skins_use_uniform_buffers(&render_device) {
+                if let Some(current_skin_index) = current_skin_index {
+                    dynamic_offsets[offset_count] = current_skin_index.byte_offset;
+                    offset_count += 1;
                 }
-                offset_count += 1;
             }
 
             // Attach the previous morph index for motion vector computation. If

crates/bevy_pbr/src/render/mesh_preprocess.wgsl

@@ -193,13 +193,15 @@ fn main(@builtin(global_invocation_id) global_invocation_id: vec3<u32>) {
 #endif
 
     // Look up the previous model matrix.
+    let previous_input_frame_number = current_input[input_index].previous_input_frame_number;
     let previous_input_index = current_input[input_index].previous_input_index;
+    let previous_input_is_valid = previous_input_frame_number + 1 == view.frame_number;
     var previous_world_from_local_affine_transpose: mat3x4<f32>;
-    if (previous_input_index == 0xffffffff) {
-        previous_world_from_local_affine_transpose = world_from_local_affine_transpose;
-    } else {
+    if (previous_input_is_valid && previous_input_index != 0xffffffffu) {
         previous_world_from_local_affine_transpose =
             previous_input[previous_input_index].world_from_local;
+    } else {
+        previous_world_from_local_affine_transpose = world_from_local_affine_transpose;
     }
     let previous_world_from_local =
         maths::affine3_to_square(previous_world_from_local_affine_transpose);
@@ -342,7 +344,6 @@ fn main(@builtin(global_invocation_id) global_invocation_id: vec3<u32>) {
     output[mesh_output_index].lightmap_uv_rect = current_input[input_index].lightmap_uv_rect;
     output[mesh_output_index].first_vertex_index = current_input[input_index].first_vertex_index;
     output[mesh_output_index].current_skin_index = current_input[input_index].current_skin_index;
-    output[mesh_output_index].previous_skin_index = current_input[input_index].previous_skin_index;
     output[mesh_output_index].material_and_lightmap_bind_group_slot =
         current_input[input_index].material_and_lightmap_bind_group_slot;
 }

crates/bevy_pbr/src/render/mesh_types.wgsl

@@ -18,10 +18,10 @@ struct Mesh {
     // The index of the mesh's first vertex in the vertex buffer.
     first_vertex_index: u32,
     current_skin_index: u32,
-    previous_skin_index: u32,
     // Low 16 bits: index of the material inside the bind group data.
     // High 16 bits: index of the lightmap in the binding array.
     material_and_lightmap_bind_group_slot: u32,
+    pad: u32,
 };
 
 #ifdef SKINNED