Reduce the size of MeshUniform

Before:
mat4x4 x3
u32
= 196 bytes, but in an array, practically 208 bytes for 16-byte alignment.

After:
mat3x4 x2
mat2x4
f32
u32
= 136 bytes, but in an array, practically 144 bytes for 16-byte alignment.

That is a reduction of over 30% VRAM space and bandwidth usage, plus less data
to serialize.

assets/shaders/custom_vertex_attribute.wgsl

@@ -1,5 +1,5 @@
 #import bevy_pbr::mesh_bindings   mesh
-#import bevy_pbr::mesh_functions  mesh_position_local_to_clip
+#import bevy_pbr::mesh_functions  affine_to_square, mesh_position_local_to_clip
 #import bevy_render::instance_index
 
 struct CustomMaterial {
@@ -23,7 +23,7 @@ struct VertexOutput {
 fn vertex(vertex: Vertex) -> VertexOutput {
     var out: VertexOutput;
     out.clip_position = mesh_position_local_to_clip(
-        mesh[bevy_render::instance_index::get_instance_index(vertex.instance_index)].model,
+        affine_to_square(mesh[bevy_render::instance_index::get_instance_index(vertex.instance_index)].model),
         vec4<f32>(vertex.position, 1.0),
     );
     out.blend_color = vertex.blend_color;

assets/shaders/instancing.wgsl

@@ -1,4 +1,4 @@
-#import bevy_pbr::mesh_functions  mesh_position_local_to_clip
+#import bevy_pbr::mesh_functions  affine_to_square, mesh_position_local_to_clip
 #import bevy_pbr::mesh_bindings   mesh
 
 struct Vertex {
@@ -24,7 +24,7 @@ fn vertex(vertex: Vertex) -> VertexOutput {
     // This index could be passed in via another uniform instead but it's
     // unnecessary for the example.
     out.clip_position = mesh_position_local_to_clip(
-        mesh[0].model,
+        affine_to_square(mesh[0].model),
         vec4<f32>(position, 1.0)
     );
     out.color = vertex.i_color;

crates/bevy_pbr/src/light.rs

@@ -2025,7 +2025,7 @@ pub fn check_light_mesh_visibility(
                         view_frusta.iter().zip(view_visible_entities)
                     {
                         // Disable near-plane culling, as a shadow caster could lie before the near plane.
-                        if !frustum.intersects_obb(aabb, &transform.compute_matrix(), false, true) {
+                        if !frustum.intersects_obb(aabb, &transform.affine(), false, true) {
                             continue;
                         }
 
@@ -2098,7 +2098,7 @@ pub fn check_light_mesh_visibility(
 
                     // If we have an aabb and transform, do frustum culling
                     if let (Some(aabb), Some(transform)) = (maybe_aabb, maybe_transform) {
-                        let model_to_world = transform.compute_matrix();
+                        let model_to_world = transform.affine();
                         // Do a cheap sphere vs obb test to prune out most meshes outside the sphere of the light
                         if !light_sphere.intersects_obb(aabb, &model_to_world) {
                             continue;
@@ -2162,7 +2162,7 @@ pub fn check_light_mesh_visibility(
 
                     // If we have an aabb and transform, do frustum culling
                     if let (Some(aabb), Some(transform)) = (maybe_aabb, maybe_transform) {
-                        let model_to_world = transform.compute_matrix();
+                        let model_to_world = transform.affine();
                         // Do a cheap sphere vs obb test to prune out most meshes outside the sphere of the light
                         if !light_sphere.intersects_obb(aabb, &model_to_world) {
                             continue;

crates/bevy_pbr/src/material.rs

@@ -1,6 +1,6 @@
 use crate::{
     render, AlphaMode, DrawMesh, DrawPrepass, EnvironmentMapLight, MeshPipeline, MeshPipelineKey,
-    MeshUniform, PrepassPipelinePlugin, PrepassPlugin, RenderLightSystems,
+    MeshTransforms, MeshUniform, PrepassPipelinePlugin, PrepassPlugin, RenderLightSystems,
     ScreenSpaceAmbientOcclusionSettings, SetMeshBindGroup, SetMeshViewBindGroup, Shadow,
 };
 use bevy_app::{App, Plugin};
@@ -382,7 +382,7 @@ pub fn queue_material_meshes<M: Material>(
     material_meshes: Query<(
         &Handle<M>,
         &Handle<Mesh>,
-        &MeshUniform,
+        &MeshTransforms,
         &GpuArrayBufferIndex<MeshUniform>,
     )>,
     images: Res<RenderAssets<Image>>,
@@ -468,7 +468,7 @@ pub fn queue_material_meshes<M: Material>(
 
         let rangefinder = view.rangefinder3d();
         for visible_entity in &visible_entities.entities {
-            if let Ok((material_handle, mesh_handle, mesh_uniform, batch_indices)) =
+            if let Ok((material_handle, mesh_handle, mesh_transforms, batch_indices)) =
                 material_meshes.get(*visible_entity)
             {
                 if let (Some(mesh), Some(material)) = (
@@ -516,7 +516,7 @@ pub fn queue_material_meshes<M: Material>(
                         }
                     };
 
-                    let distance = rangefinder.distance(&mesh_uniform.transform)
+                    let distance = rangefinder.distance_affine(&mesh_transforms.transform)
                         + material.properties.depth_bias;
                     match material.properties.alpha_mode {
                         AlphaMode::Opaque => {

crates/bevy_pbr/src/prepass/mod.rs

@@ -15,7 +15,7 @@ use bevy_ecs::{
         SystemParamItem,
     },
 };
-use bevy_math::Mat4;
+use bevy_math::{Affine3A, Mat4};
 use bevy_reflect::TypeUuid;
 use bevy_render::{
     globals::{GlobalsBuffer, GlobalsUniform},
@@ -46,8 +46,8 @@ use bevy_utils::tracing::error;
 
 use crate::{
     prepare_lights, setup_morph_and_skinning_defs, AlphaMode, DrawMesh, Material, MaterialPipeline,
-    MaterialPipelineKey, MeshLayouts, MeshPipeline, MeshPipelineKey, MeshUniform, RenderMaterials,
-    SetMaterialBindGroup, SetMeshBindGroup,
+    MaterialPipelineKey, MeshLayouts, MeshPipeline, MeshPipelineKey, MeshTransforms, MeshUniform,
+    RenderMaterials, SetMaterialBindGroup, SetMeshBindGroup,
 };
 
 use std::{hash::Hash, marker::PhantomData};
@@ -203,7 +203,7 @@ pub fn update_previous_view_projections(
 }
 
 #[derive(Component)]
-pub struct PreviousGlobalTransform(pub Mat4);
+pub struct PreviousGlobalTransform(pub Affine3A);
 
 pub fn update_mesh_previous_global_transforms(
     mut commands: Commands,
@@ -216,7 +216,7 @@ pub fn update_mesh_previous_global_transforms(
         for (entity, transform) in &meshes {
             commands
                 .entity(entity)
-                .insert(PreviousGlobalTransform(transform.compute_matrix()));
+                .insert(PreviousGlobalTransform(transform.affine()));
         }
     }
 }
@@ -762,7 +762,7 @@ pub fn queue_prepass_material_meshes<M: Material>(
     material_meshes: Query<(
         &Handle<M>,
         &Handle<Mesh>,
-        &MeshUniform,
+        &MeshTransforms,
         &GpuArrayBufferIndex<MeshUniform>,
     )>,
     mut views: Query<(
@@ -809,7 +809,7 @@ pub fn queue_prepass_material_meshes<M: Material>(
         let rangefinder = view.rangefinder3d();
 
         for visible_entity in &visible_entities.entities {
-            let Ok((material_handle, mesh_handle, mesh_uniform, batch_indices)) = material_meshes.get(*visible_entity) else {
+            let Ok((material_handle, mesh_handle, mesh_transforms, batch_indices)) = material_meshes.get(*visible_entity) else {
                 continue;
             };
 
@@ -852,8 +852,8 @@ pub fn queue_prepass_material_meshes<M: Material>(
                 }
             };
 
-            let distance =
-                rangefinder.distance(&mesh_uniform.transform) + material.properties.depth_bias;
+            let distance = rangefinder.distance_affine(&mesh_transforms.transform)
+                + material.properties.depth_bias;
             match alpha_mode {
                 AlphaMode::Opaque => {
                     opaque_phase.add(Opaque3dPrepass {

crates/bevy_pbr/src/prepass/prepass.wgsl

@@ -3,7 +3,7 @@
 #import bevy_pbr::skinning
 #import bevy_pbr::morph
 #import bevy_pbr::mesh_bindings mesh
-#import bevy_render::instance_index
+#import bevy_render::instance_index get_instance_index
 
 // Most of these attributes are not used in the default prepass fragment shader, but they are still needed so we can
 // pass them to custom prepass shaders like pbr_prepass.wgsl.
@@ -92,7 +92,11 @@ fn vertex(vertex_no_morph: Vertex) -> VertexOutput {
 #else // SKINNED
     // Use vertex_no_morph.instance_index instead of vertex.instance_index to work around a wgpu dx12 bug.
     // See https://github.com/gfx-rs/naga/issues/2416
-    var model = mesh[bevy_render::instance_index::get_instance_index(vertex_no_morph.instance_index)].model;
+    var model = bevy_pbr::mesh_functions::affine_to_square(
+        mesh[get_instance_index(
+            vertex_no_morph.instance_index
+        )].model
+    );
 #endif // SKINNED
 
     out.clip_position = bevy_pbr::mesh_functions::mesh_position_local_to_clip(model, vec4(vertex.position, 1.0));
@@ -113,7 +117,7 @@ fn vertex(vertex_no_morph: Vertex) -> VertexOutput {
         vertex.normal,
         // Use vertex_no_morph.instance_index instead of vertex.instance_index to work around a wgpu dx12 bug.
         // See https://github.com/gfx-rs/naga/issues/2416
-        bevy_render::instance_index::get_instance_index(vertex_no_morph.instance_index)
+        get_instance_index(vertex_no_morph.instance_index)
     );
 #endif // SKINNED
 
@@ -123,7 +127,7 @@ fn vertex(vertex_no_morph: Vertex) -> VertexOutput {
         vertex.tangent,
         // Use vertex_no_morph.instance_index instead of vertex.instance_index to work around a wgpu dx12 bug.
         // See https://github.com/gfx-rs/naga/issues/2416
-        bevy_render::instance_index::get_instance_index(vertex_no_morph.instance_index)
+        get_instance_index(vertex_no_morph.instance_index)
     );
 #endif // VERTEX_TANGENTS
 #endif // NORMAL_PREPASS
@@ -133,7 +137,9 @@ fn vertex(vertex_no_morph: Vertex) -> VertexOutput {
     // Use vertex_no_morph.instance_index instead of vertex.instance_index to work around a wgpu dx12 bug.
     // See https://github.com/gfx-rs/naga/issues/2416
     out.previous_world_position = bevy_pbr::mesh_functions::mesh_position_local_to_world(
-        mesh[bevy_render::instance_index::get_instance_index(vertex_no_morph.instance_index)].previous_model,
+        bevy_pbr::mesh_functions::affine_to_square(
+            mesh[get_instance_index(vertex_no_morph.instance_index)].previous_model
+        ),
         vec4<f32>(vertex.position, 1.0)
     );
 #endif // MOTION_VECTOR_PREPASS