Fix WebGL not rendering StandardMaterial (#12110)

# Objective

- Fixes #12081

## Solution

Passing the `Affine2` as a neatly packed `mat3x2` breaks WebGL with
`drawElementsInstanced: Buffer for uniform block is smaller than
UNIFORM_BLOCK_DATA_SIZE.`
I fixed this by using a `mat3x3` instead.
Alternative solutions that come to mind:
- Pass in a `mat3x2` on non-webgl targets and a `mat3x3` otherwise. I
guess I could use `#ifdef SIXTEEN_BYTE_ALIGNMENT` for this, but it
doesn't seem quite right? This would be more efficient, but decrease
code quality.
- Do something about `UNIFORM_BLOCK_DATA_SIZE`. I don't know how, so I'd
need some guidance here.

@superdump let me know if you'd like me to implement other variants.
Otherwise, I vote for merging this as a quick fix for `main` and then
improving the packing in subsequent PRs :)

## Additional notes

Ideally we should merge this before @JMS55 rebases #10164 so that they
don't have to rebase everything a second time.

crates/bevy_pbr/src/pbr_material.rs

@@ -1,5 +1,5 @@
 use bevy_asset::Asset;
-use bevy_math::{Affine2, Vec2, Vec4};
+use bevy_math::{Affine2, Mat3, Vec4};
 use bevy_reflect::{std_traits::ReflectDefault, Reflect};
 use bevy_render::{mesh::MeshVertexBufferLayout, render_asset::RenderAssets, render_resource::*};
 
@@ -596,12 +596,8 @@ pub struct StandardMaterialUniform {
     pub emissive: Vec4,
     /// Color white light takes after travelling through the attenuation distance underneath the material surface
     pub attenuation_color: Vec4,
-    /// The x-axis of the mat2 of the transform applied to the UVs corresponding to ATTRIBUTE_UV_0 on the mesh before sampling. Default is [1, 0].
-    pub uv_transform_x_axis: Vec2,
-    /// The y-axis of the mat2 of the transform applied to the UVs corresponding to ATTRIBUTE_UV_0 on the mesh before sampling. Default is [0, 1].
-    pub uv_transform_y_axis: Vec2,
-    /// The translation of the transform applied to the UVs corresponding to ATTRIBUTE_UV_0 on the mesh before sampling. Default is [0, 0].
-    pub uv_transform_translation: Vec2,
+    /// The transform applied to the UVs corresponding to ATTRIBUTE_UV_0 on the mesh before sampling. Default is identity.
+    pub uv_transform: Mat3,
     /// Linear perceptual roughness, clamped to [0.089, 1.0] in the shader
     /// Defaults to minimum of 0.089
     pub roughness: f32,
@@ -736,9 +732,7 @@ impl AsBindGroupShaderType<StandardMaterialUniform> for StandardMaterial {
             lightmap_exposure: self.lightmap_exposure,
             max_relief_mapping_search_steps: self.parallax_mapping_method.max_steps(),
             deferred_lighting_pass_id: self.deferred_lighting_pass_id as u32,
-            uv_transform_x_axis: self.uv_transform.matrix2.x_axis,
-            uv_transform_y_axis: self.uv_transform.matrix2.y_axis,
-            uv_transform_translation: self.uv_transform.translation,
+            uv_transform: self.uv_transform.into(),
         }
     }
 }

crates/bevy_pbr/src/render/pbr_fragment.wgsl

@@ -11,7 +11,6 @@
     parallax_mapping::parallaxed_uv,
     lightmap::lightmap,
 }
-#import bevy_render::maths::affine2_to_square
 
 #ifdef SCREEN_SPACE_AMBIENT_OCCLUSION
 #import bevy_pbr::mesh_view_bindings::screen_space_ambient_occlusion_texture
@@ -74,7 +73,7 @@ fn pbr_input_from_standard_material(
     let NdotV = max(dot(pbr_input.N, pbr_input.V), 0.0001);
 
 #ifdef VERTEX_UVS
-    let uv_transform = affine2_to_square(pbr_bindings::material.uv_transform);
+    let uv_transform = pbr_bindings::material.uv_transform;
     var uv = (uv_transform * vec3(in.uv, 1.0)).xy;
 
 #ifdef VERTEX_TANGENTS

crates/bevy_pbr/src/render/pbr_prepass_functions.wgsl

@@ -7,7 +7,6 @@
     pbr_bindings,
     pbr_types,
 }
-#import bevy_render::maths::affine2_to_square
 
 // Cutoff used for the premultiplied alpha modes BLEND and ADD.
 const PREMULTIPLIED_ALPHA_CUTOFF = 0.05;
@@ -19,7 +18,7 @@ fn prepass_alpha_discard(in: VertexOutput) {
     var output_color: vec4<f32> = pbr_bindings::material.base_color;
 
 #ifdef VERTEX_UVS
-    let uv_transform = affine2_to_square(pbr_bindings::material.uv_transform);
+    let uv_transform = pbr_bindings::material.uv_transform;
     let uv = (uv_transform * vec3(in.uv, 1.0)).xy;
     if (pbr_bindings::material.flags & pbr_types::STANDARD_MATERIAL_FLAGS_BASE_COLOR_TEXTURE_BIT) != 0u {
         output_color = output_color * textureSampleBias(pbr_bindings::base_color_texture, pbr_bindings::base_color_sampler, uv, view.mip_bias);

crates/bevy_pbr/src/render/pbr_types.wgsl

@@ -6,7 +6,7 @@ struct StandardMaterial {
     base_color: vec4<f32>,
     emissive: vec4<f32>,
     attenuation_color: vec4<f32>,
-    uv_transform: mat3x2<f32>,
+    uv_transform: mat3x3<f32>,
     perceptual_roughness: f32,
     metallic: f32,
     reflectance: f32,
@@ -78,7 +78,7 @@ fn standard_material_new() -> StandardMaterial {
     material.max_relief_mapping_search_steps = 5u;
     material.deferred_lighting_pass_id = 1u;
     // scale 1, translation 0, rotation 0
-    material.uv_transform = mat3x2<f32>(1.0, 0.0, 0.0, 1.0, 0.0, 0.0);
+    material.uv_transform = mat3x3<f32>(1.0, 0.0, 0.0, 0.0, 1.0, 0.0, 0.0, 0.0, 1.0);
 
     return material;
 }