Remove WebGL padding from MotionBlur (#18727)

## Objective

The `MotionBlur` component exposes renderer internals. Users shouldn't
have to deal with this.

```rust
MotionBlur {
    shutter_angle: 1.0,
    samples: 2,
    #[cfg(all(feature = "webgl2", target_arch = "wasm32", not(feature = "webgpu")))]
    _webgl2_padding: Default::default(),
},
```

## Solution

The renderer now uses a separate `MotionBlurUniform` struct for its
internals. `MotionBlur` no longer needs padding.

I was a bit unsure about the name `MotionBlurUniform`. Other modules use
a mix of `Uniform` and `Uniforms`.

## Testing

```
cargo run --example motion_blur
```

Tested on Win10/Nvidia across Vulkan, WebGL/Chrome, WebGPU/Chrome.

crates/bevy_core_pipeline/src/motion_blur/mod.rs

@@ -9,7 +9,10 @@ use crate::{
 use bevy_app::{App, Plugin};
 use bevy_asset::{load_internal_asset, weak_handle, Handle};
 use bevy_ecs::{
-    component::Component, query::With, reflect::ReflectComponent, schedule::IntoScheduleConfigs,
+    component::Component,
+    query::{QueryItem, With},
+    reflect::ReflectComponent,
+    schedule::IntoScheduleConfigs,
 };
 use bevy_reflect::{std_traits::ReflectDefault, Reflect};
 use bevy_render::{
@@ -53,9 +56,8 @@ pub mod pipeline;
 /// ));
 /// # }
 /// ````
-#[derive(Reflect, Component, Clone, ExtractComponent, ShaderType)]
+#[derive(Reflect, Component, Clone)]
 #[reflect(Component, Default, Clone)]
-#[extract_component_filter(With<Camera>)]
 #[require(DepthPrepass, MotionVectorPrepass)]
 pub struct MotionBlur {
     /// The strength of motion blur from `0.0` to `1.0`.
@@ -88,9 +90,6 @@ pub struct MotionBlur {
     /// Setting this to `3` will result in `3 * 2 + 1 = 7` samples. Setting this to `0` is
     /// equivalent to disabling motion blur.
     pub samples: u32,
-    #[cfg(all(feature = "webgl", target_arch = "wasm32", not(feature = "webgpu")))]
-    // WebGL2 structs must be 16 byte aligned.
-    pub _webgl2_padding: bevy_math::Vec2,
 }
 
 impl Default for MotionBlur {
@@ -98,12 +97,35 @@ impl Default for MotionBlur {
         Self {
             shutter_angle: 0.5,
             samples: 1,
-            #[cfg(all(feature = "webgl", target_arch = "wasm32", not(feature = "webgpu")))]
-            _webgl2_padding: Default::default(),
         }
     }
 }
 
+impl ExtractComponent for MotionBlur {
+    type QueryData = &'static Self;
+    type QueryFilter = With<Camera>;
+    type Out = MotionBlurUniform;
+
+    fn extract_component(item: QueryItem<Self::QueryData>) -> Option<Self::Out> {
+        Some(MotionBlurUniform {
+            shutter_angle: item.shutter_angle,
+            samples: item.samples,
+            #[cfg(all(feature = "webgl", target_arch = "wasm32", not(feature = "webgpu")))]
+            _webgl2_padding: Default::default(),
+        })
+    }
+}
+
+#[doc(hidden)]
+#[derive(Component, ShaderType, Clone)]
+pub struct MotionBlurUniform {
+    shutter_angle: f32,
+    samples: u32,
+    #[cfg(all(feature = "webgl", target_arch = "wasm32", not(feature = "webgpu")))]
+    // WebGL2 structs must be 16 byte aligned.
+    _webgl2_padding: bevy_math::Vec2,
+}
+
 pub const MOTION_BLUR_SHADER_HANDLE: Handle<Shader> =
     weak_handle!("d9ca74af-fa0a-4f11-b0f2-19613b618b93");
 
@@ -119,7 +141,7 @@ impl Plugin for MotionBlurPlugin {
         );
         app.add_plugins((
             ExtractComponentPlugin::<MotionBlur>::default(),
-            UniformComponentPlugin::<MotionBlur>::default(),
+            UniformComponentPlugin::<MotionBlurUniform>::default(),
         ));
 
         let Some(render_app) = app.get_sub_app_mut(RenderApp) else {

crates/bevy_core_pipeline/src/motion_blur/node.rs

@@ -15,7 +15,7 @@ use crate::prepass::ViewPrepassTextures;
 
 use super::{
     pipeline::{MotionBlurPipeline, MotionBlurPipelineId},
-    MotionBlur,
+    MotionBlurUniform,
 };
 
 #[derive(Default)]
@@ -26,7 +26,7 @@ impl ViewNode for MotionBlurNode {
         &'static ViewTarget,
         &'static MotionBlurPipelineId,
         &'static ViewPrepassTextures,
-        &'static MotionBlur,
+        &'static MotionBlurUniform,
         &'static Msaa,
     );
     fn run(
@@ -42,7 +42,7 @@ impl ViewNode for MotionBlurNode {
 
         let motion_blur_pipeline = world.resource::<MotionBlurPipeline>();
         let pipeline_cache = world.resource::<PipelineCache>();
-        let settings_uniforms = world.resource::<ComponentUniforms<MotionBlur>>();
+        let settings_uniforms = world.resource::<ComponentUniforms<MotionBlurUniform>>();
         let Some(pipeline) = pipeline_cache.get_render_pipeline(pipeline_id.0) else {
             return Ok(());
         };

crates/bevy_core_pipeline/src/motion_blur/pipeline.rs

@@ -26,7 +26,7 @@ use bevy_render::{
 
 use crate::fullscreen_vertex_shader::fullscreen_shader_vertex_state;
 
-use super::{MotionBlur, MOTION_BLUR_SHADER_HANDLE};
+use super::{MotionBlurUniform, MOTION_BLUR_SHADER_HANDLE};
 
 #[derive(Resource)]
 pub struct MotionBlurPipeline {
@@ -49,7 +49,7 @@ impl MotionBlurPipeline {
                 // Linear Sampler
                 sampler(SamplerBindingType::Filtering),
                 // Motion blur settings uniform input
-                uniform_buffer_sized(false, Some(MotionBlur::min_size())),
+                uniform_buffer_sized(false, Some(MotionBlurUniform::min_size())),
                 // Globals uniform input
                 uniform_buffer_sized(false, Some(GlobalsUniform::min_size())),
             ),
@@ -67,7 +67,7 @@ impl MotionBlurPipeline {
                 // Linear Sampler
                 sampler(SamplerBindingType::Filtering),
                 // Motion blur settings uniform input
-                uniform_buffer_sized(false, Some(MotionBlur::min_size())),
+                uniform_buffer_sized(false, Some(MotionBlurUniform::min_size())),
                 // Globals uniform input
                 uniform_buffer_sized(false, Some(GlobalsUniform::min_size())),
             ),
@@ -155,7 +155,7 @@ pub(crate) fn prepare_motion_blur_pipelines(
     pipeline_cache: Res<PipelineCache>,
     mut pipelines: ResMut<SpecializedRenderPipelines<MotionBlurPipeline>>,
     pipeline: Res<MotionBlurPipeline>,
-    views: Query<(Entity, &ExtractedView, &Msaa), With<MotionBlur>>,
+    views: Query<(Entity, &ExtractedView, &Msaa), With<MotionBlurUniform>>,
 ) {
     for (entity, view, msaa) in &views {
         let pipeline_id = pipelines.specialize(

examples/3d/motion_blur.rs

@@ -26,8 +26,6 @@ fn setup_camera(mut commands: Commands) {
         MotionBlur {
             shutter_angle: 1.0,
             samples: 2,
-            #[cfg(all(feature = "webgl2", target_arch = "wasm32", not(feature = "webgpu")))]
-            _webgl2_padding: Default::default(),
         },
         // MSAA and Motion Blur together are not compatible on WebGL
         #[cfg(all(feature = "webgl2", target_arch = "wasm32", not(feature = "webgpu")))]