Create mesh view bind group layout on demand to remove unused bindings (#23982)

# Objective

Fixes #23627.

`MeshPipelineViewLayoutKey` uses too many bindings even if features like
ssr, environment map are unused.

## Solution

Don't pre-allocate every combination that grows exponentially. Instead,
create mesh view bind group layout on demand so that we can add more
view keys to reduce unused bindings.

`MeshPipelineViewLayouts::get_view_layout` will be slower, but I'm not
sure how slow it is. My feeling is that the overhead is not high,
compared to when we clone it before.

## Testing

```
WGPU_SETTINGS_PRIO=webgl2 cargo r --example 3d_scene
cargo r --example ssr --features bluenoise_texture
cargo r --example ssao
cargo r --example irradiance_volumes
```

---------

Co-authored-by: Alice Cecile <alice.i.cecile@gmail.com>
Co-authored-by: Kevin Chen <chen.kevin.f@gmail.com>

Author: 3 people

_release-content/migration-guides/mesh_pipeline_view_layout.md

@@ -0,0 +1,40 @@
+---
+title: Mesh view bind group layout is changed
+pull_requests: [23982]
+---
+
+`MeshPipelineViewLayouts` no longer stores all possible view layouts. Now it only stores necessary parameters for creating bind group layouts on demand. And `MeshPipelineViewLayouts::get_view_layout` returns `MeshPipelineViewLayout`
+by value instead of by reference.
+
+`generate_view_layouts` is removed and `layout_entries` is private now. Please use `MeshPipelineViewLayouts::get_view_layout`.
+
+Mesh view bind group layout has more variants now and some dynamic uniforms such as distance fog, ssr, contact shadows,
+environment map are not guaranteed to exist. Please use `MeshViewBindGroup::main_offsets` to get the dynamic offsets.
+
+Before:
+
+```rust
+    let mut offsets: SmallVec<[u32; 8]> = smallvec![
+        view_uniform_offset.offset,
+        view_lights_offset.offset,
+        view_fog_offset.offset,
+        **view_light_probes_offset,
+        **view_ssr_offset,
+        **view_contact_shadows_offset,
+        **view_environment_map_offset,
+    ];
+    if let Some(oit_settings_offset) = maybe_oit_settings_offset {
+        offsets.push(oit_settings_offset.offset);
+    }
+    pass.set_bind_group(I, &mesh_view_bind_group.main, &offsets);
+```
+
+After:
+
+```rust
+    pass.set_bind_group(
+        I,
+        &mesh_view_bind_group.main,
+        &mesh_view_bind_group.main_offsets,
+    );
+```

crates/bevy_dev_tools/src/render_debug.rs

@@ -4,7 +4,6 @@ use bevy_app::{App, Plugin};
 use bevy_asset::{embedded_asset, AssetServer, Handle};
 use bevy_core_pipeline::{
     mip_generation::experimental::depth::ViewDepthPyramid,
-    oit::OrderIndependentTransparencySettingsOffset,
     schedule::{Core3d, Core3dSystems},
     upscaling::upscaling,
     FullscreenShader,
@@ -25,7 +24,6 @@ use bevy_reflect::{std_traits::ReflectDefault, Reflect};
 use bevy_render::{
     extract_component::{ExtractComponent, ExtractComponentPlugin},
     extract_resource::{ExtractResource, ExtractResourcePlugin},
-    render_asset::RenderAssets,
     render_resource::{
         binding_types, BindGroupEntries, BindGroupLayout, BindGroupLayoutDescriptor,
         BindGroupLayoutEntries, CachedRenderPipelineId, ColorTargetState, ColorWrites,
@@ -35,18 +33,16 @@ use bevy_render::{
         TextureSampleType, VertexState,
     },
     renderer::{RenderContext, RenderDevice, RenderQueue, ViewQuery},
-    texture::{FallbackImage, GpuImage},
-    view::{Msaa, ViewTarget, ViewUniformOffset},
+    texture::FallbackImage,
+    view::{ExtractedView, ViewTarget},
     GpuResourceAppExt, Render, RenderApp, RenderStartup, RenderSystems,
 };
 use bevy_shader::Shader;
 use bevy_ui_render::render_pass::ui_pass;
 
 use bevy_pbr::{
-    Bluenoise, MeshPipelineSystems, MeshPipelineViewLayoutKey, MeshPipelineViewLayouts,
-    MeshViewBindGroup, ViewContactShadowsUniformOffset, ViewEnvironmentMapUniformOffset,
-    ViewFogUniformOffset, ViewLightProbesUniformOffset, ViewLightsUniformOffset,
-    ViewScreenSpaceReflectionsUniformOffset,
+    MeshPipelineSystems, MeshPipelineViewLayoutKey, MeshPipelineViewLayouts, MeshViewBindGroup,
+    ViewKeyCache,
 };
 
 /// Adds a rendering debug overlay to visualize various renderer buffers.
@@ -503,8 +499,7 @@ impl SpecializedRenderPipeline for RenderDebugOverlayPipeline {
         let mesh_view_layout_descriptor = self
             .mesh_view_layouts
             .get_view_layout(key.view_layout_key)
-            .main_layout
-            .clone();
+            .main_layout;
 
         RenderPipelineDescriptor {
             label: Some("debug_overlay_pipeline".into()),
@@ -535,48 +530,26 @@ impl SpecializedRenderPipeline for RenderDebugOverlayPipeline {
 fn prepare_debug_overlay_pipelines(
     mut commands: Commands,
     pipeline_cache: Res<PipelineCache>,
+    view_key_cache: Res<ViewKeyCache>,
     mut pipelines: ResMut<SpecializedRenderPipelines<RenderDebugOverlayPipeline>>,
     pipeline: Res<RenderDebugOverlayPipeline>,
-    images: Res<RenderAssets<GpuImage>>,
-    blue_noise: Res<Bluenoise>,
-    views: Query<(
-        Entity,
-        &ViewTarget,
-        &RenderDebugOverlay,
-        &Msaa,
-        Option<&bevy_core_pipeline::prepass::ViewPrepassTextures>,
-        Has<bevy_core_pipeline::oit::OrderIndependentTransparencySettings>,
-        Has<bevy_pbr::ExtractedAtmosphere>,
-    )>,
+    views: Query<(Entity, &ExtractedView, &RenderDebugOverlay)>,
 ) {
-    for (entity, target, config, msaa, prepass_textures, has_oit, has_atmosphere) in &views {
+    for (entity, view, config) in &views {
         if !config.enabled {
             continue;
         }
-
-        let mut view_layout_key = MeshPipelineViewLayoutKey::from(*msaa)
-            | MeshPipelineViewLayoutKey::from(prepass_textures);
-
-        if has_oit {
-            view_layout_key |= MeshPipelineViewLayoutKey::OIT_ENABLED;
-        }
-        if has_atmosphere {
-            view_layout_key |= MeshPipelineViewLayoutKey::ATMOSPHERE;
-        }
-
-        if let Some(gpu_image) = images.get(&blue_noise.texture)
-            && gpu_image.texture.depth_or_array_layers() > 1
-        {
-            view_layout_key |= MeshPipelineViewLayoutKey::STBN;
-        }
+        let Some(view_key) = view_key_cache.get(&view.retained_view_entity) else {
+            continue;
+        };
 
         let pipeline_id = pipelines.specialize(
             &pipeline_cache,
             &pipeline,
             RenderDebugOverlayPipelineKey {
                 mode: config.mode,
-                view_layout_key,
-                target_format: target.main_texture_format(),
+                view_layout_key: (*view_key).into(),
+                target_format: view.target_format,
             },
         );
 
@@ -631,15 +604,6 @@ fn render_debug_overlay(
         &RenderDebugOverlayPipelineId,
         &RenderDebugOverlayUniformOffset,
         &MeshViewBindGroup,
-        &ViewUniformOffset,
-        &ViewLightsUniformOffset,
-        &ViewFogUniformOffset,
-        &ViewLightProbesUniformOffset,
-        &ViewScreenSpaceReflectionsUniformOffset,
-        &ViewContactShadowsUniformOffset,
-        &ViewEnvironmentMapUniformOffset,
-        Has<bevy_core_pipeline::oit::OrderIndependentTransparencySettings>,
-        Option<&OrderIndependentTransparencySettingsOffset>,
         Option<&ViewDepthPyramid>,
     )>,
     pipeline_cache: Res<PipelineCache>,
@@ -648,23 +612,8 @@ fn render_debug_overlay(
     fallback_image: Res<FallbackImage>,
     mut ctx: RenderContext,
 ) {
-    let (
-        target,
-        config,
-        pipeline_id,
-        uniform_offset,
-        mesh_view_bind_group,
-        view_uniform_offset,
-        view_lights_offset,
-        view_fog_offset,
-        view_light_probes_offset,
-        view_ssr_offset,
-        view_contact_shadows_offset,
-        view_environment_map_offset,
-        has_oit,
-        view_oit_offset,
-        depth_pyramid,
-    ) = view.into_inner();
+    let (target, config, pipeline_id, uniform_offset, mesh_view_bind_group, depth_pyramid) =
+        view.into_inner();
 
     if !config.enabled {
         return;
@@ -719,20 +668,11 @@ fn render_debug_overlay(
 
     render_pass.set_pipeline(pipeline);
 
-    let mut dynamic_offsets = vec![
-        view_uniform_offset.offset,
-        view_lights_offset.offset,
-        view_fog_offset.offset,
-        **view_light_probes_offset,
-        **view_ssr_offset,
-        **view_contact_shadows_offset,
-        **view_environment_map_offset,
-    ];
-    if has_oit && let Some(view_oit_offset) = view_oit_offset {
-        dynamic_offsets.push(view_oit_offset.offset);
-    }
-
-    render_pass.set_bind_group(0, &mesh_view_bind_group.main, &dynamic_offsets);
+    render_pass.set_bind_group(
+        0,
+        &mesh_view_bind_group.main,
+        &mesh_view_bind_group.main_offsets,
+    );
     render_pass.set_bind_group(1, &debug_bind_group, &[uniform_offset.offset]);
 
     render_pass.draw(0..3, 0..1);

crates/bevy_gizmos_render/src/pipeline_3d.rs

@@ -136,10 +136,7 @@ impl Specializer<RenderPipeline> for LineGizmoPipelineSpecializer {
         key: Self::Key,
         descriptor: &mut RenderPipelineDescriptor,
     ) -> Result<Canonical<Self::Key>, BevyError> {
-        let view_layout = self
-            .mesh_pipeline
-            .get_view_layout(key.view_key.into())
-            .clone();
+        let view_layout = self.mesh_pipeline.get_view_layout(key.view_key.into());
 
         descriptor.set_layout(0, view_layout.main_layout.clone());
         descriptor.vertex.buffers = line_gizmo_vertex_buffer_layouts(key.strip);
@@ -207,10 +204,7 @@ impl SpecializedRenderPipeline for LineJointGizmoPipeline {
 
         let format = key.view_key.target_format();
 
-        let view_layout = self
-            .mesh_pipeline
-            .get_view_layout(key.view_key.into())
-            .clone();
+        let view_layout = self.mesh_pipeline.get_view_layout(key.view_key.into());
         let layout = vec![view_layout.main_layout.clone(), self.uniform_layout.clone()];
 
         if key.joints == GizmoLineJoint::None {

crates/bevy_pbr/src/contact_shadows.rs

@@ -20,7 +20,6 @@ use bevy_render::{
     view::ExtractedView,
     GpuResourceAppExt, Render, RenderApp, RenderSystems,
 };
-use bevy_utils::default;
 
 /// Enables contact shadows for a camera.
 pub struct ContactShadowsPlugin;
@@ -59,7 +58,7 @@ impl Default for ContactShadows {
 }
 
 /// A version of [`ContactShadows`] for upload to the GPU.
-#[derive(Clone, Copy, Component, ShaderType, Default)]
+#[derive(Clone, Copy, ShaderType, Default)]
 pub struct ContactShadowsUniform {
     pub linear_steps: u32,
     pub thickness: f32,
@@ -81,7 +80,7 @@ impl From<ContactShadows> for ContactShadowsUniform {
 }
 
 impl SyncComponent for ContactShadows {
-    type Target = Self;
+    type Target = (Self, ViewContactShadowsUniformOffset);
 }
 
 impl ExtractComponent for ContactShadows {
@@ -118,29 +117,25 @@ impl Plugin for ContactShadowsPlugin {
 
 fn prepare_contact_shadows_settings(
     mut commands: Commands,
-    views: Query<(Entity, Option<&ContactShadows>), With<ExtractedView>>,
+    views: Query<(Entity, &ContactShadows), With<ExtractedView>>,
     mut contact_shadows_buffer: ResMut<ContactShadowsBuffer>,
     render_device: Res<RenderDevice>,
     render_queue: Res<RenderQueue>,
 ) {
-    contact_shadows_buffer.0.clear();
+    let Some(mut writer) =
+        contact_shadows_buffer
+            .0
+            .get_writer(views.iter().len(), &render_device, &render_queue)
+    else {
+        return;
+    };
     for (entity, settings) in &views {
-        let uniform = if let Some(settings) = settings {
-            ContactShadowsUniform::from(*settings)
-        } else {
-            ContactShadowsUniform {
-                linear_steps: 0,
-                ..default()
-            }
-        };
-        let offset = contact_shadows_buffer.0.push(&uniform);
+        let uniform = ContactShadowsUniform::from(*settings);
+        let offset = writer.write(&uniform);
         commands
             .entity(entity)
             .insert(ViewContactShadowsUniformOffset(offset));
     }
-    contact_shadows_buffer
-        .0
-        .write_buffer(&render_device, &render_queue);
 }
 
 /// A component that stores the offset within the [`ContactShadowsBuffer`] for