Added SSAO support on WebGPU, with R32Float fallback. (#20960)

# Objective

This PR is to add SSAO support on WebGPU.

## Solution
Add r16float detect and fallback to r32float if not supported. FYI the
initial ssao PR [here](#7402).

## Testing

- Did you test these changes? If so, how?
     Yes, here is the command to test the ssao example 
`RUSTFLAGS="--cfg getrandom_backend=\"wasm_js\"" cargo run --example
ssao --target wasm32-unknown-unknown --features webgpu`
and then http://localhost:1334, make sure it supports
[WebGPU](https://caniuse.com/webgpu)

- Are there any parts that need more testing?
 N/A
- How can other people (reviewers) test your changes? Is there anything
specific they need to know?
1. For the R32Float fallback, only the 1st commit is needed. However, I
ran into some strange flickering issue on Chrome (and Chrome canary
too), so I added a "detect_r16float_support" flag and a temp fix in the
2nd and 3rd commit, which are intended to be reverted when merging.
2. with the 1st commit, Safari works fine, but Chrome has the
flickering, and I fixed it by partially reverting a shader change from
#20313, which is very strange. It
is probably caused by some shader optimization issue in Chrome, and I
have no clue why, as the change is just moving the calculation to a
different function.
Here is the flickering on Mac Chrome(140.0.7339.133 (Official Build)
(arm64))
<img width="353" height="327" alt="chrome_ssao"
src="https://github.com/user-attachments/assets/0666673f-508e-4b57-a152-19327ffdb6f3"
/>


- If relevant, what platforms did you test these changes on, and are
there any important ones you can't test?
Tested on native(mac) and WebGPU. To test on native, set
"detect_r16float_support" to false to force R32Float.
I couldn't make the WebGPU ssao example running on Windows 11 Chrome or
Firefox, there is some error in 'taa_pipeline' .
 
---

Author: diyu-motif

crates/bevy_pbr/src/ssao/mod.rs

@@ -60,17 +60,6 @@ impl Plugin for ScreenSpaceAmbientOcclusionPlugin {
             return;
         };
 
-        if !render_app
-            .world()
-            .resource::<RenderAdapter>()
-            .get_texture_format_features(TextureFormat::R16Float)
-            .allowed_usages
-            .contains(TextureUsages::STORAGE_BINDING)
-        {
-            warn!("ScreenSpaceAmbientOcclusionPlugin not loaded. GPU lacks support: TextureFormat::R16Float does not support TextureUsages::STORAGE_BINDING.");
-            return;
-        }
-
         if render_app
             .world()
             .resource::<RenderDevice>()
@@ -299,6 +288,7 @@ struct SsaoPipelines {
     linear_clamp_sampler: Sampler,
 
     shader: Handle<Shader>,
+    depth_format: TextureFormat,
 }
 
 impl FromWorld for SsaoPipelines {
@@ -307,6 +297,18 @@ impl FromWorld for SsaoPipelines {
         let render_queue = world.resource::<RenderQueue>();
         let pipeline_cache = world.resource::<PipelineCache>();
 
+        // Detect the depth format support
+        let render_adapter = world.resource::<RenderAdapter>();
+        let depth_format = if render_adapter
+            .get_texture_format_features(TextureFormat::R16Float)
+            .allowed_usages
+            .contains(TextureUsages::STORAGE_BINDING)
+        {
+            TextureFormat::R16Float
+        } else {
+            TextureFormat::R32Float
+        };
+
         let hilbert_index_lut = render_device
             .create_texture_with_data(
                 render_queue,
@@ -364,11 +366,11 @@ impl FromWorld for SsaoPipelines {
                 ShaderStages::COMPUTE,
                 (
                     texture_depth_2d(),
-                    texture_storage_2d(TextureFormat::R16Float, StorageTextureAccess::WriteOnly),
-                    texture_storage_2d(TextureFormat::R16Float, StorageTextureAccess::WriteOnly),
-                    texture_storage_2d(TextureFormat::R16Float, StorageTextureAccess::WriteOnly),
-                    texture_storage_2d(TextureFormat::R16Float, StorageTextureAccess::WriteOnly),
-                    texture_storage_2d(TextureFormat::R16Float, StorageTextureAccess::WriteOnly),
+                    texture_storage_2d(depth_format, StorageTextureAccess::WriteOnly),
+                    texture_storage_2d(depth_format, StorageTextureAccess::WriteOnly),
+                    texture_storage_2d(depth_format, StorageTextureAccess::WriteOnly),
+                    texture_storage_2d(depth_format, StorageTextureAccess::WriteOnly),
+                    texture_storage_2d(depth_format, StorageTextureAccess::WriteOnly),
                 ),
             ),
         );
@@ -381,7 +383,7 @@ impl FromWorld for SsaoPipelines {
                     texture_2d(TextureSampleType::Float { filterable: true }),
                     texture_2d(TextureSampleType::Float { filterable: false }),
                     texture_2d(TextureSampleType::Uint),
-                    texture_storage_2d(TextureFormat::R16Float, StorageTextureAccess::WriteOnly),
+                    texture_storage_2d(depth_format, StorageTextureAccess::WriteOnly),
                     texture_storage_2d(TextureFormat::R32Uint, StorageTextureAccess::WriteOnly),
                     uniform_buffer::<GlobalsUniform>(false),
                     uniform_buffer::<f32>(false),
@@ -396,11 +398,16 @@ impl FromWorld for SsaoPipelines {
                 (
                     texture_2d(TextureSampleType::Float { filterable: false }),
                     texture_2d(TextureSampleType::Uint),
-                    texture_storage_2d(TextureFormat::R16Float, StorageTextureAccess::WriteOnly),
+                    texture_storage_2d(depth_format, StorageTextureAccess::WriteOnly),
                 ),
             ),
         );
 
+        let mut shader_defs = Vec::new();
+        if depth_format == TextureFormat::R16Float {
+            shader_defs.push("USE_R16FLOAT".into());
+        }
+
         let preprocess_depth_pipeline =
             pipeline_cache.queue_compute_pipeline(ComputePipelineDescriptor {
                 label: Some("ssao_preprocess_depth_pipeline".into()),
@@ -409,6 +416,7 @@ impl FromWorld for SsaoPipelines {
                     common_bind_group_layout.clone(),
                 ],
                 shader: load_embedded_asset!(world, "preprocess_depth.wgsl"),
+                shader_defs: shader_defs.clone(),
                 ..default()
             });
 
@@ -420,6 +428,7 @@ impl FromWorld for SsaoPipelines {
                     common_bind_group_layout.clone(),
                 ],
                 shader: load_embedded_asset!(world, "spatial_denoise.wgsl"),
+                shader_defs,
                 ..default()
             });
 
@@ -437,6 +446,7 @@ impl FromWorld for SsaoPipelines {
             linear_clamp_sampler,
 
             shader: load_embedded_asset!(world, "ssao.wgsl"),
+            depth_format,
         }
     }
 }
@@ -465,6 +475,10 @@ impl SpecializedComputePipeline for SsaoPipelines {
             shader_defs.push("TEMPORAL_JITTER".into());
         }
 
+        if self.depth_format == TextureFormat::R16Float {
+            shader_defs.push("USE_R16FLOAT".into());
+        }
+
         ComputePipelineDescriptor {
             label: Some("ssao_ssao_pipeline".into()),
             layout: vec![
@@ -519,6 +533,7 @@ fn prepare_ssao_textures(
     mut commands: Commands,
     mut texture_cache: ResMut<TextureCache>,
     render_device: Res<RenderDevice>,
+    pipelines: Res<SsaoPipelines>,
     views: Query<(Entity, &ExtractedCamera, &ScreenSpaceAmbientOcclusion)>,
 ) {
     for (entity, camera, ssao_settings) in &views {
@@ -535,7 +550,7 @@ fn prepare_ssao_textures(
                 mip_level_count: 5,
                 sample_count: 1,
                 dimension: TextureDimension::D2,
-                format: TextureFormat::R16Float,
+                format: pipelines.depth_format,
                 usage: TextureUsages::STORAGE_BINDING | TextureUsages::TEXTURE_BINDING,
                 view_formats: &[],
             },
@@ -549,7 +564,7 @@ fn prepare_ssao_textures(
                 mip_level_count: 1,
                 sample_count: 1,
                 dimension: TextureDimension::D2,
-                format: TextureFormat::R16Float,
+                format: pipelines.depth_format,
                 usage: TextureUsages::STORAGE_BINDING | TextureUsages::TEXTURE_BINDING,
                 view_formats: &[],
             },
@@ -563,7 +578,7 @@ fn prepare_ssao_textures(
                 mip_level_count: 1,
                 sample_count: 1,
                 dimension: TextureDimension::D2,
-                format: TextureFormat::R16Float,
+                format: pipelines.depth_format,
                 usage: TextureUsages::STORAGE_BINDING | TextureUsages::TEXTURE_BINDING,
                 view_formats: &[],
             },
@@ -671,7 +686,7 @@ fn prepare_ssao_bind_groups(
                 .create_view(&TextureViewDescriptor {
                     label: Some("ssao_preprocessed_depth_texture_mip_view"),
                     base_mip_level: mip_level,
-                    format: Some(TextureFormat::R16Float),
+                    format: Some(pipelines.depth_format),
                     dimension: Some(TextureViewDimension::D2),
                     mip_level_count: Some(1),
                     ..default()

crates/bevy_pbr/src/ssao/preprocess_depth.wgsl

@@ -8,11 +8,19 @@
 #import bevy_render::view::View
 
 @group(0) @binding(0) var input_depth: texture_depth_2d;
+#ifdef USE_R16FLOAT
 @group(0) @binding(1) var preprocessed_depth_mip0: texture_storage_2d<r16float, write>;
 @group(0) @binding(2) var preprocessed_depth_mip1: texture_storage_2d<r16float, write>;
 @group(0) @binding(3) var preprocessed_depth_mip2: texture_storage_2d<r16float, write>;
 @group(0) @binding(4) var preprocessed_depth_mip3: texture_storage_2d<r16float, write>;
 @group(0) @binding(5) var preprocessed_depth_mip4: texture_storage_2d<r16float, write>;
+#else
+@group(0) @binding(1) var preprocessed_depth_mip0: texture_storage_2d<r32float, write>;
+@group(0) @binding(2) var preprocessed_depth_mip1: texture_storage_2d<r32float, write>;
+@group(0) @binding(3) var preprocessed_depth_mip2: texture_storage_2d<r32float, write>;
+@group(0) @binding(4) var preprocessed_depth_mip3: texture_storage_2d<r32float, write>;
+@group(0) @binding(5) var preprocessed_depth_mip4: texture_storage_2d<r32float, write>;
+#endif
 @group(1) @binding(0) var point_clamp_sampler: sampler;
 @group(1) @binding(1) var linear_clamp_sampler: sampler;
 @group(1) @binding(2) var<uniform> view: View;

crates/bevy_pbr/src/ssao/spatial_denoise.wgsl

@@ -13,7 +13,11 @@
 
 @group(0) @binding(0) var ambient_occlusion_noisy: texture_2d<f32>;
 @group(0) @binding(1) var depth_differences: texture_2d<u32>;
+#ifdef USE_R16FLOAT
 @group(0) @binding(2) var ambient_occlusion: texture_storage_2d<r16float, write>;
+#else
+@group(0) @binding(2) var ambient_occlusion: texture_storage_2d<r32float, write>;
+#endif
 @group(1) @binding(0) var point_clamp_sampler: sampler;
 @group(1) @binding(1) var linear_clamp_sampler: sampler;
 @group(1) @binding(2) var<uniform> view: View;

crates/bevy_pbr/src/ssao/ssao.wgsl

@@ -21,7 +21,11 @@
 @group(0) @binding(0) var preprocessed_depth: texture_2d<f32>;
 @group(0) @binding(1) var normals: texture_2d<f32>;
 @group(0) @binding(2) var hilbert_index_lut: texture_2d<u32>;
+#ifdef USE_R16FLOAT
 @group(0) @binding(3) var ambient_occlusion: texture_storage_2d<r16float, write>;
+#else
+@group(0) @binding(3) var ambient_occlusion: texture_storage_2d<r32float, write>;
+#endif
 @group(0) @binding(4) var depth_differences: texture_storage_2d<r32uint, write>;
 @group(0) @binding(5) var<uniform> globals: Globals;
 @group(0) @binding(6) var<uniform> thickness: f32;