Use prepass shaders for shadows (#7784)

# Objective

- Fixes #4372.

## Solution

- Use the prepass shaders for the shadow passes.
- Move `DEPTH_CLAMP_ORTHO` from `ShadowPipelineKey` to `MeshPipelineKey` and the associated clamp operation from `depth.wgsl` to `prepass.wgsl`.
- Remove `depth.wgsl` .
- Replace `ShadowPipeline` with `ShadowSamplers`.

Instead of running the custom `ShadowPipeline` we run the `PrepassPipeline` with the `DEPTH_PREPASS` flag and additionally the `DEPTH_CLAMP_ORTHO` flag for directional lights as well as the `ALPHA_MASK` flag for materials that use `AlphaMode::Mask(_)`.

crates/bevy_pbr/src/lib.rs

@@ -52,8 +52,8 @@ use bevy_render::{
     extract_resource::ExtractResourcePlugin,
     prelude::Color,
     render_graph::RenderGraph,
-    render_phase::{sort_phase_system, AddRenderCommand, DrawFunctions},
-    render_resource::{Shader, SpecializedMeshPipelines},
+    render_phase::sort_phase_system,
+    render_resource::Shader,
     view::{ViewSet, VisibilitySystems},
     ExtractSchedule, RenderApp, RenderSet,
 };
@@ -80,8 +80,6 @@ pub const PBR_FUNCTIONS_HANDLE: HandleUntyped =
     HandleUntyped::weak_from_u64(Shader::TYPE_UUID, 16550102964439850292);
 pub const PBR_AMBIENT_HANDLE: HandleUntyped =
     HandleUntyped::weak_from_u64(Shader::TYPE_UUID, 2441520459096337034);
-pub const SHADOW_SHADER_HANDLE: HandleUntyped =
-    HandleUntyped::weak_from_u64(Shader::TYPE_UUID, 1836745567947005696);
 
 /// Sets up the entire PBR infrastructure of bevy.
 pub struct PbrPlugin {
@@ -144,12 +142,6 @@ impl Plugin for PbrPlugin {
             Shader::from_wgsl
         );
         load_internal_asset!(app, PBR_SHADER_HANDLE, "render/pbr.wgsl", Shader::from_wgsl);
-        load_internal_asset!(
-            app,
-            SHADOW_SHADER_HANDLE,
-            "render/depth.wgsl",
-            Shader::from_wgsl
-        );
         load_internal_asset!(
             app,
             PBR_PREPASS_SHADER_HANDLE,
@@ -293,17 +285,12 @@ impl Plugin for PbrPlugin {
                     .after(render::prepare_lights)
                     .in_set(RenderLightSystems::PrepareClusters),
             )
-            .add_system(render::queue_shadows.in_set(RenderLightSystems::QueueShadows))
-            .add_system(render::queue_shadow_view_bind_group.in_set(RenderSet::Queue))
             .add_system(sort_phase_system::<Shadow>.in_set(RenderSet::PhaseSort))
-            .init_resource::<ShadowPipeline>()
-            .init_resource::<DrawFunctions<Shadow>>()
+            .init_resource::<ShadowSamplers>()
             .init_resource::<LightMeta>()
-            .init_resource::<GlobalLightMeta>()
-            .init_resource::<SpecializedMeshPipelines<ShadowPipeline>>();
+            .init_resource::<GlobalLightMeta>();
 
         let shadow_pass_node = ShadowPassNode::new(&mut render_app.world);
-        render_app.add_render_command::<Shadow, DrawShadowMesh>();
         let mut graph = render_app.world.resource_mut::<RenderGraph>();
         let draw_3d_graph = graph
             .get_sub_graph_mut(bevy_core_pipeline::core_3d::graph::NAME)

crates/bevy_pbr/src/material.rs

@@ -1,6 +1,7 @@
 use crate::{
-    AlphaMode, DrawMesh, EnvironmentMapLight, MeshPipeline, MeshPipelineKey, MeshUniform,
-    PrepassPlugin, SetMeshBindGroup, SetMeshViewBindGroup,
+    queue_mesh_view_bind_groups, render, AlphaMode, DrawMesh, DrawPrepass, EnvironmentMapLight,
+    MeshPipeline, MeshPipelineKey, MeshUniform, PrepassPlugin, RenderLightSystems,
+    SetMeshBindGroup, SetMeshViewBindGroup, Shadow,
 };
 use bevy_app::{App, IntoSystemAppConfig, Plugin};
 use bevy_asset::{AddAsset, AssetEvent, AssetServer, Assets, Handle};
@@ -188,6 +189,8 @@ where
 
         if let Ok(render_app) = app.get_sub_app_mut(RenderApp) {
             render_app
+                .init_resource::<DrawFunctions<Shadow>>()
+                .add_render_command::<Shadow, DrawPrepass<M>>()
                 .add_render_command::<Transparent3d, DrawMaterial<M>>()
                 .add_render_command::<Opaque3d, DrawMaterial<M>>()
                 .add_render_command::<AlphaMask3d, DrawMaterial<M>>()
@@ -201,6 +204,12 @@ where
                         .in_set(RenderSet::Prepare)
                         .after(PrepareAssetSet::PreAssetPrepare),
                 )
+                .add_system(render::queue_shadows::<M>.in_set(RenderLightSystems::QueueShadows))
+                .add_system(
+                    render::queue_shadow_view_bind_group::<M>
+                        .in_set(RenderSet::Queue)
+                        .ambiguous_with(queue_mesh_view_bind_groups), // queue_mesh_view_bind_groups does not read `shadow_view_bind_group`),
+                )
                 .add_system(queue_material_meshes::<M>.in_set(RenderSet::Queue));
         }
 

crates/bevy_pbr/src/prepass/mod.rs

@@ -202,6 +202,13 @@ where
             shader_defs.push("ALPHA_MASK".into());
         }
 
+        let blend_key = key
+            .mesh_key
+            .intersection(MeshPipelineKey::BLEND_RESERVED_BITS);
+        if blend_key == MeshPipelineKey::BLEND_PREMULTIPLIED_ALPHA {
+            shader_defs.push("BLEND_PREMULTIPLIED_ALPHA".into());
+        }
+
         if layout.contains(Mesh::ATTRIBUTE_POSITION) {
             shader_defs.push("VERTEX_POSITIONS".into());
             vertex_attributes.push(Mesh::ATTRIBUTE_POSITION.at_shader_location(0));
@@ -215,6 +222,9 @@ where
             "MAX_CASCADES_PER_LIGHT".to_string(),
             MAX_CASCADES_PER_LIGHT as i32,
         ));
+        if key.mesh_key.contains(MeshPipelineKey::DEPTH_CLAMP_ORTHO) {
+            shader_defs.push("DEPTH_CLAMP_ORTHO".into());
+        }
 
         if layout.contains(Mesh::ATTRIBUTE_UV_0) {
             shader_defs.push("VERTEX_UVS".into());
@@ -244,9 +254,11 @@ where
 
         let vertex_buffer_layout = layout.get_layout(&vertex_attributes)?;
 
-        // The fragment shader is only used when the normal prepass is enabled or the material uses an alpha mask
-        let fragment = if key.mesh_key.contains(MeshPipelineKey::NORMAL_PREPASS)
-            || key.mesh_key.contains(MeshPipelineKey::ALPHA_MASK)
+        // The fragment shader is only used when the normal prepass is enabled or the material uses alpha cutoff values
+        let fragment = if key
+            .mesh_key
+            .intersects(MeshPipelineKey::NORMAL_PREPASS | MeshPipelineKey::ALPHA_MASK)
+            || blend_key == MeshPipelineKey::BLEND_PREMULTIPLIED_ALPHA
         {
             // Use the fragment shader from the material if present
             let frag_shader_handle = if let Some(handle) = &self.material_fragment_shader {

crates/bevy_pbr/src/prepass/prepass.wgsl

@@ -49,6 +49,9 @@ fn vertex(vertex: Vertex) -> VertexOutput {
 #endif // SKINNED
 
     out.clip_position = mesh_position_local_to_clip(model, vec4(vertex.position, 1.0));
+#ifdef DEPTH_CLAMP_ORTHO
+        out.clip_position.z = min(out.clip_position.z, 1.0);
+#endif // DEPTH_CLAMP_ORTHO
 
 #ifdef VERTEX_UVS
     out.uv = vertex.uv;