Move prepass functions to prepass_utils (#7354)

# Objective

- The functions added to utils.wgsl by the prepass assume that mesh_view_bindings are present, which isn't always the case
- Fixes https://github.com/bevyengine/bevy/issues/7353

## Solution

- Move these functions to their own `prepass_utils.wgsl` file


Co-authored-by: IceSentry <IceSentry@users.noreply.github.com>

assets/shaders/show_prepass.wgsl

@@ -1,6 +1,6 @@
 #import bevy_pbr::mesh_types
 #import bevy_pbr::mesh_view_bindings
-#import bevy_pbr::utils
+#import bevy_pbr::prepass_utils
 
 @group(1) @binding(0)
 var<uniform> show_depth: f32;

crates/bevy_core_pipeline/src/prepass/mod.rs

@@ -16,7 +16,7 @@
 //! it will always create a depth buffer that will be used by the main pass.
 //!
 //! When using the default mesh view bindings you should be able to use `prepass_depth()`
-//! and `prepass_normal()` to load the related textures. These functions are defined in `bevy_pbr::utils`.
+//! and `prepass_normal()` to load the related textures. These functions are defined in `bevy_pbr::prepass_utils`.
 //! See the `shader_prepass` example that shows how to use it.
 //!
 //! The prepass runs for each `Material`. You can control if the prepass should run per-material by setting the `prepass_enabled`

crates/bevy_pbr/src/prepass/mod.rs

@@ -57,6 +57,9 @@ pub const PREPASS_SHADER_HANDLE: HandleUntyped =
 pub const PREPASS_BINDINGS_SHADER_HANDLE: HandleUntyped =
     HandleUntyped::weak_from_u64(Shader::TYPE_UUID, 5533152893177403494);
 
+pub const PREPASS_UTILS_SHADER_HANDLE: HandleUntyped =
+    HandleUntyped::weak_from_u64(Shader::TYPE_UUID, 4603948296044544);
+
 pub struct PrepassPlugin<M: Material>(PhantomData<M>);
 
 impl<M: Material> Default for PrepassPlugin<M> {
@@ -84,6 +87,13 @@ where
             Shader::from_wgsl
         );
 
+        load_internal_asset!(
+            app,
+            PREPASS_UTILS_SHADER_HANDLE,
+            "prepass_utils.wgsl",
+            Shader::from_wgsl
+        );
+
         let Ok(render_app) = app.get_sub_app_mut(RenderApp) else {
             return;
         };

crates/bevy_pbr/src/prepass/prepass_utils.wgsl

@@ -0,0 +1,23 @@
+#define_import_path bevy_pbr::prepass_utils
+
+#ifndef NORMAL_PREPASS
+fn prepass_normal(frag_coord: vec4<f32>, sample_index: u32) -> vec3<f32> {
+#ifdef MULTISAMPLED
+    let normal_sample = textureLoad(normal_prepass_texture, vec2<i32>(frag_coord.xy), i32(sample_index));
+#else
+    let normal_sample = textureLoad(normal_prepass_texture, vec2<i32>(frag_coord.xy), 0);
+#endif
+    return normal_sample.xyz * 2.0 - vec3(1.0);
+}
+#endif // NORMAL_PREPASS
+
+#ifndef DEPTH_PREPASS
+fn prepass_depth(frag_coord: vec4<f32>, sample_index: u32) -> f32 {
+#ifdef MULTISAMPLED
+    let depth_sample = textureLoad(depth_prepass_texture, vec2<i32>(frag_coord.xy), i32(sample_index));
+#else
+    let depth_sample = textureLoad(depth_prepass_texture, vec2<i32>(frag_coord.xy), 0);
+#endif
+    return depth_sample;
+}
+#endif // DEPTH_PREPASS

crates/bevy_pbr/src/render/utils.wgsl

@@ -25,25 +25,3 @@ fn random1D(s: f32) -> f32 {
 fn coords_to_viewport_uv(position: vec2<f32>, viewport: vec4<f32>) -> vec2<f32> {
     return (position - viewport.xy) / viewport.zw;
 }
-
-#ifndef NORMAL_PREPASS
-fn prepass_normal(frag_coord: vec4<f32>, sample_index: u32) -> vec3<f32> {
-#ifdef MULTISAMPLED
-    let normal_sample = textureLoad(normal_prepass_texture, vec2<i32>(frag_coord.xy), i32(sample_index));
-#else
-    let normal_sample = textureLoad(normal_prepass_texture, vec2<i32>(frag_coord.xy), 0);
-#endif
-    return normal_sample.xyz * 2.0 - vec3(1.0);
-}
-#endif // NORMAL_PREPASS
-
-#ifndef DEPTH_PREPASS
-fn prepass_depth(frag_coord: vec4<f32>, sample_index: u32) -> f32 {
-#ifdef MULTISAMPLED
-    let depth_sample = textureLoad(depth_prepass_texture, vec2<i32>(frag_coord.xy), i32(sample_index));
-#else
-    let depth_sample = textureLoad(depth_prepass_texture, vec2<i32>(frag_coord.xy), 0);
-#endif
-    return depth_sample;
-}
-#endif // DEPTH_PREPASS