fix normal prepass (#8890)

# Objective

- Fix broken normals when the NormalPrepass is enabled

## Solution

- Don't use the normal prepass for the world_normal
- Only loadthe normal prepass 
    - when msaa is disabled
- for opaque or alpha mask meshes and only for use it for N not
world_normal

crates/bevy_pbr/src/render/mesh.rs

@@ -682,10 +682,6 @@ impl SpecializedMeshPipeline for MeshPipeline {
         let mut shader_defs = Vec::new();
         let mut vertex_attributes = Vec::new();
 
-        if key.contains(MeshPipelineKey::NORMAL_PREPASS) {
-            shader_defs.push("LOAD_PREPASS_NORMALS".into());
-        }
-
         if layout.contains(Mesh::ATTRIBUTE_POSITION) {
             shader_defs.push("VERTEX_POSITIONS".into());
             vertex_attributes.push(Mesh::ATTRIBUTE_POSITION.at_shader_location(0));
@@ -747,6 +743,7 @@ impl SpecializedMeshPipeline for MeshPipeline {
 
         let (label, blend, depth_write_enabled);
         let pass = key.intersection(MeshPipelineKey::BLEND_RESERVED_BITS);
+        let mut is_opaque = false;
         if pass == MeshPipelineKey::BLEND_ALPHA {
             label = "alpha_blend_mesh_pipeline".into();
             blend = Some(BlendState::ALPHA_BLENDING);
@@ -783,6 +780,11 @@ impl SpecializedMeshPipeline for MeshPipeline {
             // the current fragment value in the output and the depth is written to the
             // depth buffer
             depth_write_enabled = true;
+            is_opaque = true;
+        }
+
+        if key.contains(MeshPipelineKey::NORMAL_PREPASS) && key.msaa_samples() == 1 && is_opaque {
+            shader_defs.push("LOAD_PREPASS_NORMALS".into());
         }
 
         if key.contains(MeshPipelineKey::TONEMAP_IN_SHADER) {

crates/bevy_pbr/src/render/pbr.wgsl

@@ -109,18 +109,17 @@ fn fragment(in: FragmentInput) -> @location(0) vec4<f32> {
         pbr_input.frag_coord = in.frag_coord;
         pbr_input.world_position = in.world_position;
 
-#ifdef LOAD_PREPASS_NORMALS
-        pbr_input.world_normal = prepass_normal(in.frag_coord, 0u);
-#else // LOAD_PREPASS_NORMALS
         pbr_input.world_normal = prepare_world_normal(
             in.world_normal,
             (material.flags & STANDARD_MATERIAL_FLAGS_DOUBLE_SIDED_BIT) != 0u,
             in.is_front,
         );
-#endif // LOAD_PREPASS_NORMALS
 
         pbr_input.is_orthographic = is_orthographic;
 
+#ifdef LOAD_PREPASS_NORMALS
+        pbr_input.N = prepass_normal(in.frag_coord, 0u);
+#else
         pbr_input.N = apply_normal_mapping(
             material.flags,
             pbr_input.world_normal,
@@ -133,6 +132,8 @@ fn fragment(in: FragmentInput) -> @location(0) vec4<f32> {
             uv,
 #endif
         );
+#endif
+
         pbr_input.V = V;
         pbr_input.occlusion = occlusion;