Fix prepass binding issues causing crashes when not all prepass bindi…

…ngs are used (bevyengine#10788)

# Objective

Fixes bevyengine#10786

## Solution

The bind_group_layout entries for the prepass were wrong when not all 4
prepass textures were used, as it just zipped [17, 18, 19, 20] with the
smallvec of prepass `bind_group_layout` entries that potentially didn't
contain 4 entries. (eg. if you had a depth and motion vector prepass but
no normal prepass, then depth would be correct but the entry for the
motion vector prepass would be 18 (normal prepass' spot) instead of 19).

Change the prepass `get_bind_group_layout_entries` function to return an
array of `[Option<BindGroupLayoutEntryBuilder>; 4]` and only add the
layout entry if it exists.

crates/bevy_pbr/src/prepass/prepass_bindings.rs

@@ -7,58 +7,53 @@ use bevy_render::render_resource::{
     TextureViewDescriptor,
 };
 use bevy_utils::default;
-use smallvec::SmallVec;
 
 use crate::MeshPipelineViewLayoutKey;
 
 pub fn get_bind_group_layout_entries(
     layout_key: MeshPipelineViewLayoutKey,
-) -> SmallVec<[BindGroupLayoutEntryBuilder; 4]> {
-    let mut result = SmallVec::<[BindGroupLayoutEntryBuilder; 4]>::new();
+) -> [Option<BindGroupLayoutEntryBuilder>; 4] {
+    let mut entries: [Option<BindGroupLayoutEntryBuilder>; 4] = [None; 4];
 
     let multisampled = layout_key.contains(MeshPipelineViewLayoutKey::MULTISAMPLED);
 
     if layout_key.contains(MeshPipelineViewLayoutKey::DEPTH_PREPASS) {
-        result.push(
-            // Depth texture
-            if multisampled {
-                texture_depth_2d_multisampled()
-            } else {
-                texture_depth_2d()
-            },
-        );
+        // Depth texture
+        entries[0] = if multisampled {
+            Some(texture_depth_2d_multisampled())
+        } else {
+            Some(texture_depth_2d())
+        };
     }
 
     if layout_key.contains(MeshPipelineViewLayoutKey::NORMAL_PREPASS) {
-        result.push(
-            // Normal texture
-            if multisampled {
-                texture_2d_multisampled(TextureSampleType::Float { filterable: false })
-            } else {
-                texture_2d(TextureSampleType::Float { filterable: false })
-            },
-        );
+        // Normal texture
+        entries[1] = if multisampled {
+            Some(texture_2d_multisampled(TextureSampleType::Float {
+                filterable: false,
+            }))
+        } else {
+            Some(texture_2d(TextureSampleType::Float { filterable: false }))
+        };
     }
 
     if layout_key.contains(MeshPipelineViewLayoutKey::MOTION_VECTOR_PREPASS) {
-        result.push(
-            // Motion Vectors texture
-            if multisampled {
-                texture_2d_multisampled(TextureSampleType::Float { filterable: false })
-            } else {
-                texture_2d(TextureSampleType::Float { filterable: false })
-            },
-        );
+        // Motion Vectors texture
+        entries[2] = if multisampled {
+            Some(texture_2d_multisampled(TextureSampleType::Float {
+                filterable: false,
+            }))
+        } else {
+            Some(texture_2d(TextureSampleType::Float { filterable: false }))
+        };
     }
 
     if layout_key.contains(MeshPipelineViewLayoutKey::DEFERRED_PREPASS) {
-        result.push(
-            // Deferred texture
-            texture_2d(TextureSampleType::Uint),
-        );
+        // Deferred texture
+        entries[3] = Some(texture_2d(TextureSampleType::Uint));
     }
 
-    result
+    entries
 }
 
 pub fn get_bindings(prepass_textures: Option<&ViewPrepassTextures>) -> [Option<TextureView>; 4] {

crates/bevy_pbr/src/render/mesh_view_bindings.rs

@@ -274,7 +274,9 @@ fn layout_entries(
             .iter()
             .zip([17, 18, 19, 20])
         {
-            entries = entries.extend_with_indices(((binding as u32, *entry),));
+            if let Some(entry) = entry {
+                entries = entries.extend_with_indices(((binding as u32, *entry),));
+            }
         }
     }