Allow custom depth texture usage (#6815)

# Objective
Sometimes we might want to read from the depth texture in some custom
rendering features. We must then add `STORAGE_BINDING` or
`TEXTURE_BINDING` to the texture usage flags when creating them.

## Solution

This PR allows one to customize the usage flags in the `Camera3d`
component.

crates/bevy_core_pipeline/src/core_3d/camera_3d.rs

@@ -8,21 +8,47 @@ use bevy_render::{
     camera::{Camera, CameraRenderGraph, Projection},
     extract_component::ExtractComponent,
     primitives::Frustum,
-    render_resource::LoadOp,
+    render_resource::{LoadOp, TextureUsages},
     view::{ColorGrading, VisibleEntities},
 };
 use bevy_transform::prelude::{GlobalTransform, Transform};
 use serde::{Deserialize, Serialize};
 
 /// Configuration for the "main 3d render graph".
-#[derive(Component, Reflect, Clone, Default, ExtractComponent)]
+#[derive(Component, Reflect, Clone, ExtractComponent)]
 #[extract_component_filter(With<Camera>)]
 #[reflect(Component)]
 pub struct Camera3d {
     /// The clear color operation to perform for the main 3d pass.
     pub clear_color: ClearColorConfig,
     /// The depth clear operation to perform for the main 3d pass.
     pub depth_load_op: Camera3dDepthLoadOp,
+    /// The texture usages for the depth texture created for the main 3d pass.
+    pub depth_texture_usages: Camera3dDepthTextureUsage,
+}
+
+impl Default for Camera3d {
+    fn default() -> Self {
+        Self {
+            clear_color: ClearColorConfig::Default,
+            depth_load_op: Default::default(),
+            depth_texture_usages: TextureUsages::RENDER_ATTACHMENT.into(),
+        }
+    }
+}
+
+#[derive(Clone, Copy, Reflect)]
+pub struct Camera3dDepthTextureUsage(u32);
+
+impl From<TextureUsages> for Camera3dDepthTextureUsage {
+    fn from(value: TextureUsages) -> Self {
+        Self(value.bits())
+    }
+}
+impl From<Camera3dDepthTextureUsage> for TextureUsages {
+    fn from(value: Camera3dDepthTextureUsage) -> Self {
+        Self::from_bits_truncate(value.0)
+    }
 }
 
 /// The depth clear operation to perform for the main 3d pass.

crates/bevy_core_pipeline/src/core_3d/mod.rs

@@ -257,7 +257,7 @@ pub fn prepare_core_3d_depth_textures(
     msaa: Res<Msaa>,
     render_device: Res<RenderDevice>,
     views_3d: Query<
-        (Entity, &ExtractedCamera, Option<&DepthPrepass>),
+        (Entity, &ExtractedCamera, Option<&DepthPrepass>, &Camera3d),
         (
             With<RenderPhase<Opaque3d>>,
             With<RenderPhase<AlphaMask3d>>,
@@ -266,7 +266,7 @@ pub fn prepare_core_3d_depth_textures(
     >,
 ) {
     let mut textures = HashMap::default();
-    for (entity, camera, depth_prepass) in &views_3d {
+    for (entity, camera, depth_prepass, camera_3d) in &views_3d {
         let Some(physical_target_size) = camera.physical_target_size else {
             continue;
         };
@@ -275,7 +275,7 @@ pub fn prepare_core_3d_depth_textures(
             .entry(camera.target.clone())
             .or_insert_with(|| {
                 // Default usage required to write to the depth texture
-                let mut usage = TextureUsages::RENDER_ATTACHMENT;
+                let mut usage = camera_3d.depth_texture_usages.into();
                 if depth_prepass.is_some() {
                     // Required to read the output of the prepass
                     usage |= TextureUsages::COPY_SRC;