Add ClearColor Resource to Pipelined Renderer (#2631)

# Objective

- Allow the user to set the clear color when using the pipelined renderer

## Solution

- Add a `ClearColor` resource that can be added to the world to configure the clear color

## Remaining Issues

Currently the `ClearColor` resource is cloned from the app world to the render world every frame. There are two ways I can think of around this:

1. Figure out why `app_world.is_resource_changed::<ClearColor>()` always returns `true` in the `extract` step and fix it so that we are only updating the resource when it changes
2. Require the users to add the `ClearColor` resource to the render sub-app instead of the parent app. This is currently sub-optimal until we have labled sub-apps, and probably a helper funciton on `App` such as `app.with_sub_app(RenderApp, |app| { ... })`. Even if we had that, I think it would be more than we want the user to have to think about. They shouldn't have to know about the render sub-app I don't think.

I think the first option is the best, but I could really use some help figuring out the nuance of why `is_resource_changed` is always returning true in that context.

Cargo.toml

@@ -493,6 +493,10 @@ path = "examples/ui/ui.rs"
 name = "clear_color"
 path = "examples/window/clear_color.rs"
 
+[[example]]
+name = "clear_color_pipelined"
+path = "examples/window/clear_color_pipelined.rs"
+
 [[example]]
 name = "multiple_windows"
 path = "examples/window/multiple_windows.rs"

examples/README.md

@@ -254,6 +254,7 @@ Example | File | Description
 Example | File | Description
 --- | --- | ---
 `clear_color` | [`window/clear_color.rs`](./window/clear_color.rs) | Creates a solid color window
+`clear_color_pipelined` | [`window/clear_color_pipelined.rs`](./window/clear_color_pipelined.rs) | Creates a solid color window with the pipelined renderer
 `multiple_windows` | [`window/multiple_windows.rs`](./window/multiple_windows.rs) | Creates two windows and cameras viewing the same mesh
 `scale_factor_override` | [`window/scale_factor_override.rs`](./window/scale_factor_override.rs) | Illustrates how to customize the default window settings
 `window_settings` | [`window/window_settings.rs`](./window/window_settings.rs) | Demonstrates customizing default window settings

examples/window/clear_color_pipelined.rs

@@ -0,0 +1,25 @@
+use bevy::{
+    core_pipeline::ClearColor,
+    prelude::*,
+    render2::{camera::OrthographicCameraBundle, color::Color},
+    PipelinedDefaultPlugins,
+};
+
+fn main() {
+    App::new()
+        .insert_resource(ClearColor(Color::rgb(0.5, 0.5, 0.9)))
+        .add_plugins(PipelinedDefaultPlugins)
+        .add_startup_system(setup)
+        .add_system(change_clear_color)
+        .run();
+}
+
+fn setup(mut commands: Commands) {
+    commands.spawn_bundle(OrthographicCameraBundle::new_2d());
+}
+
+fn change_clear_color(input: Res<Input<KeyCode>>, mut clear_color: ResMut<ClearColor>) {
+    if input.just_pressed(KeyCode::Space) {
+        clear_color.0 = Color::PURPLE;
+    }
+}

pipelined/bevy_core_pipeline/src/lib.rs

@@ -10,6 +10,7 @@ use bevy_app::{App, Plugin};
 use bevy_ecs::prelude::*;
 use bevy_render2::{
     camera::{ActiveCameras, CameraPlugin},
+    color::Color,
     render_graph::{EmptyNode, RenderGraph, SlotInfo, SlotType},
     render_phase::{sort_phase_system, RenderPhase},
     render_resource::{
@@ -19,9 +20,19 @@ use bevy_render2::{
     renderer::RenderDevice,
     texture::TextureCache,
     view::{ExtractedView, ViewPlugin},
-    RenderStage,
+    RenderStage, RenderWorld,
 };
 
+/// Resource that configures the clear color
+#[derive(Clone, Debug)]
+pub struct ClearColor(pub Color);
+
+impl Default for ClearColor {
+    fn default() -> Self {
+        Self(Color::rgb(0.4, 0.4, 0.4))
+    }
+}
+
 // Plugins that contribute to the RenderGraph should use the following label conventions:
 // 1. Graph modules should have a NAME, input module, and node module (where relevant)
 // 2. The "top level" graph is the plugin module root. Just add things like `pub mod node` directly under the plugin module
@@ -61,8 +72,11 @@ pub struct CorePipelinePlugin;
 
 impl Plugin for CorePipelinePlugin {
     fn build(&self, app: &mut App) {
+        app.init_resource::<ClearColor>();
+
         let render_app = app.sub_app_mut(0);
         render_app
+            .add_system_to_stage(RenderStage::Extract, extract_clear_color)
             .add_system_to_stage(RenderStage::Extract, extract_core_pipeline_camera_phases)
             .add_system_to_stage(RenderStage::Prepare, prepare_core_views_system)
             .add_system_to_stage(
@@ -154,6 +168,14 @@ pub struct ViewDepthTexture {
     pub view: TextureView,
 }
 
+pub fn extract_clear_color(clear_color: Res<ClearColor>, mut render_world: ResMut<RenderWorld>) {
+    // If the clear color has changed
+    if clear_color.is_changed() {
+        // Update the clear color resource in the render world
+        render_world.insert_resource(clear_color.clone())
+    }
+}
+
 pub fn extract_core_pipeline_camera_phases(
     mut commands: Commands,
     active_cameras: Res<ActiveCameras>,

pipelined/bevy_core_pipeline/src/main_pass_2d.rs

@@ -1,7 +1,6 @@
-use crate::Transparent2dPhase;
+use crate::{ClearColor, Transparent2dPhase};
 use bevy_ecs::prelude::*;
 use bevy_render2::{
-    color::Color,
     render_graph::{Node, NodeRunError, RenderGraphContext, SlotInfo, SlotType},
     render_phase::{DrawFunctions, RenderPhase, TrackedRenderPass},
     render_resource::{LoadOp, Operations, RenderPassColorAttachment, RenderPassDescriptor},
@@ -43,13 +42,14 @@ impl Node for MainPass2dNode {
         world: &World,
     ) -> Result<(), NodeRunError> {
         let color_attachment_texture = graph.get_input_texture(Self::IN_COLOR_ATTACHMENT)?;
+        let clear_color = world.get_resource::<ClearColor>().unwrap();
         let pass_descriptor = RenderPassDescriptor {
             label: Some("main_pass_2d"),
             color_attachments: &[RenderPassColorAttachment {
                 view: color_attachment_texture,
                 resolve_target: None,
                 ops: Operations {
-                    load: LoadOp::Clear(Color::rgb(0.4, 0.4, 0.4).into()),
+                    load: LoadOp::Clear(clear_color.0.into()),
                     store: true,
                 },
             }],

pipelined/bevy_core_pipeline/src/main_pass_3d.rs

@@ -1,7 +1,6 @@
-use crate::Transparent3dPhase;
+use crate::{ClearColor, Transparent3dPhase};
 use bevy_ecs::prelude::*;
 use bevy_render2::{
-    color::Color,
     render_graph::{Node, NodeRunError, RenderGraphContext, SlotInfo, SlotType},
     render_phase::{DrawFunctions, RenderPhase, TrackedRenderPass},
     render_resource::{
@@ -48,14 +47,15 @@ impl Node for MainPass3dNode {
         world: &World,
     ) -> Result<(), NodeRunError> {
         let color_attachment_texture = graph.get_input_texture(Self::IN_COLOR_ATTACHMENT)?;
+        let clear_color = world.get_resource::<ClearColor>().unwrap();
         let depth_texture = graph.get_input_texture(Self::IN_DEPTH)?;
         let pass_descriptor = RenderPassDescriptor {
             label: Some("main_pass_3d"),
             color_attachments: &[RenderPassColorAttachment {
                 view: color_attachment_texture,
                 resolve_target: None,
                 ops: Operations {
-                    load: LoadOp::Clear(Color::rgb(0.4, 0.4, 0.4).into()),
+                    load: LoadOp::Clear(clear_color.0.into()),
                     store: true,
                 },
             }],