render: add ClearColor resource

Cargo.toml

@@ -187,6 +187,10 @@ path = "examples/ui/ui.rs"
 name = "ui_bench"
 path = "examples/ui/ui_bench.rs"
 
+[[example]]
+name = "clear_color"
+path = "examples/window/clear_color.rs"
+
 [[example]]
 name = "multiple_windows"
 path = "examples/window/multiple_windows.rs"

crates/bevy_render/src/base_render_graph/mod.rs

@@ -114,6 +114,8 @@ impl BaseRenderGraphBuilder for RenderGraph {
                 sample_count: 1,
             });
 
+            main_pass_node.use_default_clear_color(0);
+
             if config.add_3d_camera {
                 main_pass_node.add_camera(camera::CAMERA);
             }

crates/bevy_render/src/pass/pass.rs

@@ -18,6 +18,28 @@ impl TextureAttachment {
     }
 }
 
+#[derive(Clone, Debug)]
+pub struct ClearColor {
+    pub color: Color,
+}
+
+impl ClearColor {
+    pub fn new(color: Color) -> Self {
+        ClearColor {
+            color,
+        }
+    }
+}
+
+impl Default for ClearColor {
+    fn default() -> Self {
+        Self {
+            color: Color::rgb(0.1, 0.1, 0.1),
+        }
+    }
+    
+}
+
 #[derive(Debug, Clone)]
 pub struct RenderPassColorAttachmentDescriptor {
     /// The actual color attachment.

crates/bevy_render/src/render_graph/nodes/pass_node.rs

@@ -1,6 +1,6 @@
 use crate::{
     draw::{Draw, RenderCommand},
-    pass::{PassDescriptor, TextureAttachment},
+    pass::{PassDescriptor, TextureAttachment, ClearColor},
     pipeline::PipelineDescriptor,
     render_graph::{Node, ResourceSlotInfo, ResourceSlots},
     render_resource::{BindGroupId, BufferId, RenderResourceBindings, RenderResourceType},
@@ -15,6 +15,7 @@ pub struct PassNode {
     cameras: Vec<String>,
     color_attachment_input_indices: Vec<Option<usize>>,
     depth_stencil_attachment_input_index: Option<usize>,
+    default_clear_color_inputs: Vec<usize>,
 }
 
 impl PassNode {
@@ -50,12 +51,17 @@ impl PassNode {
             cameras: Vec::new(),
             color_attachment_input_indices,
             depth_stencil_attachment_input_index,
+            default_clear_color_inputs: Vec::new(),
         }
     }
 
     pub fn add_camera(&mut self, camera_name: &str) {
         self.cameras.push(camera_name.to_string());
     }
+
+    pub fn use_default_clear_color(&mut self, color_attachment_index: usize) {
+        self.default_clear_color_inputs.push(color_attachment_index);
+    }
 }
 
 impl Node for PassNode {
@@ -76,6 +82,11 @@ impl Node for PassNode {
         let active_cameras= resources.get::<ActiveCameras>().unwrap();
 
         for (i, color_attachment) in self.descriptor.color_attachments.iter_mut().enumerate() {
+            if self.default_clear_color_inputs.contains(&i) {
+                if let Some(default_clear_color) = resources.get::<ClearColor>() {
+                    color_attachment.clear_color = default_clear_color.color; 
+                }
+            }
             if let Some(input_index) = self.color_attachment_input_indices[i] {
                 color_attachment.attachment =
                     TextureAttachment::Id(input.get(input_index).unwrap().get_texture().unwrap());

examples/window/clear_color.rs

@@ -0,0 +1,8 @@
+use bevy::prelude::*;
+
+fn main() {
+    App::build()
+        .add_resource(ClearColor::new(Color::rgb(0.2, 0.2, 0.8)))
+        .add_default_plugins()
+        .run();
+}

src/prelude.rs

@@ -17,6 +17,7 @@ pub use crate::{
         draw::Draw,
         entity::*,
         mesh::{shape, Mesh},
+        pass::ClearColor,
         pipeline::{PipelineDescriptor, RenderPipelines},
         render_graph::{
             nodes::{