Add "end of main pass post processing" render graph node (bevyengine#…

…6468)

# Objective

Bevy UI (and third party plugins) currently have no good way to position themselves after all post processing effects. They currently use the tonemapping node, but this is not adequate if there is anything after tonemapping (such as FXAA).

## Solution

Add a logical `END_MAIN_PASS_POST_PROCESSING` RenderGraph node that main pass post processing effects position themselves before, and things like UIs can position themselves after.

crates/bevy_core_pipeline/src/core_2d/mod.rs

@@ -10,6 +10,7 @@ pub mod graph {
         pub const MAIN_PASS: &str = "main_pass";
         pub const TONEMAPPING: &str = "tonemapping";
         pub const UPSCALING: &str = "upscaling";
+        pub const END_MAIN_PASS_POST_PROCESSING: &str = "end_main_pass_post_processing";
     }
 }
 
@@ -21,7 +22,7 @@ use bevy_ecs::prelude::*;
 use bevy_render::{
     camera::Camera,
     extract_component::ExtractComponentPlugin,
-    render_graph::{RenderGraph, SlotInfo, SlotType},
+    render_graph::{EmptyNode, RenderGraph, SlotInfo, SlotType},
     render_phase::{
         batch_phase_system, sort_phase_system, BatchedPhaseItem, CachedRenderPipelinePhaseItem,
         DrawFunctionId, DrawFunctions, EntityPhaseItem, PhaseItem, RenderPhase,
@@ -63,6 +64,7 @@ impl Plugin for Core2dPlugin {
         let mut draw_2d_graph = RenderGraph::default();
         draw_2d_graph.add_node(graph::node::MAIN_PASS, pass_node_2d);
         draw_2d_graph.add_node(graph::node::TONEMAPPING, tonemapping);
+        draw_2d_graph.add_node(graph::node::END_MAIN_PASS_POST_PROCESSING, EmptyNode);
         draw_2d_graph.add_node(graph::node::UPSCALING, upscaling);
         let input_node_id = draw_2d_graph.set_input(vec![SlotInfo::new(
             graph::input::VIEW_ENTITY,
@@ -96,7 +98,16 @@ impl Plugin for Core2dPlugin {
             .add_node_edge(graph::node::MAIN_PASS, graph::node::TONEMAPPING)
             .unwrap();
         draw_2d_graph
-            .add_node_edge(graph::node::TONEMAPPING, graph::node::UPSCALING)
+            .add_node_edge(
+                graph::node::TONEMAPPING,
+                graph::node::END_MAIN_PASS_POST_PROCESSING,
+            )
+            .unwrap();
+        draw_2d_graph
+            .add_node_edge(
+                graph::node::END_MAIN_PASS_POST_PROCESSING,
+                graph::node::UPSCALING,
+            )
             .unwrap();
         graph.add_sub_graph(graph::NAME, draw_2d_graph);
     }

crates/bevy_core_pipeline/src/core_3d/mod.rs

@@ -10,6 +10,7 @@ pub mod graph {
         pub const MAIN_PASS: &str = "main_pass";
         pub const TONEMAPPING: &str = "tonemapping";
         pub const UPSCALING: &str = "upscaling";
+        pub const END_MAIN_PASS_POST_PROCESSING: &str = "end_main_pass_post_processing";
     }
 }
 
@@ -24,7 +25,7 @@ use bevy_render::{
     camera::{Camera, ExtractedCamera},
     extract_component::ExtractComponentPlugin,
     prelude::Msaa,
-    render_graph::{RenderGraph, SlotInfo, SlotType},
+    render_graph::{EmptyNode, RenderGraph, SlotInfo, SlotType},
     render_phase::{
         sort_phase_system, CachedRenderPipelinePhaseItem, DrawFunctionId, DrawFunctions,
         EntityPhaseItem, PhaseItem, RenderPhase,
@@ -73,6 +74,7 @@ impl Plugin for Core3dPlugin {
         let mut draw_3d_graph = RenderGraph::default();
         draw_3d_graph.add_node(graph::node::MAIN_PASS, pass_node_3d);
         draw_3d_graph.add_node(graph::node::TONEMAPPING, tonemapping);
+        draw_3d_graph.add_node(graph::node::END_MAIN_PASS_POST_PROCESSING, EmptyNode);
         draw_3d_graph.add_node(graph::node::UPSCALING, upscaling);
         let input_node_id = draw_3d_graph.set_input(vec![SlotInfo::new(
             graph::input::VIEW_ENTITY,
@@ -106,7 +108,16 @@ impl Plugin for Core3dPlugin {
             .add_node_edge(graph::node::MAIN_PASS, graph::node::TONEMAPPING)
             .unwrap();
         draw_3d_graph
-            .add_node_edge(graph::node::TONEMAPPING, graph::node::UPSCALING)
+            .add_node_edge(
+                graph::node::TONEMAPPING,
+                graph::node::END_MAIN_PASS_POST_PROCESSING,
+            )
+            .unwrap();
+        draw_3d_graph
+            .add_node_edge(
+                graph::node::END_MAIN_PASS_POST_PROCESSING,
+                graph::node::UPSCALING,
+            )
             .unwrap();
         graph.add_sub_graph(graph::NAME, draw_3d_graph);
     }

crates/bevy_core_pipeline/src/fxaa/mod.rs

@@ -118,6 +118,12 @@ impl Plugin for FxaaPlugin {
             graph
                 .add_node_edge(core_3d::graph::node::TONEMAPPING, FXAA_NODE_3D)
                 .unwrap();
+            graph
+                .add_node_edge(
+                    FXAA_NODE_3D,
+                    core_3d::graph::node::END_MAIN_PASS_POST_PROCESSING,
+                )
+                .unwrap();
         }
         {
             let fxaa_node = FxaaNode::new(&mut render_app.world);
@@ -138,6 +144,12 @@ impl Plugin for FxaaPlugin {
             graph
                 .add_node_edge(core_2d::graph::node::TONEMAPPING, FXAA_NODE_2D)
                 .unwrap();
+            graph
+                .add_node_edge(
+                    FXAA_NODE_2D,
+                    core_2d::graph::node::END_MAIN_PASS_POST_PROCESSING,
+                )
+                .unwrap();
         }
     }
 }

crates/bevy_ui/src/render/mod.rs

@@ -117,7 +117,7 @@ pub fn build_ui_render(app: &mut App) {
             .unwrap();
         graph_2d
             .add_node_edge(
-                bevy_core_pipeline::core_2d::graph::node::TONEMAPPING,
+                bevy_core_pipeline::core_2d::graph::node::END_MAIN_PASS_POST_PROCESSING,
                 draw_ui_graph::node::UI_PASS,
             )
             .unwrap();
@@ -143,7 +143,7 @@ pub fn build_ui_render(app: &mut App) {
             .unwrap();
         graph_3d
             .add_node_edge(
-                bevy_core_pipeline::core_3d::graph::node::TONEMAPPING,
+                bevy_core_pipeline::core_3d::graph::node::END_MAIN_PASS_POST_PROCESSING,
                 draw_ui_graph::node::UI_PASS,
             )
             .unwrap();