use ViewNodeRunner in the post_processing example (#9127)

# Objective

- I forgot to update the example after the `ViewNodeRunner` was merged.
It was even partially mentioned in one of the comments.

## Solution

- Use the `ViewNodeRunner` in the post_processing example
- I also broke up a few lines that were a bit long

---------

Co-authored-by: JMS55 <47158642+JMS55@users.noreply.github.com>

examples/shader/post_processing.rs

@@ -16,7 +16,7 @@ use bevy::{
         extract_component::{
             ComponentUniforms, ExtractComponent, ExtractComponentPlugin, UniformComponentPlugin,
         },
-        render_graph::{Node, NodeRunError, RenderGraphApp, RenderGraphContext},
+        render_graph::{NodeRunError, RenderGraphApp, RenderGraphContext},
         render_resource::{
             BindGroupDescriptor, BindGroupEntry, BindGroupLayout, BindGroupLayoutDescriptor,
             BindGroupLayoutEntry, BindingResource, BindingType, CachedRenderPipelineId,
@@ -27,11 +27,15 @@ use bevy::{
         },
         renderer::{RenderContext, RenderDevice},
         texture::BevyDefault,
-        view::{ExtractedView, ViewTarget},
+        view::ViewTarget,
         RenderApp,
     },
     utils::Duration,
 };
+use bevy_internal::{
+    ecs::query::QueryItem,
+    render::render_graph::{ViewNode, ViewNodeRunner},
+};
 
 fn main() {
     App::new()
@@ -83,7 +87,10 @@ impl Plugin for PostProcessPlugin {
             // you need to extract it manually or with the plugin like above.
             // Add a [`Node`] to the [`RenderGraph`]
             // The Node needs to impl FromWorld
-            .add_render_graph_node::<PostProcessNode>(
+            //
+            // The [`ViewNodeRunner`] is a special [`Node`] that will automatically run the node for each view
+            // matching the [`ViewQuery`]
+            .add_render_graph_node::<ViewNodeRunner<PostProcessNode>>(
                 // Specify the name of the graph, in this case we want the graph for 3d
                 core_3d::graph::NAME,
                 // It also needs the name of the node
@@ -113,60 +120,42 @@ impl Plugin for PostProcessPlugin {
     }
 }
 
-/// The post process node used for the render graph
-struct PostProcessNode {
-    // The node needs a query to gather data from the ECS in order to do its rendering,
-    // but it's not a normal system so we need to define it manually.
-    query: QueryState<&'static ViewTarget, With<ExtractedView>>,
-}
-
+// The post process node used for the render graph
+#[derive(Default)]
+struct PostProcessNode;
 impl PostProcessNode {
     pub const NAME: &str = "post_process";
 }
 
-impl FromWorld for PostProcessNode {
-    fn from_world(world: &mut World) -> Self {
-        Self {
-            query: QueryState::new(world),
-        }
-    }
-}
-
-impl Node for PostProcessNode {
-    // This will run every frame before the run() method
-    // The important difference is that `self` is `mut` here
-    fn update(&mut self, world: &mut World) {
-        // Since this is not a system we need to update the query manually.
-        // This is mostly boilerplate. There are plans to remove this in the future.
-        // For now, you can just copy it.
-        self.query.update_archetypes(world);
-    }
+// The ViewNode trait is required by the ViewNodeRunner
+impl ViewNode for PostProcessNode {
+    // The node needs a query to gather data from the ECS in order to do its rendering,
+    // but it's not a normal system so we need to define it manually.
+    //
+    // This query will only run on the view entity
+    type ViewQuery = &'static ViewTarget;
 
     // Runs the node logic
     // This is where you encode draw commands.
     //
-    // This will run on every view on which the graph is running. If you don't want your effect to run on every camera,
-    // you'll need to make sure you have a marker component to identify which camera(s) should run the effect.
+    // This will run on every view on which the graph is running.
+    // If you don't want your effect to run on every camera,
+    // you'll need to make sure you have a marker component as part of [`ViewQuery`]
+    // to identify which camera(s) should run the effect.
     fn run(
         &self,
-        graph_context: &mut RenderGraphContext,
+        _graph: &mut RenderGraphContext,
         render_context: &mut RenderContext,
+        view_target: QueryItem<Self::ViewQuery>,
         world: &World,
     ) -> Result<(), NodeRunError> {
-        // Get the entity of the view for the render graph where this node is running
-        let view_entity = graph_context.view_entity();
-
-        // We get the data we need from the world based on the view entity passed to the node.
-        // The data is the query that was defined earlier in the [`PostProcessNode`]
-        let Ok(view_target) = self.query.get_manual(world, view_entity) else {
-            return Ok(());
-        };
-
-        // Get the pipeline resource that contains the global data we need to create the render pipeline
+        // Get the pipeline resource that contains the global data we need
+        // to create the render pipeline
         let post_process_pipeline = world.resource::<PostProcessPipeline>();
 
         // The pipeline cache is a cache of all previously created pipelines.
-        // It is required to avoid creating a new pipeline each frame, which is expensive due to shader compilation.
+        // It is required to avoid creating a new pipeline each frame,
+        // which is expensive due to shader compilation.
         let pipeline_cache = world.resource::<PipelineCache>();
 
         // Get the pipeline from the cache
@@ -191,9 +180,11 @@ impl Node for PostProcessNode {
 
         // The bind_group gets created each frame.
         //
-        // Normally, you would create a bind_group in the Queue set, but this doesn't work with the post_process_write().
+        // Normally, you would create a bind_group in the Queue set,
+        // but this doesn't work with the post_process_write().
         // The reason it doesn't work is because each post_process_write will alternate the source/destination.
-        // The only way to have the correct source/destination for the bind_group is to make sure you get it during the node execution.
+        // The only way to have the correct source/destination for the bind_group
+        // is to make sure you get it during the node execution.
         let bind_group = render_context
             .render_device()
             .create_bind_group(&BindGroupDescriptor {
@@ -407,7 +398,8 @@ fn update_settings(mut settings: Query<&mut PostProcessSettings>, time: Res<Time
         // Scale it to a more reasonable level
         intensity *= 0.015;
 
-        // Set the intensity. This will then be extracted to the render world and uploaded to the gpu automatically.
+        // Set the intensity.
+        // This will then be extracted to the render world and uploaded to the gpu automatically by the [`UniformComponentPlugin`]
         setting.intensity = intensity;
     }
 }