Shaders / Post Processing - Custom Render Pass

Back to examples View in GitHub

Support Warning

WebGPU is currently only supported on Chrome starting with version 113, and only on desktop. If they don't work on your configuration, you can check the WebGL2 examples here.
Support for WebGPU in Bevy hasn't been released yet, this example has been compiled using the main branch.

//! This example shows how to create a custom render pass that runs after the main pass
//! and reads the texture generated by the main pass.
//! The example shader is a very simple implementation of chromatic aberration.
//! This is a fairly low level example and assumes some familiarity with rendering concepts and wgpu.

use bevy::{
        clear_color::ClearColorConfig, core_3d,
            ComponentUniforms, ExtractComponent, ExtractComponentPlugin, UniformComponentPlugin,
        render_graph::{Node, NodeRunError, RenderGraphApp, RenderGraphContext},
            BindGroupDescriptor, BindGroupEntry, BindGroupLayout, BindGroupLayoutDescriptor,
            BindGroupLayoutEntry, BindingResource, BindingType, CachedRenderPipelineId,
            ColorTargetState, ColorWrites, FragmentState, MultisampleState, Operations,
            PipelineCache, PrimitiveState, RenderPassColorAttachment, RenderPassDescriptor,
            RenderPipelineDescriptor, Sampler, SamplerBindingType, SamplerDescriptor, ShaderStages,
            ShaderType, TextureFormat, TextureSampleType, TextureViewDimension,
        renderer::{RenderContext, RenderDevice},
        view::{ExtractedView, ViewTarget},

fn main() {
        .add_plugins(DefaultPlugins.set(AssetPlugin {
            // Hot reloading the shader works correctly
            watch_for_changes: ChangeWatcher::with_delay(Duration::from_millis(200)),
        .add_systems(Startup, setup)
        .add_systems(Update, (rotate, update_settings))

/// It is generally encouraged to set up post processing effects as a plugin
struct PostProcessPlugin;

impl Plugin for PostProcessPlugin {
    fn build(&self, app: &mut App) {
            // The settings will be a component that lives in the main world but will
            // be extracted to the render world every frame.
            // This makes it possible to control the effect from the main world.
            // This plugin will take care of extracting it automatically.
            // It's important to derive [`ExtractComponent`] on [`PostProcessingSettings`]
            // for this plugin to work correctly.
            // The settings will also be the data used in the shader.
            // This plugin will prepare the component for the GPU by creating a uniform buffer
            // and writing the data to that buffer every frame.

        // We need to get the render app from the main app
        let Ok(render_app) = app.get_sub_app_mut(RenderApp) else {

            // Bevy's renderer uses a render graph which is a collection of nodes in a directed acyclic graph.
            // It currently runs on each view/camera and executes each node in the specified order.
            // It will make sure that any node that needs a dependency from another node
            // only runs when that dependency is done.
            // Each node can execute arbitrary work, but it generally runs at least one render pass.
            // A node only has access to the render world, so if you need data from the main world
            // you need to extract it manually or with the plugin like above.
            // Add a [`Node`] to the [`RenderGraph`]
            // The Node needs to impl FromWorld
                // Specifiy the name of the graph, in this case we want the graph for 3d
                // It also needs the name of the node
                // Specify the node ordering.
                // This will automatically create all required node edges to enforce the given ordering.

    fn finish(&self, app: &mut App) {
        // We need to get the render app from the main app
        let Ok(render_app) = app.get_sub_app_mut(RenderApp) else {

            // Initialize the pipeline

/// 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>>,

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.

    // 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.
    fn run(
        graph_context: &mut RenderGraphContext,
        render_context: &mut RenderContext,
        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
        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.
        let pipeline_cache = world.resource::<PipelineCache>();

        // Get the pipeline from the cache
        let Some(pipeline) = pipeline_cache.get_render_pipeline(post_process_pipeline.pipeline_id) else {
            return Ok(());

        // Get the settings uniform binding
        let settings_uniforms = world.resource::<ComponentUniforms<PostProcessSettings>>();
        let Some(settings_binding) = settings_uniforms.uniforms().binding() else {
            return Ok(());

        // This will start a new "post process write", obtaining two texture
        // views from the view target - a `source` and a `destination`.
        // `source` is the "current" main texture and you _must_ write into
        // `destination` because calling `post_process_write()` on the
        // [`ViewTarget`] will internally flip the [`ViewTarget`]'s main
        // texture to the `destination` texture. Failing to do so will cause
        // the current main texture information to be lost.
        let post_process = view_target.post_process_write();

        // 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().
        // 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.
        let bind_group = render_context
            .create_bind_group(&BindGroupDescriptor {
                label: Some("post_process_bind_group"),
                layout: &post_process_pipeline.layout,
                // It's important for this to match the BindGroupLayout defined in the PostProcessPipeline
                entries: &[
                    BindGroupEntry {
                        binding: 0,
                        // Make sure to use the source view
                        resource: BindingResource::TextureView(post_process.source),
                    BindGroupEntry {
                        binding: 1,
                        // Use the sampler created for the pipeline
                        resource: BindingResource::Sampler(&post_process_pipeline.sampler),
                    BindGroupEntry {
                        binding: 2,
                        // Set the settings binding
                        resource: settings_binding.clone(),

        // Begin the render pass
        let mut render_pass = render_context.begin_tracked_render_pass(RenderPassDescriptor {
            label: Some("post_process_pass"),
            color_attachments: &[Some(RenderPassColorAttachment {
                // We need to specify the post process destination view here
                // to make sure we write to the appropriate texture.
                view: post_process.destination,
                resolve_target: None,
                ops: Operations::default(),
            depth_stencil_attachment: None,

        // This is mostly just wgpu boilerplate for drawing a fullscreen triangle,
        // using the pipeline/bind_group created above
        render_pass.set_bind_group(0, &bind_group, &[]);
        render_pass.draw(0..3, 0..1);


// This contains global data used by the render pipeline. This will be created once on startup.
struct PostProcessPipeline {
    layout: BindGroupLayout,
    sampler: Sampler,
    pipeline_id: CachedRenderPipelineId,

impl FromWorld for PostProcessPipeline {
    fn from_world(world: &mut World) -> Self {
        let render_device = world.resource::<RenderDevice>();

        // We need to define the bind group layout used for our pipeline
        let layout = render_device.create_bind_group_layout(&BindGroupLayoutDescriptor {
            label: Some("post_process_bind_group_layout"),
            entries: &[
                // The screen texture
                BindGroupLayoutEntry {
                    binding: 0,
                    visibility: ShaderStages::FRAGMENT,
                    ty: BindingType::Texture {
                        sample_type: TextureSampleType::Float { filterable: true },
                        view_dimension: TextureViewDimension::D2,
                        multisampled: false,
                    count: None,
                // The sampler that will be used to sample the screen texture
                BindGroupLayoutEntry {
                    binding: 1,
                    visibility: ShaderStages::FRAGMENT,
                    ty: BindingType::Sampler(SamplerBindingType::Filtering),
                    count: None,
                // The settings uniform that will control the effect
                BindGroupLayoutEntry {
                    binding: 2,
                    visibility: ShaderStages::FRAGMENT,
                    ty: BindingType::Buffer {
                        ty: bevy::render::render_resource::BufferBindingType::Uniform,
                        has_dynamic_offset: false,
                        min_binding_size: None,
                    count: None,

        // We can create the sampler here since it won't change at runtime and doesn't depend on the view
        let sampler = render_device.create_sampler(&SamplerDescriptor::default());

        // Get the shader handle
        let shader = world

        let pipeline_id = world
            // This will add the pipeline to the cache and queue it's creation
            .queue_render_pipeline(RenderPipelineDescriptor {
                label: Some("post_process_pipeline".into()),
                layout: vec![layout.clone()],
                // This will setup a fullscreen triangle for the vertex state
                vertex: fullscreen_shader_vertex_state(),
                fragment: Some(FragmentState {
                    shader_defs: vec![],
                    // Make sure this matches the entry point of your shader.
                    // It can be anything as long as it matches here and in the shader.
                    entry_point: "fragment".into(),
                    targets: vec![Some(ColorTargetState {
                        format: TextureFormat::bevy_default(),
                        blend: None,
                        write_mask: ColorWrites::ALL,
                // All of the following property are not important for this effect so just use the default values.
                // This struct doesn't have the Default trai implemented because not all field can have a default value.
                primitive: PrimitiveState::default(),
                depth_stencil: None,
                multisample: MultisampleState::default(),
                push_constant_ranges: vec![],

        Self {

// This is the component that will get passed to the shader
#[derive(Component, Default, Clone, Copy, ExtractComponent, ShaderType)]
struct PostProcessSettings {
    intensity: f32,

/// Set up a simple 3D scene
fn setup(
    mut commands: Commands,
    mut meshes: ResMut<Assets<Mesh>>,
    mut materials: ResMut<Assets<StandardMaterial>>,
) {
    // camera
        Camera3dBundle {
            transform: Transform::from_translation(Vec3::new(0.0, 0.0, 5.0))
                .looking_at(Vec3::default(), Vec3::Y),
            camera_3d: Camera3d {
                clear_color: ClearColorConfig::Custom(Color::WHITE),
        // Add the setting to the camera.
        // This component is also used to determine on which camera to run the post processing effect.
        PostProcessSettings { intensity: 0.02 },

    // cube
        PbrBundle {
            mesh: meshes.add(Mesh::from(shape::Cube { size: 1.0 })),
            material: materials.add(Color::rgb(0.8, 0.7, 0.6).into()),
            transform: Transform::from_xyz(0.0, 0.5, 0.0),
    // light
    commands.spawn(PointLightBundle {
        transform: Transform::from_translation(Vec3::new(0.0, 0.0, 10.0)),

struct Rotates;

/// Rotates any entity around the x and y axis
fn rotate(time: Res<Time>, mut query: Query<&mut Transform, With<Rotates>>) {
    for mut transform in &mut query {
        transform.rotate_x(0.55 * time.delta_seconds());
        transform.rotate_z(0.15 * time.delta_seconds());

// Change the intensity over time to show that the effect is controlled from the main world
fn update_settings(mut settings: Query<&mut PostProcessSettings>, time: Res<Time>) {
    for mut setting in &mut settings {
        let mut intensity = time.elapsed_seconds().sin();
        // Make it loop periodically
        intensity = intensity.sin();
        // Remap it to 0..1 because the intensity can't be negative
        intensity = intensity * 0.5 + 0.5;
        // 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.
        setting.intensity = intensity;