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.custom_post_processing.rs:
//! 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.
//! To adapt this example for 2D, replace all instances of 3D structures (such as `Core3D`, etc.) with their corresponding 2D counterparts.
//!
//! This is a fairly low level example and assumes some familiarity with rendering concepts and wgpu.
use bevy::{
core_pipeline::{
core_3d::graph::{Core3d, Node3d},
fullscreen_vertex_shader::fullscreen_shader_vertex_state,
},
ecs::query::QueryItem,
prelude::*,
render::{
extract_component::{
ComponentUniforms, DynamicUniformIndex, ExtractComponent, ExtractComponentPlugin,
UniformComponentPlugin,
},
render_graph::{
NodeRunError, RenderGraphApp, RenderGraphContext, RenderLabel, ViewNode, ViewNodeRunner,
},
render_resource::{
binding_types::{sampler, texture_2d, uniform_buffer},
*,
},
renderer::{RenderContext, RenderDevice},
view::ViewTarget,
RenderApp,
},
};
/// This example uses a shader source file from the assets subdirectory
const SHADER_ASSET_PATH: &str = "shaders/post_processing.wgsl";
fn main() {
App::new()
.add_plugins((DefaultPlugins, PostProcessPlugin))
.add_systems(Startup, setup)
.add_systems(Update, (rotate, update_settings))
.run();
}
/// 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) {
app.add_plugins((
// 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.
ExtractComponentPlugin::<PostProcessSettings>::default(),
// 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.
UniformComponentPlugin::<PostProcessSettings>::default(),
));
// We need to get the render app from the main app
let Some(render_app) = app.get_sub_app_mut(RenderApp) else {
return;
};
render_app
// 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
//
// 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 label of the graph, in this case we want the graph for 3d
Core3d,
// It also needs the label of the node
PostProcessLabel,
)
.add_render_graph_edges(
Core3d,
// Specify the node ordering.
// This will automatically create all required node edges to enforce the given ordering.
(
Node3d::Tonemapping,
PostProcessLabel,
Node3d::EndMainPassPostProcessing,
),
);
}
fn finish(&self, app: &mut App) {
// We need to get the render app from the main app
let Some(render_app) = app.get_sub_app_mut(RenderApp) else {
return;
};
render_app
// Initialize the pipeline
.init_resource::<PostProcessPipeline>();
}
}
#[derive(Debug, Hash, PartialEq, Eq, Clone, RenderLabel)]
struct PostProcessLabel;
// The post process node used for the render graph
#[derive(Default)]
struct PostProcessNode;
// 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,
// This makes sure the node only runs on cameras with the PostProcessSettings component
&'static PostProcessSettings,
// As there could be multiple post processing components sent to the GPU (one per camera),
// we need to get the index of the one that is associated with the current view.
&'static DynamicUniformIndex<PostProcessSettings>,
);
// 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 as part of [`ViewQuery`]
// to identify which camera(s) should run the effect.
fn run(
&self,
_graph: &mut RenderGraphContext,
render_context: &mut RenderContext,
(view_target, _post_process_settings, settings_index): QueryItem<Self::ViewQuery>,
world: &World,
) -> Result<(), NodeRunError> {
// 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.render_device().create_bind_group(
"post_process_bind_group",
&post_process_pipeline.layout,
// It's important for this to match the BindGroupLayout defined in the PostProcessPipeline
&BindGroupEntries::sequential((
// Make sure to use the source view
post_process.source,
// Use the sampler created for the pipeline
&post_process_pipeline.sampler,
// Set the settings binding
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,
timestamp_writes: None,
occlusion_query_set: None,
});
// This is mostly just wgpu boilerplate for drawing a fullscreen triangle,
// using the pipeline/bind_group created above
render_pass.set_render_pipeline(pipeline);
// By passing in the index of the post process settings on this view, we ensure
// that in the event that multiple settings were sent to the GPU (as would be the
// case with multiple cameras), we use the correct one.
render_pass.set_bind_group(0, &bind_group, &[settings_index.index()]);
render_pass.draw(0..3, 0..1);
Ok(())
}
}
// This contains global data used by the render pipeline. This will be created once on startup.
#[derive(Resource)]
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(
"post_process_bind_group_layout",
&BindGroupLayoutEntries::sequential(
// The layout entries will only be visible in the fragment stage
ShaderStages::FRAGMENT,
(
// The screen texture
texture_2d(TextureSampleType::Float { filterable: true }),
// The sampler that will be used to sample the screen texture
sampler(SamplerBindingType::Filtering),
// The settings uniform that will control the effect
uniform_buffer::<PostProcessSettings>(true),
),
),
);
// 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.load_asset(SHADER_ASSET_PATH);
let pipeline_id = world
.resource_mut::<PipelineCache>()
// This will add the pipeline to the cache and queue its 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,
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 properties are not important for this effect so just use the default values.
// This struct doesn't have the Default trait implemented because not all fields can have a default value.
primitive: PrimitiveState::default(),
depth_stencil: None,
multisample: MultisampleState::default(),
push_constant_ranges: vec![],
zero_initialize_workgroup_memory: false,
});
Self {
layout,
sampler,
pipeline_id,
}
}
}
// This is the component that will get passed to the shader
#[derive(Component, Default, Clone, Copy, ExtractComponent, ShaderType)]
struct PostProcessSettings {
intensity: f32,
// WebGL2 structs must be 16 byte aligned.
#[cfg(feature = "webgl2")]
_webgl2_padding: Vec3,
}
/// Set up a simple 3D scene
fn setup(
mut commands: Commands,
mut meshes: ResMut<Assets<Mesh>>,
mut materials: ResMut<Assets<StandardMaterial>>,
) {
// camera
commands.spawn((
Camera3d::default(),
Transform::from_translation(Vec3::new(0.0, 0.0, 5.0)).looking_at(Vec3::default(), Vec3::Y),
Camera {
clear_color: Color::WHITE.into(),
..default()
},
// 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,
..default()
},
));
// cube
commands.spawn((
Mesh3d(meshes.add(Cuboid::default())),
MeshMaterial3d(materials.add(Color::srgb(0.8, 0.7, 0.6))),
Transform::from_xyz(0.0, 0.5, 0.0),
Rotates,
));
// light
commands.spawn(DirectionalLight {
illuminance: 1_000.,
..default()
});
}
#[derive(Component)]
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_secs());
transform.rotate_z(0.15 * time.delta_secs());
}
}
// 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 = ops::sin(time.elapsed_secs());
// Make it loop periodically
intensity = ops::sin(intensity);
// 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 by the [`UniformComponentPlugin`]
setting.intensity = intensity;
}
}
shaders/post_processing.wgsl:
// This shader computes the chromatic aberration effect
// Since post processing is a fullscreen effect, we use the fullscreen vertex shader provided by bevy.
// This will import a vertex shader that renders a single fullscreen triangle.
//
// A fullscreen triangle is a single triangle that covers the entire screen.
// The box in the top left in that diagram is the screen. The 4 x are the corner of the screen
//
// Y axis
// 1 | x-----x......
// 0 | | s | . ´
// -1 | x_____x´
// -2 | : .´
// -3 | :´
// +--------------- X axis
// -1 0 1 2 3
//
// As you can see, the triangle ends up bigger than the screen.
//
// You don't need to worry about this too much since bevy will compute the correct UVs for you.
#import bevy_core_pipeline::fullscreen_vertex_shader::FullscreenVertexOutput
@group(0) @binding(0) var screen_texture: texture_2d<f32>;
@group(0) @binding(1) var texture_sampler: sampler;
struct PostProcessSettings {
intensity: f32,
#ifdef SIXTEEN_BYTE_ALIGNMENT
// WebGL2 structs must be 16 byte aligned.
_webgl2_padding: vec3<f32>
#endif
}
@group(0) @binding(2) var<uniform> settings: PostProcessSettings;
@fragment
fn fragment(in: FullscreenVertexOutput) -> @location(0) vec4<f32> {
// Chromatic aberration strength
let offset_strength = settings.intensity;
// Sample each color channel with an arbitrary shift
return vec4<f32>(
textureSample(screen_texture, texture_sampler, in.uv + vec2<f32>(offset_strength, -offset_strength)).r,
textureSample(screen_texture, texture_sampler, in.uv + vec2<f32>(-offset_strength, 0.0)).g,
textureSample(screen_texture, texture_sampler, in.uv + vec2<f32>(0.0, offset_strength)).b,
1.0
);
}