bevy_post_process/motion_blur/
mod.rs

1//! Per-object, per-pixel motion blur.
2//!
3//! Add the [`MotionBlur`] component to a camera to enable motion blur.
4
5use bevy_app::{App, Plugin};
6use bevy_asset::embedded_asset;
7use bevy_camera::Camera;
8use bevy_core_pipeline::{
9    core_3d::graph::{Core3d, Node3d},
10    prepass::{DepthPrepass, MotionVectorPrepass},
11};
12use bevy_ecs::{
13    component::Component,
14    query::{QueryItem, With},
15    reflect::ReflectComponent,
16    schedule::IntoScheduleConfigs,
17};
18use bevy_reflect::{std_traits::ReflectDefault, Reflect};
19use bevy_render::{
20    extract_component::{ExtractComponent, ExtractComponentPlugin, UniformComponentPlugin},
21    render_graph::{RenderGraphExt, ViewNodeRunner},
22    render_resource::{ShaderType, SpecializedRenderPipelines},
23    Render, RenderApp, RenderStartup, RenderSystems,
24};
25
26pub mod node;
27pub mod pipeline;
28
29/// A component that enables and configures motion blur when added to a camera.
30///
31/// Motion blur is an effect that simulates how moving objects blur as they change position during
32/// the exposure of film, a sensor, or an eyeball.
33///
34/// Because rendering simulates discrete steps in time, we use per-pixel motion vectors to estimate
35/// the path of objects between frames. This kind of implementation has some artifacts:
36/// - Fast moving objects in front of a stationary object or when in front of empty space, will not
37///   have their edges blurred.
38/// - Transparent objects do not write to depth or motion vectors, so they cannot be blurred.
39///
40/// Other approaches, such as *A Reconstruction Filter for Plausible Motion Blur* produce more
41/// correct results, but are more expensive and complex, and have other kinds of artifacts. This
42/// implementation is relatively inexpensive and effective.
43///
44/// # Usage
45///
46/// Add the [`MotionBlur`] component to a camera to enable and configure motion blur for that
47/// camera.
48///
49/// ```
50/// # use bevy_post_process::motion_blur::MotionBlur;
51/// # use bevy_camera::Camera3d;
52/// # use bevy_ecs::prelude::*;
53/// # fn test(mut commands: Commands) {
54/// commands.spawn((
55///     Camera3d::default(),
56///     MotionBlur::default(),
57/// ));
58/// # }
59/// ````
60#[derive(Reflect, Component, Clone)]
61#[reflect(Component, Default, Clone)]
62#[require(DepthPrepass, MotionVectorPrepass)]
63pub struct MotionBlur {
64    /// The strength of motion blur from `0.0` to `1.0`.
65    ///
66    /// The shutter angle describes the fraction of a frame that a camera's shutter is open and
67    /// exposing the film/sensor. For 24fps cinematic film, a shutter angle of 0.5 (180 degrees) is
68    /// common. This means that the shutter was open for half of the frame, or 1/48th of a second.
69    /// The lower the shutter angle, the less exposure time and thus less blur.
70    ///
71    /// A value greater than one is non-physical and results in an object's blur stretching further
72    /// than it traveled in that frame. This might be a desirable effect for artistic reasons, but
73    /// consider allowing users to opt out of this.
74    ///
75    /// This value is intentionally tied to framerate to avoid the aforementioned non-physical
76    /// over-blurring. If you want to emulate a cinematic look, your options are:
77    ///   - Framelimit your app to 24fps, and set the shutter angle to 0.5 (180 deg). Note that
78    ///     depending on artistic intent or the action of a scene, it is common to set the shutter
79    ///     angle between 0.125 (45 deg) and 0.5 (180 deg). This is the most faithful way to
80    ///     reproduce the look of film.
81    ///   - Set the shutter angle greater than one. For example, to emulate the blur strength of
82    ///     film while rendering at 60fps, you would set the shutter angle to `60/24 * 0.5 = 1.25`.
83    ///     Note that this will result in artifacts where the motion of objects will stretch further
84    ///     than they moved between frames; users may find this distracting.
85    pub shutter_angle: f32,
86    /// The quality of motion blur, corresponding to the number of per-pixel samples taken in each
87    /// direction during blur.
88    ///
89    /// Setting this to `1` results in each pixel being sampled once in the leading direction, once
90    /// in the trailing direction, and once in the middle, for a total of 3 samples (`1 * 2 + 1`).
91    /// Setting this to `3` will result in `3 * 2 + 1 = 7` samples. Setting this to `0` is
92    /// equivalent to disabling motion blur.
93    pub samples: u32,
94}
95
96impl Default for MotionBlur {
97    fn default() -> Self {
98        Self {
99            shutter_angle: 0.5,
100            samples: 1,
101        }
102    }
103}
104
105impl ExtractComponent for MotionBlur {
106    type QueryData = &'static Self;
107    type QueryFilter = With<Camera>;
108    type Out = MotionBlurUniform;
109
110    fn extract_component(item: QueryItem<Self::QueryData>) -> Option<Self::Out> {
111        Some(MotionBlurUniform {
112            shutter_angle: item.shutter_angle,
113            samples: item.samples,
114            #[cfg(all(feature = "webgl", target_arch = "wasm32", not(feature = "webgpu")))]
115            _webgl2_padding: Default::default(),
116        })
117    }
118}
119
120#[doc(hidden)]
121#[derive(Component, ShaderType, Clone)]
122pub struct MotionBlurUniform {
123    shutter_angle: f32,
124    samples: u32,
125    #[cfg(all(feature = "webgl", target_arch = "wasm32", not(feature = "webgpu")))]
126    // WebGL2 structs must be 16 byte aligned.
127    _webgl2_padding: bevy_math::Vec2,
128}
129
130/// Adds support for per-object motion blur to the app. See [`MotionBlur`] for details.
131#[derive(Default)]
132pub struct MotionBlurPlugin;
133impl Plugin for MotionBlurPlugin {
134    fn build(&self, app: &mut App) {
135        embedded_asset!(app, "motion_blur.wgsl");
136
137        app.add_plugins((
138            ExtractComponentPlugin::<MotionBlur>::default(),
139            UniformComponentPlugin::<MotionBlurUniform>::default(),
140        ));
141
142        let Some(render_app) = app.get_sub_app_mut(RenderApp) else {
143            return;
144        };
145
146        render_app
147            .init_resource::<SpecializedRenderPipelines<pipeline::MotionBlurPipeline>>()
148            .add_systems(RenderStartup, pipeline::init_motion_blur_pipeline)
149            .add_systems(
150                Render,
151                pipeline::prepare_motion_blur_pipelines.in_set(RenderSystems::Prepare),
152            );
153
154        render_app
155            .add_render_graph_node::<ViewNodeRunner<node::MotionBlurNode>>(
156                Core3d,
157                Node3d::MotionBlur,
158            )
159            .add_render_graph_edges(
160                Core3d,
161                (
162                    Node3d::StartMainPassPostProcessing,
163                    Node3d::MotionBlur,
164                    Node3d::Bloom, // we want blurred areas to bloom and tonemap properly.
165                ),
166            );
167    }
168}
bevy_post_process/motion_blur/mod.rs

bevy_post_process/motion_blur/
mod.rs
