shader_prepass/
shader_prepass.rs

1//! Bevy has an optional prepass that is controlled per-material. A prepass is a rendering pass that runs before the main pass.
2//! It will optionally generate various view textures. Currently it supports depth, normal, and motion vector textures.
3//! The textures are not generated for any material using alpha blending.
4
5use bevy::{
6    core_pipeline::prepass::{DepthPrepass, MotionVectorPrepass, NormalPrepass},
7    light::NotShadowCaster,
8    pbr::PbrPlugin,
9    prelude::*,
10    reflect::TypePath,
11    render::render_resource::{AsBindGroup, ShaderType},
12    shader::ShaderRef,
13};
14
15/// This example uses a shader source file from the assets subdirectory
16const PREPASS_SHADER_ASSET_PATH: &str = "shaders/show_prepass.wgsl";
17const MATERIAL_SHADER_ASSET_PATH: &str = "shaders/custom_material.wgsl";
18
19fn main() {
20    App::new()
21        .add_plugins((
22            DefaultPlugins.set(PbrPlugin {
23                // The prepass is enabled by default on the StandardMaterial,
24                // but you can disable it if you need to.
25                //
26                // prepass_enabled: false,
27                ..default()
28            }),
29            MaterialPlugin::<CustomMaterial>::default(),
30            MaterialPlugin::<PrepassOutputMaterial> {
31                // This material only needs to read the prepass textures,
32                // but the meshes using it should not contribute to the prepass render, so we can disable it.
33                prepass_enabled: false,
34                ..default()
35            },
36        ))
37        .add_systems(Startup, setup)
38        .add_systems(Update, (rotate, toggle_prepass_view))
39        .run();
40}
41
42/// set up a simple 3D scene
43fn setup(
44    mut commands: Commands,
45    mut meshes: ResMut<Assets<Mesh>>,
46    mut materials: ResMut<Assets<CustomMaterial>>,
47    mut std_materials: ResMut<Assets<StandardMaterial>>,
48    mut depth_materials: ResMut<Assets<PrepassOutputMaterial>>,
49    asset_server: Res<AssetServer>,
50) {
51    // camera
52    commands.spawn((
53        Camera3d::default(),
54        Transform::from_xyz(-2.0, 3., 5.0).looking_at(Vec3::ZERO, Vec3::Y),
55        // Disabling MSAA for maximum compatibility. Shader prepass with MSAA needs GPU capability MULTISAMPLED_SHADING
56        Msaa::Off,
57        // To enable the prepass you need to add the components associated with the ones you need
58        // This will write the depth buffer to a texture that you can use in the main pass
59        DepthPrepass,
60        // This will generate a texture containing world normals (with normal maps applied)
61        NormalPrepass,
62        // This will generate a texture containing screen space pixel motion vectors
63        MotionVectorPrepass,
64    ));
65
66    // plane
67    commands.spawn((
68        Mesh3d(meshes.add(Plane3d::default().mesh().size(5.0, 5.0))),
69        MeshMaterial3d(std_materials.add(Color::srgb(0.3, 0.5, 0.3))),
70    ));
71
72    // A quad that shows the outputs of the prepass
73    // To make it easy, we just draw a big quad right in front of the camera.
74    // For a real application, this isn't ideal.
75    commands.spawn((
76        Mesh3d(meshes.add(Rectangle::new(20.0, 20.0))),
77        MeshMaterial3d(depth_materials.add(PrepassOutputMaterial {
78            settings: ShowPrepassSettings::default(),
79        })),
80        Transform::from_xyz(-0.75, 1.25, 3.0).looking_at(Vec3::new(2.0, -2.5, -5.0), Vec3::Y),
81        NotShadowCaster,
82    ));
83
84    // Opaque cube
85    commands.spawn((
86        Mesh3d(meshes.add(Cuboid::default())),
87        MeshMaterial3d(materials.add(CustomMaterial {
88            color: LinearRgba::WHITE,
89            color_texture: Some(asset_server.load("branding/icon.png")),
90            alpha_mode: AlphaMode::Opaque,
91        })),
92        Transform::from_xyz(-1.0, 0.5, 0.0),
93        Rotates,
94    ));
95
96    // Cube with alpha mask
97    commands.spawn((
98        Mesh3d(meshes.add(Cuboid::default())),
99        MeshMaterial3d(std_materials.add(StandardMaterial {
100            alpha_mode: AlphaMode::Mask(1.0),
101            base_color_texture: Some(asset_server.load("branding/icon.png")),
102            ..default()
103        })),
104        Transform::from_xyz(0.0, 0.5, 0.0),
105    ));
106
107    // Cube with alpha blending.
108    // Transparent materials are ignored by the prepass
109    commands.spawn((
110        Mesh3d(meshes.add(Cuboid::default())),
111        MeshMaterial3d(materials.add(CustomMaterial {
112            color: LinearRgba::WHITE,
113            color_texture: Some(asset_server.load("branding/icon.png")),
114            alpha_mode: AlphaMode::Blend,
115        })),
116        Transform::from_xyz(1.0, 0.5, 0.0),
117    ));
118
119    // light
120    commands.spawn((
121        PointLight {
122            shadows_enabled: true,
123            ..default()
124        },
125        Transform::from_xyz(4.0, 8.0, 4.0),
126    ));
127
128    commands.spawn((
129        Text::default(),
130        Node {
131            position_type: PositionType::Absolute,
132            top: px(12),
133            left: px(12),
134            ..default()
135        },
136        children![
137            TextSpan::new("Prepass Output: transparent\n"),
138            TextSpan::new("\n\n"),
139            TextSpan::new("Controls\n"),
140            TextSpan::new("---------------\n"),
141            TextSpan::new("Space - Change output\n"),
142        ],
143    ));
144}
145
146// This is the struct that will be passed to your shader
147#[derive(Asset, TypePath, AsBindGroup, Debug, Clone)]
148struct CustomMaterial {
149    #[uniform(0)]
150    color: LinearRgba,
151    #[texture(1)]
152    #[sampler(2)]
153    color_texture: Option<Handle<Image>>,
154    alpha_mode: AlphaMode,
155}
156
157/// Not shown in this example, but if you need to specialize your material, the specialize
158/// function will also be used by the prepass
159impl Material for CustomMaterial {
160    fn fragment_shader() -> ShaderRef {
161        MATERIAL_SHADER_ASSET_PATH.into()
162    }
163
164    fn alpha_mode(&self) -> AlphaMode {
165        self.alpha_mode
166    }
167
168    // You can override the default shaders used in the prepass if your material does
169    // anything not supported by the default prepass
170    // fn prepass_fragment_shader() -> ShaderRef {
171    //     "shaders/custom_material.wgsl".into()
172    // }
173}
174
175#[derive(Component)]
176struct Rotates;
177
178fn rotate(mut q: Query<&mut Transform, With<Rotates>>, time: Res<Time>) {
179    for mut t in q.iter_mut() {
180        let rot = (ops::sin(time.elapsed_secs()) * 0.5 + 0.5) * std::f32::consts::PI * 2.0;
181        t.rotation = Quat::from_rotation_z(rot);
182    }
183}
184
185#[derive(Debug, Clone, Default, ShaderType)]
186struct ShowPrepassSettings {
187    show_depth: u32,
188    show_normals: u32,
189    show_motion_vectors: u32,
190    padding_1: u32,
191    padding_2: u32,
192}
193
194// This shader simply loads the prepass texture and outputs it directly
195#[derive(Asset, TypePath, AsBindGroup, Debug, Clone)]
196struct PrepassOutputMaterial {
197    #[uniform(0)]
198    settings: ShowPrepassSettings,
199}
200
201impl Material for PrepassOutputMaterial {
202    fn fragment_shader() -> ShaderRef {
203        PREPASS_SHADER_ASSET_PATH.into()
204    }
205
206    // This needs to be transparent in order to show the scene behind the mesh
207    fn alpha_mode(&self) -> AlphaMode {
208        AlphaMode::Blend
209    }
210}
211
212/// Every time you press space, it will cycle between transparent, depth and normals view
213fn toggle_prepass_view(
214    mut prepass_view: Local<u32>,
215    keycode: Res<ButtonInput<KeyCode>>,
216    material_handle: Single<&MeshMaterial3d<PrepassOutputMaterial>>,
217    mut materials: ResMut<Assets<PrepassOutputMaterial>>,
218    text: Single<Entity, With<Text>>,
219    mut writer: TextUiWriter,
220) {
221    if keycode.just_pressed(KeyCode::Space) {
222        *prepass_view = (*prepass_view + 1) % 4;
223
224        let label = match *prepass_view {
225            0 => "transparent",
226            1 => "depth",
227            2 => "normals",
228            3 => "motion vectors",
229            _ => unreachable!(),
230        };
231        let text = *text;
232        *writer.text(text, 1) = format!("Prepass Output: {label}\n");
233        writer.for_each_color(text, |mut color| {
234            color.0 = Color::WHITE;
235        });
236
237        let mat = materials.get_mut(*material_handle).unwrap();
238        mat.settings.show_depth = (*prepass_view == 1) as u32;
239        mat.settings.show_normals = (*prepass_view == 2) as u32;
240        mat.settings.show_motion_vectors = (*prepass_view == 3) as u32;
241    }
242}
shader_prepass/shader_prepass.rs

shader_prepass/
shader_prepass.rs
