docs/bevy/examples/shader/automatic_instancing.rs 3.8 K · 100 lines · raw · history

1 //! Shows that multiple instances of a cube are automatically instanced in one draw call
2 //! Try running this example in a graphics profiler and all the cubes should be only a single draw call.
3 //! Also demonstrates how to use `MeshTag` to use external data in a custom material.
4
5 use bevy::{
6 mesh::MeshTag, prelude::*, reflect::TypePath, render::render_resource::AsBindGroup,
7 shader::ShaderRef,
8 };
9
10 const SHADER_ASSET_PATH: &str = "shaders/automatic_instancing.wesl";
11
12 fn main() {
13 App::new()
14 .add_plugins((DefaultPlugins, MaterialPlugin::<CustomMaterial>::default()))
15 .add_systems(Startup, setup)
16 .add_systems(Update, update)
17 .run();
18 }
19
20 /// Sets up an instanced grid of cubes, where each cube is colored based on an image that is
21 /// sampled in the vertex shader. The cubes are then animated in a spiral pattern.
22 ///
23 /// This example demonstrates one use of automatic instancing and how to use `MeshTag` to use
24 /// external data in a custom material. For example, here we use the "index" of each cube to
25 /// determine the texel coordinate to sample from the image in the shader.
26 fn setup(
27 mut commands: Commands,
28 assets: Res<AssetServer>,
29 mut meshes: ResMut<Assets<Mesh>>,
30 mut materials: ResMut<Assets<CustomMaterial>>,
31 ) {
32 // We will use this image as our external data for our material to sample from in the vertex shader
33 let image = assets.load("branding/icon.png");
34
35 // Our single mesh handle that will be instanced
36 let mesh_handle = meshes.add(Cuboid::from_size(Vec3::splat(0.01)));
37
38 // Create the custom material with a reference to our texture
39 // Automatic instancing works with any Material, including the `StandardMaterial`.
40 // This custom material is used to demonstrate the optional `MeshTag` feature.
41 let material_handle = materials.add(CustomMaterial {
42 image: image.clone(),
43 });
44
45 // We're hardcoding the image dimensions for simplicity
46 let image_dims = UVec2::new(256, 256);
47 let total_pixels = image_dims.x * image_dims.y;
48
49 for index in 0..total_pixels {
50 // Get x,y from index - x goes left to right, y goes top to bottom
51 let x = index % image_dims.x;
52 let y = index / image_dims.x;
53
54 // Convert to centered world coordinates
55 let world_x = (x as f32 - image_dims.x as f32 / 2.0) / 50.0;
56 let world_y = -((y as f32 - image_dims.y as f32 / 2.0) / 50.0); // Still need negative for world space
57
58 commands.spawn((
59 // For automatic instancing to take effect you need to
60 // use the same mesh handle and material handle for each instance
61 Mesh3d(mesh_handle.clone()),
62 MeshMaterial3d(material_handle.clone()),
63 // This is an optional component that can be used to help tie external data to a mesh instance
64 MeshTag::new(index),
65 Transform::from_xyz(world_x, world_y, 0.0),
66 ));
67 }
68
69 // Camera
70 commands.spawn((
71 Camera3d::default(),
72 Transform::from_xyz(0.0, 0.0, 5.0).looking_at(Vec3::ZERO, Vec3::Y),
73 ));
74 }
75
76 // Animate the transform
77 fn update(time: Res<Time>, mut transforms: Query<(&mut Transform, &MeshTag)>) {
78 for (mut transform, index) in transforms.iter_mut() {
79 // Animate the z position based on time using the index to create a spiral
80 transform.translation.z = ops::sin(time.elapsed_secs() + index.value as f32 * 0.01);
81 }
82 }
83
84 // This struct defines the data that will be passed to your shader
85 #[derive(Asset, TypePath, AsBindGroup, Debug, Clone)]
86 struct CustomMaterial {
87 #[texture(0)]
88 #[sampler(1)]
89 image: Handle<Image>,
90 }
91
92 impl Material for CustomMaterial {
93 fn vertex_shader() -> ShaderRef {
94 SHADER_ASSET_PATH.into()
95 }
96
97 fn fragment_shader() -> ShaderRef {
98 SHADER_ASSET_PATH.into()
99 }
100 }