generated_assets/
generated_assets.rs

1//! Shows how to generate and store assets at runtime.
2
3use bevy::prelude::*;
4
5fn main() {
6    App::new()
7        .add_plugins(DefaultPlugins)
8        .add_systems(Startup, setup)
9        .add_systems(Update, generate_mesh_system.run_if(run_once))
10        .run();
11}
12
13fn setup(
14    mut commands: Commands,
15    asset_server: Res<AssetServer>,
16    mut materials: ResMut<Assets<StandardMaterial>>,
17    meshes: Res<Assets<Mesh>>,
18) {
19    commands.spawn((Camera3d::default(), Transform::from_xyz(0.0, 0.0, 5.0)));
20
21    commands.spawn((
22        DirectionalLight::default(),
23        Transform::default().looking_to(Dir3::new(Vec3::new(-1.0, -1.0, -1.0)).unwrap(), Dir3::Y),
24    ));
25
26    // The simplest way to generate an asset is to add it directly to the `Assets`.
27    let material_handle = materials.add(StandardMaterial::default());
28
29    commands.spawn((
30        Transform::from_xyz(-2.0, 0.0, 0.0),
31        MeshMaterial3d(material_handle.clone()),
32        // Alternatively, `add_async` creates a task that runs your async function. Once it
33        // completes, the asset is added to the `Assets`. This is "deferred" meaning that the asset
34        // may take a frame to be added after the task completes.
35        Mesh3d(asset_server.add_async(generate_mesh_async())),
36    ));
37
38    // The last way to generate assets is to reserve a handle, and then use `Assets::insert` to
39    // populate the asset later. In this example, the `generate_mesh_system` system runs to populate
40    // the mesh.
41    let mesh_handle = meshes.reserve_handle();
42    commands.insert_resource(HandleToGenerate(mesh_handle.clone()));
43    commands.spawn((
44        Transform::from_xyz(2.0, 0.0, 0.0)
45            .with_rotation(Quat::from_rotation_x(50.0f32.to_radians())),
46        Mesh3d(mesh_handle),
47        MeshMaterial3d(material_handle),
48    ));
49}
50
51async fn generate_mesh_async() -> Result<Mesh, std::io::Error> {
52    // This mesh could take a while to generate. It could even take several frames (though in this
53    // example it should be ~instant).
54
55    Ok(Mesh::from(Cone::new(1.0, 2.0)))
56}
57
58#[derive(Resource)]
59struct HandleToGenerate(Handle<Mesh>);
60
61/// This system runs once to populate the handle in [`HandleToGenerate`].
62///
63/// This generates a runtime mesh. Since it's a system, it can use other data in the world to
64/// generate the asset!
65fn generate_mesh_system(
66    handle_to_generate: Res<HandleToGenerate>,
67    mut meshes: ResMut<Assets<Mesh>>,
68) {
69    let mesh = Mesh::from(Torus::new(0.8, 1.2));
70    meshes.insert(&handle_to_generate.0, mesh).unwrap();
71}
generated_assets/generated_assets.rs

generated_assets/
generated_assets.rs
