custom_gltf_vertex_attribute/
custom_gltf_vertex_attribute.rs

1//! Renders a glTF mesh in 2D with a custom vertex attribute.
2
3use bevy::{
4    gltf::GltfPlugin,
5    mesh::{MeshVertexAttribute, MeshVertexBufferLayoutRef},
6    prelude::*,
7    reflect::TypePath,
8    render::render_resource::*,
9    shader::ShaderRef,
10    sprite_render::{Material2d, Material2dKey, Material2dPlugin},
11};
12
13/// This example uses a shader source file from the assets subdirectory
14const SHADER_ASSET_PATH: &str = "shaders/custom_gltf_2d.wgsl";
15
16/// This vertex attribute supplies barycentric coordinates for each triangle.
17///
18/// Each component of the vector corresponds to one corner of a triangle. It's
19/// equal to 1.0 in that corner and 0.0 in the other two. Hence, its value in
20/// the fragment shader indicates proximity to a corner or the opposite edge.
21const ATTRIBUTE_BARYCENTRIC: MeshVertexAttribute =
22    MeshVertexAttribute::new("Barycentric", 2137464976, VertexFormat::Float32x3);
23
24fn main() {
25    App::new()
26        .insert_resource(AmbientLight {
27            color: Color::WHITE,
28            brightness: 1.0 / 5.0f32,
29            ..default()
30        })
31        .add_plugins((
32            DefaultPlugins.set(
33                GltfPlugin::default()
34                    // Map a custom glTF attribute name to a `MeshVertexAttribute`.
35                    // The glTF file used here has an attribute name with *two*
36                    // underscores: __BARYCENTRIC
37                    // One is stripped to do the comparison here.
38                    .add_custom_vertex_attribute("_BARYCENTRIC", ATTRIBUTE_BARYCENTRIC),
39            ),
40            Material2dPlugin::<CustomMaterial>::default(),
41        ))
42        .add_systems(Startup, setup)
43        .run();
44}
45
46fn setup(
47    mut commands: Commands,
48    asset_server: Res<AssetServer>,
49    mut materials: ResMut<Assets<CustomMaterial>>,
50) {
51    // Add a mesh loaded from a glTF file. This mesh has data for `ATTRIBUTE_BARYCENTRIC`.
52    let mesh = asset_server.load(
53        GltfAssetLabel::Primitive {
54            mesh: 0,
55            primitive: 0,
56        }
57        .from_asset("models/barycentric/barycentric.gltf"),
58    );
59    commands.spawn((
60        Mesh2d(mesh),
61        MeshMaterial2d(materials.add(CustomMaterial {})),
62        Transform::from_scale(150.0 * Vec3::ONE),
63    ));
64
65    commands.spawn(Camera2d);
66}
67
68/// This custom material uses barycentric coordinates from
69/// `ATTRIBUTE_BARYCENTRIC` to shade a white border around each triangle. The
70/// thickness of the border is animated using the global time shader uniform.
71#[derive(Asset, TypePath, AsBindGroup, Debug, Clone)]
72struct CustomMaterial {}
73
74impl Material2d for CustomMaterial {
75    fn vertex_shader() -> ShaderRef {
76        SHADER_ASSET_PATH.into()
77    }
78    fn fragment_shader() -> ShaderRef {
79        SHADER_ASSET_PATH.into()
80    }
81
82    fn specialize(
83        descriptor: &mut RenderPipelineDescriptor,
84        layout: &MeshVertexBufferLayoutRef,
85        _key: Material2dKey<Self>,
86    ) -> Result<(), SpecializedMeshPipelineError> {
87        let vertex_layout = layout.0.get_layout(&[
88            Mesh::ATTRIBUTE_POSITION.at_shader_location(0),
89            Mesh::ATTRIBUTE_COLOR.at_shader_location(1),
90            ATTRIBUTE_BARYCENTRIC.at_shader_location(2),
91        ])?;
92        descriptor.vertex.buffers = vec![vertex_layout];
93        Ok(())
94    }
95}
custom_gltf_vertex_attribute/custom_gltf_vertex_attribute.rs

custom_gltf_vertex_attribute/
custom_gltf_vertex_attribute.rs
