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custom_gltf_vertex_attribute.rs
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custom_gltf_vertex_attribute.rs
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//! Renders a glTF mesh in 2D with a custom vertex attribute.
use bevy::{
gltf::GltfPlugin,
prelude::*,
reflect::TypePath,
render::{
mesh::{MeshVertexAttribute, MeshVertexBufferLayout},
render_resource::*,
},
sprite::{Material2d, Material2dKey, Material2dPlugin, MaterialMesh2dBundle, Mesh2dHandle},
};
/// This vertex attribute supplies barycentric coordinates for each triangle.
/// Each component of the vector corresponds to one corner of a triangle. It's
/// equal to 1.0 in that corner and 0.0 in the other two. Hence, its value in
/// the fragment shader indicates proximity to a corner or the opposite edge.
const ATTRIBUTE_BARYCENTRIC: MeshVertexAttribute =
MeshVertexAttribute::new("Barycentric", 2137464976, VertexFormat::Float32x3);
fn main() {
App::new()
.insert_resource(AmbientLight {
color: Color::WHITE,
brightness: 1.0 / 5.0f32,
})
.add_plugins((
DefaultPlugins.set(
GltfPlugin::default()
// Map a custom glTF attribute name to a `MeshVertexAttribute`.
.add_custom_vertex_attribute("_BARYCENTRIC", ATTRIBUTE_BARYCENTRIC),
),
Material2dPlugin::<CustomMaterial>::default(),
))
.add_systems(Startup, setup)
.run();
}
fn setup(
mut commands: Commands,
asset_server: Res<AssetServer>,
mut materials: ResMut<Assets<CustomMaterial>>,
) {
// Add a mesh loaded from a glTF file. This mesh has data for `ATTRIBUTE_BARYCENTRIC`.
let mesh = asset_server.load("models/barycentric/barycentric.gltf#Mesh0/Primitive0");
commands.spawn(MaterialMesh2dBundle {
mesh: Mesh2dHandle(mesh),
material: materials.add(CustomMaterial {}),
transform: Transform::from_scale(150.0 * Vec3::ONE),
..default()
});
// Add a camera
commands.spawn(Camera2dBundle { ..default() });
}
/// This custom material uses barycentric coordinates from
/// `ATTRIBUTE_BARYCENTRIC` to shade a white border around each triangle. The
/// thickness of the border is animated using the global time shader uniform.
#[derive(Asset, TypePath, AsBindGroup, Debug, Clone)]
struct CustomMaterial {}
impl Material2d for CustomMaterial {
fn vertex_shader() -> ShaderRef {
"shaders/custom_gltf_2d.wgsl".into()
}
fn fragment_shader() -> ShaderRef {
"shaders/custom_gltf_2d.wgsl".into()
}
fn specialize(
descriptor: &mut RenderPipelineDescriptor,
layout: &MeshVertexBufferLayout,
_key: Material2dKey<Self>,
) -> Result<(), SpecializedMeshPipelineError> {
let vertex_layout = layout.get_layout(&[
Mesh::ATTRIBUTE_POSITION.at_shader_location(0),
Mesh::ATTRIBUTE_COLOR.at_shader_location(1),
ATTRIBUTE_BARYCENTRIC.at_shader_location(2),
])?;
descriptor.vertex.buffers = vec![vertex_layout];
Ok(())
}
}