1#import bevy_pbr::{
2    meshlet_bindings::{
3        meshlet_cluster_meshlet_ids,
4        meshlets,
5        meshlet_cluster_instance_ids,
6        meshlet_instance_uniforms,
7        meshlet_raster_clusters,
8        meshlet_visibility_buffer,
9        view,
10        get_meshlet_triangle_count,
11        get_meshlet_vertex_id,
12        get_meshlet_vertex_position,
13    },
14    mesh_functions::mesh_position_local_to_world,
15}
16#import bevy_render::maths::affine3_to_square
17var<push_constant> meshlet_raster_cluster_rightmost_slot: u32;
18
19/// Vertex/fragment shader for rasterizing large clusters into a visibility buffer.
20
21struct VertexOutput {
22    @builtin(position) position: vec4<f32>,
23#ifdef MESHLET_VISIBILITY_BUFFER_RASTER_PASS_OUTPUT
24    @location(0) @interpolate(flat) packed_ids: u32,
25#endif
26}
27
28@vertex
29fn vertex(@builtin(instance_index) instance_index: u32, @builtin(vertex_index) vertex_index: u32) -> VertexOutput {
30    let cluster_id = meshlet_raster_clusters[meshlet_raster_cluster_rightmost_slot - instance_index];
31    let meshlet_id = meshlet_cluster_meshlet_ids[cluster_id];
32    var meshlet = meshlets[meshlet_id];
33
34    let triangle_id = vertex_index / 3u;
35    if triangle_id >= get_meshlet_triangle_count(&meshlet) { return dummy_vertex(); }
36    let index_id = (triangle_id * 3u) + (vertex_index % 3u);
37    let vertex_id = get_meshlet_vertex_id(meshlet.start_index_id + index_id);
38
39    let instance_id = meshlet_cluster_instance_ids[cluster_id];
40    let instance_uniform = meshlet_instance_uniforms[instance_id];
41
42    let vertex_position = get_meshlet_vertex_position(&meshlet, vertex_id);
43    let world_from_local = affine3_to_square(instance_uniform.world_from_local);
44    let world_position = mesh_position_local_to_world(world_from_local, vec4(vertex_position, 1.0));
45    let clip_position = view.clip_from_world * vec4(world_position.xyz, 1.0);
46
47    return VertexOutput(
48        clip_position,
49#ifdef MESHLET_VISIBILITY_BUFFER_RASTER_PASS_OUTPUT
50        (cluster_id << 7u) | triangle_id,
51#endif
52    );
53}
54
55@fragment
56fn fragment(vertex_output: VertexOutput) {
57    let depth = bitcast<u32>(vertex_output.position.z);
58#ifdef MESHLET_VISIBILITY_BUFFER_RASTER_PASS_OUTPUT
59    let visibility = (u64(depth) << 32u) | u64(vertex_output.packed_ids);
60#else
61    let visibility = depth;
62#endif
63    textureAtomicMax(meshlet_visibility_buffer, vec2<u32>(vertex_output.position.xy), visibility);
64}
65
66fn dummy_vertex() -> VertexOutput {
67    return VertexOutput(
68        vec4(divide(0.0, 0.0)), // NaN vertex position
69#ifdef MESHLET_VISIBILITY_BUFFER_RASTER_PASS_OUTPUT
70        0u,
71#endif
72    );
73}
74
75// Naga doesn't allow divide by zero literals, but this lets us work around it
76fn divide(a: f32, b: f32) -> f32 {
77    return a / b;
78}