1#define_import_path bevy_pbr::lightmap
2
3#import bevy_pbr::mesh_bindings::mesh
4
5@group(1) @binding(4) var lightmaps_texture: texture_2d<f32>;
6@group(1) @binding(5) var lightmaps_sampler: sampler;
7
8// Samples the lightmap, if any, and returns indirect illumination from it.
9fn lightmap(uv: vec2<f32>, exposure: f32, instance_index: u32) -> vec3<f32> {
10    let packed_uv_rect = mesh[instance_index].lightmap_uv_rect;
11    let uv_rect = vec4<f32>(vec4<u32>(
12        packed_uv_rect.x & 0xffffu,
13        packed_uv_rect.x >> 16u,
14        packed_uv_rect.y & 0xffffu,
15        packed_uv_rect.y >> 16u)) / 65535.0;
16
17    let lightmap_uv = mix(uv_rect.xy, uv_rect.zw, uv);
18
19    // Mipmapping lightmaps is usually a bad idea due to leaking across UV
20    // islands, so there's no harm in using mip level 0 and it lets us avoid
21    // control flow uniformity problems.
22    //
23    // TODO(pcwalton): Consider bicubic filtering.
24    return textureSampleLevel(
25        lightmaps_texture,
26        lightmaps_sampler,
27        lightmap_uv,
28        0.0).rgb * exposure;
29}