1#define_import_path bevy_pbr::irradiance_volume
2
3#import bevy_pbr::light_probe::query_light_probe
4#import bevy_pbr::mesh_view_bindings::{
5    irradiance_volumes,
6    irradiance_volume,
7    irradiance_volume_sampler,
8    light_probes,
9};
10#import bevy_pbr::clustered_forward::ClusterableObjectIndexRanges
11
12#ifdef IRRADIANCE_VOLUMES_ARE_USABLE
13
14// See:
15// https://advances.realtimerendering.com/s2006/Mitchell-ShadingInValvesSourceEngine.pdf
16// Slide 28, "Ambient Cube Basis"
17fn irradiance_volume_light(
18    world_position: vec3<f32>,
19    N: vec3<f32>,
20    clusterable_object_index_ranges: ptr<function, ClusterableObjectIndexRanges>,
21) -> vec3<f32> {
22    // Search for an irradiance volume that contains the fragment.
23    let query_result = query_light_probe(
24        world_position,
25        /*is_irradiance_volume=*/ true,
26        clusterable_object_index_ranges,
27    );
28
29    // If there was no irradiance volume found, bail out.
30    if (query_result.texture_index < 0) {
31        return vec3(0.0f);
32    }
33
34    // If we're lightmapped, and the irradiance volume contributes no diffuse
35    // light, then bail out.
36#ifdef LIGHTMAP
37    if (!query_result.affects_lightmapped_mesh_diffuse) {
38        return vec3(0.0f);
39    }
40#endif  // LIGHTMAP
41
42#ifdef MULTIPLE_LIGHT_PROBES_IN_ARRAY
43    let irradiance_volume_texture = irradiance_volumes[query_result.texture_index];
44#else
45    let irradiance_volume_texture = irradiance_volume;
46#endif
47
48    let atlas_resolution = vec3<f32>(textureDimensions(irradiance_volume_texture));
49    let resolution = vec3<f32>(textureDimensions(irradiance_volume_texture) / vec3(1u, 2u, 3u));
50
51    // Make sure to clamp to the edges to avoid texture bleed.
52    var unit_pos = (query_result.light_from_world * vec4(world_position, 1.0f)).xyz;
53    let stp = clamp((unit_pos + 0.5) * resolution, vec3(0.5f), resolution - vec3(0.5f));
54    let uvw = stp / atlas_resolution;
55
56    // The bottom half of each cube slice is the negative part, so choose it if applicable on each
57    // slice.
58    let neg_offset = select(vec3(0.0f), vec3(0.5f), N < vec3(0.0f));
59
60    let uvw_x = uvw + vec3(0.0f, neg_offset.x, 0.0f);
61    let uvw_y = uvw + vec3(0.0f, neg_offset.y, 1.0f / 3.0f);
62    let uvw_z = uvw + vec3(0.0f, neg_offset.z, 2.0f / 3.0f);
63
64    let rgb_x = textureSampleLevel(irradiance_volume_texture, irradiance_volume_sampler, uvw_x, 0.0).rgb;
65    let rgb_y = textureSampleLevel(irradiance_volume_texture, irradiance_volume_sampler, uvw_y, 0.0).rgb;
66    let rgb_z = textureSampleLevel(irradiance_volume_texture, irradiance_volume_sampler, uvw_z, 0.0).rgb;
67
68    // Use Valve's formula to sample.
69    let NN = N * N;
70    return (rgb_x * NN.x + rgb_y * NN.y + rgb_z * NN.z) * query_result.intensity;
71}
72
73#endif  // IRRADIANCE_VOLUMES_ARE_USABLE