1#define_import_path bevy_pbr::irradiance_volume
2
3#import bevy_pbr::light_probe::{light_probe_iterator_new, light_probe_iterator_next}
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    // Find all irradiance volumes that contain the fragment. We're going to
23    // accumulate all the irradiance from them in a weighted sum.
24    var iterator = light_probe_iterator_new(
25        world_position,
26        /*is_irradiance_volume=*/ true,
27        clusterable_object_index_ranges,
28    );
29
30    var total_weight = 0.0;
31    var total_irradiance = vec3(0.0);
32
33    while (true) {
34        var query_result = light_probe_iterator_next(&iterator);
35
36        // If there was no irradiance volume found, we're done.
37        if (query_result.texture_index < 0) {
38            break;
39        }
40
41        // If we're lightmapped, and the irradiance volume contributes no diffuse
42        // light, then bail out.
43    #ifdef LIGHTMAP
44        if ((query_result.flags & LIGHT_PROBE_FLAG_AFFECTS_LIGHTMAPPED_MESH_DIFFUSE) == 0u) {
45            continue;
46        }
47    #endif  // LIGHTMAP
48
49    #ifdef MULTIPLE_LIGHT_PROBES_IN_ARRAY
50        let irradiance_volume_texture = irradiance_volumes[query_result.texture_index];
51    #else
52        let irradiance_volume_texture = irradiance_volume;
53    #endif
54
55        let atlas_resolution = vec3<f32>(textureDimensions(irradiance_volume_texture));
56        let resolution = vec3<f32>(textureDimensions(irradiance_volume_texture) / vec3(1u, 2u, 3u));
57
58        // Make sure to clamp to the edges to avoid texture bleed.
59        var unit_pos = (query_result.light_from_world * vec4(world_position, 1.0f)).xyz;
60        let stp = clamp((unit_pos + 0.5) * resolution, vec3(0.5f), resolution - vec3(0.5f));
61        let uvw = stp / atlas_resolution;
62
63        // The bottom half of each cube slice is the negative part, so choose it if applicable on each
64        // slice.
65        let neg_offset = select(vec3(0.0f), vec3(0.5f), N < vec3(0.0f));
66
67        let uvw_x = uvw + vec3(0.0f, neg_offset.x, 0.0f);
68        let uvw_y = uvw + vec3(0.0f, neg_offset.y, 1.0f / 3.0f);
69        let uvw_z = uvw + vec3(0.0f, neg_offset.z, 2.0f / 3.0f);
70
71        let rgb_x = textureSampleLevel(irradiance_volume_texture, irradiance_volume_sampler, uvw_x, 0.0).rgb;
72        let rgb_y = textureSampleLevel(irradiance_volume_texture, irradiance_volume_sampler, uvw_y, 0.0).rgb;
73        let rgb_z = textureSampleLevel(irradiance_volume_texture, irradiance_volume_sampler, uvw_z, 0.0).rgb;
74
75        // Use Valve's formula to sample.
76        let NN = N * N;
77        total_irradiance += (rgb_x * NN.x + rgb_y * NN.y + rgb_z * NN.z) * query_result.intensity *
78            query_result.weight;
79
80        total_weight += query_result.weight;
81    }
82
83    if (total_weight != 0.0) {
84        total_irradiance /= total_weight;
85    }
86
87    return total_irradiance;
88}
89
90#endif  // IRRADIANCE_VOLUMES_ARE_USABLE