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 LIGHTMAP
13#import bevy_pbr::mesh_view_types::LIGHT_PROBE_FLAG_AFFECTS_LIGHTMAPPED_MESH_DIFFUSE;
14#endif
15
16#ifdef IRRADIANCE_VOLUMES_ARE_USABLE
17
18// See:
19// https://advances.realtimerendering.com/s2006/Mitchell-ShadingInValvesSourceEngine.pdf
20// Slide 28, "Ambient Cube Basis"
21fn irradiance_volume_light(
22    world_position: vec3<f32>,
23    N: vec3<f32>,
24    clusterable_object_index_ranges: ptr<function, ClusterableObjectIndexRanges>,
25) -> vec3<f32> {
26    // Find all irradiance volumes that contain the fragment. We're going to
27    // accumulate all the irradiance from them in a weighted sum.
28    var iterator = light_probe_iterator_new(
29        world_position,
30        /*is_irradiance_volume=*/ true,
31        clusterable_object_index_ranges,
32    );
33
34    var total_weight = 0.0;
35    var total_irradiance = vec3(0.0);
36
37    while (true) {
38        var query_result = light_probe_iterator_next(&iterator);
39
40        // If there was no irradiance volume found, we're done.
41        if (query_result.texture_index < 0) {
42            break;
43        }
44
45        // If we're lightmapped, and the irradiance volume contributes no diffuse
46        // light, then bail out.
47    #ifdef LIGHTMAP
48        if ((query_result.flags & LIGHT_PROBE_FLAG_AFFECTS_LIGHTMAPPED_MESH_DIFFUSE) == 0u) {
49            continue;
50        }
51    #endif  // LIGHTMAP
52
53    #ifdef MULTIPLE_LIGHT_PROBES_IN_ARRAY
54        let irradiance_volume_texture = irradiance_volumes[query_result.texture_index];
55    #else
56        let irradiance_volume_texture = irradiance_volume;
57    #endif
58
59        let atlas_resolution = vec3<f32>(textureDimensions(irradiance_volume_texture));
60        let resolution = vec3<f32>(textureDimensions(irradiance_volume_texture) / vec3(1u, 2u, 3u));
61
62        // Make sure to clamp to the edges to avoid texture bleed.
63        var unit_pos = (query_result.light_from_world * vec4(world_position, 1.0f)).xyz;
64        let stp = clamp((unit_pos + 0.5) * resolution, vec3(0.5f), resolution - vec3(0.5f));
65        let uvw = stp / atlas_resolution;
66
67        // The bottom half of each cube slice is the negative part, so choose it if applicable on each
68        // slice.
69        let neg_offset = select(vec3(0.0f), vec3(0.5f), N < vec3(0.0f));
70
71        let uvw_x = uvw + vec3(0.0f, neg_offset.x, 0.0f);
72        let uvw_y = uvw + vec3(0.0f, neg_offset.y, 1.0f / 3.0f);
73        let uvw_z = uvw + vec3(0.0f, neg_offset.z, 2.0f / 3.0f);
74
75        let rgb_x = textureSampleLevel(irradiance_volume_texture, irradiance_volume_sampler, uvw_x, 0.0).rgb;
76        let rgb_y = textureSampleLevel(irradiance_volume_texture, irradiance_volume_sampler, uvw_y, 0.0).rgb;
77        let rgb_z = textureSampleLevel(irradiance_volume_texture, irradiance_volume_sampler, uvw_z, 0.0).rgb;
78
79        // Use Valve's formula to sample.
80        let NN = N * N;
81        total_irradiance += (rgb_x * NN.x + rgb_y * NN.y + rgb_z * NN.z) * query_result.intensity *
82            query_result.weight;
83
84        total_weight += query_result.weight;
85    }
86
87    if (total_weight != 0.0) {
88        total_irradiance /= total_weight;
89    }
90
91    return total_irradiance;
92}
93
94#endif  // IRRADIANCE_VOLUMES_ARE_USABLE