1import package::light_probe::{light_probe_iterator_new, light_probe_iterator_next};
2import package::render::mesh_view_bindings::{
3    irradiance_volumes,
4    irradiance_volume,
5    irradiance_volume_sampler,
6    light_probes,
7};
8import package::render::clustered_forward::ClusterableObjectIndexRanges;
9
10@if(LIGHTMAP) import package::render::mesh_view_types::LIGHT_PROBE_FLAG_AFFECTS_LIGHTMAPPED_MESH_DIFFUSE;
11
12@if(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        @if(LIGHTMAP)
44        if ((query_result.flags & LIGHT_PROBE_FLAG_AFFECTS_LIGHTMAPPED_MESH_DIFFUSE) == 0u) {
45            continue;
46        }
47
48        @if(MULTIPLE_LIGHT_PROBES_IN_ARRAY)
49        let irradiance_volume_texture = irradiance_volumes[query_result.texture_index];
50        @else
51        let irradiance_volume_texture = irradiance_volume;
52
53        let atlas_resolution = vec3<f32>(textureDimensions(irradiance_volume_texture));
54        let resolution = vec3<f32>(textureDimensions(irradiance_volume_texture) / vec3(1u, 2u, 3u));
55
56        // Make sure to clamp to the edges to avoid texture bleed.
57        var unit_pos = (query_result.light_from_world * vec4(world_position, 1.0f)).xyz;
58        let stp = clamp((unit_pos + 0.5) * resolution, vec3(0.5f), resolution - vec3(0.5f));
59        let uvw = stp / atlas_resolution;
60
61        // The bottom half of each cube slice is the negative part, so choose it if applicable on each
62        // slice.
63        let neg_offset = select(vec3(0.0f), vec3(0.5f), N < vec3(0.0f));
64
65        let uvw_x = uvw + vec3(0.0f, neg_offset.x, 0.0f);
66        let uvw_y = uvw + vec3(0.0f, neg_offset.y, 1.0f / 3.0f);
67        let uvw_z = uvw + vec3(0.0f, neg_offset.z, 2.0f / 3.0f);
68
69        let rgb_x = textureSampleLevel(irradiance_volume_texture, irradiance_volume_sampler, uvw_x, 0.0).rgb;
70        let rgb_y = textureSampleLevel(irradiance_volume_texture, irradiance_volume_sampler, uvw_y, 0.0).rgb;
71        let rgb_z = textureSampleLevel(irradiance_volume_texture, irradiance_volume_sampler, uvw_z, 0.0).rgb;
72
73        // Use Valve's formula to sample.
74        let NN = N * N;
75        total_irradiance += (rgb_x * NN.x + rgb_y * NN.y + rgb_z * NN.z) * query_result.intensity *
76            query_result.weight;
77
78        total_weight += query_result.weight;
79    }
80
81    if (total_weight != 0.0) {
82        total_irradiance /= total_weight;
83    }
84
85    return total_irradiance;
86}