1#define_import_path bevy_pbr::light_probe
2
3#import bevy_pbr::mesh_view_bindings::light_probes
4#import bevy_pbr::mesh_view_types::LightProbe
5
6// The result of searching for a light probe.
7struct LightProbeQueryResult {
8    // The index of the light probe texture or textures in the binding array or
9    // arrays.
10    texture_index: i32,
11    // A scale factor that's applied to the diffuse and specular light from the
12    // light probe. This is in units of cd/m² (candela per square meter).
13    intensity: f32,
14    // Transform from world space to the light probe model space. In light probe
15    // model space, the light probe is a 1×1×1 cube centered on the origin.
16    light_from_world: mat4x4<f32>,
17};
18
19fn transpose_affine_matrix(matrix: mat3x4<f32>) -> mat4x4<f32> {
20    let matrix4x4 = mat4x4<f32>(
21        matrix[0],
22        matrix[1],
23        matrix[2],
24        vec4<f32>(0.0, 0.0, 0.0, 1.0));
25    return transpose(matrix4x4);
26}
27
28// Searches for a light probe that contains the fragment.
29//
30// TODO: Interpolate between multiple light probes.
31fn query_light_probe(
32    world_position: vec3<f32>,
33    is_irradiance_volume: bool,
34) -> LightProbeQueryResult {
35    var result: LightProbeQueryResult;
36    result.texture_index = -1;
37
38    var light_probe_count: i32;
39    if is_irradiance_volume {
40        light_probe_count = light_probes.irradiance_volume_count;
41    } else {
42        light_probe_count = light_probes.reflection_probe_count;
43    }
44
45    for (var light_probe_index: i32 = 0;
46            light_probe_index < light_probe_count && result.texture_index < 0;
47            light_probe_index += 1) {
48        var light_probe: LightProbe;
49        if is_irradiance_volume {
50            light_probe = light_probes.irradiance_volumes[light_probe_index];
51        } else {
52            light_probe = light_probes.reflection_probes[light_probe_index];
53        }
54
55        // Unpack the inverse transform.
56        let light_from_world =
57            transpose_affine_matrix(light_probe.light_from_world_transposed);
58
59        // Check to see if the transformed point is inside the unit cube
60        // centered at the origin.
61        let probe_space_pos = (light_from_world * vec4<f32>(world_position, 1.0f)).xyz;
62        if (all(abs(probe_space_pos) <= vec3(0.5f))) {
63            result.texture_index = light_probe.cubemap_index;
64            result.intensity = light_probe.intensity;
65            result.light_from_world = light_from_world;
66
67            // TODO: Workaround for ICE in DXC https://github.com/microsoft/DirectXShaderCompiler/issues/6183
68            // We can't use `break` here because of the ICE.
69            // So instead we rely on the fact that we set `result.texture_index`
70            // above and check its value in the `for` loop header before
71            // looping.
72            // break;
73        }
74    }
75
76    return result;
77}
78