1#define_import_path bevy_solari::brdf
2
3#import bevy_pbr::lighting::{F_AB, D_GGX, V_SmithGGXCorrelated, fresnel, specular_multiscatter}
4#import bevy_pbr::pbr_functions::{calculate_diffuse_color, calculate_F0}
5#import bevy_render::maths::PI
6#import bevy_solari::scene_bindings::ResolvedMaterial
7
8fn evaluate_brdf(
9    world_normal: vec3<f32>,
10    wo: vec3<f32>,
11    wi: vec3<f32>,
12    material: ResolvedMaterial,
13) -> vec3<f32> {
14    let diffuse_brdf = diffuse_brdf(material.base_color, material.metallic);
15    let specular_brdf = specular_brdf(
16        world_normal,
17        wo,
18        wi,
19        material.base_color,
20        material.metallic,
21        material.reflectance,
22        material.perceptual_roughness,
23        material.roughness,
24    );
25    return diffuse_brdf + specular_brdf;
26}
27
28fn diffuse_brdf(base_color: vec3<f32>, metallic: f32) -> vec3<f32> {
29    let diffuse_color = calculate_diffuse_color(base_color, metallic, 0.0, 0.0);
30    return diffuse_color / PI;
31}
32
33fn specular_brdf(
34    N: vec3<f32>,
35    V: vec3<f32>,
36    L: vec3<f32>,
37    base_color: vec3<f32>,
38    metallic: f32,
39    reflectance: vec3<f32>,
40    perceptual_roughness: f32,
41    roughness: f32,
42) -> vec3<f32> {
43    let H = normalize(L + V);
44    let NdotL = saturate(dot(N, L));
45    let NdotH = saturate(dot(N, H));
46    let LdotH = saturate(dot(L, H));
47    let NdotV = max(dot(N, V), 0.0001);
48
49    let F0 = calculate_F0(base_color, metallic, reflectance);
50    let F_ab = F_AB(perceptual_roughness, NdotV);
51
52    let D = D_GGX(roughness, NdotH);
53    let Vs = V_SmithGGXCorrelated(roughness, NdotV, NdotL);
54    let F = fresnel(F0, LdotH);
55    return specular_multiscatter(D, Vs, F, F0, F_ab, 1.0);
56}