1import package::render::{
2    pbr_lighting::{EnvBRDFApprox, F_AB},
3    mesh_view_bindings::lights,
4};
5
6/// A precomputed `NdotV` is provided because it is computed regardless,
7/// but `world_normal` and the view vector `V` are provided separately for more advanced uses.
8fn ambient_light(
9    world_position: vec4<f32>,
10    world_normal: vec3<f32>,
11    V: vec3<f32>,
12    NdotV: f32,
13    diffuse_color: vec3<f32>,
14    specular_color: vec3<f32>,
15    perceptual_roughness: f32,
16    occlusion: vec3<f32>,
17) -> vec3<f32> {
18    let diffuse_ambient = EnvBRDFApprox(diffuse_color, F_AB(1.0, NdotV));
19    let specular_ambient = EnvBRDFApprox(specular_color, F_AB(perceptual_roughness, NdotV));
20
21    // No real world material has specular values under 0.02, so we use this range as a
22    // "pre-baked specular occlusion" that extinguishes the fresnel term, for artistic control.
23    // See: https://google.github.io/filament/Filament.md.html#specularocclusion
24    let specular_occlusion = saturate(dot(specular_color, vec3(50.0 * 0.33)));
25
26    return (diffuse_ambient + specular_ambient * specular_occlusion) * lights.ambient_color.rgb * occlusion;
27}