Function shade_point 

pub fn shade_point(
    material: &ShadeMaterial,
    lights: &[Light],
    n: Vec3,
    v: Vec3,
    position: Vec3,
    env: Option<&PrefilterEnv>,
    brdf_lut: Option<&BrdfLut>,
) -> Vec3

Full shading of a surface point given material, lights, geometry, and an optional IBL environment.

Returns linear HDR radiance (before tone-mapping).