Function fresnel_schlick

tools/bloom-reference/src/main.rs:1071–1074

Schlick's Fresnel approximation. `f0` is reflectance at normal incidence; `cos_theta` is dot(surface_normal, view_dir).

(cos_theta: f32, f0: Vec3)

/// Schlick's Fresnel approximation. `f0` is reflectance at normal
/// incidence; `cos_theta` is dot(surface_normal, view_dir).
fn fresnel_schlick(cos_theta: f32, f0: Vec3) -> Vec3 {
    let m = (1.0 - cos_theta).clamp(0.0, 1.0);
    f0 + (Vec3::ONE - f0) * (m * m * m * m * m)
}

/// GGX (Trowbridge-Reitz) normal distribution.
fn d_ggx(n_dot_h: f32, alpha: f32) -> f32 {