Function sky

examples/shaders/sky-shader/src/lib.rs:74–129

(dir: Vec3, sun_position: Vec3, sun_intensity_extra_spec_const_factor: u32)

}

fn sky(dir: Vec3, sun_position: Vec3, sun_intensity_extra_spec_const_factor: u32) -> Vec3 {
    let up = vec3(0.0, 1.0, 0.0);
    let sunfade = 1.0 - (1.0 - saturate(sun_position.y / 450000.0).exp());
    let rayleigh_coefficient = RAYLEIGH - (1.0 * (1.0 - sunfade));
    let beta_r = total_rayleigh(PRIMARIES) * rayleigh_coefficient;

    // Mie coefficient
    let beta_m = total_mie(PRIMARIES, MIE_K_COEFFICIENT, TURBIDITY) * MIE_COEFFICIENT;

    // Optical length, cutoff angle at 90 to avoid singularity
    let zenith_angle = acos_approx(up.dot(dir).max(0.0));
    let denom = (zenith_angle).cos() + 0.15 * (93.885 - ((zenith_angle * 180.0) / PI)).powf(-1.253);

    let s_r = RAYLEIGH_ZENITH_LENGTH / denom;
    let s_m = MIE_ZENITH_LENGTH / denom;

    // Combined extinction factor
    let fex = exp(-(beta_r * s_r + beta_m * s_m));

    // In-scattering
    let sun_direction = sun_position.normalize();
    let cos_theta = dir.dot(sun_direction);
    let beta_r_theta = beta_r * rayleigh_phase(cos_theta * 0.5 + 0.5);

    let beta_m_theta = beta_m * henyey_greenstein_phase(cos_theta, MIE_DIRECTIONAL_G);
    let sun_e = sun_intensity(sun_direction.dot(up))

    // HACK(eddyb) this acts like an integration test for specialization constants,
    // but the correct value is only obtained when this is a noop (multiplies by `1`).
        * (sun_intensity_extra_spec_const_factor as f32 / 100.0);

    let mut lin = pow(
        sun_e * ((beta_r_theta + beta_m_theta) / (beta_r + beta_m)) * (Vec3::splat(1.0) - fex),
        1.5,
    );

    lin *= Vec3::splat(1.0).lerp(
        pow(
            sun_e * ((beta_r_theta + beta_m_theta) / (beta_r + beta_m)) * fex,
            0.5,
        ),
        saturate((1.0 - up.dot(sun_direction)).powf(5.0)),
    );

    // Composition + solar disc
    let sun_angular_diameter_cos = SUN_ANGULAR_DIAMETER_DEGREES.cos();
    let sundisk = smoothstep(
        sun_angular_diameter_cos,
        sun_angular_diameter_cos + 0.00002,
        cos_theta,
    );
    let mut l0 = 0.1 * fex;
    l0 += sun_e * 19000.0 * fex * sundisk;

    lin + l0
}

fn get_ray_dir(uv: Vec2, pos: Vec3, look_at_pos: Vec3) -> Vec3 {