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let mut n1 = 1.0;
    let mut n2 = ior;

    let cos_theta_incidence = normal_normalized.dot(angle_of_incidence_normalized);
    let sin_theta_incidence = (1.0 - cos_theta_incidence * cos_theta_incidence).sqrt();

    if cos_theta_incidence > 0.0 {
        n1 = ior;
        n2 = 1.0;
    }

    let sin_theta_transmittance = n1 * (sin_theta_incidence / n2);
    let cos_theta_transmittance = (1.0 - sin_theta_transmittance * sin_theta_transmittance).sqrt();

    let n1_cos_theta_transmittance = n1 * cos_theta_transmittance;
    let n2_cos_theta_transmittance = n2 * cos_theta_transmittance;
    let n1_cos_theta_incidence = n1 * cos_theta_incidence;
    let n2_cos_theta_incidence = n2 * cos_theta_incidence;

    let s_polarized_sqrt = (n1_cos_theta_incidence - n2_cos_theta_transmittance)
        / (n1_cos_theta_incidence + n2_cos_theta_transmittance);
    let s_polarized = s_polarized_sqrt * s_polarized_sqrt;

    let p_polarized_sqrt = (n2_cos_theta_incidence - n1_cos_theta_transmittance)
        / (n2_cos_theta_incidence + n1_cos_theta_transmittance);
    let p_polarized = p_polarized_sqrt * p_polarized_sqrt;

    fresnel_ratio = (s_polarized + p_polarized) / 2.0;