vec3 EricHeitz2018GGX(in vec3 V, in vec3 L, in float roughness, in float anisotropic, in float ior)
{
    float alpha = roughness * roughness;
    float aspect = sqrt(1.0 - 0.9 * anisotropic);
    float alpha_x = alpha * aspect;
    float alpha_y = alpha / aspect;

    vec3 H = normalize(L + V);
    float NoV = CosTheta(V);
    float NoL = CosTheta(L);
    if (NoV < 0.0 || NoL < 0.0) return vec3(0);

    float VoH = dot(V, H);
    float NoH = CosTheta(H);
    vec3 F0 = vec3(abs((1.0 - ior) / (1.0 + ior)));
    F0 = F0 * F0;

    float D = EricHeitz2018GGXD(H, alpha_x, alpha_y);
    vec3 F = SchlickFresnel(max(NoV, 0.0), F0);
    float G = EricHeitz2018GGXG2(V, L, alpha_x, alpha_y);
    return (F * D * G) / (4.0f * VoH * NoH);
}