public Vector3 ComputeDirectLightContribution()
        {
            Vector3 specularColor = MaterialPixelStream.MaterialSpecularVisible;

            Vector3 fresnel            = Fresnel.Compute(specularColor);
            float   visibility         = Visibility.Compute();
            float   normalDistribution = NormalDistribution.Compute();

            Vector3 reflected = fresnel * visibility * normalDistribution / 4.0f;

            return(reflected * LightStream.LightSpecularColorNDotL);
        }