/// <summary>
/// Computes the ratio of self-masked area to visible area. Used by <see cref="MaskingShadowing(Vector3)"/>.
/// </summary>
/// <param name="normal">Normal of the microfacets, in shading space.</param>
/// <returns>Ratio of self-masked area to visible area.</returns>
public float MaskingRatio(Vector3 normal)
{
float absTanTheta = MathF.Abs(ShadingSpace.TanTheta(normal));
if (float.IsInfinity(absTanTheta))
{
return(0);
}
float alpha = MathF.Sqrt(ShadingSpace.CosPhiSqr(normal) * AlphaX * AlphaX + ShadingSpace.SinPhiSqr(normal) * AlphaY * AlphaY);
float alpha2Tan2Theta = alpha * absTanTheta * (alpha * absTanTheta);
return((-1 + MathF.Sqrt(1 + alpha2Tan2Theta)) / 2);
}
/// <summary>
/// Computes the distribution of microfacets with the given normal.
/// </summary>
/// <param name="normal">The normal vector of the microfacets, in shading space.</param>
/// <returns>The fraction of microfacets that are oriented with the given normal.</returns>
public float NormalDistribution(Vector3 normal)
{
float tan2Theta = ShadingSpace.TanThetaSqr(normal);
if (float.IsInfinity(tan2Theta))
{
return(0);
}
float cos4Theta = ShadingSpace.CosThetaSqr(normal) * ShadingSpace.CosThetaSqr(normal);
float e = tan2Theta * (
ShadingSpace.CosPhiSqr(normal) / (AlphaX * AlphaX)
+ ShadingSpace.SinPhiSqr(normal) / (AlphaY * AlphaY)
);
return(1 / (MathF.PI * AlphaX * AlphaY * cos4Theta * (1 + e) * (1 + e)));
}