/// <summary>
/// Sample returns a single possible direction
/// </summary>
/// <param name="woL"></param>
/// <returns></returns>
public override (Spectrum, Vector3, double) Sample_f(Vector3 wo)
{
var F = fresnel.Evaluate(Utils.CosTheta(wo));
bool entering = Utils.CosTheta(wo) > 0;
var etaI = entering ? fresnel.EtaI : fresnel.EtaT;
var etaT = entering ? fresnel.EtaT : fresnel.EtaI;
var n = new Vector3(0, 0, 1);
n = Vector3.Dot(n, wo) < 0 ? -n : n;
var(refracted, wt) = Refract(wo, n, etaI / etaT);
if (!refracted)
{
return(Spectrum.ZeroSpectrum, null, 0);
}
Spectrum ft = r * (1 - F.Max());
var pdf = 1 - F.Max();
return(ft / Utils.AbsCosTheta(wt), wt, pdf);
}
/// <summary>
/// Sample returns a single possible direction
/// </summary>
/// <param name="woL"></param>
/// <returns></returns>
public override (Spectrum, Vector3, double) Sample_f(Vector3 woL)
{
// perfect specular reflection
Vector3 wiL = new Vector3(-woL.x, -woL.y, woL.z);
Spectrum ft = r * fresnel.Evaluate(Utils.CosTheta(wiL));
return(ft / Utils.AbsCosTheta(wiL), wiL, 1);
}
public override Spectrum f(Vector3 wo, Vector3 wi)
{
Vector3 wh = wo + wi;
if (wh.z < 0.0)
{
wi = -wi;
wh = -wh;
}
if (wh.LengthSquared() == 0.0) // epsilon ?
{
return(Spectrum.ZeroSpectrum);
}
wh = wh.Normalize();
double cos_phi_h = Utils.CosPhi(wh);
double sin_phi_h = Utils.SinPhi(wh);
double cos_theta_h = Utils.CosTheta(wh);
double sin_theta_h = Utils.SinTheta(wh);
Vector3 w_hx = new Vector3(cos_phi_h * cos_theta_h, sin_phi_h * cos_theta_h, -sin_theta_h);
Vector3 w_hy = new Vector3(-sin_phi_h, cos_phi_h, 0.0);
Vector3 w_d = new Vector3(Vector3.Dot(wi, w_hx), Vector3.Dot(wi, w_hy), Vector3.Dot(wi, wh));
double theta_h = SphericalTheta(wh);
double theta_d = SphericalTheta(w_d);
double phi_d = SphericalPhi(w_d);
if (phi_d > Math.PI)
{
phi_d = phi_d - Math.PI;
}
// Get i.
int theta_h_idx = ThetaHalfIndex(theta_h);
int theta_d_idx = ThetaDiffIndex(theta_d);
int phi_d_idx = PhiDiffIndex(phi_d);
int i = phi_d_idx + (BRDF_SAMPLING_RES_PHI_D / 2) * (theta_d_idx + theta_h_idx * BRDF_SAMPLING_RES_THETA_D);
return(Spectrum.Create(Vector <double> .Build.Dense(new[] { brdf[3 * i], brdf[3 * i + 1], brdf[3 * i + 2] })));
}