static Vector3f TrowbridgeReitzSample(const Vector3f &wi, Float alpha_x,
Float alpha_y, Float U1, Float U2) {
// 1. stretch wi
Vector3f wiStretched =
Normalize(Vector3f(alpha_x * wi.x, alpha_y * wi.y, wi.z));
// 2. simulate P22_{wi}(x_slope, y_slope, 1, 1)
Float slope_x, slope_y;
TrowbridgeReitzSample11(CosTheta(wiStretched), U1, U2, &slope_x, &slope_y);
// 3. rotate
Float tmp = CosPhi(wiStretched) * slope_x - SinPhi(wiStretched) * slope_y;
slope_y = SinPhi(wiStretched) * slope_x + CosPhi(wiStretched) * slope_y;
slope_x = tmp;
// 4. unstretch
slope_x = alpha_x * slope_x;
slope_y = alpha_y * slope_y;
// 5. compute normal
return Normalize(Vector3f(-slope_x, -slope_y, 1.));
}
// commented, dpl 10 august 2005
Spectrum OrenNayar::f(const Vector &wo,
const Vector &wi) const {
float sinthetai = SinTheta(wi);
float sinthetao = SinTheta(wo);
// Compute cosine term of Oren--Nayar model
float sinphii = SinPhi(wi), cosphii = CosPhi(wi);
float sinphio = SinPhi(wo), cosphio = CosPhi(wo);
float dcos = cosphii * cosphio + sinphii * sinphio;
float maxcos = max(0.f, dcos);
// Compute sine and tangent terms of Oren--Nayar model
float sinalpha, tanbeta;
if (fabsf(CosTheta(wi)) > fabsf(CosTheta(wo))) {
sinalpha = sinthetao;
tanbeta = sinthetai / fabsf(CosTheta(wi));
}
else {
sinalpha = sinthetai;
tanbeta = sinthetao / fabsf(CosTheta(wo));
}
return R * INV_PI *
(A + B * maxcos * sinalpha * tanbeta);
}
Spectrum OrenNayar::f(const Vector3f &wo, const Vector3f &wi) const {
Float sinThetaI = SinTheta(wi);
Float sinThetaO = SinTheta(wo);
// Compute cosine term of Oren-Nayar model
Float maxCos = 0;
if (sinThetaI > 1e-4 && sinThetaO > 1e-4) {
Float sinPhiI = SinPhi(wi), cosPhiI = CosPhi(wi);
Float sinPhiO = SinPhi(wo), cosPhiO = CosPhi(wo);
Float dCos = cosPhiI * cosPhiO + sinPhiI * sinPhiO;
maxCos = std::max((Float)0, dCos);
}
// Compute sine and tangent terms of Oren-Nayar model
Float sinAlpha, tanBeta;
if (AbsCosTheta(wi) > AbsCosTheta(wo)) {
sinAlpha = sinThetaO;
tanBeta = sinThetaI / AbsCosTheta(wi);
} else {
sinAlpha = sinThetaI;
tanBeta = sinThetaO / AbsCosTheta(wo);
}
return R * InvPi * (A + B * maxCos * sinAlpha * tanBeta);
}