RGB SpecularTransmission::Sample_f(const Vector& wo, Vector* wi, float u1,
float u2, float *pdf) const {
bool entering = CosTheta(wo) > 0.;
float ei = mEtaI, et = mEtaT;
if (!entering) //判断wo是从外面射入还是从内部射出
swap(ei, et);
//根据Snell's law 计算折射方向
float sini2 = SinTheta2(wo);
float eta = ei / et;
float sint2 = eta * eta * sini2;
if (sint2 >= 1.)
return 0.; //所有的光线全部反射，所以没有折射
float cost = sqrtf(max(0.f, 1.f - sint2));
if (entering)
cost = -cost; //设置符号
float sintOverSini = eta;
*wi = Vector(sintOverSini * -wo.x, sintOverSini * -wo.y, cost);
*pdf = 1.f;
RGB F = mFresnel.Evaluate(CosTheta(wo)); //计算反射系数
return (ei * ei) / (et * et) * (RGB(1.0f) - F) * mScale / AbsCosTheta(*wi);
}
// commented, dpl 10 august 2005
Spectrum SpecularTransmission::Sample_f(const Vector &wo,
Vector *wi, float u1, float u2, float *pdf) const {
// Figure out which $\eta$ is incident and which is transmitted
bool entering = CosTheta(wo) > 0.;
float ei = etai, et = etat;
if (!entering)
swap(ei, et);
// Compute transmitted ray direction
float sini2 = SinTheta2(wo);
float eta = ei / et;
float sint2 = eta * eta * sini2;
// Handle total internal reflection for transmission
if (sint2 > 1.) return 0.;
float cost = sqrtf(max(0.f, 1.f - sint2));
if (entering) cost = -cost;
float sintOverSini = eta;
*wi = Vector(sintOverSini * -wo.x,
sintOverSini * -wo.y,
cost);
*pdf = 1.f;
Spectrum F = fresnel.Evaluate(CosTheta(wo));
return (ei*ei)/(et*et) * (Spectrum(1.)-F) * T /
fabsf(CosTheta(*wi));
}
