// commented, dpl 10 august 2005
void Anisotropic::Sample_f(const Vector &wo, Vector *wi,
float u1, float u2, float *pdf) const {
// Sample from first quadrant and remap to hemisphere to sample \wh
float phi, costheta;
if (u1 < .25f) {
sampleFirstQuadrant(4.f * u1, u2, &phi, &costheta);
} else if (u1 < .5f) {
u1 = 4.f * (.5f - u1);
sampleFirstQuadrant(u1, u2, &phi, &costheta);
phi = M_PI - phi;
} else if (u1 < .75f) {
u1 = 4.f * (u1 - .5f);
sampleFirstQuadrant(u1, u2, &phi, &costheta);
phi += M_PI;
} else {
u1 = 4.f * (1.f - u1);
sampleFirstQuadrant(u1, u2, &phi, &costheta);
phi = 2.f * M_PI - phi;
}
float sintheta = sqrtf(max(0.f, 1.f - costheta*costheta));
Vector H = SphericalDirection(sintheta, costheta, phi);
if (Dot(wo, H) < 0.f) H = -H;
// Compute incident direction by reflecting about $\wh$
*wi = -wo + 2.f * Dot(wo, H) * H;
// Compute PDF for \wi from Anisotropic distribution
float anisotropic_pdf = D(H) / (4.f * Dot(wo, H));
*pdf = anisotropic_pdf;
}
//复制自PBRT
void Anisotropic::Sample_f(const Vector3f &wo, Vector3f *wi, Float u1, Float u2,
Float *pdf) const {
Float phi, costheta;
if (u1 < .25f) {
sampleFirstQuadrant(4.f * u1, u2, &phi, &costheta);
} else if (u1 < .5f) {
u1 = 4.f * (.5f - u1);
sampleFirstQuadrant(u1, u2, &phi, &costheta);
phi = Pi - phi;
} else if (u1 < .75f) {
u1 = 4.f * (u1 - .5f);
sampleFirstQuadrant(u1, u2, &phi, &costheta);
phi += Pi;
} else {
u1 = 4.f * (1.f - u1);
sampleFirstQuadrant(u1, u2, &phi, &costheta);
phi = 2.f * Pi - phi;
}
Float sintheta = sqrtf(std::max(0.f, 1.f - costheta * costheta));
Vector3f wh = SphericalDirection(sintheta, costheta, phi);
if (!SameHemisphere(wo, wh))
wh = -wh;
// Compute incident direction by reflecting about $\wh$
*wi = -wo + 2.f * Dot(wo, wh) * wh;
// Compute PDF for $\wi$ from anisotropic distribution
Float costhetah = AbsCosTheta(wh);
Float ds = 1.f - costhetah * costhetah;
Float anisotropic_pdf = 0.f;
if (ds > 0.f && Dot(wo, wh) > 0.f) {
Float e = (ex * wh.x * wh.x + ey * wh.y * wh.y) / ds;
Float d = sqrtf((ex + 1.f) * (ey + 1.f)) * InvTwoPi
* powf(costhetah, e);
anisotropic_pdf = d / (4.f * Dot(wo, wh));
}
*pdf = anisotropic_pdf;
}
