bool HomogeneousVolumeDensity::SampleDirection(const Point &p, const Vector& wi,
Vector& wo, float* pdf, RNG &rng) const {
const Point Pobj = WorldToVolume(p);
if(extent.Inside(Pobj)) {
wo = SampleHG(wi, g, rng.RandomFloat(), rng.RandomFloat());
*pdf = PhaseHG(wi, wo, g);
return true;
} else {
return false;
}
}
// HenyeyGreenstein Method Definitions
Float HenyeyGreenstein::Sample_p(const Vector3f &wo, Vector3f *wi,
const Point2f &u) const {
// Compute $\cos \theta$ for Henyey--Greenstein sample
Float cosTheta;
if (std::abs(g) < 1e-3)
cosTheta = 1 - 2 * u[0];
else {
Float sqrTerm = (1 - g * g) / (1 - g + 2 * g * u[0]);
cosTheta = (1 + g * g - sqrTerm * sqrTerm) / (2 * g);
}
// Compute direction _wi_ for Henyey--Greenstein sample
Float sinTheta = std::sqrt(std::max((Float)0, 1 - cosTheta * cosTheta));
Float phi = 2 * Pi * u[1];
Vector3f v1, v2;
CoordinateSystem(wo, &v1, &v2);
*wi = SphericalDirection(sinTheta, cosTheta, phi, v1, v2, -wo);
return PhaseHG(-cosTheta, g);
}
Float BeamDiffusionSS(Float sigma_s, Float sigma_a, Float g, Float eta,
Float r) {
// Compute material parameters and minimum $t$ below the critical angle
Float sigma_t = sigma_a + sigma_s, rho = sigma_s / sigma_t;
Float tCrit = r * std::sqrt(eta * eta - 1);
Float Ess = 0;
const int nSamples = 100;
for (int i = 0; i < nSamples; ++i) {
// Evaluate single scattering integrand and add to _Ess_
Float ti = tCrit - std::log(1 - (i + .5f) / nSamples) / sigma_t;
// Determine length $d$ of connecting segment and $\cos\theta_\roman{o}$
Float d = std::sqrt(r * r + ti * ti);
Float cosThetaO = ti / d;
// Add contribution of single scattering at depth $t$
Ess += rho * std::exp(-sigma_t * (d + tCrit)) / (d * d) *
PhaseHG(cosThetaO, g) * (1 - FrDielectric(-cosThetaO, 1, eta)) *
std::abs(cosThetaO);
}
return Ess / nSamples;
}
float HGPdf(const Vector &w, const Vector &wp, float g) {
return PhaseHG(w, wp, g);
}
Float HenyeyGreenstein::p(const Vector3f &wo, const Vector3f &wi) const {
return PhaseHG(Dot(wo, wi), g);
}
float p(const Point &p, const Vector &wi, const Vector &wo) const {
if (!extent.Inside(WorldToVolume(p))) return 0.;
return PhaseHG(wi, wo, g);
}
