Spectrum GridDensityMedium::Sample(const Ray &_ray, Sampler &sampler,
MemoryArena &arena,
MediumInteraction *mi) const {
// Transform the ray into local coordinates and determine overlap interval
// [_tMin, tMax_]
const Bounds3f dataBounds(Point3f(0.f, 0.f, 0.f), Point3f(1.f, 1.f, 1.f));
Ray ray = WorldToMedium(
Ray(_ray.o, Normalize(_ray.d), _ray.tMax * _ray.d.Length()));
Float tMin, tMax;
if (!dataBounds.IntersectP(ray, &tMin, &tMax)) return Spectrum(1.f);
tMin = std::max(tMin, (Float)0.f);
tMax = std::min(tMax, ray.tMax);
if (tMin >= tMax) return Spectrum(1.f);
// Run Delta-Tracking iterations to sample a medium interaction
Float t = tMin;
while (true) {
t -= std::log(1 - sampler.Get1D()) * invMaxDensity;
if (t >= tMax) break;
Float density = Density(ray(t));
if (density * invMaxDensity * sigma_t > sampler.Get1D()) {
// Populate _mi_ with medium interaction information and return
PhaseFunction *phase = ARENA_ALLOC(arena, HenyeyGreenstein)(g);
*mi = MediumInteraction(_ray(t), -_ray.d, _ray.time, this, phase);
return sigma_s / sigma_t;
}
}
return Spectrum(1.0f);
}
Spectrum GridDensityMedium::Sample(const Ray &rWorld, Sampler &sampler,
MemoryArena &arena,
MediumInteraction *mi) const {
Ray ray = WorldToMedium(
Ray(rWorld.o, Normalize(rWorld.d), rWorld.tMax * rWorld.d.Length()));
// Compute $[\tmin, \tmax]$ interval of _ray_'s overlap with medium bounds
const Bounds3f b(Point3f(0, 0, 0), Point3f(1, 1, 1));
Float tMin, tMax;
if (!b.IntersectP(ray, &tMin, &tMax)) return Spectrum(1.f);
// Run delta-tracking iterations to sample a medium interaction
Float t = tMin;
while (true) {
t -= std::log(1 - sampler.Get1D()) * invMaxDensity;
if (t >= tMax) break;
if (Density(ray(t)) * invMaxDensity * sigma_t > sampler.Get1D()) {
// Populate _mi_ with medium interaction information and return
PhaseFunction *phase = ARENA_ALLOC(arena, HenyeyGreenstein)(g);
*mi = MediumInteraction(rWorld(t), -rWorld.d, rWorld.time, this,
phase);
return sigma_s / sigma_t;
}
}
return Spectrum(1.f);
}
Spectrum GridDensityMedium::Tr(const Ray &rWorld, Sampler &sampler) const {
Ray ray = WorldToMedium(
Ray(rWorld.o, Normalize(rWorld.d), rWorld.tMax * rWorld.d.Length()));
// Compute $[\tmin, \tmax]$ interval of _ray_'s overlap with medium bounds
const Bounds3f b(Point3f(0, 0, 0), Point3f(1, 1, 1));
Float tMin, tMax;
if (!b.IntersectP(ray, &tMin, &tMax)) return Spectrum(1.f);
// Perform ratio tracking to estimate the transmittance value
Float Tr = 1, t = tMin;
while (true) {
t += -std::log(1 - sampler.Get1D()) * invMaxDensity;
if (t >= tMax) break;
Float density = Density(ray(t));
Tr *= 1 - std::max((Float)0, sigma_t * density * invMaxDensity);
}
return Spectrum(Tr);
}
Spectrum GridDensityMedium::T(const Ray &_ray, Sampler &sampler) const {
// Transform the ray into local coordinates and determine overlap interval
// [_tMin, tMax_]
const Bounds3f dataBounds(Point3f(0.f, 0.f, 0.f), Point3f(1.f, 1.f, 1.f));
Ray ray = WorldToMedium(
Ray(_ray.o, Normalize(_ray.d), _ray.tMax * _ray.d.Length()));
Float tMin, tMax;
if (!dataBounds.IntersectP(ray, &tMin, &tMax)) return Spectrum(1.f);
tMin = std::max(tMin, (Float)0.f);
tMax = std::min(tMax, ray.tMax);
if (tMin >= tMax) return Spectrum(1.f);
Float tr = 1.f;
// Perform ratio tracking to estimate the transmittance value
Float t = tMin;
while (true) {
t -= std::log(1 - sampler.Get1D()) * invMaxDensity;
if (t >= tMax) break;
Float density = Density(ray(t));
tr *= 1.f - std::max((Float)0, sigma_t * density * invMaxDensity);
}
return Spectrum(tr);
}
