Spectrum BSDF::Sample_f(const Vector3f &woWorld, Vector3f *wiWorld,
const Point2f &u, Float *pdf, BxDFType type,
BxDFType *sampledType) const {
ProfilePhase pp(Prof::BSDFEvaluation);
// Choose which _BxDF_ to sample
int matchingComps = NumComponents(type);
if (matchingComps == 0) {
*pdf = 0;
if (sampledType) *sampledType = BxDFType(0);
return Spectrum(0);
}
int comp =
std::min((int)std::floor(u[0] * matchingComps), matchingComps - 1);
// Get _BxDF_ pointer for chosen component
BxDF *bxdf = nullptr;
int count = comp;
for (int i = 0; i < nBxDFs; ++i)
if (bxdfs[i]->MatchesFlags(type) && count-- == 0) {
bxdf = bxdfs[i];
break;
}
Assert(bxdf);
// Remap _BxDF_ sample _u_ to $[0,1)^2$
Point2f uRemapped(u[0] * matchingComps - comp, u[1]);
// Sample chosen _BxDF_
Vector3f wi, wo = WorldToLocal(woWorld);
*pdf = 0;
if (sampledType) *sampledType = bxdf->type;
Spectrum f = bxdf->Sample_f(wo, &wi, uRemapped, pdf, sampledType);
if (*pdf == 0) {
if (sampledType) *sampledType = BxDFType(0);
return 0;
}
*wiWorld = LocalToWorld(wi);
// Compute overall PDF with all matching _BxDF_s
if (!(bxdf->type & BSDF_SPECULAR) && matchingComps > 1)
for (int i = 0; i < nBxDFs; ++i)
if (bxdfs[i] != bxdf && bxdfs[i]->MatchesFlags(type))
*pdf += bxdfs[i]->Pdf(wo, wi);
if (matchingComps > 1) *pdf /= matchingComps;
// Compute value of BSDF for sampled direction
if (!(bxdf->type & BSDF_SPECULAR) && matchingComps > 1) {
bool reflect = Dot(*wiWorld, ng) * Dot(woWorld, ng) > 0;
f = 0.;
for (int i = 0; i < nBxDFs; ++i)
if (bxdfs[i]->MatchesFlags(type) &&
((reflect && (bxdfs[i]->type & BSDF_REFLECTION)) ||
(!reflect && (bxdfs[i]->type & BSDF_TRANSMISSION))))
f += bxdfs[i]->f(wo, wi);
}
return f;
}
Spectrum BSDF::Sample_f(const Vector &woW, Vector *wiW,
float u1, float u2, float u3, float *pdf,
BxDFType flags, BxDFType *sampledType) const {
// Choose which _BxDF_ to sample
int matchingComps = NumComponents(flags);
if (matchingComps == 0) {
*pdf = 0.f;
return Spectrum(0.f);
}
int which = min(Floor2Int(u3 * matchingComps),
matchingComps-1);
BxDF *bxdf = NULL;
int count = which;
for (int i = 0; i < nBxDFs; ++i)
if (bxdfs[i]->MatchesFlags(flags))
if (count-- == 0) {
bxdf = bxdfs[i];
break;
}
Assert(bxdf); // NOBOOK
// Sample chosen _BxDF_
Vector wi;
Vector wo = WorldToLocal(woW);
*pdf = 0.f;
Spectrum f = bxdf->Sample_f(wo, &wi, u1, u2, pdf);
if (*pdf == 0.f) return 0.f;
if (sampledType) *sampledType = bxdf->type;
*wiW = LocalToWorld(wi);
// Compute overall PDF with all matching _BxDF_s
if (!(bxdf->type & BSDF_SPECULAR) && matchingComps > 1) {
for (int i = 0; i < nBxDFs; ++i) {
if (bxdfs[i] != bxdf &&
bxdfs[i]->MatchesFlags(flags))
*pdf += bxdfs[i]->Pdf(wo, wi);
}
}
if (matchingComps > 1) *pdf /= matchingComps;
// Compute value of BSDF for sampled direction
if (!(bxdf->type & BSDF_SPECULAR)) {
f = 0.;
if (Dot(*wiW, ng) * Dot(woW, ng) > 0)
// ignore BTDFs
flags = BxDFType(flags & ~BSDF_TRANSMISSION);
else
// ignore BRDFs
flags = BxDFType(flags & ~BSDF_REFLECTION);
for (int i = 0; i < nBxDFs; ++i)
if (bxdfs[i]->MatchesFlags(flags))
f += bxdfs[i]->f(wo, wi);
}
return f;
}
RGB BSDF::Sample_f(const Vector &woWorld, Vector *wiWorld,
const BSDFSample &bsdfSample, float *pdf, BxDFType flags,
BxDFType *sampledType) const {
int numComp = NumComponents(flags);
if (numComp == 0) {
*pdf = 0;
if (sampledType)
*sampledType = BxDFType(0);
return 0;
}
int whichComp = min(Floor2Int(bsdfSample.uComponent * numComp),
numComp - 1);
int count = whichComp;
BxDF *bxdf = nullptr; //被选中的Bxdf
for (int i = 0; i < mNumBxdf; ++i) {
if (mBxdfs[i]->MatchesFlag(flags) && count-- == 0) { //这技巧 GOOD
bxdf = mBxdfs[i];
break;
}
}
Vector wo = WorldToLocal(woWorld); //获得局部坐标下的wo
Vector wi;
*pdf = 0.f;
RGB f = bxdf->Sample_f(wo, &wi, bsdfSample.uDir[0], bsdfSample.uDir[1],
pdf); //这里的主要作用是采样出射方向
if (*pdf == 0) {
if (sampledType)
*sampledType = BxDFType(0);
return 0;
}
if (sampledType)
*sampledType = bxdf->type;
*wiWorld = LocalToWorld(wi); //获得世界坐标系下的wi
//计算pdf
if (!(bxdf->type & BSDF_SPECULAR) && numComp > 1) {
for (int i = 0; i < mNumBxdf; ++i) {
if (bxdf != mBxdfs[i] && mBxdfs[i]->MatchesFlag(flags)) {
*pdf += mBxdfs[i]->Pdf(wo, wi);
}
}
}
if (numComp > 1) {
*pdf /= numComp;
}
//开始计算BRDF系数
if (!(bxdf->type & BSDF_SPECULAR)) {
f=0;//因为不是镜面反射 所以重新计算BRDF
if (Dot(*wiWorld, mNG) * Dot(woWorld, mNG) > 0) //反射
flags = BxDFType(flags & ~BSDF_TRANSMISSION);
else//折射
flags = BxDFType(flags & ~BSDF_REFLECTION);
for (int i = 0; i < mNumBxdf; ++i)
if (mBxdfs[i]->MatchesFlag(flags))
f += mBxdfs[i]->f(wo, wi);
}
return f;
}
// sample the bsdf
Colour BSDF::sample(RenderContext *rc,
const HitContext *hc,
const Vec3 &woW,
Vec3 &wiW,
float &pdf,
const float r1,
const float r2,
const float r3,
BxDFtype flags,
BxDFtype *sampled) const
{
// Grab the number of appropriate BxDF
int matchingComps = numComponents(flags);
if (matchingComps == 0)
{
pdf = 0.f;
return Colours::black;
}
// Pick the bxdf
int which = (int)(r3 * matchingComps);//rc->rnd.randInt(matchingComps - 1);
which = which == matchingComps ? matchingComps - 1 : which;
BxDF *bxdf = NULL;
int count = which;
int bxdfNum = 0;
for (int i = 0; i < numBxDFs; ++i)
{
if (bxdfs[i]->hasFlags(flags))
{
if (count-- == 0)
{
bxdf = bxdfs[i];
bxdfNum = i;
break;
}
}
}
// Sample the appropriate BxDF
pdf = 0.0f;
Vec3 wi;
const Vec3 wo = hc->onb.untransform(woW);
const Colour C = getCol(rc, hc, bxdfNum);
Colour f = bxdf->sample(rc, wo, wi, pdf, r1, r2, C);
f = adjust(hc, f, bxdfNum, wo, wi); // custom adjustment for each BSDF
if (pdf == 0.0f) return 0.0f;
if (sampled != NULL) *sampled = bxdf->type;
wiW = hc->onb.transform(wi);
// Compute overall PDF with all matching BxDFs
if (matchingComps > 1)
{
if (!(bxdf->type & BSDF_SPECULAR))
{
for (int i = 0; i < numBxDFs; ++i)
{
if (bxdfs[i] != bxdf && bxdfs[i]->hasFlags(flags))
pdf += bxdfs[i]->pdf(wo, wi);
}
}
pdf /= matchingComps;
}
// Compute value of BSDF for sampled direction
if (!(bxdf->type & BSDF_SPECULAR))
{
f = 0.0;
if (Dot(wiW, hc->gNormal) * Dot(woW, hc->gNormal) > 0)
flags = BxDFtype(flags & ~BSDF_TRANSMISSION); // ignore BTDFs
else
flags = BxDFtype(flags & ~BSDF_REFLECTION); // ignore BRDFs
for (int i = 0; i < numBxDFs; ++i)
{
if (bxdfs[i]->hasFlags(flags))
{
// Tweak eval output to suit each BSDF
f += adjust(hc, bxdfs[i]->eval(wo, wi, getCol(rc, hc, bxdfNum)), i, wo, wi);
}
}
}
return f;
}
