static std::vector<NearestPhoton>::iterator nearest(std::vector<Photon>::const_iterator begin, std::vector<Photon>::const_iterator end, Segment3f const& bound, Point3f const& position, std::vector<NearestPhoton>::iterator nearestBegin, std::vector<NearestPhoton>::iterator nearestNext, std::vector<NearestPhoton>::iterator nearestEnd) {
if (begin == end) {
return nearestNext;
}
std::vector<Photon>::const_iterator median = begin + (end - begin) / 2;
float medianSqrDistance = sqrDistance(median->position, position);
if (nearestNext == nearestEnd) {
if (medianSqrDistance < nearestBegin->sqrDistance) {
std::pop_heap(nearestBegin, nearestNext--, SqrDistanceLess());
nearestNext->photon = median;
nearestNext->sqrDistance = medianSqrDistance;
std::push_heap(nearestBegin, ++nearestNext, SqrDistanceLess());
}
} else {
nearestNext->photon = median;
nearestNext->sqrDistance = medianSqrDistance;
std::push_heap(nearestBegin, ++nearestNext, SqrDistanceLess());
}
int splitAxis = maxAxis(bound);
if (position[splitAxis] <= median->position[splitAxis]) {
Segment3f belowBound = bound;
belowBound.max[splitAxis] = median->position[splitAxis];
nearestNext = nearest(begin, median, belowBound, position, nearestBegin, nearestNext, nearestEnd);
} else {
Segment3f aboveBound = bound;
aboveBound.min[splitAxis] = median->position[splitAxis];
nearestNext = nearest(median + 1, end, aboveBound, position, nearestBegin, nearestNext, nearestEnd);
}
if (nearestNext != nearestEnd || sqr(median->position[splitAxis] - position[splitAxis]) < nearestBegin->sqrDistance) {
if (position[splitAxis] <= median->position[splitAxis]) {
Segment3f aboveBound = bound;
aboveBound.min[splitAxis] = median->position[splitAxis];
nearestNext = nearest(median + 1, end, aboveBound, position, nearestBegin, nearestNext, nearestEnd);
} else {
Segment3f belowBound = bound;
belowBound.max[splitAxis] = median->position[splitAxis];
nearestNext = nearest(begin, median, belowBound, position, nearestBegin, nearestNext, nearestEnd);
}
}
return nearestNext;
}
void buildLevelOnSubtree(int level, int subtree, std::vector<Photon>::iterator begin, std::vector<Photon>::iterator end, Segment3f const& bound) {
if (begin == end) {
return;
}
int splitAxis = maxAxis(bound);
if (level == 0) {
std::sort(begin, end, [=](Photon const& a, Photon const& b) {
return a.position[splitAxis] < b.position[splitAxis];
});
return;
}
std::vector<Photon>::iterator median = begin + (end - begin) / 2;
int mask = 1 << (level - 1);
if ((subtree & mask) == 0) {
Segment3f belowBound = bound;
belowBound.max[splitAxis] = median->position[splitAxis];
buildLevelOnSubtree(level - 1, subtree & ~mask, begin, median, belowBound);
} else {
Segment3f aboveBound = bound;
aboveBound.min[splitAxis] = median->position[splitAxis];
buildLevelOnSubtree(level - 1, subtree & ~mask, median + 1, end, aboveBound);
}
}
/**
* Get the maximum component in the vector (according to signed comparison). To compare absolute values, use maxAbs()
* instead.
*/
T const & max() const { return values[maxAxis()]; }
int maxAxis(Segment3<T> const& segment) {
return maxAxis(extent(segment));
}
