bool GridAccel::IntersectP(const Ray &ray) const {
PBRT_GRID_INTERSECTIONP_TEST(const_cast<GridAccel *>(this), const_cast<Ray *>(&ray));
RWMutexLock lock(*rwMutex, READ);
// Check ray against overall grid bounds
float rayT;
if (bounds.Inside(ray(ray.mint)))
rayT = ray.mint;
else if (!bounds.IntersectP(ray, &rayT)) {
PBRT_GRID_RAY_MISSED_BOUNDS();
return false;
}
Point gridIntersect = ray(rayT);
// Set up 3D DDA for ray
float NextCrossingT[3], DeltaT[3];
int Step[3], Out[3], Pos[3];
for (int axis = 0; axis < 3; ++axis) {
// Compute current voxel for axis
Pos[axis] = posToVoxel(gridIntersect, axis);
if (ray.d[axis] >= 0) {
// Handle ray with positive direction for voxel stepping
NextCrossingT[axis] = rayT +
(voxelToPos(Pos[axis]+1, axis) - gridIntersect[axis]) / ray.d[axis];
DeltaT[axis] = Width[axis] / ray.d[axis];
Step[axis] = 1;
Out[axis] = NVoxels[axis];
}
else {
// Handle ray with negative direction for voxel stepping
NextCrossingT[axis] = rayT +
(voxelToPos(Pos[axis], axis) - gridIntersect[axis]) / ray.d[axis];
DeltaT[axis] = -Width[axis] / ray.d[axis];
Step[axis] = -1;
Out[axis] = -1;
}
}
// Walk grid for shadow ray
for (;;) {
int o = offset(Pos[0], Pos[1], Pos[2]);
Voxel *voxel = voxels[o];
PBRT_GRID_RAY_TRAVERSED_VOXEL(Pos, voxel ? voxel->size() : 0);
if (voxel && voxel->IntersectP(ray, lock))
return true;
// Advance to next voxel
// Find _stepAxis_ for stepping to next voxel
int bits = ((NextCrossingT[0] < NextCrossingT[1]) << 2) +
((NextCrossingT[0] < NextCrossingT[2]) << 1) +
((NextCrossingT[1] < NextCrossingT[2]));
const int cmpToAxis[8] = { 2, 1, 2, 1, 2, 2, 0, 0 };
int stepAxis = cmpToAxis[bits];
if (ray.maxt < NextCrossingT[stepAxis])
break;
Pos[stepAxis] += Step[stepAxis];
if (Pos[stepAxis] == Out[stepAxis])
break;
NextCrossingT[stepAxis] += DeltaT[stepAxis];
}
return false;
}
