BBox LWObject::Face::getBBox() const
{
BBox ret = BBox::empty();
ret.extend(m_lwObject->vertices[vert1]);
ret.extend(m_lwObject->vertices[vert2]);
ret.extend(m_lwObject->vertices[vert3]);
return ret;
}
//An iterative split in the middle build for BVHs
void BVH::build(const std::vector<Primitive*> &_objects)
{
std::vector<BBox> objectBBoxes(_objects.size());
BuildStateStruct curState;
curState.centroidBBox = BBox::empty();
std::vector<CentroidWithID> centroids(objectBBoxes.size());
for(size_t i = 0; i < objectBBoxes.size(); i++)
{
objectBBoxes[i] = _objects[i]->getBBox();
centroids[i].centroid = objectBBoxes[i].min.lerp(objectBBoxes[i].max, 0.5f);
centroids[i].origIndex = i;
curState.centroidBBox.extend(centroids[i].centroid);
}
curState.segmentStart = 0;
curState.segmentEnd = objectBBoxes.size();
curState.nodeIndex = 0;
m_nodes.resize(1);
std::stack<BuildStateStruct> buildStack;
const float _EPS = 0.0000001f;
for(;;)
{
size_t objCnt = curState.segmentEnd - curState.segmentStart;
Vector boxDiag = curState.centroidBBox.diagonal();
int splitDim = boxDiag.x > boxDiag.y ? (boxDiag.x > boxDiag.z ? 0 : 2) : (boxDiag.y > boxDiag.z ? 1 : 2);
if(fabs(boxDiag[splitDim]) < _EPS || objCnt < 3)
{
//Create a leaf
const size_t NODE_TYPE_MASK = ((size_t)1 << Node::LEAF_FLAG_BIT);
m_nodes[curState.nodeIndex].bbox = BBox::empty();
m_nodes[curState.nodeIndex].dataIndex = m_leafData.size() | NODE_TYPE_MASK;
for(size_t i = curState.segmentStart; i < curState.segmentEnd; i++)
{
m_nodes[curState.nodeIndex].bbox.extend(objectBBoxes[centroids[i].origIndex]);
m_leafData.push_back(_objects[centroids[i].origIndex]);
}
m_leafData.push_back(NULL);
if(buildStack.empty())
break;
curState = buildStack.top();
buildStack.pop();
continue;
}
float splitVal = (curState.centroidBBox.min[splitDim] + curState.centroidBBox.max[splitDim]) / 2.f;
size_t leftPtr = curState.segmentStart, rightPtr = curState.segmentEnd - 1;
BBox nodeBBox = BBox::empty();
BuildStateStruct rightState;
curState.centroidBBox = BBox::empty();
rightState.centroidBBox = BBox::empty();
while(leftPtr < rightPtr)
{
while(leftPtr < curState.segmentEnd && centroids[leftPtr].centroid[splitDim] <= splitVal)
{
curState.centroidBBox.extend(centroids[leftPtr].centroid);
nodeBBox.extend(objectBBoxes[centroids[leftPtr].origIndex]);
leftPtr++;
}
while(rightPtr >= curState.segmentStart && centroids[rightPtr].centroid[splitDim] > splitVal)
{
rightState.centroidBBox.extend(centroids[rightPtr].centroid);
nodeBBox.extend(objectBBoxes[centroids[rightPtr].origIndex]);
rightPtr--;
}
if(leftPtr >= rightPtr)
break;
std::swap(centroids[leftPtr], centroids[rightPtr]);
}
m_nodes[curState.nodeIndex].bbox = nodeBBox;
m_nodes[curState.nodeIndex].dataIndex = m_nodes.size();
_ASSERT(leftPtr > curState.segmentStart && leftPtr < curState.segmentEnd);
_ASSERT(leftPtr == rightPtr + 1);
rightState.segmentStart = leftPtr;
rightState.segmentEnd = curState.segmentEnd;
curState.segmentEnd = leftPtr;
curState.nodeIndex = m_nodes.size();
rightState.nodeIndex = curState.nodeIndex + 1;
buildStack.push(rightState);
m_nodes.resize(rightState.nodeIndex + 1);
}
}