private void Build()
{
int stackptr = 0;
uint Untouched = 0xffffffff;
uint TouchedTwice = 0xfffffffd;
PREALLOC[stackptr].mStart = 0;
PREALLOC[stackptr].mEnd = (uint)mBuildPrims.Count;
PREALLOC[stackptr].mParent = 0xfffffffc;
stackptr++;
List <BVHFlatNode> buildnodes = new List <BVHFlatNode>(mBuildPrims.Count * 2);
while (stackptr > 0)
{
BVHBuildEntry bnode = PREALLOC[--stackptr];
uint start = bnode.mStart;
uint end = bnode.mEnd;
uint nPrims = end - start;
mNumNodes++;
BVHFlatNode node = new BVHFlatNode();
node.mStartIndex = start;
node.mLeafCount = nPrims;
node.mRightOffset = Untouched;
BVHBox bb = new BVHBox(mBuildPrims[(int)start].GetBBox().mMin, mBuildPrims[(int)start].GetBBox().mMax);
BVHBox bc = new BVHBox(mBuildPrims[(int)start].GetCentroid());
for (uint p = start + 1; p < end; ++p)
{
bb.ExpandToInclude(mBuildPrims[(int)p].GetBBox());
bc.ExpandToInclude(mBuildPrims[(int)p].GetCentroid());
}
node.mBox = bb;
if (nPrims <= mNodeMaxLeafSize)
{
node.mRightOffset = 0;
mNumLeafs++;
}
buildnodes.Add(node);
// 记录父节点关于右孩子结点相对父结点的偏移值mRightOffset
// 第一次为左孩子，相对父结点的偏移值为1
// 每个父节点最多被两次 hit
if (bnode.mParent != 0xfffffffc)
{
buildnodes[(int)bnode.mParent].mRightOffset--;
if (buildnodes[(int)bnode.mParent].mRightOffset == TouchedTwice)
{
buildnodes[(int)bnode.mParent].mRightOffset = (uint)mNumNodes - 1 - bnode.mParent;
}
}
if (node.mRightOffset == 0)
{
continue;
}
// 选择合适的分割维度
uint split_dim = (uint)bc.MaxDimension();
float split_coord = 0.5f * (bc.mMin[(int)split_dim] + bc.mMax[(int)split_dim]);
uint mid = start;
// 交换 start 和 end 之间 的数据
for (uint i = start; i < end; ++i)
{
if (mBuildPrims[(int)i].GetCentroid()[(int)split_dim] < split_coord)
{
BVHObject temp = mBuildPrims[(int)i];
mBuildPrims[(int)i] = mBuildPrims[(int)mid];
mBuildPrims[(int)mid] = temp;
++mid;
}
}
if (mid == start || mid == end)
{
mid = start + (end - start) / 2;
}
// 右孩子
PREALLOC[stackptr].mStart = mid;
PREALLOC[stackptr].mEnd = end;
PREALLOC[stackptr].mParent = (uint)mNumNodes - 1;
stackptr++;
// 左孩子
PREALLOC[stackptr].mStart = start;
PREALLOC[stackptr].mEnd = mid;
PREALLOC[stackptr].mParent = (uint)mNumNodes - 1;
stackptr++;
}
if (mFlatTreeList != null)
{
mFlatTreeList.Clear();
}
mFlatTreeList = new List <BVHFlatNode>(mNumNodes);
for (uint n = 0; n < mNumNodes; ++n)
{
mFlatTreeList.Add(buildnodes[(int)n]);
}
}
private void Build()
{
int stackptr = 0;
mNumNodes = mNumLeafs = 0;
uint Untouched = 0xffffffff;
uint TouchedTwice = 0xfffffffd;
PREALLOC[stackptr].Start = 0;
PREALLOC[stackptr].End = (uint)mBuildPrims.Count;
PREALLOC[stackptr].Parent = 0xfffffffc;
stackptr++;
List <BVHFlatNode> buildnodes = new List <BVHFlatNode>(mBuildPrims.Count * 2);
while (stackptr > 0)
{
BVHBuildEntry bnode = PREALLOC[--stackptr];
uint start = bnode.Start;
uint end = bnode.End;
uint nPrims = end - start;
BVHFlatNode node = new BVHFlatNode();
node.StartIndex = start;
node.LeafCount = nPrims;
node.RightOffset = Untouched;
BVHBox bb = new BVHBox(mBuildPrims[(int)start].GetBBox().Min, mBuildPrims[(int)start].GetBBox().Max);
BVHBox bc = new BVHBox(mBuildPrims[(int)start].GetCentroid());
// 计算 bnode 的 BBox
for (uint p = start + 1; p < end; ++p)
{
bb.ExpandToInclude(mBuildPrims[(int)p].GetBBox());
bc.ExpandToInclude(mBuildPrims[(int)p].GetCentroid());
}
node.Box = bb;
// 节点数小于叶节点设置的数量，不继续划分，叶节点数量增1
if (nPrims <= mNodeMaxLeafSize)
{
node.RightOffset = 0;
mNumLeafs++;
}
// 添加
mNumNodes++; // 实际上为 buildnodes 的Count
buildnodes.Add(node);
// 记录父节点关于右孩子结点相对父结点的偏移值mRightOffset
// 第一次为左孩子，相对父结点的偏移值为1
// 每个父节点最多被两次 hit
// 后面入栈：先右孩子再左孩子
// 执行出站：先出左孩子再出右孩子
// 父节点最开始设置为 RightOffset = Untouched = 0xffffffff
// 执行到 左孩子时 RightOffset -= 1 = 0xfffffffe
// 执行到 右孩子时 RightOffset -= 1 = 0xfffffffd = TouchedTwice
if (bnode.Parent != 0xfffffffc)
{
buildnodes[(int)bnode.Parent].RightOffset--;
if (buildnodes[(int)bnode.Parent].RightOffset == TouchedTwice)
{
// 此时处理的是右孩子，记录右孩子的起始索引
buildnodes[(int)bnode.Parent].RightOffset = (uint)mNumNodes - 1 - bnode.Parent;
}
}
// 叶节点
if (node.RightOffset == 0)
{
continue;
}
// 选择合适的分割维度
uint split_dim = (uint)bc.MaxDimension();
// 计算分割值
float split_coord = 0.5f * (bc.Min[(int)split_dim] + bc.Max[(int)split_dim]);
uint mid = start;
// 交换 start 和 end 之间 的数据
for (uint i = start; i < end; ++i)
{
// 将 小于 分割值 放 左边
if (mBuildPrims[(int)i].GetCentroid()[(int)split_dim] < split_coord)
{
BVHObject temp = mBuildPrims[(int)i];
mBuildPrims[(int)i] = mBuildPrims[(int)mid];
mBuildPrims[(int)mid] = temp;
++mid;
}
}
// 全部大于 或者 全部小于 则 取中间平分两块
if (mid == start || mid == end)
{
mid = start + (end - start) / 2;
}
// 右孩子
PREALLOC[stackptr].Start = mid;
PREALLOC[stackptr].End = end;
PREALLOC[stackptr].Parent = (uint)mNumNodes - 1;
stackptr++;
// 左孩子
PREALLOC[stackptr].Start = start;
PREALLOC[stackptr].End = mid;
PREALLOC[stackptr].Parent = (uint)mNumNodes - 1;
stackptr++;
}
if (mFlatTreeList != null)
{
mFlatTreeList.Clear();
}
mFlatTreeList = new List <BVHFlatNode>(mNumNodes);
for (uint n = 0; n < mNumNodes; ++n)
{
mFlatTreeList.Add(buildnodes[(int)n]);
}
}