List <LinearBVHNode> nodes; //改为array?
// BVHAccel Method Definitions
public void InitBVHAccel(List <BaseShape> p, int mp, string sm)
{
maxPrimsInNode = Max(255, mp);
Shapes = p;
var shapeCount = Shapes.Count;
if (shapeCount == 0)
{
nodes = null;
return;
}
// Initialize _buildData_ array for Shapes
List <BVHShapeInfo> buildData = new List <BVHShapeInfo>(shapeCount);
for (int i = 0; i < shapeCount; ++i)
{
AABB bbox = Shapes[i].GetBound();
buildData.Add(new BVHShapeInfo(i, bbox));
}
// Recursively build BVH tree for Shapes
MemoryArena buildArena = new MemoryArena();
int totalNodes = 0;
List <Shape> orderedPrims = new List <BaseShape>(shapeCount);
BVHBuildNode root = recursiveBuild(buildArena, buildData, 0, Shapes.Count, ref totalNodes, orderedPrims);
// Compute representation of depth-first traversal of BVH tree
nodes = new List <LinearBVHNode>(totalNodes);
int offset = 0;
//flattenBVHTree(root, &offset);
}
BVHBuildNode recursiveBuild(MemoryArena buildArena, List <BVHShapeInfo> buildData, int start, int end,
ref int totalNodes, List <Shape> orderedPrims)
{
Debug.Assert(start != end);
++totalNodes;
BVHBuildNode node = buildArena.AllocOne <BVHBuildNode>();
// Compute bounds of all Shapes in BVH node
AABB bbox = new AABB(buildData[start].bounds);
for (int i = start + 1; i < end; ++i)
{
bbox = Union(bbox, buildData[i].bounds);
}
int nShapes = end - start;
if (nShapes == 1)
{
// Create leaf _BVHBuildNode_
int firstPrimOffset = orderedPrims.Count;
for (int i = start; i < end; ++i)
{
int primNum = buildData[i].ShapeNumber;
orderedPrims.Add(Shapes[primNum]);
}
node.InitLeaf(firstPrimOffset, nShapes, bbox);
}
else
{
// Compute bound of Shape centroids, choose split dimension _dim_
AABB centroidBounds = new AABB(buildData[start].bounds);
for (int i = start; i < end; ++i)
{
centroidBounds = Union(centroidBounds, buildData[i].centroid);
}
int dim = centroidBounds.MaximumExtent();
// Partition Shapes into two sets and build children
int mid = (start + end) / 2;
if (centroidBounds.max[dim] == centroidBounds.min[dim])
{
// If nShapes is no greater than maxPrimsInNode,
// then all the nodes can be stored in a compact bvh node.
if (nShapes <= maxPrimsInNode)
{
// Create leaf _BVHBuildNode_
int firstPrimOffset = orderedPrims.Count;
for (int i = start; i < end; ++i)
{
int primNum = buildData[i].ShapeNumber;
orderedPrims.Add(Shapes[primNum]);
}
node.InitLeaf(firstPrimOffset, nShapes, bbox);
return(node);
}
else
{
// else if nShapes is greater than maxPrimsInNode, we
// need to split it further to guarantee each node contains
// no more than maxPrimsInNode Shapes.
node.InitInterior(dim,
recursiveBuild(buildArena, buildData, start, mid,
ref totalNodes, orderedPrims),
recursiveBuild(buildArena, buildData, mid, end,
ref totalNodes, orderedPrims));
return(node);
}
}
// Partition Shapes based on _splitMethod_
// Partition Shapes using approximate SAH
if (nShapes <= 4)
{
// Partition Shapes into equally-sized subsets
mid = (start + end) / 2;
NthElement(buildData, start, mid, end, new ComparePoints(dim).Compare);
}
else
{
// Allocate _BucketInfo_ for SAH partition buckets
int nBuckets = 12;
BucketInfo[] buckets = new BucketInfo[nBuckets];
// Initialize _BucketInfo_ for SAH partition buckets
for (int i = start; i < end; ++i)
{
int b = (nBuckets * (
(buildData[i].centroid[dim] - centroidBounds.min[dim]) /
(centroidBounds.max[dim] - centroidBounds.min[dim]))).ToInt();
if (b == nBuckets)
{
b = nBuckets - 1;
}
Debug.Assert(b >= 0 && b < nBuckets);
buckets[b].count++;
buckets[b].bounds = Union(buckets[b].bounds, buildData[i].bounds);
}
// Compute costs for splitting after each bucket
LFloat[] cost = new LFloat[nBuckets - 1];
for (int i = 0; i < nBuckets - 1; ++i)
{
var b0 = new AABB();
var b1 = new AABB();
int count0 = 0, count1 = 0;
for (int j = 0; j <= i; ++j)
{
b0 = Union(b0, buckets[j].bounds);
count0 += buckets[j].count;
}
for (int j = i + 1; j < nBuckets; ++j)
{
b1 = Union(b1, buckets[j].bounds);
count1 += buckets[j].count;
}
cost[i] = LFloat.one / 8 + (count0 * b0.SurfaceArea() + count1 * b1.SurfaceArea()) /
bbox.SurfaceArea();
}
// Find bucket to split at that minimizes SAH metric
LFloat minCost = cost[0];
int minCostSplit = 0;
for (int i = 1; i < nBuckets - 1; ++i)
{
if (cost[i] < minCost)
{
minCost = cost[i];
minCostSplit = i;
}
}
// Either create leaf or split Shapes at selected SAH bucket
if (nShapes > maxPrimsInNode || minCost < nShapes)
{
//var func = ;
int pmid = Partition(buildData, start, end,
new CompareToBucket(minCostSplit, nBuckets, dim, centroidBounds).Compare);
mid = pmid - 0;
}
else
{
// Create leaf _BVHBuildNode_
int firstPrimOffset = orderedPrims.Count;
for (int i = start; i < end; ++i)
{
int primNum = buildData[i].ShapeNumber;
orderedPrims.Add(Shapes[primNum]);
}
node.InitLeaf(firstPrimOffset, nShapes, bbox);
return(node);
}
}
node.InitInterior(dim,
recursiveBuild(buildArena, buildData, start, mid, ref totalNodes, orderedPrims),
recursiveBuild(buildArena, buildData, mid, end, ref totalNodes, orderedPrims));
}
return(node);
}