// This function encodes a Region as a 64-bit integer so that it can be used as a key to access chunk data in the SQLite database.
// A region actually contains more than 64-bits of data so some has to be lost here. Specifically we assume that we already know
// the size of the region (so we only have to encode it's lower corner and not its upper corner or extents), and we also restrict
// the range of valid coordinates. A Region's coordinates are represented by 3-bits of data, but we only support converting to a key
// if every coordinate can be represented by 21 bits of data. This way we can fit three coordinates only 63 bits of data. This limits
// the range of values to +/- 2^20, which is enough for our purposes.
uint64_t regionToKey(const PolyVox::Region& region)
{
// Cast to unsigned values so that bit shifting works predictably.
uint32_t x = static_cast<uint32_t>(region.getLowerX());
uint32_t y = static_cast<uint32_t>(region.getLowerY());
uint32_t z = static_cast<uint32_t>(region.getLowerZ());
// The magnitude of our input values is fairly restricted, but the values could stil be negative. This means the sign bit could
// be set and this needs to be encoded as well. We therefore perform a left rotate on the bits to bring the sign bit into the LSB.
x = rotateLeft(x);
y = rotateLeft(y);
z = rotateLeft(z);
// Now convert to 64-bits
uint64_t x64 = x;
uint64_t y64 = y;
uint64_t z64 = z;
// Morten-encode the components to give our final key
uint64_t result = EncodeMorton3(x64, y64, z64);
// Return the combined value
return result;
}
BVHBuildNode *CBVH_PBRT::HLBVHBuild( const std::vector<BVHPrimitiveInfo> &primitiveInfo,
int *totalNodes,
CONST_VECTOR_OBJECT &orderedPrims )
{
// Compute bounding box of all primitive centroids
CBBOX bounds;
bounds.Reset();
for( unsigned int i = 0; i < primitiveInfo.size(); ++i )
bounds.Union( primitiveInfo[i].centroid );
// Compute Morton indices of primitives
std::vector<MortonPrimitive> mortonPrims( primitiveInfo.size() );
for( int i = 0; i < (int)primitiveInfo.size(); ++i )
{
// Initialize _mortonPrims[i]_ for _i_th primitive
const int mortonBits = 10;
const int mortonScale = 1 << mortonBits;
wxASSERT( primitiveInfo[i].primitiveNumber < (int)primitiveInfo.size() );
mortonPrims[i].primitiveIndex = primitiveInfo[i].primitiveNumber;
const SFVEC3F centroidOffset = bounds.Offset( primitiveInfo[i].centroid );
wxASSERT( (centroidOffset.x >= 0.0f) && (centroidOffset.x <= 1.0f) );
wxASSERT( (centroidOffset.y >= 0.0f) && (centroidOffset.y <= 1.0f) );
wxASSERT( (centroidOffset.z >= 0.0f) && (centroidOffset.z <= 1.0f) );
mortonPrims[i].mortonCode = EncodeMorton3( centroidOffset *
SFVEC3F( (float)mortonScale ) );
}
// Radix sort primitive Morton indices
RadixSort( &mortonPrims );
// Create LBVH treelets at bottom of BVH
// Find intervals of primitives for each treelet
std::vector<LBVHTreelet> treeletsToBuild;
for( int start = 0, end = 1; end <= (int)mortonPrims.size(); ++end )
{
const uint32_t mask = 0b00111111111111000000000000000000;
if( (end == (int)mortonPrims.size()) ||
( (mortonPrims[start].mortonCode & mask) !=
(mortonPrims[end].mortonCode & mask) ) )
{
// Add entry to _treeletsToBuild_ for this treelet
const int numPrimitives = end - start;
const int maxBVHNodes = 2 * numPrimitives;
// !TODO: implement a memory arena
BVHBuildNode *nodes = static_cast<BVHBuildNode *>( _mm_malloc( maxBVHNodes *
sizeof( BVHBuildNode ),
L1_CACHE_LINE_SIZE ) );
m_addresses_pointer_to_mm_free.push_back( nodes );
for( int i = 0; i < maxBVHNodes; ++i )
{
nodes[i].bounds.Reset();
nodes[i].firstPrimOffset = 0;
nodes[i].nPrimitives = 0;
nodes[i].splitAxis = 0;
nodes[i].children[0] = NULL;
nodes[i].children[1] = NULL;
}
LBVHTreelet tmpTreelet;
tmpTreelet.startIndex = start;
tmpTreelet.numPrimitives = numPrimitives;
tmpTreelet.buildNodes = nodes;
treeletsToBuild.push_back( tmpTreelet );
start = end;
}
}
// Create LBVHs for treelets in parallel
int atomicTotal = 0;
int orderedPrimsOffset = 0;
orderedPrims.resize( m_primitives.size() );
for( int index = 0; index < (int)treeletsToBuild.size(); ++index )
{
// Generate _index_th LBVH treelet
int nodesCreated = 0;
const int firstBit = 29 - 12;
LBVHTreelet &tr = treeletsToBuild[index];
wxASSERT( tr.startIndex < (int)mortonPrims.size() );
tr.buildNodes = emitLBVH( tr.buildNodes,
primitiveInfo,
&mortonPrims[tr.startIndex],
tr.numPrimitives,
&nodesCreated,
orderedPrims,
&orderedPrimsOffset,
firstBit );
atomicTotal += nodesCreated;
}
*totalNodes = atomicTotal;
// Initialize _finishedTreelets_ with treelet root node pointers
std::vector<BVHBuildNode *> finishedTreelets;
finishedTreelets.reserve( treeletsToBuild.size() );
for( int index = 0; index < (int)treeletsToBuild.size(); ++index )
finishedTreelets.push_back( treeletsToBuild[index].buildNodes );
// Create and return SAH BVH from LBVH treelets
return buildUpperSAH( finishedTreelets,
0,
finishedTreelets.size(),
totalNodes );
}
BVHBuildNode *BVHAccel::HLBVHBuild(
MemoryArena &arena, const std::vector<BVHPrimitiveInfo> &primitiveInfo,
int *totalNodes,
std::vector<std::shared_ptr<Primitive>> &orderedPrims) const {
// Compute bounding box of all primitive centroids
Bounds3f bounds;
for (const BVHPrimitiveInfo &pi : primitiveInfo)
bounds = Union(bounds, pi.centroid);
// Compute Morton indices of primitives
std::vector<MortonPrimitive> mortonPrims(primitiveInfo.size());
ParallelFor([&](int i) {
// Initialize _mortionPrims[i]_ for _i_th primitive
constexpr int mortonBits = 10;
constexpr int mortonScale = 1 << mortonBits;
mortonPrims[i].primitiveIndex = primitiveInfo[i].primitiveNumber;
Vector3f centroidOffset = bounds.Offset(primitiveInfo[i].centroid);
mortonPrims[i].mortonCode = EncodeMorton3(centroidOffset * mortonScale);
}, primitiveInfo.size(), 512);
// Radix sort primitive Morton indices
RadixSort(&mortonPrims);
// Create LBVH treelets at bottom of BVH
// Find intervals of primitives for each treelet
std::vector<LBVHTreelet> treeletsToBuild;
for (int start = 0, end = 1; end <= (int)mortonPrims.size(); ++end) {
uint32_t mask = 0b00111111111111000000000000000000;
if (end == (int)mortonPrims.size() ||
((mortonPrims[start].mortonCode & mask) !=
(mortonPrims[end].mortonCode & mask))) {
// Add entry to _treeletsToBuild_ for this treelet
int nPrimitives = end - start;
int maxBVHNodes = 2 * nPrimitives;
BVHBuildNode *nodes = arena.Alloc<BVHBuildNode>(maxBVHNodes, false);
treeletsToBuild.push_back({start, nPrimitives, nodes});
start = end;
}
}
// Create LBVHs for treelets in parallel
std::atomic<int> atomicTotal(0), orderedPrimsOffset(0);
orderedPrims.resize(primitives.size());
ParallelFor([&](int i) {
// Generate _i_th LBVH treelet
int nodesCreated = 0;
const int firstBitIndex = 29 - 12;
LBVHTreelet &tr = treeletsToBuild[i];
tr.buildNodes =
emitLBVH(tr.buildNodes, primitiveInfo, &mortonPrims[tr.startIndex],
tr.nPrimitives, &nodesCreated, orderedPrims,
&orderedPrimsOffset, firstBitIndex);
atomicTotal += nodesCreated;
}, treeletsToBuild.size());
*totalNodes = atomicTotal;
// Create and return SAH BVH from LBVH treelets
std::vector<BVHBuildNode *> finishedTreelets;
finishedTreelets.reserve(treeletsToBuild.size());
for (LBVHTreelet &treelet : treeletsToBuild)
finishedTreelets.push_back(treelet.buildNodes);
return buildUpperSAH(arena, finishedTreelets, 0, finishedTreelets.size(),
totalNodes);
}
