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https://github.com/scratchfoundation/bgfx.git
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351 lines
14 KiB
C++
351 lines
14 KiB
C++
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//-----------------------------------------------------------------------------
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// This is an implementation of Tom Forsyth's "Linear-Speed Vertex Cache
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// Optimization" algorithm as described here:
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// http://home.comcast.net/~tom_forsyth/papers/fast_vert_cache_opt.html
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//
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// This code was authored and released into the public domain by
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// Adrian Stone (stone@gameangst.com).
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//
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// THIS SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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// FITNESS FOR A PARTICULAR PURPOSE, TITLE AND NON-INFRINGEMENT. IN NO EVENT
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// SHALL ANYONE DISTRIBUTING THE SOFTWARE BE LIABLE FOR ANY DAMAGES OR OTHER
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// LIABILITY, WHETHER IN CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR
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// IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
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//-----------------------------------------------------------------------------
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#include <assert.h>
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#include <math.h>
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#include <vector>
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#include <limits>
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#include <algorithm>
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namespace Forsyth
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{
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typedef unsigned int uint;
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typedef unsigned short uint16;
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typedef unsigned char byte;
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//-----------------------------------------------------------------------------
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// OptimizeFaces
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//-----------------------------------------------------------------------------
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// Parameters:
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// indexList
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// input index list
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// indexCount
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// the number of indices in the list
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// vertexCount
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// the largest index value in indexList
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// newIndexList
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// a pointer to a preallocated buffer the same size as indexList to
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// hold the optimized index list
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// lruCacheSize
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// the size of the simulated post-transform cache (max:64)
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//-----------------------------------------------------------------------------
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void OptimizeFaces(const uint16* indexList, uint indexCount, uint vertexCount, uint16* newIndexList, uint16 lruCacheSize);
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namespace
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{
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// code for computing vertex score was taken, as much as possible
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// directly from the original publication.
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float ComputeVertexCacheScore(int cachePosition, int vertexCacheSize)
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{
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const float FindVertexScore_CacheDecayPower = 1.5f;
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const float FindVertexScore_LastTriScore = 0.75f;
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float score = 0.0f;
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if ( cachePosition < 0 )
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{
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// Vertex is not in FIFO cache - no score.
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}
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else
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{
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if ( cachePosition < 3 )
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{
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// This vertex was used in the last triangle,
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// so it has a fixed score, whichever of the three
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// it's in. Otherwise, you can get very different
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// answers depending on whether you add
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// the triangle 1,2,3 or 3,1,2 - which is silly.
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score = FindVertexScore_LastTriScore;
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}
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else
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{
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assert ( cachePosition < vertexCacheSize );
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// Points for being high in the cache.
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const float scaler = 1.0f / ( vertexCacheSize - 3 );
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score = 1.0f - ( cachePosition - 3 ) * scaler;
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score = powf ( score, FindVertexScore_CacheDecayPower );
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}
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}
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return score;
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}
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float ComputeVertexValenceScore(uint numActiveFaces)
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{
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const float FindVertexScore_ValenceBoostScale = 2.0f;
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const float FindVertexScore_ValenceBoostPower = 0.5f;
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float score = 0.f;
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// Bonus points for having a low number of tris still to
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// use the vert, so we get rid of lone verts quickly.
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float valenceBoost = powf ( static_cast<float>(numActiveFaces),
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-FindVertexScore_ValenceBoostPower );
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score += FindVertexScore_ValenceBoostScale * valenceBoost;
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return score;
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}
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const uint kMaxVertexCacheSize = 64;
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const uint kMaxPrecomputedVertexValenceScores = 64;
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float s_vertexCacheScores[kMaxVertexCacheSize+1][kMaxVertexCacheSize];
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float s_vertexValenceScores[kMaxPrecomputedVertexValenceScores];
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bool ComputeVertexScores()
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{
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for (int cacheSize=0; cacheSize<=kMaxVertexCacheSize; ++cacheSize)
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{
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for (int cachePos=0; cachePos<cacheSize; ++cachePos)
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{
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s_vertexCacheScores[cacheSize][cachePos] = ComputeVertexCacheScore(cachePos, cacheSize);
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}
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}
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for (uint valence=0; valence<kMaxPrecomputedVertexValenceScores; ++valence)
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{
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s_vertexValenceScores[valence] = ComputeVertexValenceScore(valence);
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}
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return true;
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}
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bool s_vertexScoresComputed = ComputeVertexScores();
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inline float FindVertexCacheScore(uint cachePosition, uint maxSizeVertexCache)
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{
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return s_vertexCacheScores[maxSizeVertexCache][cachePosition];
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}
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inline float FindVertexValenceScore(uint numActiveTris)
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{
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return s_vertexValenceScores[numActiveTris];
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}
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float FindVertexScore(uint numActiveFaces, uint cachePosition, uint vertexCacheSize)
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{
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assert(s_vertexScoresComputed);
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if ( numActiveFaces == 0 )
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{
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// No tri needs this vertex!
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return -1.0f;
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}
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float score = 0.f;
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if (cachePosition < vertexCacheSize)
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{
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score += s_vertexCacheScores[vertexCacheSize][cachePosition];
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}
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if (numActiveFaces < kMaxPrecomputedVertexValenceScores)
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{
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score += s_vertexValenceScores[numActiveFaces];
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}
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else
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{
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score += ComputeVertexValenceScore(numActiveFaces);
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}
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return score;
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}
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struct OptimizeVertexData
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{
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float score;
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uint activeFaceListStart;
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uint activeFaceListSize;
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uint16 cachePos0;
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uint16 cachePos1;
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OptimizeVertexData() : score(0.f), activeFaceListStart(0), activeFaceListSize(0), cachePos0(0), cachePos1(0) { }
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};
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}
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void OptimizeFaces(const uint16* indexList, uint indexCount, uint vertexCount, uint16* newIndexList, uint16 lruCacheSize)
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{
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std::vector<OptimizeVertexData> vertexDataList;
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vertexDataList.resize(vertexCount);
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// compute face count per vertex
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for (uint i=0; i<indexCount; ++i)
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{
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uint16 index = indexList[i];
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assert(index < vertexCount);
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OptimizeVertexData& vertexData = vertexDataList[index];
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vertexData.activeFaceListSize++;
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}
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std::vector<uint> activeFaceList;
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const uint16 kEvictedCacheIndex = std::numeric_limits<uint16>::max();
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{
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// allocate face list per vertex
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uint curActiveFaceListPos = 0;
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for (uint i=0; i<vertexCount; ++i)
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{
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OptimizeVertexData& vertexData = vertexDataList[i];
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vertexData.cachePos0 = kEvictedCacheIndex;
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vertexData.cachePos1 = kEvictedCacheIndex;
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vertexData.activeFaceListStart = curActiveFaceListPos;
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curActiveFaceListPos += vertexData.activeFaceListSize;
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vertexData.score = FindVertexScore(vertexData.activeFaceListSize, vertexData.cachePos0, lruCacheSize);
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vertexData.activeFaceListSize = 0;
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}
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activeFaceList.resize(curActiveFaceListPos);
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}
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// fill out face list per vertex
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for (uint i=0; i<indexCount; i+=3)
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{
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for (uint j=0; j<3; ++j)
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{
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uint16 index = indexList[i+j];
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OptimizeVertexData& vertexData = vertexDataList[index];
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activeFaceList[vertexData.activeFaceListStart + vertexData.activeFaceListSize] = i;
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vertexData.activeFaceListSize++;
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}
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}
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std::vector<byte> processedFaceList;
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processedFaceList.resize(indexCount);
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uint16 vertexCacheBuffer[(kMaxVertexCacheSize+3)*2];
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uint16* cache0 = vertexCacheBuffer;
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uint16* cache1 = vertexCacheBuffer+(kMaxVertexCacheSize+3);
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uint16 entriesInCache0 = 0;
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uint bestFace = 0;
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float bestScore = -1.f;
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const float maxValenceScore = FindVertexScore(1, kEvictedCacheIndex, lruCacheSize) * 3.f;
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for (uint i = 0; i < indexCount; i += 3)
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{
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if (bestScore < 0.f)
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{
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// no verts in the cache are used by any unprocessed faces so
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// search all unprocessed faces for a new starting point
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for (uint j = 0; j < indexCount; j += 3)
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{
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if (processedFaceList[j] == 0)
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{
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uint face = j;
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float faceScore = 0.f;
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for (uint k=0; k<3; ++k)
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{
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uint16 index = indexList[face+k];
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OptimizeVertexData& vertexData = vertexDataList[index];
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assert(vertexData.activeFaceListSize > 0);
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assert(vertexData.cachePos0 >= lruCacheSize);
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faceScore += vertexData.score;
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}
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if (faceScore > bestScore)
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{
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bestScore = faceScore;
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bestFace = face;
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assert(bestScore <= maxValenceScore);
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if (bestScore >= maxValenceScore)
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{
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break;
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}
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}
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}
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}
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assert(bestScore >= 0.f);
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}
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processedFaceList[bestFace] = 1;
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uint16 entriesInCache1 = 0;
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// add bestFace to LRU cache and to newIndexList
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for (uint v = 0; v < 3; ++v)
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{
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uint16 index = indexList[bestFace+v];
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newIndexList[i+v] = index;
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OptimizeVertexData& vertexData = vertexDataList[index];
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if (vertexData.cachePos1 >= entriesInCache1)
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{
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vertexData.cachePos1 = entriesInCache1;
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cache1[entriesInCache1++] = index;
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if (vertexData.activeFaceListSize == 1)
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{
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--vertexData.activeFaceListSize;
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continue;
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}
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}
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assert(vertexData.activeFaceListSize > 0);
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uint* begin = &activeFaceList[vertexData.activeFaceListStart];
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uint* end = &activeFaceList[vertexData.activeFaceListStart + vertexData.activeFaceListSize];
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uint* it = std::find(begin, end, bestFace);
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assert(it != end);
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std::swap(*it, *(end-1));
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--vertexData.activeFaceListSize;
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vertexData.score = FindVertexScore(vertexData.activeFaceListSize, vertexData.cachePos1, lruCacheSize);
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}
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// move the rest of the old verts in the cache down and compute their new scores
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for (uint c0 = 0; c0 < entriesInCache0; ++c0)
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{
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uint16 index = cache0[c0];
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OptimizeVertexData& vertexData = vertexDataList[index];
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if (vertexData.cachePos1 >= entriesInCache1)
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{
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vertexData.cachePos1 = entriesInCache1;
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cache1[entriesInCache1++] = index;
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vertexData.score = FindVertexScore(vertexData.activeFaceListSize, vertexData.cachePos1, lruCacheSize);
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}
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}
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// find the best scoring triangle in the current cache (including up to 3 that were just evicted)
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bestScore = -1.f;
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for (uint c1 = 0; c1 < entriesInCache1; ++c1)
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{
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uint16 index = cache1[c1];
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OptimizeVertexData& vertexData = vertexDataList[index];
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vertexData.cachePos0 = vertexData.cachePos1;
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vertexData.cachePos1 = kEvictedCacheIndex;
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for (uint j=0; j<vertexData.activeFaceListSize; ++j)
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{
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uint face = activeFaceList[vertexData.activeFaceListStart+j];
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float faceScore = 0.f;
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for (uint v=0; v<3; v++)
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{
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uint16 faceIndex = indexList[face+v];
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OptimizeVertexData& faceVertexData = vertexDataList[faceIndex];
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faceScore += faceVertexData.score;
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}
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if (faceScore > bestScore)
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{
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bestScore = faceScore;
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bestFace = face;
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}
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}
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}
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std::swap(cache0, cache1);
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entriesInCache0 = std::min(entriesInCache1, lruCacheSize);
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}
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}
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} // namespace Forsyth
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