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//-----------------------------------------------------------------------------
// This is an implementation of Tom Forsyth's "Linear-Speed Vertex Cache
// Optimization" algorithm as described here:
// http://home.comcast.net/~tom_forsyth/papers/fast_vert_cache_opt.html
//
// This code was authored and released into the public domain by
// Adrian Stone (stone@gameangst.com).
//
// THIS SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE, TITLE AND NON-INFRINGEMENT. IN NO EVENT
// SHALL ANYONE DISTRIBUTING THE SOFTWARE BE LIABLE FOR ANY DAMAGES OR OTHER
// LIABILITY, WHETHER IN CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR
// IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
//-----------------------------------------------------------------------------
#include <stdint.h>
#include <assert.h>
#include <math.h>
#include <vector>
#include <algorithm>
namespace Forsyth
{
//-----------------------------------------------------------------------------
// OptimizeFaces
//-----------------------------------------------------------------------------
// Parameters:
// indexList
// input index list
// indexCount
// the number of indices in the list
// vertexCount
// the largest index value in indexList
// vertexBaseIndex
// starting vertex index subtracted from each index in indexList to
// allow safe operation on multiple objects in a single index buffer
// newIndexList
// a pointer to a preallocated buffer the same size as indexList to
// hold the optimized index list
// lruCacheSize
// the size of the simulated post-transform cache (max:64)
//-----------------------------------------------------------------------------
template<class IndexT>
void OptimizeFacesImpl(const IndexT* indexList, uint32_t indexCount, uint32_t vertexCount, IndexT vertexBaseIndex, IndexT* newIndexList, uint16_t lruCacheSize);
void OptimizeFaces(const uint16_t* indexList, uint32_t indexCount, uint32_t vertexCount, uint16_t vertexBaseIndex, uint16_t* newIndexList, uint16_t lruCacheSize)
{
OptimizeFacesImpl<uint16_t>( indexList, indexCount, vertexCount, vertexBaseIndex, newIndexList, lruCacheSize );
}
void OptimizeFaces(const uint32_t* indexList, uint32_t indexCount, uint32_t vertexCount, uint32_t vertexBaseIndex, uint32_t* newIndexList, uint16_t lruCacheSize)
{
OptimizeFacesImpl<uint32_t>( indexList, indexCount, vertexCount, vertexBaseIndex, newIndexList, lruCacheSize );
}
namespace
{
// code for computing vertex score was taken, as much as possible
// directly from the original publication.
float ComputeVertexCacheScore(int cachePosition, int vertexCacheSize)
{
const float FindVertexScore_CacheDecayPower = 1.5f;
const float FindVertexScore_LastTriScore = 0.75f;
float score = 0.0f;
if ( cachePosition < 0 )
{
// Vertex is not in FIFO cache - no score.
}
else
{
if ( cachePosition < 3 )
{
// This vertex was used in the last triangle,
// so it has a fixed score, whichever of the three
// it's in. Otherwise, you can get very different
// answers depending on whether you add
// the triangle 1,2,3 or 3,1,2 - which is silly.
score = FindVertexScore_LastTriScore;
}
else
{
assert ( cachePosition < vertexCacheSize );
// Points for being high in the cache.
const float scaler = 1.0f / ( vertexCacheSize - 3 );
score = 1.0f - ( cachePosition - 3 ) * scaler;
score = powf ( score, FindVertexScore_CacheDecayPower );
}
}
return score;
}
float ComputeVertexValenceScore(uint32_t numActiveFaces)
{
const float FindVertexScore_ValenceBoostScale = 2.0f;
const float FindVertexScore_ValenceBoostPower = 0.5f;
float score = 0.f;
// Bonus points for having a low number of tris still to
// use the vert, so we get rid of lone verts quickly.
float valenceBoost = powf ( static_cast<float>(numActiveFaces),
-FindVertexScore_ValenceBoostPower );
score += FindVertexScore_ValenceBoostScale * valenceBoost;
return score;
}
const int kMaxVertexCacheSize = 64;
const uint32_t kMaxPrecomputedVertexValenceScores = 64;
float s_vertexCacheScores[kMaxVertexCacheSize+1][kMaxVertexCacheSize];
float s_vertexValenceScores[kMaxPrecomputedVertexValenceScores];
bool ComputeVertexScores()
{
for (int cacheSize=0; cacheSize<=kMaxVertexCacheSize; ++cacheSize)
{
for (int cachePos=0; cachePos<cacheSize; ++cachePos)
{
s_vertexCacheScores[cacheSize][cachePos] = ComputeVertexCacheScore(cachePos, cacheSize);
}
}
for (uint32_t valence=0; valence<kMaxPrecomputedVertexValenceScores; ++valence)
{
s_vertexValenceScores[valence] = ComputeVertexValenceScore(valence);
}
return true;
}
bool s_vertexScoresComputed = ComputeVertexScores();
// inline float FindVertexCacheScore(uint cachePosition, uint maxSizeVertexCache)
// {
// return s_vertexCacheScores[maxSizeVertexCache][cachePosition];
// }
// inline float FindVertexValenceScore(uint numActiveTris)
// {
// return s_vertexValenceScores[numActiveTris];
// }
float FindVertexScore(uint32_t numActiveFaces, uint32_t cachePosition, uint32_t vertexCacheSize)
{
assert(s_vertexScoresComputed); (void)s_vertexScoresComputed;
if ( numActiveFaces == 0 )
{
// No tri needs this vertex!
return -1.0f;
}
float score = 0.f;
if (cachePosition < vertexCacheSize)
{
score += s_vertexCacheScores[vertexCacheSize][cachePosition];
}
if (numActiveFaces < kMaxPrecomputedVertexValenceScores)
{
score += s_vertexValenceScores[numActiveFaces];
}
else
{
score += ComputeVertexValenceScore(numActiveFaces);
}
return score;
}
struct OptimizeVertexData
{
float score;
uint32_t activeFaceListStart;
uint32_t activeFaceListSize;
uint16_t cachePos0;
uint16_t cachePos1;
OptimizeVertexData() : score(0.f), activeFaceListStart(0), activeFaceListSize(0), cachePos0(0), cachePos1(0) { }
};
}
template<class IndexT>
void OptimizeFacesImpl(const IndexT* indexList, uint32_t indexCount, uint32_t vertexCount, IndexT vertexBaseIndex, IndexT* newIndexList, uint16_t lruCacheSize)
{
std::vector< OptimizeVertexData > vertexDataList;
vertexDataList.resize(vertexCount);
// compute face count per vertex
for (uint32_t i=0; i<indexCount; ++i)
{
IndexT index = indexList[i] - vertexBaseIndex;
assert((index >= 0) && (index < vertexCount));
OptimizeVertexData& vertexData = vertexDataList[index];
vertexData.activeFaceListSize++;
}
std::vector<uint32_t> activeFaceList;
const IndexT kEvictedCacheIndex = std::numeric_limits<uint16_t>::max();
{
// allocate face list per vertex
uint32_t curActiveFaceListPos = 0;
for (uint32_t i=0; i<vertexCount; ++i)
{
OptimizeVertexData& vertexData = vertexDataList[i];
vertexData.cachePos0 = kEvictedCacheIndex;
vertexData.cachePos1 = kEvictedCacheIndex;
vertexData.activeFaceListStart = curActiveFaceListPos;
curActiveFaceListPos += vertexData.activeFaceListSize;
vertexData.score = FindVertexScore(vertexData.activeFaceListSize, vertexData.cachePos0, lruCacheSize);
vertexData.activeFaceListSize = 0;
}
activeFaceList.resize(curActiveFaceListPos);
}
// fill out face list per vertex
for (uint32_t i=0; i<indexCount; i+=3)
{
for (uint32_t j=0; j<3; ++j)
{
IndexT index = indexList[i+j] - vertexBaseIndex;
OptimizeVertexData& vertexData = vertexDataList[index];
activeFaceList[vertexData.activeFaceListStart + vertexData.activeFaceListSize] = i;
vertexData.activeFaceListSize++;
}
}
std::vector<uint8_t> processedFaceList;
processedFaceList.resize(indexCount);
IndexT vertexCacheBuffer[(kMaxVertexCacheSize+3)*2];
IndexT* cache0 = vertexCacheBuffer;
IndexT* cache1 = vertexCacheBuffer+(kMaxVertexCacheSize+3);
IndexT entriesInCache0 = 0;
uint32_t bestFace = 0;
float bestScore = -1.f;
const float maxValenceScore = FindVertexScore(1, kEvictedCacheIndex, lruCacheSize) * 3.f;
for (uint32_t i = 0; i < indexCount; i += 3)
{
if (bestScore < 0.f)
{
// no verts in the cache are used by any unprocessed faces so
// search all unprocessed faces for a new starting point
for (uint32_t j = 0; j < indexCount; j += 3)
{
if (processedFaceList[j] == 0)
{
uint32_t face = j;
float faceScore = 0.f;
for (uint32_t k=0; k<3; ++k)
{
IndexT index = indexList[face+k] - vertexBaseIndex;
OptimizeVertexData& vertexData = vertexDataList[index];
assert(vertexData.activeFaceListSize > 0);
assert(vertexData.cachePos0 >= lruCacheSize);
faceScore += vertexData.score;
}
if (faceScore > bestScore)
{
bestScore = faceScore;
bestFace = face;
assert(bestScore <= maxValenceScore);
if (bestScore >= maxValenceScore)
{
break;
}
}
}
}
assert(bestScore >= 0.f);
}
processedFaceList[bestFace] = 1;
uint16_t entriesInCache1 = 0;
// add bestFace to LRU cache and to newIndexList
for (uint32_t v = 0; v < 3; ++v)
{
IndexT index = indexList[bestFace+v] - vertexBaseIndex;
newIndexList[i+v] = index + vertexBaseIndex;
OptimizeVertexData& vertexData = vertexDataList[index];
if (vertexData.cachePos1 >= entriesInCache1)
{
vertexData.cachePos1 = entriesInCache1;
cache1[entriesInCache1++] = index;
if (vertexData.activeFaceListSize == 1)
{
--vertexData.activeFaceListSize;
continue;
}
}
assert(vertexData.activeFaceListSize > 0);
uint32_t* begin = &activeFaceList[vertexData.activeFaceListStart];
uint32_t* end = &(activeFaceList[vertexData.activeFaceListStart + vertexData.activeFaceListSize - 1]) + 1;
uint32_t* it = std::find(begin, end, bestFace);
assert(it != end);
std::swap(*it, *(end-1));
--vertexData.activeFaceListSize;
vertexData.score = FindVertexScore(vertexData.activeFaceListSize, vertexData.cachePos1, lruCacheSize);
}
// move the rest of the old verts in the cache down and compute their new scores
for (uint32_t c0 = 0; c0 < entriesInCache0; ++c0)
{
IndexT index = cache0[c0];
OptimizeVertexData& vertexData = vertexDataList[index];
if (vertexData.cachePos1 >= entriesInCache1)
{
vertexData.cachePos1 = entriesInCache1;
cache1[entriesInCache1++] = index;
vertexData.score = FindVertexScore(vertexData.activeFaceListSize, vertexData.cachePos1, lruCacheSize);
}
}
// find the best scoring triangle in the current cache (including up to 3 that were just evicted)
bestScore = -1.f;
for (uint32_t c1 = 0; c1 < entriesInCache1; ++c1)
{
IndexT index = cache1[c1];
OptimizeVertexData& vertexData = vertexDataList[index];
vertexData.cachePos0 = vertexData.cachePos1;
vertexData.cachePos1 = kEvictedCacheIndex;
for (uint32_t j=0; j<vertexData.activeFaceListSize; ++j)
{
uint32_t face = activeFaceList[vertexData.activeFaceListStart+j];
float faceScore = 0.f;
for (uint32_t v=0; v<3; v++)
{
IndexT faceIndex = indexList[face+v] - vertexBaseIndex;
OptimizeVertexData& faceVertexData = vertexDataList[faceIndex];
faceScore += faceVertexData.score;
}
if (faceScore > bestScore)
{
bestScore = faceScore;
bestFace = face;
}
}
}
std::swap(cache0, cache1);
entriesInCache0 = std::min(entriesInCache1, lruCacheSize);
}
}
} // namespace Forsyth
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