assimp/code/ImproveCacheLocality.cpp

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/** @file Implementation of the post processing to improve the
 *   cache locality of a mesh.
 * <br>
 * The algorithm is roughly basing on this paper:
 * http://www.cs.princeton.edu/gfx/pubs/Sander_2007_%3ETR/tipsy.pdf
 */

#include "AssimpPCH.h"

// internal headers
#include "ImproveCacheLocality.h"
#include "VertexTriangleAdjacency.h"

using namespace Assimp;

#if _MSC_VER >= 1400
#	define sprintf sprintf_s
#endif

// ------------------------------------------------------------------------------------------------
// Constructor to be privately used by Importer
ImproveCacheLocalityProcess::ImproveCacheLocalityProcess()
{
	// nothing to do here
	configCacheDepth = 12; // hardcoded to 12 at the moment
}

// ------------------------------------------------------------------------------------------------
// Destructor, private as well
ImproveCacheLocalityProcess::~ImproveCacheLocalityProcess()
{
	// nothing to do here
}

// ------------------------------------------------------------------------------------------------
// Returns whether the processing step is present in the given flag field.
bool ImproveCacheLocalityProcess::IsActive( unsigned int pFlags) const
{
	return (pFlags & aiProcess_ImproveCacheLocality) != 0;
}

// ------------------------------------------------------------------------------------------------
// Executes the post processing step on the given imported data.
void ImproveCacheLocalityProcess::Execute( aiScene* pScene)
{
	if (!pScene->mNumMeshes)
	{
		DefaultLogger::get()->debug("ImproveCacheLocalityProcess skipped; there are no meshes");
		return;
	}

	DefaultLogger::get()->debug("ImproveCacheLocalityProcess begin");

	for( unsigned int a = 0; a < pScene->mNumMeshes; a++)
	{
		this->ProcessMesh( pScene->mMeshes[a],a);
	}
	DefaultLogger::get()->debug("ImproveCacheLocalityProcess finished. ");
}

// ------------------------------------------------------------------------------------------------
// Improves the cache coherency of a specific mesh
void ImproveCacheLocalityProcess::ProcessMesh( aiMesh* pMesh, unsigned int meshNum)
{
	ai_assert(NULL != pMesh);

	// check whether the input data is valid ->
	// - there must be vertices and faces (haha)
	// - all faces must be triangulated
	if (!pMesh->HasFaces() || !pMesh->HasPositions())
		return;

	if (pMesh->mPrimitiveTypes != aiPrimitiveType_TRIANGLE)
	{
		DefaultLogger::get()->error("This algorithm works on triangle meshes only");
		return;
	}

	// find the input ACMR ...
	unsigned int* piFIFOStack = new unsigned int[this->configCacheDepth];
	::memset(piFIFOStack,0xff,this->configCacheDepth*sizeof(unsigned int));
	unsigned int* piCur = piFIFOStack;
	const unsigned int* const piCurEnd = piFIFOStack + this->configCacheDepth;

	// count the number of cache misses
	unsigned int iCacheMisses = 0;

	const aiFace* const pcEnd = pMesh->mFaces+pMesh->mNumFaces;
	for (const aiFace* pcFace = pMesh->mFaces;pcFace != pcEnd;++pcFace)
	{
		for (unsigned int qq = 0; qq < 3;++qq)
		{
			bool bInCache = false;
			for (unsigned int* pp = piFIFOStack;pp < piCurEnd;++pp)
			{
				if (*pp == pcFace->mIndices[qq])
				{
					// the vertex is in cache
					bInCache = true;
					break;
				}
			}
			if (!bInCache)
			{
				++iCacheMisses;
				if (piCurEnd == piCur)piCur = piFIFOStack;
				*piCur++ = pcFace->mIndices[qq];
			}
		}
	}
	delete[] piFIFOStack;
	float fACMR = (float)iCacheMisses / pMesh->mNumFaces;
	if (3.0 == fACMR)
	{
		char szBuff[128]; // should be sufficiently large in every case

		// the JoinIdenticalVertices process has not been executed on this
		// mesh, otherwise this value would normally be at least minimally#
		// smaller than 3.0 ...
		::sprintf(szBuff,"Mesh %i: JIV-Step has not been executed properly (precondition)",meshNum);
		DefaultLogger::get()->warn(szBuff);
		return;
	}

	// first we need to build a vertex-triangle adjacency list
	VertexTriangleAdjacency adj(pMesh->mFaces,pMesh->mNumFaces, pMesh->mNumVertices,true);

	// build a list to store per-vertex caching time stamps
	unsigned int* const piCachingStamps = new unsigned int[pMesh->mNumVertices];
	::memset(piCachingStamps,0x0,pMesh->mNumVertices*sizeof(unsigned int));

	// allocate an empty output index buffer. We store the output
	// indices in one large array. Since the number of triangles
	// won't change the input faces can be reused. This is how we save
	// thousands of redundant mini allocations for aiFace::mIndices
	const unsigned int iIdxCnt = pMesh->mNumFaces*3;
	unsigned int* const piIBOutput = new unsigned int[iIdxCnt];
	unsigned int* piCSIter = piIBOutput;

	// allocate the flag array to hold the information
	// whether a face has already been emitted or not
	std::vector<bool> abEmitted(pMesh->mNumFaces,false);

	// dead-end vertex index stack
	std::stack<unsigned int> sDeadEndVStack;

	// create a copy of the piNumTriPtr buffer
	unsigned int* const piNumTriPtr = adj.mLiveTriangles;
	const unsigned int* const piNumTriPtrNoModify = new unsigned int[pMesh->mNumVertices];
	::memcpy(const_cast<unsigned int* const> (piNumTriPtrNoModify),piNumTriPtr,
		pMesh->mNumVertices * sizeof(unsigned int));

	// get the largest number of referenced triangles
	// and allocate the "candidate buffer"
	unsigned int iMaxRefTris = 0;
	{
		const unsigned int* piCur = adj.mLiveTriangles;
		const unsigned int* const piCurEnd = adj.mLiveTriangles+pMesh->mNumVertices;
		for (;piCur != piCurEnd;++piCur)
			iMaxRefTris = std::max(iMaxRefTris,*piCur);
	}
	unsigned int* piCandidates = new unsigned int[iMaxRefTris*3];
	iCacheMisses = 0;

	/** PSEUDOCODE for the algorithm

		A = Build-Adjacency(I) Vertex-triangle adjacency
		L = Get-Triangle-Counts(A) Per-vertex live triangle counts
		C = Zero(Vertex-Count(I)) Per-vertex caching time stamps
		D = Empty-Stack() Dead-end vertex stack
		E = False(Triangle-Count(I)) Per triangle emitted flag
		O = Empty-Index-Buffer() Empty output buffer
		f = 0 Arbitrary starting vertex
		s = k+1, i = 1 Time stamp and cursor
		while f >= 0 For all valid fanning vertices
			N = Empty-Set() 1-ring of next candidates
			for each Triangle t in Neighbors(A, f)
				if !Emitted(E,t)
					for each Vertex v in t
						Append(O,v) Output vertex
						Push(D,v) Add to dead-end stack
						Insert(N,v) Register as candidate
						L[v] = L[v]-1 Decrease live triangle count
						if s-C[v] > k If not in cache
							C[v] = s Set time stamp
							s = s+1 Increment time stamp
					E[t] = true Flag triangle as emitted
			Select next fanning vertex
			f = Get-Next-Vertex(I,i,k,N,C,s,L,D)
		return O
		*/

	int ivdx = 0;
	int ics = 1;
	int iStampCnt = this->configCacheDepth+1;
	while (ivdx >= 0)
	{
		unsigned int icnt = piNumTriPtrNoModify[ivdx]; 
		unsigned int* piList = adj.GetAdjacentTriangles(ivdx);
		unsigned int* piCurCandidate = piCandidates;

		// get all triangles in the neighborhood
		for (unsigned int tri = 0; tri < icnt;++tri)
		{
			// if they have not yet been emitted, add them to the output IB
			const unsigned int fidx = *piList++;
			if (!abEmitted[fidx])
			{
				// so iterate through all vertices of the current triangle
				const aiFace* pcFace = &pMesh->mFaces[ fidx ];
				const unsigned int* const p2 = pcFace->mIndices+3;
				for (unsigned int* p = pcFace->mIndices;p != p2;++p)
				{
					const unsigned int dp = *p;

					// the current vertex won't have any free triangles after this step
					if (ivdx != (int)dp)
					{
						// append the vertex to the dead-end stack
						sDeadEndVStack.push(dp);

						// register as candidate for the next step
						*piCurCandidate++ = dp;

						// decrease the per-vertex triangle counts
						piNumTriPtr[dp]--;
					}

					// append the vertex to the output index buffer
					*piCSIter++ = dp;

					// if the vertex is not yet in cache, set its cache count
					if (iStampCnt-piCachingStamps[dp] > this->configCacheDepth)
					{
						piCachingStamps[dp] = iStampCnt++;
						++iCacheMisses;
					}
				}
				// flag triangle as emitted
				abEmitted[fidx] = true;
			}
		}

		// the vertex has now no living adjacent triangles anymore
		piNumTriPtr[ivdx] = 0;

		// get next fanning vertex
		ivdx = -1; 
		int max_priority = -1;
		for (unsigned int* piCur = piCandidates;piCur != piCurCandidate;++piCur)
		{
			register const unsigned int dp = *piCur;

			// must have live triangles
			if (piNumTriPtr[dp] > 0)
			{
				int priority = 0;

				// will the vertex be in cache, even after fanning occurs?
				unsigned int tmp;
				if ((tmp = iStampCnt-piCachingStamps[dp]) + 2*piNumTriPtr[dp] <= this->configCacheDepth)
					priority = tmp;
				// keep best candidate
				if (priority > max_priority)
				{
					max_priority = priority;
					ivdx = dp;
				}
			}
		}
		// did we reach a dead end?
		if (-1 == ivdx)
		{
			// need to get a non-local vertex for which we have a good
			// chance that it is still in the cache ...
			while (!sDeadEndVStack.empty())
			{
				unsigned int iCachedIdx = sDeadEndVStack.top();
				sDeadEndVStack.pop();
				if (piNumTriPtr[ iCachedIdx ] > 0)
				{
					ivdx = iCachedIdx;
					break;
				}
			}

			if (-1 == ivdx)
			{
				// well, there isn't such a vertex. Simply get the next
				// vertex in input order and hope it is not too bad ...
				while (ics < (int)pMesh->mNumVertices)
				{
					++ics;
					if (piNumTriPtr[ics] > 0)
					{
						ivdx = ics;
						break;
					}
				}
			}
		}
	}
	if (!DefaultLogger::isNullLogger())
	{
		char szBuff[128]; // should be sufficiently large in every case
		float fACMR2 = (float)iCacheMisses / pMesh->mNumFaces;

		::sprintf(szBuff,"Mesh %i | ACMR in: %f out: %f | ~%.1f%%",meshNum,fACMR,fACMR2,
			((fACMR - fACMR2) / fACMR) * 100.f);
		DefaultLogger::get()->info(szBuff);
	}
	// sort the output index buffer back to the input array
	piCSIter = piIBOutput;

	for (aiFace* pcFace = pMesh->mFaces; pcFace != pcEnd;++pcFace)
	{
		pcFace->mIndices[0] = *piCSIter++;
		pcFace->mIndices[1] = *piCSIter++;
		pcFace->mIndices[2] = *piCSIter++;
	}

	// delete temporary storage
	delete[] piCachingStamps;
	delete[] piIBOutput;
	delete[] piCandidates;
	delete[] piNumTriPtrNoModify;
}