assimp/code/VertexTriangleAdjacency.cpp

/*
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Open Asset Import Library (ASSIMP)
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/** @file Implementation of the VertexTriangleAdjacency helper class */
#include "AssimpPCH.h"

// internal headers
#include "VertexTriangleAdjacency.h"
using namespace Assimp;

// ------------------------------------------------------------------------------------------------
// Compute a vertex-to-faces adjacency table. To save small memory allocations, the information
// is encoded in three continous buffers - the offset table maps a single vertex index to an
// entry in the adjacency table, which in turn contains n entries, which are the faces adjacent
// to the vertex. n is taken from the third buffer, which stores face counts per vertex.
// ------------------------------------------------------------------------------------------------
VertexTriangleAdjacency::VertexTriangleAdjacency(aiFace *pcFaces,
	unsigned int iNumFaces,
	unsigned int iNumVertices /*= 0*/,
	bool bComputeNumTriangles /*= false*/)
{
	// ---------------------------------------------------------------------
	// 0: compute the number of referenced vertices if not 
	// specified by the caller.
	// ---------------------------------------------------------------------
	const aiFace* const pcFaceEnd = pcFaces + iNumFaces;
	if (!iNumVertices)	{

		for (aiFace* pcFace = pcFaces; pcFace != pcFaceEnd; ++pcFace)	{
			for (unsigned int i = 0; i < pcFace->mNumIndices; ++i) {
				iNumVertices = std::max(iNumVertices,pcFace->mIndices[i]);
			}
		}
	}
	unsigned int* pi;

	// ---------------------------------------------------------------------
	// 1. Allocate output storage
	// ---------------------------------------------------------------------
	if (bComputeNumTriangles)	{
		pi = mLiveTriangles = new unsigned int[iNumVertices+1];
		memset(mLiveTriangles,0,sizeof(unsigned int)*(iNumVertices+1));

		mOffsetTable = new unsigned int[iNumVertices+2]+1;
	}
	else {
		pi = mOffsetTable = new unsigned int[iNumVertices+2]+1;
		memset(mOffsetTable,0,sizeof(unsigned int)*(iNumVertices+1));
		 // important, otherwise the d'tor would crash
		mLiveTriangles = NULL;
	}

	unsigned int* piEnd = pi+iNumVertices;
	*piEnd++ = 0u;

	// ---------------------------------------------------------------------
	// 2. Compute the number of faces referencing each vertex
	// ---------------------------------------------------------------------
	for (aiFace* pcFace = pcFaces; pcFace != pcFaceEnd; ++pcFace)	{
		for (unsigned int i = 0; i < pcFace->mNumIndices; ++i) {
			pi[pcFace->mIndices[i]]++;	
		}
	}

	// ---------------------------------------------------------------------
	// 3. Compute the offset table to map each face to a
	// start position in the adjacency table.
	// ---------------------------------------------------------------------
	unsigned int iSum = 0;
	unsigned int* piCurOut = mOffsetTable;
	for (unsigned int* piCur = pi; piCur != piEnd;++piCur,++piCurOut)	{

		unsigned int iLastSum = iSum;
		iSum += *piCur; 
		*piCurOut = iLastSum;
	}
	pi = mOffsetTable;

	// ---------------------------------------------------------------------
	// 4. Compute the final adjacency table
	// ---------------------------------------------------------------------
	mAdjacencyTable = new unsigned int[iSum];
	iSum = 0;
	for (aiFace* pcFace = pcFaces; pcFace != pcFaceEnd; ++pcFace,++iSum)	{
		
		for (unsigned int i = 0; i < pcFace->mNumIndices; ++i) {
			mAdjacencyTable[pi[pcFace->mIndices[i]]++] = iSum;
		}
	}

	// ---------------------------------------------------------------------
	// 5. Undo the offset computations made during step 4
	// ---------------------------------------------------------------------
	--mOffsetTable;
	*mOffsetTable = 0u;
}

// ------------------------------------------------------------------------------------------------
VertexTriangleAdjacency::~VertexTriangleAdjacency()
{
	delete[] mOffsetTable;
	delete[] mAdjacencyTable;
	delete[] mLiveTriangles;
}