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Open Asset Import Library (assimp)
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/** @file Generation of normal vectors basing on smoothing groups */

#ifndef AI_SMOOTHINGGROUPS_INL_INCLUDED
#define AI_SMOOTHINGGROUPS_INL_INCLUDED

// internal headers
#include "SGSpatialSort.h"

// CRT header
#include <algorithm>

using namespace Assimp;

// ------------------------------------------------------------------------------------------------
template <class T>
void ComputeNormalsWithSmoothingsGroups(MeshWithSmoothingGroups<T>& sMesh)
{
	// First generate face normals
	sMesh.mNormals.resize(sMesh.mPositions.size(),aiVector3D());
	for( unsigned int a = 0; a < sMesh.mFaces.size(); a++)
	{
		T& face = sMesh.mFaces[a];

		aiVector3D* pV1 = &sMesh.mPositions[face.mIndices[0]];
		aiVector3D* pV2 = &sMesh.mPositions[face.mIndices[1]];
		aiVector3D* pV3 = &sMesh.mPositions[face.mIndices[2]];

		aiVector3D pDelta1 = *pV2 - *pV1;
		aiVector3D pDelta2 = *pV3 - *pV1;
		aiVector3D vNor = pDelta1 ^ pDelta2;

		for (unsigned int c = 0; c < 3;++c)
			sMesh.mNormals[face.mIndices[c]] = vNor;
	}

	// calculate the position bounds so we have a reliable epsilon to check position differences against 
	aiVector3D minVec( 1e10f, 1e10f, 1e10f), maxVec( -1e10f, -1e10f, -1e10f);
	for( unsigned int a = 0; a < sMesh.mPositions.size(); a++)
	{
		minVec.x = std::min( minVec.x, sMesh.mPositions[a].x);
		minVec.y = std::min( minVec.y, sMesh.mPositions[a].y);
		minVec.z = std::min( minVec.z, sMesh.mPositions[a].z);
		maxVec.x = std::max( maxVec.x, sMesh.mPositions[a].x);
		maxVec.y = std::max( maxVec.y, sMesh.mPositions[a].y);
		maxVec.z = std::max( maxVec.z, sMesh.mPositions[a].z);
	}
	const float posEpsilon = (maxVec - minVec).Length() * 1e-5f;
	std::vector<aiVector3D> avNormals;
	avNormals.resize(sMesh.mNormals.size());
	
	// now generate the spatial sort tree
	SGSpatialSort sSort;
	for( typename std::vector<T>::iterator i =  sMesh.mFaces.begin();
		i != sMesh.mFaces.end();++i)
	{
		for (unsigned int c = 0; c < 3;++c)
			sSort.Add(sMesh.mPositions[(*i).mIndices[c]],(*i).mIndices[c],(*i).iSmoothGroup);
	}
	sSort.Prepare();

	std::vector<bool> vertexDone(sMesh.mPositions.size(),false);
	for( typename std::vector<T>::iterator i =  sMesh.mFaces.begin();
		i != sMesh.mFaces.end();++i)
	{
		std::vector<unsigned int> poResult;
		for (unsigned int c = 0; c < 3;++c)
		{
			unsigned int idx = (*i).mIndices[c];
			if (vertexDone[idx])continue;

			sSort.FindPositions(sMesh.mPositions[idx],(*i).iSmoothGroup,
				posEpsilon,poResult);

			aiVector3D vNormals;
			for (std::vector<unsigned int>::const_iterator
				a =  poResult.begin();
				a != poResult.end();++a)
			{
				vNormals += sMesh.mNormals[(*a)];
			}
			vNormals.Normalize();

			// write back into all affected normals
			for (std::vector<unsigned int>::const_iterator
				a =  poResult.begin();
				a != poResult.end();++a)
			{
				idx = *a;
				avNormals [idx] = vNormals;
				vertexDone[idx] = true;
			}
		}
	}
	sMesh.mNormals = avNormals;
}

#endif // !! AI_SMOOTHINGGROUPS_INL_INCLUDED
