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Open Asset Import Library (assimp)
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/** @file Implementation of the post processing step to calculate 
 *  tangents and bitangents for all imported meshes
 */

#include "AssimpPCH.h"

// internal headers
#include "CalcTangentsProcess.h"
#include "ProcessHelper.h"
#include "TinyFormatter.h"

using namespace Assimp;

// ------------------------------------------------------------------------------------------------
// Constructor to be privately used by Importer
CalcTangentsProcess::CalcTangentsProcess()
{
	this->configMaxAngle = AI_DEG_TO_RAD(45.f);
}

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

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

// ------------------------------------------------------------------------------------------------
// Executes the post processing step on the given imported data.
void CalcTangentsProcess::SetupProperties(const Importer* pImp)
{
	// get the current value of the property
	configMaxAngle = pImp->GetPropertyFloat(AI_CONFIG_PP_CT_MAX_SMOOTHING_ANGLE,45.f);
	configMaxAngle = std::max(std::min(configMaxAngle,45.0f),0.0f);
	configMaxAngle = AI_DEG_TO_RAD(configMaxAngle);

	configSourceUV = pImp->GetPropertyInteger(AI_CONFIG_PP_CT_TEXTURE_CHANNEL_INDEX,0);
}

// ------------------------------------------------------------------------------------------------
// Executes the post processing step on the given imported data.
void CalcTangentsProcess::Execute( aiScene* pScene)
{
	DefaultLogger::get()->debug("CalcTangentsProcess begin");

	bool bHas = false;
	for( unsigned int a = 0; a < pScene->mNumMeshes; a++)
		if(ProcessMesh( pScene->mMeshes[a],a))bHas = true;

	if (bHas)DefaultLogger::get()->info("CalcTangentsProcess finished. Tangents have been calculated");
	else DefaultLogger::get()->debug("CalcTangentsProcess finished");
}

// ------------------------------------------------------------------------------------------------
// Calculates tangents and bitangents for the given mesh
bool CalcTangentsProcess::ProcessMesh( aiMesh* pMesh, unsigned int meshIndex)
{
	// we assume that the mesh is still in the verbose vertex format where each face has its own set
	// of vertices and no vertices are shared between faces. Sadly I don't know any quick test to 
	// assert() it here.
    //assert( must be verbose, dammit);

	if (pMesh->mTangents) // thisimplies that mBitangents is also there
		return false;

	// If the mesh consists of lines and/or points but not of
	// triangles or higher-order polygons the normal vectors
	// are undefined.
	if (!(pMesh->mPrimitiveTypes & (aiPrimitiveType_TRIANGLE | aiPrimitiveType_POLYGON)))
	{
		DefaultLogger::get()->info("Tangents are undefined for line and point meshes");
		return false;
	}

	// what we can check, though, is if the mesh has normals and texture coordinates. That's a requirement
	if( pMesh->mNormals == NULL)
	{
		DefaultLogger::get()->error("Failed to compute tangents; need normals");
		return false;
	}
	if( configSourceUV >= AI_MAX_NUMBER_OF_TEXTURECOORDS || !pMesh->mTextureCoords[configSourceUV] )
	{
		DefaultLogger::get()->error((Formatter::format("Failed to compute tangents; need UV data in channel"),configSourceUV));
		return false;
	}
	 
	const float angleEpsilon = 0.9999f;

	std::vector<bool> vertexDone( pMesh->mNumVertices, false);
	const float qnan = get_qnan();

	// create space for the tangents and bitangents
	pMesh->mTangents = new aiVector3D[pMesh->mNumVertices];
	pMesh->mBitangents = new aiVector3D[pMesh->mNumVertices];

	const aiVector3D* meshPos = pMesh->mVertices;
	const aiVector3D* meshNorm = pMesh->mNormals;
	const aiVector3D* meshTex = pMesh->mTextureCoords[configSourceUV];
	aiVector3D* meshTang = pMesh->mTangents;
	aiVector3D* meshBitang = pMesh->mBitangents;
	
	// calculate the tangent and bitangent for every face
	for( unsigned int a = 0; a < pMesh->mNumFaces; a++)
	{
		const aiFace& face = pMesh->mFaces[a];
		if (face.mNumIndices < 3)
		{
			// There are less than three indices, thus the tangent vector
			// is not defined. We are finished with these vertices now,
			// their tangent vectors are set to qnan.
			for (unsigned int i = 0; i < face.mNumIndices;++i)
			{
				register unsigned int idx = face.mIndices[i];
				vertexDone  [idx] = true;
				meshTang    [idx] = aiVector3D(qnan);
				meshBitang  [idx] = aiVector3D(qnan);
			}

			continue;
		}

		// triangle or polygon... we always use only the first three indices. A polygon
		// is supposed to be planar anyways....
		// FIXME: (thom) create correct calculation for multi-vertex polygons maybe?
		const unsigned int p0 = face.mIndices[0], p1 = face.mIndices[1], p2 = face.mIndices[2];

		// position differences p1->p2 and p1->p3
		aiVector3D v = meshPos[p1] - meshPos[p0], w = meshPos[p2] - meshPos[p0];

		// texture offset p1->p2 and p1->p3
		float sx = meshTex[p1].x - meshTex[p0].x, sy = meshTex[p1].y - meshTex[p0].y;
        float tx = meshTex[p2].x - meshTex[p0].x, ty = meshTex[p2].y - meshTex[p0].y;
		float dirCorrection = (tx * sy - ty * sx) < 0.0f ? -1.0f : 1.0f;

		// tangent points in the direction where to positive X axis of the texture coords would point in model space
		// bitangents points along the positive Y axis of the texture coords, respectively
		aiVector3D tangent, bitangent;
		tangent.x = (w.x * sy - v.x * ty) * dirCorrection;
        tangent.y = (w.y * sy - v.y * ty) * dirCorrection;
        tangent.z = (w.z * sy - v.z * ty) * dirCorrection;
        bitangent.x = (w.x * sx - v.x * tx) * dirCorrection;
        bitangent.y = (w.y * sx - v.y * tx) * dirCorrection;
        bitangent.z = (w.z * sx - v.z * tx) * dirCorrection;

		// store for every vertex of that face
		for( unsigned int b = 0; b < face.mNumIndices; b++)
		{
			unsigned int p = face.mIndices[b];

			// project tangent and bitangent into the plane formed by the vertex' normal
			aiVector3D localTangent = tangent - meshNorm[p] * (tangent * meshNorm[p]);
			aiVector3D localBitangent = bitangent - meshNorm[p] * (bitangent * meshNorm[p]);
			localTangent.Normalize(); localBitangent.Normalize();

			// and write it into the mesh.
			meshTang[p] = localTangent;
			meshBitang[p] = localBitangent;
		}
    }


	// create a helper to quickly find locally close vertices among the vertex array
	// FIX: check whether we can reuse the SpatialSort of a previous step
	SpatialSort* vertexFinder = NULL;
	SpatialSort  _vertexFinder;
	float posEpsilon;
	if (shared)
	{
		std::vector<std::pair<SpatialSort,float> >* avf;
		shared->GetProperty(AI_SPP_SPATIAL_SORT,avf);
		if (avf)
		{
			std::pair<SpatialSort,float>& blubb = avf->operator [] (meshIndex);
			vertexFinder = &blubb.first;
			posEpsilon = blubb.second;;
		}
	}
	if (!vertexFinder)
	{
		_vertexFinder.Fill(pMesh->mVertices, pMesh->mNumVertices, sizeof( aiVector3D));
		vertexFinder = &_vertexFinder;
		posEpsilon = ComputePositionEpsilon(pMesh);
	}
	std::vector<unsigned int> verticesFound;

	const float fLimit = math::cosf(configMaxAngle);
	std::vector<unsigned int> closeVertices;

	// in the second pass we now smooth out all tangents and bitangents at the same local position 
	// if they are not too far off.
	for( unsigned int a = 0; a < pMesh->mNumVertices; a++)
	{
		if( vertexDone[a])
			continue;

		const aiVector3D& origPos = pMesh->mVertices[a];
		const aiVector3D& origNorm = pMesh->mNormals[a];
		const aiVector3D& origTang = pMesh->mTangents[a];
		const aiVector3D& origBitang = pMesh->mBitangents[a];
		closeVertices.clear();

		// find all vertices close to that position
		vertexFinder->FindPositions( origPos, posEpsilon, verticesFound);

		closeVertices.reserve (verticesFound.size()+5);
		closeVertices.push_back( a);

		// look among them for other vertices sharing the same normal and a close-enough tangent/bitangent
		for( unsigned int b = 0; b < verticesFound.size(); b++)
		{
			unsigned int idx = verticesFound[b];
			if( vertexDone[idx])
				continue;
			if( meshNorm[idx] * origNorm < angleEpsilon)
				continue;
			if(  meshTang[idx] * origTang < fLimit)
				continue;
			if( meshBitang[idx] * origBitang < fLimit)
				continue;

			// it's similar enough -> add it to the smoothing group
			closeVertices.push_back( idx);
			vertexDone[idx] = true;
		}

		// smooth the tangents and bitangents of all vertices that were found to be close enough
		aiVector3D smoothTangent( 0, 0, 0), smoothBitangent( 0, 0, 0);
		for( unsigned int b = 0; b < closeVertices.size(); ++b)
		{
			smoothTangent += meshTang[ closeVertices[b] ];
			smoothBitangent += meshBitang[ closeVertices[b] ];
		}
		smoothTangent.Normalize();
		smoothBitangent.Normalize();

		// and write it back into all affected tangents
		for( unsigned int b = 0; b < closeVertices.size(); ++b)
		{
			meshTang[ closeVertices[b] ] = smoothTangent;
			meshBitang[ closeVertices[b] ] = smoothBitangent;
		}
	}
	return true;
}