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/** @file Implementation of the post processing step to calculate
 *  tangents and bitangents for all imported meshes
 */

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

using namespace Assimp;

// ------------------------------------------------------------------------------------------------
// Constructor to be privately used by Importer
CalcTangentsProcess::CalcTangentsProcess()
: configMaxAngle( AI_DEG_TO_RAD(45.f) )
, configSourceUV( 0 ) {
    // nothing to do here
}

// ------------------------------------------------------------------------------------------------
// 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)
{
    ai_assert( NULL != 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)
{
    ai_assert( NULL != 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 bi-tangents 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) // this implies 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)
            {
                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;
        // when t1, t2, t3 in same position in UV space, just use default UV direction.
        if ( 0 == sx && 0 ==sy && 0 == tx && 0 == ty ) {
            sx = 0.0; sy = 1.0;
            tx = 1.0; ty = 0.0;
        }

        // tangent points in the direction where to positive X axis of the texture coord's would point in model space
        // bitangent's points along the positive Y axis of the texture coord's, 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();

            // reconstruct tangent/bitangent according to normal and bitangent/tangent when it's infinite or NaN.
            bool invalid_tangent = is_special_float(localTangent.x) || is_special_float(localTangent.y) || is_special_float(localTangent.z);
            bool invalid_bitangent = is_special_float(localBitangent.x) || is_special_float(localBitangent.y) || is_special_float(localBitangent.z);
            if (invalid_tangent != invalid_bitangent) {
                if (invalid_tangent) {
                    localTangent = meshNorm[p] ^ localBitangent;
                    localTangent.Normalize();
                } else {
                    localBitangent = localTangent ^ meshNorm[p];
                    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::cos(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.resize( 0 );

        // 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;
}
