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/** @file Implementation of the post processing step to join identical vertices
 * for all imported meshes
 */

#ifndef ASSIMP_BUILD_NO_JOINVERTICES_PROCESS

#include "JoinVerticesProcess.h"
#include "ProcessHelper.h"
#include <assimp/Vertex.h>
#include <assimp/TinyFormatter.h>

#include <stdio.h>
#include <unordered_set>
#include <unordered_map>
#include <memory>

using namespace Assimp;

// ------------------------------------------------------------------------------------------------
// Returns whether the processing step is present in the given flag field.
bool JoinVerticesProcess::IsActive( unsigned int pFlags) const {
    return (pFlags & aiProcess_JoinIdenticalVertices) != 0;
}
// ------------------------------------------------------------------------------------------------
// Executes the post processing step on the given imported data.
void JoinVerticesProcess::Execute( aiScene* pScene) {
    ASSIMP_LOG_DEBUG("JoinVerticesProcess begin");

    // get the total number of vertices BEFORE the step is executed
    int iNumOldVertices = 0;
    if (!DefaultLogger::isNullLogger()) {
        for( unsigned int a = 0; a < pScene->mNumMeshes; a++)   {
            iNumOldVertices +=  pScene->mMeshes[a]->mNumVertices;
        }
    }

    // execute the step
    int iNumVertices = 0;
    for( unsigned int a = 0; a < pScene->mNumMeshes; a++) {
        iNumVertices += ProcessMesh( pScene->mMeshes[a],a);
    }

    pScene->mFlags |= AI_SCENE_FLAGS_NON_VERBOSE_FORMAT;

    // if logging is active, print detailed statistics
    if (!DefaultLogger::isNullLogger()) {
        if (iNumOldVertices == iNumVertices) {
            ASSIMP_LOG_DEBUG("JoinVerticesProcess finished ");
            return;
        }

        // Show statistics
        ASSIMP_LOG_INFO("JoinVerticesProcess finished | Verts in: ", iNumOldVertices,
            " out: ", iNumVertices, " | ~",
            ((iNumOldVertices - iNumVertices) / (float)iNumOldVertices) * 100.f );
    }
}

namespace {

bool areVerticesEqual(
    const Vertex &lhs,
    const Vertex &rhs,
    unsigned numUVChannels,
    unsigned numColorChannels) {
    // A little helper to find locally close vertices faster.
    // Try to reuse the lookup table from the last step.
    const static float epsilon = 1e-5f;
    // Squared because we check against squared length of the vector difference
    static const float squareEpsilon = epsilon * epsilon;

    // Square compare is useful for animeshes vertices compare
    if ((lhs.position - rhs.position).SquareLength() > squareEpsilon) {
        return false;
    }

    // We just test the other attributes even if they're not present in the mesh.
    // In this case they're initialized to 0 so the comparison succeeds.
    // By this method the non-present attributes are effectively ignored in the comparison.
    if ((lhs.normal - rhs.normal).SquareLength() > squareEpsilon) {
        return false;
    }

    if ((lhs.tangent - rhs.tangent).SquareLength() > squareEpsilon) {
        return false;
    }

    if ((lhs.bitangent - rhs.bitangent).SquareLength() > squareEpsilon) {
        return false;
    }

    for (unsigned i = 0; i < numUVChannels; i++) {
        if ((lhs.texcoords[i] - rhs.texcoords[i]).SquareLength() > squareEpsilon) {
            return false;
        }
    }

    for (unsigned i = 0; i < numColorChannels; i++) {
        if (GetColorDifference(lhs.colors[i], rhs.colors[i]) > squareEpsilon) {
            return false;
        }
    }

    return true;
}

template<class XMesh>
void updateXMeshVertices(XMesh *pMesh, std::vector<int> &uniqueVertices) {
    // replace vertex data with the unique data sets
    pMesh->mNumVertices = (unsigned int)uniqueVertices.size();

    // ----------------------------------------------------------------------------
    // NOTE - we're *not* calling Vertex::SortBack() because it would check for
    // presence of every single vertex component once PER VERTEX. And our CPU
    // dislikes branches, even if they're easily predictable.
    // ----------------------------------------------------------------------------

    // Position, if present (check made for aiAnimMesh)
    if (pMesh->mVertices) {  
        std::unique_ptr<aiVector3D[]> oldVertices(pMesh->mVertices);
        pMesh->mVertices = new aiVector3D[pMesh->mNumVertices];
        for (unsigned int a = 0; a < pMesh->mNumVertices; a++)
            pMesh->mVertices[a] = oldVertices[uniqueVertices[a]];
    }

    // Normals, if present
    if (pMesh->mNormals) {
        std::unique_ptr<aiVector3D[]> oldNormals(pMesh->mNormals);
        pMesh->mNormals = new aiVector3D[pMesh->mNumVertices];
        for (unsigned int a = 0; a < pMesh->mNumVertices; a++)
            pMesh->mNormals[a] = oldNormals[uniqueVertices[a]];
    }
    // Tangents, if present
    if (pMesh->mTangents) {
        std::unique_ptr<aiVector3D[]> oldTangents(pMesh->mTangents);
        pMesh->mTangents = new aiVector3D[pMesh->mNumVertices];
        for (unsigned int a = 0; a < pMesh->mNumVertices; a++)
            pMesh->mTangents[a] = oldTangents[uniqueVertices[a]];
    }
    // Bitangents as well
    if (pMesh->mBitangents) {
        std::unique_ptr<aiVector3D[]> oldBitangents(pMesh->mBitangents);
        pMesh->mBitangents = new aiVector3D[pMesh->mNumVertices];
        for (unsigned int a = 0; a < pMesh->mNumVertices; a++)
            pMesh->mBitangents[a] = oldBitangents[uniqueVertices[a]];
    }
    // Vertex colors
    for (unsigned int a = 0; pMesh->HasVertexColors(a); a++) {
        std::unique_ptr<aiColor4D[]> oldColors(pMesh->mColors[a]);
        pMesh->mColors[a] = new aiColor4D[pMesh->mNumVertices];
        for (unsigned int b = 0; b < pMesh->mNumVertices; b++)
            pMesh->mColors[a][b] = oldColors[uniqueVertices[b]];
    }
    // Texture coords
    for (unsigned int a = 0; pMesh->HasTextureCoords(a); a++) {
        std::unique_ptr<aiVector3D[]> oldTextureCoords(pMesh->mTextureCoords[a]);
        pMesh->mTextureCoords[a] = new aiVector3D[pMesh->mNumVertices];
        for (unsigned int b = 0; b < pMesh->mNumVertices; b++)
            pMesh->mTextureCoords[a][b] = oldTextureCoords[uniqueVertices[b]];
    }
}

} // namespace

// ------------------------------------------------------------------------------------------------
// Unites identical vertices in the given mesh
// combine hashes
inline void hash_combine(std::size_t &) {
    // empty
}

template <typename T, typename... Rest>
inline void hash_combine(std::size_t& seed, const T& v, Rest... rest) {
    std::hash<T> hasher;
    seed ^= hasher(v) + 0x9e3779b9 + (seed<<6) + (seed>>2);
    hash_combine(seed, rest...);
}
//template specialization for std::hash for Vertex
template<>
struct std::hash<Vertex> {
    std::size_t operator()(Vertex const& v) const noexcept {
        size_t seed = 0;
        hash_combine(seed, v.position.x ,v.position.y,v.position.z);
        return seed;
    }
};
//template specialization for std::equal_to for Vertex
template<>
struct std::equal_to<Vertex> {
    equal_to(unsigned numUVChannels, unsigned numColorChannels) :
            mNumUVChannels(numUVChannels),
            mNumColorChannels(numColorChannels) {}
    bool operator()(const Vertex &lhs, const Vertex &rhs) const {
        return areVerticesEqual(lhs, rhs, mNumUVChannels, mNumColorChannels);
    }

private:
    unsigned mNumUVChannels;
    unsigned mNumColorChannels;
};

static constexpr size_t JOINED_VERTICES_MARK = 0x80000000u;

// now start the JoinVerticesProcess
int JoinVerticesProcess::ProcessMesh( aiMesh* pMesh, unsigned int meshIndex) {
    static_assert( AI_MAX_NUMBER_OF_COLOR_SETS    == 8, "AI_MAX_NUMBER_OF_COLOR_SETS    == 8");
	static_assert( AI_MAX_NUMBER_OF_TEXTURECOORDS == 8, "AI_MAX_NUMBER_OF_TEXTURECOORDS == 8");

    // Return early if we don't have any positions
    if (!pMesh->HasPositions() || !pMesh->HasFaces()) {
        return 0;
    }

    // We should care only about used vertices, not all of them
    // (this can happen due to original file vertices buffer being used by
    // multiple meshes)
    std::vector<bool> usedVertexIndicesMask;
    usedVertexIndicesMask.resize(pMesh->mNumVertices, false);
    for (unsigned int a = 0; a < pMesh->mNumFaces; a++) {
        aiFace& face = pMesh->mFaces[a];
        for (unsigned int b = 0; b < face.mNumIndices; b++) {
            usedVertexIndicesMask[face.mIndices[b]] = true;
        }
    }

    // We'll never have more vertices afterwards.
    std::vector<int> uniqueVertices;
    uniqueVertices.reserve( pMesh->mNumVertices);

    // For each vertex the index of the vertex it was replaced by.
    // Since the maximal number of vertices is 2^31-1, the most significand bit can be used to mark
    //  whether a new vertex was created for the index (true) or if it was replaced by an existing
    //  unique vertex (false). This saves an additional std::vector<bool> and greatly enhances
    //  branching performance.
    static_assert(AI_MAX_VERTICES == 0x7fffffff, "AI_MAX_VERTICES == 0x7fffffff");
    std::vector<unsigned int> replaceIndex( pMesh->mNumVertices, 0xffffffff);

    // float posEpsilonSqr;
    SpatialSort *vertexFinder = nullptr;
    SpatialSort _vertexFinder;

    typedef std::pair<SpatialSort,float> SpatPair;
    if (shared) {
        std::vector<SpatPair >* avf;
        shared->GetProperty(AI_SPP_SPATIAL_SORT,avf);
        if (avf)    {
            SpatPair& blubb = (*avf)[meshIndex];
            vertexFinder  = &blubb.first;
            // posEpsilonSqr = blubb.second;
        }
    }
    if (!vertexFinder)  {
        // bad, need to compute it.
        _vertexFinder.Fill(pMesh->mVertices, pMesh->mNumVertices, sizeof( aiVector3D));
        vertexFinder = &_vertexFinder;
        // posEpsilonSqr = ComputePositionEpsilon(pMesh);
    }

    // Again, better waste some bytes than a realloc ...
    std::vector<unsigned int> verticesFound;
    verticesFound.reserve(10);

    // Run an optimized code path if we don't have multiple UVs or vertex colors.
    // This should yield false in more than 99% of all imports ...
    const bool hasAnimMeshes = pMesh->mNumAnimMeshes > 0;

    // We'll never have more vertices afterwards.
    std::vector<std::vector<int>> uniqueAnimatedVertices;
    if (hasAnimMeshes) {
        uniqueAnimatedVertices.resize(pMesh->mNumAnimMeshes);
        for (unsigned int animMeshIndex = 0; animMeshIndex < pMesh->mNumAnimMeshes; animMeshIndex++) {
            uniqueAnimatedVertices[animMeshIndex].reserve(pMesh->mNumVertices);
        }
    }
    // a map that maps a vertex to its new index
    const auto numBuckets = pMesh->mNumVertices;
    const auto hasher = std::hash<Vertex>();
    const auto comparator = std::equal_to<Vertex>(
            pMesh->GetNumUVChannels(),
            pMesh->GetNumColorChannels());
    std::unordered_map<Vertex, int> vertex2Index(numBuckets, hasher, comparator);
    // we can not end up with more vertices than we started with
    vertex2Index.reserve(pMesh->mNumVertices);
    // Now check each vertex if it brings something new to the table
    int newIndex = 0;
    for( unsigned int a = 0; a < pMesh->mNumVertices; a++)  {
        // if the vertex is unused Do nothing
        if (!usedVertexIndicesMask[a]) {
            continue;
        }
        // collect the vertex data
        Vertex v(pMesh,a);
        // is the vertex already in the map?
        auto it = vertex2Index.find(v);
        // if the vertex is not in the map then it is a new vertex add it.
        if (it == vertex2Index.end()) {
            // this is a new vertex give it a new index
            vertex2Index[v] = newIndex;
            //keep track of its index and increment 1
            replaceIndex[a] = newIndex++;
            // add the vertex to the unique vertices
            uniqueVertices.push_back(a);
            if (hasAnimMeshes) {
                for (unsigned int animMeshIndex = 0; animMeshIndex < pMesh->mNumAnimMeshes; animMeshIndex++) {
                    uniqueAnimatedVertices[animMeshIndex].emplace_back(a);
                }
            }
        } else{
            // if the vertex is already there just find the replace index that is appropriate to it
			// mark it with JOINED_VERTICES_MARK
            replaceIndex[a] = it->second | JOINED_VERTICES_MARK;
        }
    }

    if (!DefaultLogger::isNullLogger() && DefaultLogger::get()->getLogSeverity() == Logger::VERBOSE)    {
        ASSIMP_LOG_VERBOSE_DEBUG(
            "Mesh ",meshIndex,
            " (",
            (pMesh->mName.length ? pMesh->mName.data : "unnamed"),
            ") | Verts in: ",pMesh->mNumVertices,
            " out: ",
            uniqueVertices.size(),
            " | ~",
            ((pMesh->mNumVertices - uniqueVertices.size()) / (float)pMesh->mNumVertices) * 100.f,
            "%"
        );
    }

    updateXMeshVertices(pMesh, uniqueVertices);
    if (hasAnimMeshes) {
        for (unsigned int animMeshIndex = 0; animMeshIndex < pMesh->mNumAnimMeshes; animMeshIndex++) {
            updateXMeshVertices(pMesh->mAnimMeshes[animMeshIndex], uniqueAnimatedVertices[animMeshIndex]);
        }
    }

    // adjust the indices in all faces
    for( unsigned int a = 0; a < pMesh->mNumFaces; a++) {
        aiFace& face = pMesh->mFaces[a];
        for( unsigned int b = 0; b < face.mNumIndices; b++) {
            face.mIndices[b] = replaceIndex[face.mIndices[b]] & ~JOINED_VERTICES_MARK;
        }
    }

    // adjust bone vertex weights.
    for( int a = 0; a < (int)pMesh->mNumBones; a++) {
        aiBone* bone = pMesh->mBones[a];
        std::vector<aiVertexWeight> newWeights;
        newWeights.reserve( bone->mNumWeights);

        if (nullptr != bone->mWeights) {
            for ( unsigned int b = 0; b < bone->mNumWeights; b++ ) {
                const aiVertexWeight& ow = bone->mWeights[ b ];
                // if the vertex is a unique one, translate it
				// filter out joined vertices by JOINED_VERTICES_MARK.
                if ( !( replaceIndex[ ow.mVertexId ] & JOINED_VERTICES_MARK ) ) {
                    aiVertexWeight nw;
                    nw.mVertexId = replaceIndex[ ow.mVertexId ];
                    nw.mWeight = ow.mWeight;
                    newWeights.push_back( nw );
                }
            }
        } else {
            ASSIMP_LOG_ERROR( "X-Export: aiBone shall contain weights, but pointer to them is nullptr." );
        }

        if (newWeights.size() > 0) {
            // kill the old and replace them with the translated weights
            delete [] bone->mWeights;
            bone->mNumWeights = (unsigned int)newWeights.size();

            bone->mWeights = new aiVertexWeight[bone->mNumWeights];
            memcpy( bone->mWeights, &newWeights[0], bone->mNumWeights * sizeof( aiVertexWeight));
        }
    }
    return pMesh->mNumVertices;
}

#endif // !! ASSIMP_BUILD_NO_JOINVERTICES_PROCESS
