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/// @file SplitByBoneCountProcess.cpp
/// Implementation of the SplitByBoneCount postprocessing step

// internal headers of the post-processing framework
#include "SplitByBoneCountProcess.h"
#include <assimp/postprocess.h>
#include <assimp/DefaultLogger.hpp>

#include <limits>
#include <assimp/TinyFormatter.h>

using namespace Assimp;
using namespace Assimp::Formatter;

// ------------------------------------------------------------------------------------------------
// Constructor
SplitByBoneCountProcess::SplitByBoneCountProcess()
{
    // set default, might be overridden by importer config
    mMaxBoneCount = AI_SBBC_DEFAULT_MAX_BONES;
}

// ------------------------------------------------------------------------------------------------
// Destructor
SplitByBoneCountProcess::~SplitByBoneCountProcess()
{
    // nothing to do here
}

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

// ------------------------------------------------------------------------------------------------
// Updates internal properties
void SplitByBoneCountProcess::SetupProperties(const Importer* pImp)
{
    mMaxBoneCount = pImp->GetPropertyInteger(AI_CONFIG_PP_SBBC_MAX_BONES,AI_SBBC_DEFAULT_MAX_BONES);
}

// ------------------------------------------------------------------------------------------------
// Executes the post processing step on the given imported data.
void SplitByBoneCountProcess::Execute( aiScene* pScene)
{
    ASSIMP_LOG_DEBUG("SplitByBoneCountProcess begin");

    // early out
    bool isNecessary = false;
    for( unsigned int a = 0; a < pScene->mNumMeshes; ++a)
        if( pScene->mMeshes[a]->mNumBones > mMaxBoneCount )
            isNecessary = true;

    if( !isNecessary )
    {
        ASSIMP_LOG_DEBUG( format() << "SplitByBoneCountProcess early-out: no meshes with more than " << mMaxBoneCount << " bones." );
        return;
    }

    // we need to do something. Let's go.
    mSubMeshIndices.clear();
    mSubMeshIndices.resize( pScene->mNumMeshes);

    // build a new array of meshes for the scene
    std::vector<aiMesh*> meshes;

    for( unsigned int a = 0; a < pScene->mNumMeshes; ++a)
    {
        aiMesh* srcMesh = pScene->mMeshes[a];

        std::vector<aiMesh*> newMeshes;
        SplitMesh( pScene->mMeshes[a], newMeshes);

        // mesh was split
        if( !newMeshes.empty() )
        {
            // store new meshes and indices of the new meshes
            for( unsigned int b = 0; b < newMeshes.size(); ++b)
            {
                mSubMeshIndices[a].push_back( static_cast<unsigned int>(meshes.size()));
                meshes.push_back( newMeshes[b]);
            }

            // and destroy the source mesh. It should be completely contained inside the new submeshes
            delete srcMesh;
        }
        else
        {
            // Mesh is kept unchanged - store it's new place in the mesh array
            mSubMeshIndices[a].push_back( static_cast<unsigned int>(meshes.size()));
            meshes.push_back( srcMesh);
        }
    }

    // rebuild the scene's mesh array
    pScene->mNumMeshes = static_cast<unsigned int>(meshes.size());
    delete [] pScene->mMeshes;
    pScene->mMeshes = new aiMesh*[pScene->mNumMeshes];
    std::copy( meshes.begin(), meshes.end(), pScene->mMeshes);

    // recurse through all nodes and translate the node's mesh indices to fit the new mesh array
    UpdateNode( pScene->mRootNode);

    ASSIMP_LOG_DEBUG( format() << "SplitByBoneCountProcess end: split " << mSubMeshIndices.size() << " meshes into " << meshes.size() << " submeshes." );
}

// ------------------------------------------------------------------------------------------------
// Splits the given mesh by bone count.
void SplitByBoneCountProcess::SplitMesh( const aiMesh* pMesh, std::vector<aiMesh*>& poNewMeshes) const
{
    // skip if not necessary
    if( pMesh->mNumBones <= mMaxBoneCount )
        return;

    // necessary optimisation: build a list of all affecting bones for each vertex
    // TODO: (thom) maybe add a custom allocator here to avoid allocating tens of thousands of small arrays
    typedef std::pair<unsigned int, float> BoneWeight;
    std::vector< std::vector<BoneWeight> > vertexBones( pMesh->mNumVertices);
    for( unsigned int a = 0; a < pMesh->mNumBones; ++a)
    {
        const aiBone* bone = pMesh->mBones[a];
        for( unsigned int b = 0; b < bone->mNumWeights; ++b)
            vertexBones[ bone->mWeights[b].mVertexId ].emplace_back( a, bone->mWeights[b].mWeight);
    }

    unsigned int numFacesHandled = 0;
    std::vector<bool> isFaceHandled( pMesh->mNumFaces, false);
    while( numFacesHandled < pMesh->mNumFaces )
    {
        // which bones are used in the current submesh
        unsigned int numBones = 0;
        std::vector<bool> isBoneUsed( pMesh->mNumBones, false);
        // indices of the faces which are going to go into this submesh
        std::vector<unsigned int> subMeshFaces;
        subMeshFaces.reserve( pMesh->mNumFaces);
        // accumulated vertex count of all the faces in this submesh
        unsigned int numSubMeshVertices = 0;
        // a small local array of new bones for the current face. State of all used bones for that face
        // can only be updated AFTER the face is completely analysed. Thanks to imre for the fix.
        std::vector<unsigned int> newBonesAtCurrentFace;

        // add faces to the new submesh as long as all bones affecting the faces' vertices fit in the limit
        for( unsigned int a = 0; a < pMesh->mNumFaces; ++a)
        {
            // skip if the face is already stored in a submesh
            if( isFaceHandled[a] )
                continue;

            const aiFace& face = pMesh->mFaces[a];
            // check every vertex if its bones would still fit into the current submesh
            for( unsigned int b = 0; b < face.mNumIndices; ++b )
            {
                const std::vector<BoneWeight>& vb = vertexBones[face.mIndices[b]];
                for( unsigned int c = 0; c < vb.size(); ++c)
                {
                    unsigned int boneIndex = vb[c].first;
                    // if the bone is already used in this submesh, it's ok
                    if( isBoneUsed[boneIndex] )
                        continue;

                    // if it's not used, yet, we would need to add it. Store its bone index
                    if( std::find( newBonesAtCurrentFace.begin(), newBonesAtCurrentFace.end(), boneIndex) == newBonesAtCurrentFace.end() )
                        newBonesAtCurrentFace.push_back( boneIndex);
                }
            }

            // leave out the face if the new bones required for this face don't fit the bone count limit anymore
            if( numBones + newBonesAtCurrentFace.size() > mMaxBoneCount )
                continue;

            // mark all new bones as necessary
            while( !newBonesAtCurrentFace.empty() )
            {
                unsigned int newIndex = newBonesAtCurrentFace.back();
                newBonesAtCurrentFace.pop_back(); // this also avoids the deallocation which comes with a clear()
                if( isBoneUsed[newIndex] )
                    continue;

                isBoneUsed[newIndex] = true;
                numBones++;
            }

            // store the face index and the vertex count
            subMeshFaces.push_back( a);
            numSubMeshVertices += face.mNumIndices;

            // remember that this face is handled
            isFaceHandled[a] = true;
            numFacesHandled++;
        }

        // create a new mesh to hold this subset of the source mesh
        aiMesh* newMesh = new aiMesh;
        if( pMesh->mName.length > 0 )
            newMesh->mName.Set( format() << pMesh->mName.data << "_sub" << poNewMeshes.size());
        newMesh->mMaterialIndex = pMesh->mMaterialIndex;
        newMesh->mPrimitiveTypes = pMesh->mPrimitiveTypes;
        poNewMeshes.push_back( newMesh);

        // create all the arrays for this mesh if the old mesh contained them
        newMesh->mNumVertices = numSubMeshVertices;
        newMesh->mNumFaces = static_cast<unsigned int>(subMeshFaces.size());
        newMesh->mVertices = new aiVector3D[newMesh->mNumVertices];
        if( pMesh->HasNormals() )
            newMesh->mNormals = new aiVector3D[newMesh->mNumVertices];
        if( pMesh->HasTangentsAndBitangents() )
        {
            newMesh->mTangents = new aiVector3D[newMesh->mNumVertices];
            newMesh->mBitangents = new aiVector3D[newMesh->mNumVertices];
        }
        for( unsigned int a = 0; a < AI_MAX_NUMBER_OF_TEXTURECOORDS; ++a )
        {
            if( pMesh->HasTextureCoords( a) )
                newMesh->mTextureCoords[a] = new aiVector3D[newMesh->mNumVertices];
            newMesh->mNumUVComponents[a] = pMesh->mNumUVComponents[a];
        }
        for( unsigned int a = 0; a < AI_MAX_NUMBER_OF_COLOR_SETS; ++a )
        {
            if( pMesh->HasVertexColors( a) )
                newMesh->mColors[a] = new aiColor4D[newMesh->mNumVertices];
        }

        // and copy over the data, generating faces with linear indices along the way
        newMesh->mFaces = new aiFace[subMeshFaces.size()];
        unsigned int nvi = 0; // next vertex index
        std::vector<unsigned int> previousVertexIndices( numSubMeshVertices, std::numeric_limits<unsigned int>::max()); // per new vertex: its index in the source mesh
        for( unsigned int a = 0; a < subMeshFaces.size(); ++a )
        {
            const aiFace& srcFace = pMesh->mFaces[subMeshFaces[a]];
            aiFace& dstFace = newMesh->mFaces[a];
            dstFace.mNumIndices = srcFace.mNumIndices;
            dstFace.mIndices = new unsigned int[dstFace.mNumIndices];

            // accumulate linearly all the vertices of the source face
            for( unsigned int b = 0; b < dstFace.mNumIndices; ++b )
            {
                unsigned int srcIndex = srcFace.mIndices[b];
                dstFace.mIndices[b] = nvi;
                previousVertexIndices[nvi] = srcIndex;

                newMesh->mVertices[nvi] = pMesh->mVertices[srcIndex];
                if( pMesh->HasNormals() )
                    newMesh->mNormals[nvi] = pMesh->mNormals[srcIndex];
                if( pMesh->HasTangentsAndBitangents() )
                {
                    newMesh->mTangents[nvi] = pMesh->mTangents[srcIndex];
                    newMesh->mBitangents[nvi] = pMesh->mBitangents[srcIndex];
                }
                for( unsigned int c = 0; c < AI_MAX_NUMBER_OF_TEXTURECOORDS; ++c )
                {
                    if( pMesh->HasTextureCoords( c) )
                        newMesh->mTextureCoords[c][nvi] = pMesh->mTextureCoords[c][srcIndex];
                }
                for( unsigned int c = 0; c < AI_MAX_NUMBER_OF_COLOR_SETS; ++c )
                {
                    if( pMesh->HasVertexColors( c) )
                        newMesh->mColors[c][nvi] = pMesh->mColors[c][srcIndex];
                }

                nvi++;
            }
        }

        ai_assert( nvi == numSubMeshVertices );

        // Create the bones for the new submesh: first create the bone array
        newMesh->mNumBones = 0;
        newMesh->mBones = new aiBone*[numBones];

        std::vector<unsigned int> mappedBoneIndex( pMesh->mNumBones, std::numeric_limits<unsigned int>::max());
        for( unsigned int a = 0; a < pMesh->mNumBones; ++a )
        {
            if( !isBoneUsed[a] )
                continue;

            // create the new bone
            const aiBone* srcBone = pMesh->mBones[a];
            aiBone* dstBone = new aiBone;
            mappedBoneIndex[a] = newMesh->mNumBones;
            newMesh->mBones[newMesh->mNumBones++] = dstBone;
            dstBone->mName = srcBone->mName;
            dstBone->mOffsetMatrix = srcBone->mOffsetMatrix;
            dstBone->mNumWeights = 0;
        }

        ai_assert( newMesh->mNumBones == numBones );

        // iterate over all new vertices and count which bones affected its old vertex in the source mesh
        for( unsigned int a = 0; a < numSubMeshVertices; ++a )
        {
            unsigned int oldIndex = previousVertexIndices[a];
            const std::vector<BoneWeight>& bonesOnThisVertex = vertexBones[oldIndex];

            for( unsigned int b = 0; b < bonesOnThisVertex.size(); ++b )
            {
                unsigned int newBoneIndex = mappedBoneIndex[ bonesOnThisVertex[b].first ];
                if( newBoneIndex != std::numeric_limits<unsigned int>::max() )
                    newMesh->mBones[newBoneIndex]->mNumWeights++;
            }
        }

        // allocate all bone weight arrays accordingly
        for( unsigned int a = 0; a < newMesh->mNumBones; ++a )
        {
            aiBone* bone = newMesh->mBones[a];
            ai_assert( bone->mNumWeights > 0 );
            bone->mWeights = new aiVertexWeight[bone->mNumWeights];
            bone->mNumWeights = 0; // for counting up in the next step
        }

        // now copy all the bone vertex weights for all the vertices which made it into the new submesh
        for( unsigned int a = 0; a < numSubMeshVertices; ++a)
        {
            // find the source vertex for it in the source mesh
            unsigned int previousIndex = previousVertexIndices[a];
            // these bones were affecting it
            const std::vector<BoneWeight>& bonesOnThisVertex = vertexBones[previousIndex];
            // all of the bones affecting it should be present in the new submesh, or else
            // the face it comprises shouldn't be present
            for( unsigned int b = 0; b < bonesOnThisVertex.size(); ++b)
            {
                unsigned int newBoneIndex = mappedBoneIndex[ bonesOnThisVertex[b].first ];
                ai_assert( newBoneIndex != std::numeric_limits<unsigned int>::max() );
                aiVertexWeight* dstWeight = newMesh->mBones[newBoneIndex]->mWeights + newMesh->mBones[newBoneIndex]->mNumWeights;
                newMesh->mBones[newBoneIndex]->mNumWeights++;

                dstWeight->mVertexId = a;
                dstWeight->mWeight = bonesOnThisVertex[b].second;
            }
        }

        // I have the strange feeling that this will break apart at some point in time...
    }
}

// ------------------------------------------------------------------------------------------------
// Recursively updates the node's mesh list to account for the changed mesh list
void SplitByBoneCountProcess::UpdateNode( aiNode* pNode) const
{
    // rebuild the node's mesh index list
    if( pNode->mNumMeshes > 0 )
    {
        std::vector<unsigned int> newMeshList;
        for( unsigned int a = 0; a < pNode->mNumMeshes; ++a)
        {
            unsigned int srcIndex = pNode->mMeshes[a];
            const std::vector<unsigned int>& replaceMeshes = mSubMeshIndices[srcIndex];
            newMeshList.insert( newMeshList.end(), replaceMeshes.begin(), replaceMeshes.end());
        }

        delete [] pNode->mMeshes;
        pNode->mNumMeshes = static_cast<unsigned int>(newMeshList.size());
        pNode->mMeshes = new unsigned int[pNode->mNumMeshes];
        std::copy( newMeshList.begin(), newMeshList.end(), pNode->mMeshes);
    }

    // do that also recursively for all children
    for( unsigned int a = 0; a < pNode->mNumChildren; ++a )
    {
        UpdateNode( pNode->mChildren[a]);
    }
}