Torque3D/Engine/lib/assimp/code/AssetLib/Collada/ColladaLoader.cpp

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/** @file Implementation of the Collada loader */

#ifndef ASSIMP_BUILD_NO_COLLADA_IMPORTER

#include "ColladaLoader.h"
#include "ColladaParser.h"
#include <assimp/ColladaMetaData.h>
#include <assimp/CreateAnimMesh.h>
#include <assimp/ParsingUtils.h>
#include <assimp/SkeletonMeshBuilder.h>
#include <assimp/ZipArchiveIOSystem.h>
#include <assimp/anim.h>
#include <assimp/fast_atof.h>
#include <assimp/importerdesc.h>
#include <assimp/scene.h>
#include <assimp/DefaultLogger.hpp>
#include <assimp/Importer.hpp>

#include <numeric>

namespace Assimp {

using namespace Assimp::Formatter;
using namespace Assimp::Collada;

static constexpr aiImporterDesc desc = {
    "Collada Importer",
    "",
    "",
    "http://collada.org",
    aiImporterFlags_SupportTextFlavour | aiImporterFlags_SupportCompressedFlavour,
    1,
    3,
    1,
    5,
    "dae xml zae"
};

static constexpr float kMillisecondsFromSeconds = 1000.f;

// Add an item of metadata to a node
// Assumes the key is not already in the list
template <typename T>
void AddNodeMetaData(aiNode *node, const std::string &key, const T &value) {
    if (nullptr == node->mMetaData) {
        node->mMetaData = new aiMetadata();
    }
    node->mMetaData->Add(key, value);
}

// ------------------------------------------------------------------------------------------------
// Reads a float value from an accessor and its data array.
static ai_real ReadFloat(const Accessor &pAccessor, const Data &pData, size_t pIndex, size_t pOffset) {
    const size_t pos = pAccessor.mStride * pIndex + pAccessor.mOffset + pOffset;
    ai_assert(pos < pData.mValues.size());
    return pData.mValues[pos];
}

// ------------------------------------------------------------------------------------------------
// Constructor to be privately used by Importer
ColladaLoader::ColladaLoader() :
        noSkeletonMesh(false),
        removeEmptyBones(false),
        ignoreUpDirection(false),
        ignoreUnitSize(false),
        useColladaName(false),
        mNodeNameCounter(0) {
    // empty
}

// ------------------------------------------------------------------------------------------------
// Returns whether the class can handle the format of the given file.
bool ColladaLoader::CanRead(const std::string &pFile, IOSystem *pIOHandler, bool /*checkSig*/) const {
    // Look for a DAE file inside, but don't extract it
    ZipArchiveIOSystem zip_archive(pIOHandler, pFile);
    if (zip_archive.isOpen()) {
        return !ColladaParser::ReadZaeManifest(zip_archive).empty();
    }

    static const char *tokens[] = { "<collada" };
    return SearchFileHeaderForToken(pIOHandler, pFile, tokens, AI_COUNT_OF(tokens));
}

// ------------------------------------------------------------------------------------------------
void ColladaLoader::SetupProperties(const Importer *pImp) {
    noSkeletonMesh = pImp->GetPropertyInteger(AI_CONFIG_IMPORT_NO_SKELETON_MESHES, 0) != 0;
    removeEmptyBones = pImp->GetPropertyInteger(AI_CONFIG_IMPORT_REMOVE_EMPTY_BONES, true) != 0;
    ignoreUpDirection = pImp->GetPropertyInteger(AI_CONFIG_IMPORT_COLLADA_IGNORE_UP_DIRECTION, 0) != 0;
    ignoreUnitSize = pImp->GetPropertyInteger(AI_CONFIG_IMPORT_COLLADA_IGNORE_UNIT_SIZE, 0) != 0;
    useColladaName = pImp->GetPropertyInteger(AI_CONFIG_IMPORT_COLLADA_USE_COLLADA_NAMES, 0) != 0;
}

// ------------------------------------------------------------------------------------------------
// Get file extension list
const aiImporterDesc *ColladaLoader::GetInfo() const {
    return &desc;
}

// ------------------------------------------------------------------------------------------------
// Imports the given file into the given scene structure.
void ColladaLoader::InternReadFile(const std::string &pFile, aiScene *pScene, IOSystem *pIOHandler) {
    mFileName = pFile;

    // clean all member arrays - just for safety, it should work even if we did not
    mMeshIndexByID.clear();
    mMaterialIndexByName.clear();
    mMeshes.clear();
    mTargetMeshes.clear();
    newMats.clear();
    mLights.clear();
    mCameras.clear();
    mTextures.clear();
    mAnims.clear();

    // parse the input file
    ColladaParser parser(pIOHandler, pFile);

    if (!parser.mRootNode) {
        throw DeadlyImportError("Collada: File came out empty. Something is wrong here.");
    }

    // reserve some storage to avoid unnecessary reallocates
    newMats.reserve(parser.mMaterialLibrary.size() * 2u);
    mMeshes.reserve(parser.mMeshLibrary.size() * 2u);

    mCameras.reserve(parser.mCameraLibrary.size());
    mLights.reserve(parser.mLightLibrary.size());

    // create the materials first, for the meshes to find
    BuildMaterials(parser, pScene);

    // build the node hierarchy from it
    pScene->mRootNode = BuildHierarchy(parser, parser.mRootNode);

    // ... then fill the materials with the now adjusted settings
    FillMaterials(parser, pScene);

    if (!ignoreUnitSize) {
        // Apply unit-size scale calculation
        pScene->mRootNode->mTransformation *= aiMatrix4x4(
                parser.mUnitSize, 0, 0, 0,
                0, parser.mUnitSize, 0, 0,
                0, 0, parser.mUnitSize, 0,
                0, 0, 0, 1);
    }

    if (!ignoreUpDirection) {
        // Convert to Y_UP, if different orientation
        if (parser.mUpDirection == ColladaParser::UP_X) {
            pScene->mRootNode->mTransformation *= aiMatrix4x4(
                    0, -1, 0, 0,
                    1, 0, 0, 0,
                    0, 0, 1, 0,
                    0, 0, 0, 1);
        } else if (parser.mUpDirection == ColladaParser::UP_Z) {
            pScene->mRootNode->mTransformation *= aiMatrix4x4(
                    1, 0, 0, 0,
                    0, 0, 1, 0,
                    0, -1, 0, 0,
                    0, 0, 0, 1);
        }
    }

    // Store scene metadata
    if (!parser.mAssetMetaData.empty()) {
        const size_t numMeta(parser.mAssetMetaData.size());
        pScene->mMetaData = aiMetadata::Alloc(static_cast<unsigned int>(numMeta));
        size_t i = 0;
        for (auto it = parser.mAssetMetaData.cbegin(); it != parser.mAssetMetaData.cend(); ++it, ++i) {
            pScene->mMetaData->Set(static_cast<unsigned int>(i), (*it).first, (*it).second);
        }
    }

    StoreSceneMeshes(pScene);
    StoreSceneMaterials(pScene);
    StoreSceneTextures(pScene);
    StoreSceneLights(pScene);
    StoreSceneCameras(pScene);
    StoreAnimations(pScene, parser);

    // If no meshes have been loaded, it's probably just an animated skeleton.
    if (0u == pScene->mNumMeshes) {
        if (!noSkeletonMesh) {
            SkeletonMeshBuilder hero(pScene);
        }
        pScene->mFlags |= AI_SCENE_FLAGS_INCOMPLETE;
    }
}

// ------------------------------------------------------------------------------------------------
// Recursively constructs a scene node for the given parser node and returns it.
aiNode *ColladaLoader::BuildHierarchy(const ColladaParser &pParser, const Collada::Node *pNode) {
    // create a node for it
    auto *node = new aiNode();

    // find a name for the new node. It's more complicated than you might think
    node->mName.Set(FindNameForNode(pNode));
    // if we're not using the unique IDs, hold onto them for reference and export
    if (useColladaName) {
        if (!pNode->mID.empty()) {
            AddNodeMetaData(node, AI_METADATA_COLLADA_ID, aiString(pNode->mID));
        }
        if (!pNode->mSID.empty()) {
            AddNodeMetaData(node, AI_METADATA_COLLADA_SID, aiString(pNode->mSID));
        }
    }

    // calculate the transformation matrix for it
    node->mTransformation = pParser.CalculateResultTransform(pNode->mTransforms);

    // now resolve node instances
    std::vector<const Node*> instances;
    ResolveNodeInstances(pParser, pNode, instances);

    // add children. first the *real* ones
    node->mNumChildren = static_cast<unsigned int>(pNode->mChildren.size() + instances.size());
    if (node->mNumChildren != 0) {
        node->mChildren = new aiNode * [node->mNumChildren];
    }

    for (size_t a = 0; a < pNode->mChildren.size(); ++a) {
        node->mChildren[a] = BuildHierarchy(pParser, pNode->mChildren[a]);
        node->mChildren[a]->mParent = node;
    }

    // ... and finally the resolved node instances
    for (size_t a = 0; a < instances.size(); ++a) {
        node->mChildren[pNode->mChildren.size() + a] = BuildHierarchy(pParser, instances[a]);
        node->mChildren[pNode->mChildren.size() + a]->mParent = node;
    }

    BuildMeshesForNode(pParser, pNode, node);
    BuildCamerasForNode(pParser, pNode, node);
    BuildLightsForNode(pParser, pNode, node);

    return node;
}

// ------------------------------------------------------------------------------------------------
// Resolve node instances
void ColladaLoader::ResolveNodeInstances(const ColladaParser &pParser, const Node *pNode,
        std::vector<const Node*> &resolved) const {
    // reserve enough storage
    resolved.reserve(pNode->mNodeInstances.size());

    // ... and iterate through all nodes to be instanced as children of pNode
    for (const auto &[mNode] : pNode->mNodeInstances) {
        // find the corresponding node in the library
        const auto itt = pParser.mNodeLibrary.find(mNode);
        const Node *nd = itt == pParser.mNodeLibrary.end() ? nullptr : (*itt).second;

        // FIX for http://sourceforge.net/tracker/?func=detail&aid=3054873&group_id=226462&atid=1067632
        // need to check for both name and ID to catch all. To avoid breaking valid files,
        // the workaround is only enabled when the first attempt to resolve the node has failed.
        if (nullptr == nd) {
            nd = FindNode(pParser.mRootNode, mNode);
        }
        if (nullptr == nd) {
            ASSIMP_LOG_ERROR("Collada: Unable to resolve reference to instanced node ", mNode);
        } else {
            //  attach this node to the list of children
            resolved.push_back(nd);
        }
    }
}

// ------------------------------------------------------------------------------------------------
// Resolve UV channels
static void ApplyVertexToEffectSemanticMapping(Sampler &sampler, const SemanticMappingTable &table) {
    const auto it = table.mMap.find(sampler.mUVChannel);
    if (it == table.mMap.end()) {
        return;
    }

    if (it->second.mType != IT_Texcoord) {
        ASSIMP_LOG_ERROR("Collada: Unexpected effect input mapping");
    }

    sampler.mUVId = it->second.mSet;
}

// ------------------------------------------------------------------------------------------------
// Builds lights for the given node and references them
void ColladaLoader::BuildLightsForNode(const ColladaParser &pParser, const Node *pNode, aiNode *pTarget) {
    for (const LightInstance &lid : pNode->mLights) {
        // find the referred light
        auto srcLightIt = pParser.mLightLibrary.find(lid.mLight);
        if (srcLightIt == pParser.mLightLibrary.end()) {
            ASSIMP_LOG_WARN("Collada: Unable to find light for ID \"", lid.mLight, "\". Skipping.");
            continue;
        }
        const Collada::Light *srcLight = &srcLightIt->second;

        // now fill our ai data structure
        auto out = new aiLight();
        out->mName = pTarget->mName;
        out->mType = (aiLightSourceType)srcLight->mType;

        // collada lights point in -Z by default, rest is specified in node transform
        out->mDirection = aiVector3D(0.f, 0.f, -1.f);

        out->mAttenuationConstant = srcLight->mAttConstant;
        out->mAttenuationLinear = srcLight->mAttLinear;
        out->mAttenuationQuadratic = srcLight->mAttQuadratic;

        out->mColorDiffuse = out->mColorSpecular = out->mColorAmbient = srcLight->mColor * srcLight->mIntensity;
        if (out->mType == aiLightSource_AMBIENT) {
            out->mColorDiffuse = out->mColorSpecular = aiColor3D(0, 0, 0);
            out->mColorAmbient = srcLight->mColor * srcLight->mIntensity;
        } else {
            // collada doesn't differentiate between these color types
            out->mColorDiffuse = out->mColorSpecular = srcLight->mColor * srcLight->mIntensity;
            out->mColorAmbient = aiColor3D(0, 0, 0);
        }

        // convert falloff angle and falloff exponent in our representation, if given
        if (out->mType == aiLightSource_SPOT) {
            out->mAngleInnerCone = AI_DEG_TO_RAD(srcLight->mFalloffAngle);

            // ... some extension magic.
            if (srcLight->mOuterAngle >= ASSIMP_COLLADA_LIGHT_ANGLE_NOT_SET * (1 - ai_epsilon)) {
                // ... some deprecation magic.
                if (srcLight->mPenumbraAngle >= ASSIMP_COLLADA_LIGHT_ANGLE_NOT_SET * (1 - ai_epsilon)) {
                    // Need to rely on falloff_exponent. I don't know how to interpret it, so I need to guess ....
                    // epsilon chosen to be 0.1
                    float f = 1.0f;
                    if ( 0.0f != srcLight->mFalloffExponent ) {
                        f = 1.f / srcLight->mFalloffExponent;
                    }
                    out->mAngleOuterCone = std::acos(std::pow(0.1f, f)) +
                                           out->mAngleInnerCone;
                } else {
                    out->mAngleOuterCone = out->mAngleInnerCone + AI_DEG_TO_RAD(srcLight->mPenumbraAngle);
                    if (out->mAngleOuterCone < out->mAngleInnerCone)
                        std::swap(out->mAngleInnerCone, out->mAngleOuterCone);
                }
            } else {
                out->mAngleOuterCone = AI_DEG_TO_RAD(srcLight->mOuterAngle);
            }
        }

        // add to light list
        mLights.push_back(out);
    }
}

// ------------------------------------------------------------------------------------------------
// Builds cameras for the given node and references them
void ColladaLoader::BuildCamerasForNode(const ColladaParser &pParser, const Node *pNode, aiNode *pTarget) {
    for (const CameraInstance &cid : pNode->mCameras) {
        // find the referred light
        auto srcCameraIt = pParser.mCameraLibrary.find(cid.mCamera);
        if (srcCameraIt == pParser.mCameraLibrary.end()) {
            ASSIMP_LOG_WARN("Collada: Unable to find camera for ID \"", cid.mCamera, "\". Skipping.");
            continue;
        }
        const Collada::Camera *srcCamera = &srcCameraIt->second;

        // orthographic cameras not yet supported in Assimp
        if (srcCamera->mOrtho) {
            ASSIMP_LOG_WARN("Collada: Orthographic cameras are not supported.");
        }

        // now fill our ai data structure
        auto *out = new aiCamera();
        out->mName = pTarget->mName;

        // collada cameras point in -Z by default, rest is specified in node transform
        out->mLookAt = aiVector3D(0.f, 0.f, -1.f);

        // near/far z is already ok
        out->mClipPlaneFar = srcCamera->mZFar;
        out->mClipPlaneNear = srcCamera->mZNear;

        // ... but for the rest some values are optional
        // and we need to compute the others in any combination.
        if (srcCamera->mAspect != 10e10f) {
            out->mAspect = srcCamera->mAspect;
        }

        if (srcCamera->mHorFov != 10e10f) {
            out->mHorizontalFOV = srcCamera->mHorFov;

            if (srcCamera->mVerFov != 10e10f && srcCamera->mAspect == 10e10f) {
                out->mAspect = std::tan(AI_DEG_TO_RAD(srcCamera->mHorFov)) /
                               std::tan(AI_DEG_TO_RAD(srcCamera->mVerFov));
            }

        } else if (srcCamera->mAspect != 10e10f && srcCamera->mVerFov != 10e10f) {
            out->mHorizontalFOV = 2.0f * AI_RAD_TO_DEG(std::atan(srcCamera->mAspect *
                                                                 std::tan(AI_DEG_TO_RAD(srcCamera->mVerFov) * 0.5f)));
        }

        // Collada uses degrees, we use radians
        out->mHorizontalFOV = AI_DEG_TO_RAD(out->mHorizontalFOV);

        // add to camera list
        mCameras.push_back(out);
    }
}

// ------------------------------------------------------------------------------------------------
// Builds meshes for the given node and references them
void ColladaLoader::BuildMeshesForNode(const ColladaParser &pParser, const Node *pNode, aiNode *pTarget) {
    // accumulated mesh references by this node
    std::vector<size_t> newMeshRefs;
    newMeshRefs.reserve(pNode->mMeshes.size());

    // add a mesh for each subgroup in each collada mesh
    for (const MeshInstance &mid : pNode->mMeshes) {
        const Mesh *srcMesh = nullptr;
        const Controller *srcController = nullptr;

        // find the referred mesh
        auto srcMeshIt = pParser.mMeshLibrary.find(mid.mMeshOrController);
        if (srcMeshIt == pParser.mMeshLibrary.end()) {
            // if not found in the mesh-library, it might also be a controller referring to a mesh
            auto srcContrIt = pParser.mControllerLibrary.find(mid.mMeshOrController);
            if (srcContrIt != pParser.mControllerLibrary.end()) {
                srcController = &srcContrIt->second;
                srcMeshIt = pParser.mMeshLibrary.find(srcController->mMeshId);
                if (srcMeshIt != pParser.mMeshLibrary.end()) {
                    srcMesh = srcMeshIt->second;
                }
            }

            if (nullptr == srcMesh) {
                ASSIMP_LOG_WARN("Collada: Unable to find geometry for ID \"", mid.mMeshOrController, "\". Skipping.");
                continue;
            }
        } else {
            // ID found in the mesh library -> direct reference to a not skinned mesh
            srcMesh = srcMeshIt->second;
        }

        // build a mesh for each of its subgroups
        size_t vertexStart = 0, faceStart = 0;
        for (size_t sm = 0; sm < srcMesh->mSubMeshes.size(); ++sm) {
            const Collada::SubMesh &submesh = srcMesh->mSubMeshes[sm];
            if (submesh.mNumFaces == 0) {
                continue;
            }

            // find material assigned to this submesh
            std::string meshMaterial;
            auto meshMatIt = mid.mMaterials.find(submesh.mMaterial);

            const Collada::SemanticMappingTable *table = nullptr;
            if (meshMatIt != mid.mMaterials.end()) {
                table = &meshMatIt->second;
                meshMaterial = table->mMatName;
            } else {
                ASSIMP_LOG_WARN("Collada: No material specified for subgroup <", submesh.mMaterial, "> in geometry <",
                        mid.mMeshOrController, ">.");
                if (!mid.mMaterials.empty()) {
                    meshMaterial = mid.mMaterials.begin()->second.mMatName;
                }
            }

            // OK ... here the *real* fun starts ... we have the vertex-input-to-effect-semantic-table
            // given. The only mapping stuff which we do actually support is the UV channel.
            auto matIt = mMaterialIndexByName.find(meshMaterial);
            unsigned int matIdx = 0;
            if (matIt != mMaterialIndexByName.end()) {
                matIdx = static_cast<unsigned int>(matIt->second);
            }

            if (table && !table->mMap.empty()) {
                if (matIdx < newMats.size()) {
                    std::pair<Collada::Effect *, aiMaterial *> &mat = newMats[matIdx];

                    // Iterate through all texture channels assigned to the effect and
                    // check whether we have mapping information for it.
                    ApplyVertexToEffectSemanticMapping(mat.first->mTexDiffuse, *table);
                    ApplyVertexToEffectSemanticMapping(mat.first->mTexAmbient, *table);
                    ApplyVertexToEffectSemanticMapping(mat.first->mTexSpecular, *table);
                    ApplyVertexToEffectSemanticMapping(mat.first->mTexEmissive, *table);
                    ApplyVertexToEffectSemanticMapping(mat.first->mTexTransparent, *table);
                    ApplyVertexToEffectSemanticMapping(mat.first->mTexBump, *table);
                } else {
                    ASSIMP_LOG_WARN("Collada: Ignoring material mapping for mesh \"", mid.mMeshOrController, "\". Material index ", matIdx, " is out of bounds (newMats.size()=", newMats.size(), ").");
                }
            }

            // built lookup index of the Mesh-Submesh-Material combination
            ColladaMeshIndex index(mid.mMeshOrController, sm, meshMaterial);

            // if we already have the mesh at the library, just add its index to the node's array
            auto dstMeshIt = mMeshIndexByID.find(index);
            if (dstMeshIt != mMeshIndexByID.end()) {
                newMeshRefs.push_back(dstMeshIt->second);
            } else {
                // else we have to add the mesh to the collection and store its newly assigned index at the node
                aiMesh *dstMesh = CreateMesh(pParser, srcMesh, submesh, srcController, vertexStart, faceStart);

                // store the mesh, and store its new index in the node
                newMeshRefs.push_back(mMeshes.size());
                mMeshIndexByID[index] = mMeshes.size();
                mMeshes.push_back(dstMesh);
                vertexStart += dstMesh->mNumVertices;
                faceStart += submesh.mNumFaces;

                // assign the material index
                auto subMatIt = mMaterialIndexByName.find(submesh.mMaterial);
                if (subMatIt != mMaterialIndexByName.end()) {
                    dstMesh->mMaterialIndex = static_cast<unsigned int>(subMatIt->second);
                } else {
                    dstMesh->mMaterialIndex = matIdx;
                }
                if (dstMesh->mName.length == 0) {
                    dstMesh->mName = mid.mMeshOrController;
                }
            }
        }
    }

    // now place all mesh references we gathered in the target node
    pTarget->mNumMeshes = static_cast<unsigned int>(newMeshRefs.size());
    if (!newMeshRefs.empty()) {
        struct UIntTypeConverter {
            unsigned int operator()(const size_t &v) const {
                return static_cast<unsigned int>(v);
            }
        };

        pTarget->mMeshes = new unsigned int[pTarget->mNumMeshes];
        std::transform(newMeshRefs.begin(), newMeshRefs.end(), pTarget->mMeshes, UIntTypeConverter());
    }
}

// ------------------------------------------------------------------------------------------------
// Find mesh from either meshes or morph target meshes
aiMesh *ColladaLoader::findMesh(const std::string &meshid) {
    if (meshid.empty()) {
        return nullptr;
    }

    for (auto & mMeshe : mMeshes) {
        if (std::string(mMeshe->mName.data) == meshid) {
            return mMeshe;
        }
    }

    for (auto & mTargetMeshe : mTargetMeshes) {
        if (std::string(mTargetMeshe->mName.data) == meshid) {
            return mTargetMeshe;
        }
    }

    return nullptr;
}

// ------------------------------------------------------------------------------------------------
// Creates a mesh for the given ColladaMesh face subset and returns the newly created mesh
aiMesh *ColladaLoader::CreateMesh(const ColladaParser &pParser, const Mesh *pSrcMesh, const SubMesh &pSubMesh,
        const Controller *pSrcController, size_t pStartVertex, size_t pStartFace) {
    std::unique_ptr<aiMesh> dstMesh(new aiMesh);

    if (useColladaName) {
        dstMesh->mName = pSrcMesh->mName;
    } else {
        dstMesh->mName = pSrcMesh->mId;
    }

    if (pSrcMesh->mPositions.empty()) {
        return dstMesh.release();
    }

    // count the vertices addressed by its faces
    const size_t numVertices = std::accumulate(pSrcMesh->mFaceSize.begin() + pStartFace,
            pSrcMesh->mFaceSize.begin() + pStartFace + pSubMesh.mNumFaces, size_t(0));

    // copy positions
    dstMesh->mNumVertices = static_cast<unsigned int>(numVertices);
    dstMesh->mVertices = new aiVector3D[numVertices];
    std::copy(pSrcMesh->mPositions.begin() + pStartVertex, pSrcMesh->mPositions.begin() + pStartVertex + numVertices, dstMesh->mVertices);

    // normals, if given. HACK: (thom) Due to the glorious Collada spec we never
    // know if we have the same number of normals as there are positions. So we
    // also ignore any vertex attribute if it has a different count
    if (pSrcMesh->mNormals.size() >= pStartVertex + numVertices) {
        dstMesh->mNormals = new aiVector3D[numVertices];
        std::copy(pSrcMesh->mNormals.begin() + pStartVertex, pSrcMesh->mNormals.begin() + pStartVertex + numVertices, dstMesh->mNormals);
    }

    // tangents, if given.
    if (pSrcMesh->mTangents.size() >= pStartVertex + numVertices) {
        dstMesh->mTangents = new aiVector3D[numVertices];
        std::copy(pSrcMesh->mTangents.begin() + pStartVertex, pSrcMesh->mTangents.begin() + pStartVertex + numVertices, dstMesh->mTangents);
    }

    // bi-tangents, if given.
    if (pSrcMesh->mBitangents.size() >= pStartVertex + numVertices) {
        dstMesh->mBitangents = new aiVector3D[numVertices];
        std::copy(pSrcMesh->mBitangents.begin() + pStartVertex, pSrcMesh->mBitangents.begin() + pStartVertex + numVertices, dstMesh->mBitangents);
    }

    // same for texture coords, as many as we have
    for (size_t a = 0; a < AI_MAX_NUMBER_OF_TEXTURECOORDS; ++a) {
        if (pSrcMesh->mTexCoords[a].size() >= pStartVertex + numVertices) {
            dstMesh->mTextureCoords[a] = new aiVector3D[numVertices];
            for (size_t b = 0; b < numVertices; ++b) {
                dstMesh->mTextureCoords[a][b] = pSrcMesh->mTexCoords[a][pStartVertex + b];
            }

            dstMesh->mNumUVComponents[a] = pSrcMesh->mNumUVComponents[a];
        }
    }

    // same for vertex colors, as many as we have. again the same packing to avoid empty slots
    for (size_t a = 0, real = 0; a < AI_MAX_NUMBER_OF_COLOR_SETS; ++a) {
        if (pSrcMesh->mColors[a].size() >= pStartVertex + numVertices) {
            dstMesh->mColors[real] = new aiColor4D[numVertices];
            std::copy(pSrcMesh->mColors[a].begin() + pStartVertex, pSrcMesh->mColors[a].begin() + pStartVertex + numVertices, dstMesh->mColors[real]);
            ++real;
        }
    }

    // create faces. Due to the fact that each face uses unique vertices, we can simply count up on each vertex
    size_t vertex = 0;
    dstMesh->mNumFaces = static_cast<unsigned int>(pSubMesh.mNumFaces);
    dstMesh->mFaces = new aiFace[dstMesh->mNumFaces];
    for (size_t a = 0; a < dstMesh->mNumFaces; ++a) {
        size_t s = pSrcMesh->mFaceSize[pStartFace + a];
        aiFace &face = dstMesh->mFaces[a];
        face.mNumIndices = static_cast<unsigned int>(s);
        face.mIndices = new unsigned int[s];
        for (size_t b = 0; b < s; ++b) {
            face.mIndices[b] = static_cast<unsigned int>(vertex++);
        }
    }

    // create morph target meshes if any
    std::vector<aiMesh *> targetMeshes;
    std::vector<float> targetWeights;
    Collada::MorphMethod method = Normalized;

    for (auto it = pParser.mControllerLibrary.begin();
            it != pParser.mControllerLibrary.end(); ++it) {
        const Controller &c = it->second;
        const Collada::Mesh *baseMesh = pParser.ResolveLibraryReference(pParser.mMeshLibrary, c.mMeshId);

        if (c.mType == Collada::Morph && baseMesh->mName == pSrcMesh->mName) {
            const Collada::Accessor &targetAccessor = pParser.ResolveLibraryReference(pParser.mAccessorLibrary, c.mMorphTarget);
            const Collada::Accessor &weightAccessor = pParser.ResolveLibraryReference(pParser.mAccessorLibrary, c.mMorphWeight);
            const Collada::Data &targetData = pParser.ResolveLibraryReference(pParser.mDataLibrary, targetAccessor.mSource);
            const Collada::Data &weightData = pParser.ResolveLibraryReference(pParser.mDataLibrary, weightAccessor.mSource);

            // take method
            method = c.mMethod;

            if (!targetData.mIsStringArray) {
                throw DeadlyImportError("target data must contain id. ");
            }
            if (weightData.mIsStringArray) {
                throw DeadlyImportError("target weight data must not be textual ");
            }

            for (const auto & mString : targetData.mStrings) {
                const Mesh *targetMesh = pParser.ResolveLibraryReference(pParser.mMeshLibrary, mString);

                aiMesh *aimesh = findMesh(useColladaName ? targetMesh->mName : targetMesh->mId);
                if (!aimesh) {
                    if (targetMesh->mSubMeshes.size() > 1) {
                        throw DeadlyImportError("Morphing target mesh must be a single");
                    }
                    aimesh = CreateMesh(pParser, targetMesh, targetMesh->mSubMeshes.at(0), nullptr, 0, 0);
                    mTargetMeshes.push_back(aimesh);
                }
                targetMeshes.push_back(aimesh);
            }
            for (float mValue : weightData.mValues) {
                targetWeights.push_back(mValue);
            }
        }
    }
    if (!targetMeshes.empty() && targetWeights.size() == targetMeshes.size()) {
        std::vector<aiAnimMesh *> animMeshes;
        for (unsigned int i = 0; i < targetMeshes.size(); ++i) {
            aiMesh *targetMesh = targetMeshes.at(i);
            aiAnimMesh *animMesh = aiCreateAnimMesh(targetMesh);
            float weight = targetWeights[i];
            animMesh->mWeight = weight == 0 ? 1.0f : weight;
            animMesh->mName = targetMesh->mName;
            animMeshes.push_back(animMesh);
        }
        dstMesh->mMethod = (method == Relative) ? aiMorphingMethod_MORPH_RELATIVE : aiMorphingMethod_MORPH_NORMALIZED;
        dstMesh->mAnimMeshes = new aiAnimMesh *[animMeshes.size()];
        dstMesh->mNumAnimMeshes = static_cast<unsigned int>(animMeshes.size());
        for (unsigned int i = 0; i < animMeshes.size(); ++i) {
            dstMesh->mAnimMeshes[i] = animMeshes.at(i);
        }
    }

    // create bones if given
    if (pSrcController && pSrcController->mType == Collada::Skin) {
        // resolve references - joint names
        const Collada::Accessor &jointNamesAcc = pParser.ResolveLibraryReference(pParser.mAccessorLibrary, pSrcController->mJointNameSource);
        const Collada::Data &jointNames = pParser.ResolveLibraryReference(pParser.mDataLibrary, jointNamesAcc.mSource);
        // joint offset matrices
        const Collada::Accessor &jointMatrixAcc = pParser.ResolveLibraryReference(pParser.mAccessorLibrary, pSrcController->mJointOffsetMatrixSource);
        const Collada::Data &jointMatrices = pParser.ResolveLibraryReference(pParser.mDataLibrary, jointMatrixAcc.mSource);
        // joint vertex_weight name list - should refer to the same list as the joint names above. If not, report and reconsider
        const Collada::Accessor &weightNamesAcc = pParser.ResolveLibraryReference(pParser.mAccessorLibrary, pSrcController->mWeightInputJoints.mAccessor);
        if (&weightNamesAcc != &jointNamesAcc)
            throw DeadlyImportError("Temporary implementational laziness. If you read this, please report to the author.");
        // vertex weights
        const Collada::Accessor &weightsAcc = pParser.ResolveLibraryReference(pParser.mAccessorLibrary, pSrcController->mWeightInputWeights.mAccessor);
        const Collada::Data &weights = pParser.ResolveLibraryReference(pParser.mDataLibrary, weightsAcc.mSource);

        if (!jointNames.mIsStringArray || jointMatrices.mIsStringArray || weights.mIsStringArray) {
            throw DeadlyImportError("Data type mismatch while resolving mesh joints");
        }
        // sanity check: we rely on the vertex weights always coming as pairs of BoneIndex-WeightIndex
        if (pSrcController->mWeightInputJoints.mOffset != 0 || pSrcController->mWeightInputWeights.mOffset != 1) {
            throw DeadlyImportError("Unsupported vertex_weight addressing scheme. ");
        }

        // create containers to collect the weights for each bone
        size_t numBones = jointNames.mStrings.size();
        std::vector<std::vector<aiVertexWeight>> dstBones(numBones);

        // build a temporary array of pointers to the start of each vertex's weights
        using IndexPairVector = std::vector<std::pair<size_t, size_t>>;
        std::vector<IndexPairVector::const_iterator> weightStartPerVertex;
        weightStartPerVertex.resize(pSrcController->mWeightCounts.size(), pSrcController->mWeights.end());

        auto pit = pSrcController->mWeights.begin();
        for (size_t a = 0; a < pSrcController->mWeightCounts.size(); ++a) {
            weightStartPerVertex[a] = pit;
            pit += pSrcController->mWeightCounts[a];
        }

        // now for each vertex put the corresponding vertex weights into each bone's weight collection
        for (size_t a = pStartVertex; a < pStartVertex + numVertices; ++a) {
            // which position index was responsible for this vertex? that's also the index by which
            // the controller assigns the vertex weights
            size_t orgIndex = pSrcMesh->mFacePosIndices[a];
            // find the vertex weights for this vertex
            auto iit = weightStartPerVertex[orgIndex];
            size_t pairCount = pSrcController->mWeightCounts[orgIndex];

            for (size_t b = 0; b < pairCount; ++b, ++iit) {
                const size_t jointIndex = iit->first;
                const size_t vertexIndex = iit->second;
                ai_real weight = 1.0f;
                if (!weights.mValues.empty()) {
                    weight = ReadFloat(weightsAcc, weights, vertexIndex, 0);
                }

                // one day I gonna kill that XSI Collada exporter
                if (weight > 0.0f) {
                    aiVertexWeight w;
                    w.mVertexId = static_cast<unsigned int>(a - pStartVertex);
                    w.mWeight = weight;
                    dstBones[jointIndex].push_back(w);
                }
            }
        }

        // count the number of bones which influence vertices of the current submesh
        size_t numRemainingBones = 0;
        for (const auto & dstBone : dstBones) {
            if (dstBone.empty() && removeEmptyBones) {
                continue;
            }
            ++numRemainingBones;
        }

        // create bone array and copy bone weights one by one
        dstMesh->mNumBones = static_cast<unsigned int>(numRemainingBones);
        dstMesh->mBones = new aiBone *[numRemainingBones];
        size_t boneCount = 0;
        for (size_t a = 0; a < numBones; ++a) {
            // omit bones without weights
            if (dstBones[a].empty() && removeEmptyBones) {
                continue;
            }

            // create bone with its weights
            auto bone = new aiBone;
            bone->mName = ReadString(jointNamesAcc, jointNames, a);
            bone->mOffsetMatrix.a1 = ReadFloat(jointMatrixAcc, jointMatrices, a, 0);
            bone->mOffsetMatrix.a2 = ReadFloat(jointMatrixAcc, jointMatrices, a, 1);
            bone->mOffsetMatrix.a3 = ReadFloat(jointMatrixAcc, jointMatrices, a, 2);
            bone->mOffsetMatrix.a4 = ReadFloat(jointMatrixAcc, jointMatrices, a, 3);
            bone->mOffsetMatrix.b1 = ReadFloat(jointMatrixAcc, jointMatrices, a, 4);
            bone->mOffsetMatrix.b2 = ReadFloat(jointMatrixAcc, jointMatrices, a, 5);
            bone->mOffsetMatrix.b3 = ReadFloat(jointMatrixAcc, jointMatrices, a, 6);
            bone->mOffsetMatrix.b4 = ReadFloat(jointMatrixAcc, jointMatrices, a, 7);
            bone->mOffsetMatrix.c1 = ReadFloat(jointMatrixAcc, jointMatrices, a, 8);
            bone->mOffsetMatrix.c2 = ReadFloat(jointMatrixAcc, jointMatrices, a, 9);
            bone->mOffsetMatrix.c3 = ReadFloat(jointMatrixAcc, jointMatrices, a, 10);
            bone->mOffsetMatrix.c4 = ReadFloat(jointMatrixAcc, jointMatrices, a, 11);
            bone->mNumWeights = static_cast<unsigned int>(dstBones[a].size());
            bone->mWeights = new aiVertexWeight[bone->mNumWeights];
            std::copy(dstBones[a].begin(), dstBones[a].end(), bone->mWeights);

            // apply bind shape matrix to offset matrix
            aiMatrix4x4 bindShapeMatrix;
            bindShapeMatrix.a1 = pSrcController->mBindShapeMatrix[0];
            bindShapeMatrix.a2 = pSrcController->mBindShapeMatrix[1];
            bindShapeMatrix.a3 = pSrcController->mBindShapeMatrix[2];
            bindShapeMatrix.a4 = pSrcController->mBindShapeMatrix[3];
            bindShapeMatrix.b1 = pSrcController->mBindShapeMatrix[4];
            bindShapeMatrix.b2 = pSrcController->mBindShapeMatrix[5];
            bindShapeMatrix.b3 = pSrcController->mBindShapeMatrix[6];
            bindShapeMatrix.b4 = pSrcController->mBindShapeMatrix[7];
            bindShapeMatrix.c1 = pSrcController->mBindShapeMatrix[8];
            bindShapeMatrix.c2 = pSrcController->mBindShapeMatrix[9];
            bindShapeMatrix.c3 = pSrcController->mBindShapeMatrix[10];
            bindShapeMatrix.c4 = pSrcController->mBindShapeMatrix[11];
            bindShapeMatrix.d1 = pSrcController->mBindShapeMatrix[12];
            bindShapeMatrix.d2 = pSrcController->mBindShapeMatrix[13];
            bindShapeMatrix.d3 = pSrcController->mBindShapeMatrix[14];
            bindShapeMatrix.d4 = pSrcController->mBindShapeMatrix[15];
            bone->mOffsetMatrix *= bindShapeMatrix;

            // HACK: (thom) Some exporters address the bone nodes by SID, others address them by ID or even name.
            // Therefore I added a little name replacement here: I search for the bone's node by either name, ID or SID,
            // and replace the bone's name by the node's name so that the user can use the standard
            // find-by-name method to associate nodes with bones.
            const Collada::Node *bnode = FindNode(pParser.mRootNode, bone->mName.data);
            if (nullptr == bnode) {
                bnode = FindNodeBySID(pParser.mRootNode, bone->mName.data);
            }

            // assign the name that we would have assigned for the source node
            if (nullptr != bnode) {
                bone->mName.Set(FindNameForNode(bnode));
            } else {
                ASSIMP_LOG_WARN("ColladaLoader::CreateMesh(): could not find corresponding node for joint \"", bone->mName.data, "\".");
            }

            // and insert bone
            dstMesh->mBones[boneCount++] = bone;
        }
    }

    return dstMesh.release();
}

// ------------------------------------------------------------------------------------------------
// Stores all meshes in the given scene
void ColladaLoader::StoreSceneMeshes(aiScene *pScene) {
    pScene->mNumMeshes = static_cast<unsigned int>(mMeshes.size());
    if (mMeshes.empty()) {
        return;
    }
    pScene->mMeshes = new aiMesh *[mMeshes.size()];
    std::copy(mMeshes.begin(), mMeshes.end(), pScene->mMeshes);
    mMeshes.clear();
}

// ------------------------------------------------------------------------------------------------
// Stores all cameras in the given scene
void ColladaLoader::StoreSceneCameras(aiScene *pScene) {
    pScene->mNumCameras = static_cast<unsigned int>(mCameras.size());
    if (mCameras.empty()) {
        return;
    }
    pScene->mCameras = new aiCamera *[mCameras.size()];
    std::copy(mCameras.begin(), mCameras.end(), pScene->mCameras);
    mCameras.clear();
}

// ------------------------------------------------------------------------------------------------
// Stores all lights in the given scene
void ColladaLoader::StoreSceneLights(aiScene *pScene) {
    pScene->mNumLights = static_cast<unsigned int>(mLights.size());
    if (mLights.empty()) {
        return;
    }
    pScene->mLights = new aiLight *[mLights.size()];
    std::copy(mLights.begin(), mLights.end(), pScene->mLights);
    mLights.clear();
}

// ------------------------------------------------------------------------------------------------
// Stores all textures in the given scene
void ColladaLoader::StoreSceneTextures(aiScene *pScene) {
    pScene->mNumTextures = static_cast<unsigned int>(mTextures.size());
    if (mTextures.empty()) {
        return;
    }
    pScene->mTextures = new aiTexture *[mTextures.size()];
    std::copy(mTextures.begin(), mTextures.end(), pScene->mTextures);
    mTextures.clear();
}

// ------------------------------------------------------------------------------------------------
// Stores all materials in the given scene
void ColladaLoader::StoreSceneMaterials(aiScene *pScene) {
    pScene->mNumMaterials = static_cast<unsigned int>(newMats.size());
    if (newMats.empty()) {
        return;
    }
    pScene->mMaterials = new aiMaterial *[newMats.size()];
    for (unsigned int i = 0; i < newMats.size(); ++i) {
        pScene->mMaterials[i] = newMats[i].second;
    }
    newMats.clear();
}

// ------------------------------------------------------------------------------------------------
// Stores all animations
void ColladaLoader::StoreAnimations(aiScene *pScene, const ColladaParser &pParser) {
    // recursively collect all animations from the collada scene
    StoreAnimations(pScene, pParser, &pParser.mAnims, "");

    // catch special case: many animations with the same length, each affecting only a single node.
    // we need to unite all those single-node-anims to a proper combined animation
    for (size_t a = 0; a < mAnims.size(); ++a) {
        aiAnimation *templateAnim = mAnims[a];

        if (templateAnim->mNumChannels == 1) {
            // search for other single-channel-anims with the same duration
            std::vector<size_t> collectedAnimIndices;
            for (size_t b = a + 1; b < mAnims.size(); ++b) {
                aiAnimation *other = mAnims[b];
                if (other->mNumChannels == 1 && other->mDuration == templateAnim->mDuration &&
                        other->mTicksPerSecond == templateAnim->mTicksPerSecond)
                    collectedAnimIndices.push_back(b);
            }

            // We only want to combine the animations if they have different channels
            std::set<std::string> animTargets;
            animTargets.insert(templateAnim->mChannels[0]->mNodeName.C_Str());
            bool collectedAnimationsHaveDifferentChannels = true;
            for (unsigned long long collectedAnimIndice : collectedAnimIndices) {
                aiAnimation *srcAnimation = mAnims[(int)collectedAnimIndice];
                std::string channelName = std::string(srcAnimation->mChannels[0]->mNodeName.C_Str());
                if (animTargets.find(channelName) == animTargets.end()) {
                    animTargets.insert(channelName);
                } else {
                    collectedAnimationsHaveDifferentChannels = false;
                    break;
                }
            }

            if (!collectedAnimationsHaveDifferentChannels) {
                continue;
            }

            // if there are other animations which fit the template anim, combine all channels into a single anim
            if (!collectedAnimIndices.empty()) {
                auto *combinedAnim = new aiAnimation();
                combinedAnim->mName = aiString(std::string("combinedAnim_") + char('0' + a));
                combinedAnim->mDuration = templateAnim->mDuration;
                combinedAnim->mTicksPerSecond = templateAnim->mTicksPerSecond;
                combinedAnim->mNumChannels = static_cast<unsigned int>(collectedAnimIndices.size() + 1);
                combinedAnim->mChannels = new aiNodeAnim *[combinedAnim->mNumChannels];
                // add the template anim as first channel by moving its aiNodeAnim to the combined animation
                combinedAnim->mChannels[0] = templateAnim->mChannels[0];
                templateAnim->mChannels[0] = nullptr;
                delete templateAnim;
                // combined animation replaces template animation in the anim array
                mAnims[a] = combinedAnim;

                // move the memory of all other anims to the combined anim and erase them from the source anims
                for (size_t b = 0; b < collectedAnimIndices.size(); ++b) {
                    aiAnimation *srcAnimation = mAnims[collectedAnimIndices[b]];
                    combinedAnim->mChannels[1 + b] = srcAnimation->mChannels[0];
                    srcAnimation->mChannels[0] = nullptr;
                    delete srcAnimation;
                }

                // in a second go, delete all the single-channel-anims that we've stripped from their channels
                // back to front to preserve indices - you know, removing an element from a vector moves all elements behind the removed one
                while (!collectedAnimIndices.empty()) {
                    mAnims.erase(mAnims.begin() + collectedAnimIndices.back());
                    collectedAnimIndices.pop_back();
                }
            }
        }
    }

    // now store all anims in the scene
    if (!mAnims.empty()) {
        pScene->mNumAnimations = static_cast<unsigned int>(mAnims.size());
        pScene->mAnimations = new aiAnimation *[mAnims.size()];
        std::copy(mAnims.begin(), mAnims.end(), pScene->mAnimations);
    }

    mAnims.clear();
}

// ------------------------------------------------------------------------------------------------
// Constructs the animations for the given source anim
void ColladaLoader::StoreAnimations(aiScene *pScene, const ColladaParser &pParser, const Animation *pSrcAnim, const std::string &pPrefix) {
    std::string animName = pPrefix.empty() ? pSrcAnim->mName : pPrefix + "_" + pSrcAnim->mName;

    // create nested animations, if given
    for (auto mSubAnim : pSrcAnim->mSubAnims) {
        StoreAnimations(pScene, pParser, mSubAnim, animName);
    }

    // create animation channels, if any
    if (!pSrcAnim->mChannels.empty()) {
        CreateAnimation(pScene, pParser, pSrcAnim, animName);
    }
}

struct MorphTimeValues {
    float mTime;
    struct key {
        float mWeight;
        unsigned int mValue;
    };
    std::vector<key> mKeys;
};

void insertMorphTimeValue(std::vector<MorphTimeValues> &values, float time, float weight, unsigned int value) {
    MorphTimeValues::key k{};
    k.mValue = value;
    k.mWeight = weight;
    if (values.empty() || time < values[0].mTime) {
        MorphTimeValues val;
        val.mTime = time;
        val.mKeys.push_back(k);
        values.insert(values.begin(), val);
        return;
    }
    if (time > values.back().mTime) {
        MorphTimeValues val;
        val.mTime = time;
        val.mKeys.push_back(k);
        values.insert(values.end(), val);
        return;
    }
    for (unsigned int i = 0; i < values.size(); i++) {
        if (std::abs(time - values[i].mTime) < ai_epsilon) {
            values[i].mKeys.push_back(k);
            return;
        } else if (time > values[i].mTime && time < values[i + 1].mTime) {
            MorphTimeValues val;
            val.mTime = time;
            val.mKeys.push_back(k);
            values.insert(values.begin() + i, val);
            return;
        }
    }
}

static float getWeightAtKey(const std::vector<MorphTimeValues> &values, int key, unsigned int value) {
    for (auto mKey : values[key].mKeys) {
        if (mKey.mValue == value) {
            return mKey.mWeight;
        }
    }

    // no value at key found, try to interpolate if present at other keys. if not, return zero
    // TODO: interpolation
    return 0.0f;
}

// ------------------------------------------------------------------------------------------------
// Constructs the animation for the given source anim
void ColladaLoader::CreateAnimation(aiScene *pScene, const ColladaParser &pParser, const Animation *pSrcAnim, const std::string &pName) {
    // collect a list of animatable nodes
    std::vector<const aiNode *> nodes;
    CollectNodes(pScene->mRootNode, nodes);

    std::vector<aiNodeAnim *> anims;
    std::vector<aiMeshMorphAnim *> morphAnims;

    for (auto node : nodes) {
        // find all the collada anim channels which refer to the current node
        std::vector<ChannelEntry> entries;
        std::string nodeName = node->mName.data;

        // find the collada node corresponding to the aiNode
        const Node *srcNode = FindNode(pParser.mRootNode, nodeName);
        if (!srcNode) {
            continue;
        }

        // now check all channels if they affect the current node
        std::string targetID, subElement;
        for (auto cit = pSrcAnim->mChannels.begin();
                cit != pSrcAnim->mChannels.end(); ++cit) {
            const AnimationChannel &srcChannel = *cit;
            ChannelEntry entry;

            // we expect the animation target to be of type "nodeName/transformID.subElement". Ignore all others
            // find the slash that separates the node name - there should be only one
            std::string::size_type slashPos = srcChannel.mTarget.find('/');
            if (slashPos == std::string::npos) {
                std::string::size_type targetPos = srcChannel.mTarget.find(srcNode->mID);
                if (targetPos == std::string::npos) {
                    continue;
                }

                // not node transform, but something else. store as unknown animation channel for now
                entry.mChannel = &(*cit);
                entry.mTargetId = srcChannel.mTarget.substr(targetPos + pSrcAnim->mName.length(),
                        srcChannel.mTarget.length() - targetPos - pSrcAnim->mName.length());
                if (entry.mTargetId.front() == '-') {
                    entry.mTargetId = entry.mTargetId.substr(1);
                }
                entries.push_back(entry);
                continue;
            }
            if (srcChannel.mTarget.find('/', slashPos + 1) != std::string::npos) {
                continue;
            }

            targetID.clear();
            targetID = srcChannel.mTarget.substr(0, slashPos);
            if (targetID != srcNode->mID) {
                continue;
            }

            // find the dot that separates the transformID - there should be only one or zero
            std::string::size_type dotPos = srcChannel.mTarget.find('.');
            if (dotPos != std::string::npos) {
                if (srcChannel.mTarget.find('.', dotPos + 1) != std::string::npos) {
                    continue;
                }

                entry.mTransformId = srcChannel.mTarget.substr(slashPos + 1, dotPos - slashPos - 1);

                subElement.clear();
                subElement = srcChannel.mTarget.substr(dotPos + 1);
                if (subElement == "ANGLE")
                    entry.mSubElement = 3; // last number in an Axis-Angle-Transform is the angle
                else if (subElement == "X")
                    entry.mSubElement = 0;
                else if (subElement == "Y")
                    entry.mSubElement = 1;
                else if (subElement == "Z")
                    entry.mSubElement = 2;
                else
                    ASSIMP_LOG_WARN("Unknown anim subelement <", subElement, ">. Ignoring");
            } else {
                // no sub-element following, transformId is remaining string
                entry.mTransformId = srcChannel.mTarget.substr(slashPos + 1);
            }

            std::string::size_type bracketPos = srcChannel.mTarget.find('(');
            if (bracketPos != std::string::npos) {
                entry.mTransformId = srcChannel.mTarget.substr(slashPos + 1, bracketPos - slashPos - 1);
                subElement.clear();
                subElement = srcChannel.mTarget.substr(bracketPos);

                if (subElement == "(0)(0)")
                    entry.mSubElement = 0;
                else if (subElement == "(1)(0)")
                    entry.mSubElement = 1;
                else if (subElement == "(2)(0)")
                    entry.mSubElement = 2;
                else if (subElement == "(3)(0)")
                    entry.mSubElement = 3;
                else if (subElement == "(0)(1)")
                    entry.mSubElement = 4;
                else if (subElement == "(1)(1)")
                    entry.mSubElement = 5;
                else if (subElement == "(2)(1)")
                    entry.mSubElement = 6;
                else if (subElement == "(3)(1)")
                    entry.mSubElement = 7;
                else if (subElement == "(0)(2)")
                    entry.mSubElement = 8;
                else if (subElement == "(1)(2)")
                    entry.mSubElement = 9;
                else if (subElement == "(2)(2)")
                    entry.mSubElement = 10;
                else if (subElement == "(3)(2)")
                    entry.mSubElement = 11;
                else if (subElement == "(0)(3)")
                    entry.mSubElement = 12;
                else if (subElement == "(1)(3)")
                    entry.mSubElement = 13;
                else if (subElement == "(2)(3)")
                    entry.mSubElement = 14;
                else if (subElement == "(3)(3)")
                    entry.mSubElement = 15;
            }

            // determine which transform step is affected by this channel
            entry.mTransformIndex = SIZE_MAX;
            for (size_t a = 0; a < srcNode->mTransforms.size(); ++a)
                if (srcNode->mTransforms[a].mID == entry.mTransformId)
                    entry.mTransformIndex = a;

            if (entry.mTransformIndex == SIZE_MAX) {
                if (entry.mTransformId.find("morph-weights") == std::string::npos) {
                    continue;
                }
                entry.mTargetId = entry.mTransformId;
                entry.mTransformId = std::string();
            }

            entry.mChannel = &(*cit);
            entries.push_back(entry);
        }

        // if there's no channel affecting the current node, we skip it
        if (entries.empty()) {
            continue;
        }

        // resolve the data pointers for all anim channels. Find the minimum time while we're at it
        ai_real startTime = ai_real(1e20), endTime = ai_real(-1e20);
        for (ChannelEntry & e : entries) {
            e.mTimeAccessor = &pParser.ResolveLibraryReference(pParser.mAccessorLibrary, e.mChannel->mSourceTimes);
            e.mTimeData = &pParser.ResolveLibraryReference(pParser.mDataLibrary, e.mTimeAccessor->mSource);
            e.mValueAccessor = &pParser.ResolveLibraryReference(pParser.mAccessorLibrary, e.mChannel->mSourceValues);
            e.mValueData = &pParser.ResolveLibraryReference(pParser.mDataLibrary, e.mValueAccessor->mSource);

            // time count and value count must match
            if (e.mTimeAccessor->mCount != e.mValueAccessor->mCount) {
                throw DeadlyImportError("Time count / value count mismatch in animation channel \"", e.mChannel->mTarget, "\".");
            }

            if (e.mTimeAccessor->mCount > 0) {
                // find bounding times
                startTime = std::min(startTime, ReadFloat(*e.mTimeAccessor, *e.mTimeData, 0, 0));
                endTime = std::max(endTime, ReadFloat(*e.mTimeAccessor, *e.mTimeData, e.mTimeAccessor->mCount - 1, 0));
            }
        }

        std::vector<aiMatrix4x4> resultTrafos;
        if (!entries.empty() && entries.front().mTimeAccessor->mCount > 0) {
            // create a local transformation chain of the node's transforms
            std::vector<Collada::Transform> transforms = srcNode->mTransforms;

            // now for every unique point in time, find or interpolate the key values for that time
            // and apply them to the transform chain. Then the node's present transformation can be calculated.
            ai_real time = startTime;
            while (true) {
                for (ChannelEntry & e : entries) {
                    // find the keyframe behind the current point in time
                    size_t pos = 0;
                    ai_real postTime = 0.0;
                    while (true) {
                        if (pos >= e.mTimeAccessor->mCount) {
                            break;
                        }
                        postTime = ReadFloat(*e.mTimeAccessor, *e.mTimeData, pos, 0);
                        if (postTime >= time) {
                            break;
                        }
                        ++pos;
                    }

                    pos = std::min(pos, e.mTimeAccessor->mCount - 1);

                    // read values from there
                    ai_real temp[16];
                    for (size_t c = 0; c < e.mValueAccessor->mSize; ++c) {
                        temp[c] = ReadFloat(*e.mValueAccessor, *e.mValueData, pos, c);
                    }

                    // if not exactly at the key time, interpolate with previous value set
                    if (postTime > time && pos > 0) {
                        ai_real preTime = ReadFloat(*e.mTimeAccessor, *e.mTimeData, pos - 1, 0);
                        ai_real factor = (time - postTime) / (preTime - postTime);

                        for (size_t c = 0; c < e.mValueAccessor->mSize; ++c) {
                            ai_real v = ReadFloat(*e.mValueAccessor, *e.mValueData, pos - 1, c);
                            temp[c] += (v - temp[c]) * factor;
                        }
                    }

                    // Apply values to current transformation
                    std::copy(temp, temp + e.mValueAccessor->mSize, transforms[e.mTransformIndex].f + e.mSubElement);
                }

                // Calculate resulting transformation
                aiMatrix4x4 mat = pParser.CalculateResultTransform(transforms);

                // out of laziness: we store the time in matrix.d4
                mat.d4 = time;
                resultTrafos.push_back(mat);

                // find next point in time to evaluate. That's the closest frame larger than the current in any channel
                ai_real nextTime = ai_real(1e20);
                for (ChannelEntry & channelElement : entries) {
                    // find the next time value larger than the current
                    size_t pos = 0;
                    while (pos < channelElement.mTimeAccessor->mCount) {
                        const ai_real t = ReadFloat(*channelElement.mTimeAccessor, *channelElement.mTimeData, pos, 0);
                        if (t > time) {
                            nextTime = std::min(nextTime, t);
                            break;
                        }
                        ++pos;
                    }

                    // https://github.com/assimp/assimp/issues/458
                    // Sub-sample axis-angle channels if the delta between two consecutive
                    // key-frame angles is >= 180 degrees.
                    if (transforms[channelElement.mTransformIndex].mType == TF_ROTATE && channelElement.mSubElement == 3 && pos > 0 && pos < channelElement.mTimeAccessor->mCount) {
                        const ai_real cur_key_angle = ReadFloat(*channelElement.mValueAccessor, *channelElement.mValueData, pos, 0);
                        const ai_real last_key_angle = ReadFloat(*channelElement.mValueAccessor, *channelElement.mValueData, pos - 1, 0);
                        const ai_real cur_key_time = ReadFloat(*channelElement.mTimeAccessor, *channelElement.mTimeData, pos, 0);
                        const ai_real last_key_time = ReadFloat(*channelElement.mTimeAccessor, *channelElement.mTimeData, pos - 1, 0);
                        const ai_real last_eval_angle = last_key_angle + (cur_key_angle - last_key_angle) * (time - last_key_time) / (cur_key_time - last_key_time);
                        const ai_real delta = std::abs(cur_key_angle - last_eval_angle);
                        if (delta >= 180.0) {
                            const int subSampleCount = static_cast<int>(std::floor(delta / 90.0));
                            if (cur_key_time != time) {
                                const ai_real nextSampleTime = time + (cur_key_time - time) / subSampleCount;
                                nextTime = std::min(nextTime, nextSampleTime);
                            }
                        }
                    }
                }

                // no more keys on any channel after the current time -> we're done
                if (nextTime > 1e19) {
                    break;
                }

                // else construct next key-frame at this following time point
                time = nextTime;
            }
        }

        // build an animation channel for the given node out of these trafo keys
        if (!resultTrafos.empty()) {
            auto *dstAnim = new aiNodeAnim;
            dstAnim->mNodeName = nodeName;
            dstAnim->mNumPositionKeys = static_cast<unsigned int>(resultTrafos.size());
            dstAnim->mNumRotationKeys = static_cast<unsigned int>(resultTrafos.size());
            dstAnim->mNumScalingKeys = static_cast<unsigned int>(resultTrafos.size());
            dstAnim->mPositionKeys = new aiVectorKey[resultTrafos.size()];
            dstAnim->mRotationKeys = new aiQuatKey[resultTrafos.size()];
            dstAnim->mScalingKeys = new aiVectorKey[resultTrafos.size()];

            for (size_t a = 0; a < resultTrafos.size(); ++a) {
                aiMatrix4x4 mat = resultTrafos[a];
                double time = double(mat.d4); // remember? time is stored in mat.d4
                mat.d4 = 1.0f;

                dstAnim->mPositionKeys[a].mTime = time * kMillisecondsFromSeconds;
                dstAnim->mRotationKeys[a].mTime = time * kMillisecondsFromSeconds;
                dstAnim->mScalingKeys[a].mTime = time * kMillisecondsFromSeconds;
                mat.Decompose(dstAnim->mScalingKeys[a].mValue, dstAnim->mRotationKeys[a].mValue, dstAnim->mPositionKeys[a].mValue);
            }

            anims.push_back(dstAnim);
        } else {
            ASSIMP_LOG_WARN("Collada loader: found empty animation channel, ignored. Please check your exporter.");
        }

        if (!entries.empty() && entries.front().mTimeAccessor->mCount > 0) {
            std::vector<ChannelEntry> morphChannels;
            for (ChannelEntry & e : entries) {
                // skip non-transform types
                if (e.mTargetId.empty()) {
                    continue;
                }

                if (e.mTargetId.find("morph-weights") != std::string::npos) {
                    morphChannels.push_back(e);
                }
            }
            if (!morphChannels.empty()) {
                // either 1) morph weight animation count should contain morph target count channels
                // or     2) one channel with morph target count arrays
                // assume first

                auto *morphAnim = new aiMeshMorphAnim;
                morphAnim->mName.Set(nodeName);

                std::vector<MorphTimeValues> morphTimeValues;
                int morphAnimChannelIndex = 0;
                for (ChannelEntry & e : morphChannels) {
                    std::string::size_type apos = e.mTargetId.find('(');
                    std::string::size_type bpos = e.mTargetId.find(')');

                    // If unknown way to specify weight -> ignore this animation
                    if (apos == std::string::npos || bpos == std::string::npos) {
                        continue;
                    }

                    // weight target can be in format Weight_M_N, Weight_N, WeightN, or some other way
                    // we ignore the name and just assume the channels are in the right order
                    for (unsigned int i = 0; i < e.mTimeData->mValues.size(); i++) {
                        insertMorphTimeValue(morphTimeValues, e.mTimeData->mValues[i], e.mValueData->mValues[i], morphAnimChannelIndex);
                    }

                    ++morphAnimChannelIndex;
                }

                morphAnim->mNumKeys = static_cast<unsigned int>(morphTimeValues.size());
                morphAnim->mKeys = new aiMeshMorphKey[morphAnim->mNumKeys];
                for (unsigned int key = 0; key < morphAnim->mNumKeys; key++) {
                    morphAnim->mKeys[key].mNumValuesAndWeights = static_cast<unsigned int>(morphChannels.size());
                    morphAnim->mKeys[key].mValues = new unsigned int[morphChannels.size()];
                    morphAnim->mKeys[key].mWeights = new double[morphChannels.size()];

                    morphAnim->mKeys[key].mTime = morphTimeValues[key].mTime * kMillisecondsFromSeconds;
                    for (unsigned int valueIndex = 0; valueIndex < morphChannels.size(); ++valueIndex) {
                        morphAnim->mKeys[key].mValues[valueIndex] = valueIndex;
                        morphAnim->mKeys[key].mWeights[valueIndex] = getWeightAtKey(morphTimeValues, key, valueIndex);
                    }
                }

                morphAnims.push_back(morphAnim);
            }
        }
    }

    if (!anims.empty() || !morphAnims.empty()) {
        auto anim = new aiAnimation;
        anim->mName.Set(pName);
        anim->mNumChannels = static_cast<unsigned int>(anims.size());
        if (anim->mNumChannels > 0) {
            anim->mChannels = new aiNodeAnim *[anims.size()];
            std::copy(anims.begin(), anims.end(), anim->mChannels);
        }
        anim->mNumMorphMeshChannels = static_cast<unsigned int>(morphAnims.size());
        if (anim->mNumMorphMeshChannels > 0) {
            anim->mMorphMeshChannels = new aiMeshMorphAnim *[anim->mNumMorphMeshChannels];
            std::copy(morphAnims.begin(), morphAnims.end(), anim->mMorphMeshChannels);
        }
        anim->mDuration = 0.0f;
        for (auto & a : anims) {
            anim->mDuration = std::max(anim->mDuration, a->mPositionKeys[a->mNumPositionKeys - 1].mTime);
            anim->mDuration = std::max(anim->mDuration, a->mRotationKeys[a->mNumRotationKeys - 1].mTime);
            anim->mDuration = std::max(anim->mDuration, a->mScalingKeys[a->mNumScalingKeys - 1].mTime);
        }
        for (auto & morphAnim : morphAnims) {
            anim->mDuration = std::max(anim->mDuration, morphAnim->mKeys[morphAnim->mNumKeys - 1].mTime);
        }
        anim->mTicksPerSecond = 1000.0;
        mAnims.push_back(anim);
    }
}

// ------------------------------------------------------------------------------------------------
// Add a texture to a material structure
void ColladaLoader::AddTexture(aiMaterial &mat,
        const ColladaParser &pParser,
        const Effect &effect,
        const Sampler &sampler,
        aiTextureType type,
        unsigned int idx) {
    // first of all, basic file name
    const aiString name = FindFilenameForEffectTexture(pParser, effect, sampler.mName);
    mat.AddProperty(&name, _AI_MATKEY_TEXTURE_BASE, type, idx);

    // mapping mode
    int map = aiTextureMapMode_Clamp;
    if (sampler.mWrapU) {
        map = aiTextureMapMode_Wrap;
    }
    if (sampler.mWrapU && sampler.mMirrorU) {
        map = aiTextureMapMode_Mirror;
    }

    mat.AddProperty(&map, 1, _AI_MATKEY_MAPPINGMODE_U_BASE, type, idx);

    map = aiTextureMapMode_Clamp;
    if (sampler.mWrapV) {
        map = aiTextureMapMode_Wrap;
    }
    if (sampler.mWrapV && sampler.mMirrorV) {
        map = aiTextureMapMode_Mirror;
    }

    mat.AddProperty(&map, 1, _AI_MATKEY_MAPPINGMODE_V_BASE, type, idx);

    // UV transformation
    mat.AddProperty(&sampler.mTransform, 1,
            _AI_MATKEY_UVTRANSFORM_BASE, type, idx);

    // Blend mode
    mat.AddProperty((int *)&sampler.mOp, 1,
            _AI_MATKEY_TEXBLEND_BASE, type, idx);

    // Blend factor
    mat.AddProperty((ai_real *)&sampler.mWeighting, 1,
            _AI_MATKEY_TEXBLEND_BASE, type, idx);

    // UV source index ... if we didn't resolve the mapping, it is actually just
    // a guess but it works in most cases. We search for the frst occurrence of a
    // number in the channel name. We assume it is the zero-based index into the
    // UV channel array of all corresponding meshes. It could also be one-based
    // for some exporters, but we won't care of it unless someone complains about.
    if (sampler.mUVId != UINT_MAX) {
        map = sampler.mUVId;
    } else {
        map = -1;
        for (auto it = sampler.mUVChannel.begin(); it != sampler.mUVChannel.end(); ++it) {
            if (IsNumeric(*it)) {
                map = strtoul10(&(*it));
                break;
            }
        }
        if (-1 == map) {
            ASSIMP_LOG_WARN("Collada: unable to determine UV channel for texture");
            map = 0;
        }
    }
    mat.AddProperty(&map, 1, _AI_MATKEY_UVWSRC_BASE, type, idx);
}

// ------------------------------------------------------------------------------------------------
// Fills materials from the collada material definitions
void ColladaLoader::FillMaterials(const ColladaParser &pParser, aiScene * /*pScene*/) {
    for (auto &elem : newMats) {
        auto &mat = (aiMaterial &)*elem.second;
        Collada::Effect &effect = *elem.first;

        // resolve shading mode
        int shadeMode;
        if (effect.mFaceted) {
            shadeMode = aiShadingMode_Flat;
        } else {
            switch (effect.mShadeType) {
            case Collada::Shade_Constant:
                shadeMode = aiShadingMode_NoShading;
                break;
            case Collada::Shade_Lambert:
                shadeMode = aiShadingMode_Gouraud;
                break;
            case Collada::Shade_Blinn:
                shadeMode = aiShadingMode_Blinn;
                break;
            case Collada::Shade_Phong:
                shadeMode = aiShadingMode_Phong;
                break;

            default:
                ASSIMP_LOG_WARN("Collada: Unrecognized shading mode, using gouraud shading");
                shadeMode = aiShadingMode_Gouraud;
                break;
            }
        }
        mat.AddProperty<int>(&shadeMode, 1, AI_MATKEY_SHADING_MODEL);

        // double-sided?
        shadeMode = effect.mDoubleSided;
        mat.AddProperty<int>(&shadeMode, 1, AI_MATKEY_TWOSIDED);

        // wire-frame?
        shadeMode = effect.mWireframe;
        mat.AddProperty<int>(&shadeMode, 1, AI_MATKEY_ENABLE_WIREFRAME);

        // add material colors
        mat.AddProperty(&effect.mAmbient, 1, AI_MATKEY_COLOR_AMBIENT);
        mat.AddProperty(&effect.mDiffuse, 1, AI_MATKEY_COLOR_DIFFUSE);
        mat.AddProperty(&effect.mSpecular, 1, AI_MATKEY_COLOR_SPECULAR);
        mat.AddProperty(&effect.mEmissive, 1, AI_MATKEY_COLOR_EMISSIVE);
        mat.AddProperty(&effect.mReflective, 1, AI_MATKEY_COLOR_REFLECTIVE);

        // scalar properties
        mat.AddProperty(&effect.mShininess, 1, AI_MATKEY_SHININESS);
        mat.AddProperty(&effect.mReflectivity, 1, AI_MATKEY_REFLECTIVITY);
        mat.AddProperty(&effect.mRefractIndex, 1, AI_MATKEY_REFRACTI);

        // transparency, a very hard one. seemingly not all files are following the
        // specification here (1.0 transparency => completely opaque)...
        // therefore, we let the opportunity for the user to manually invert
        // the transparency if necessary and we add preliminary support for RGB_ZERO mode
        if (effect.mTransparency >= 0.f && effect.mTransparency <= 1.f) {
            // handle RGB transparency completely, cf Collada specs 1.5.0 pages 249 and 304
            if (effect.mRGBTransparency) {
                // use luminance as defined by ISO/CIE color standards (see ITU-R Recommendation BT.709-4)
                effect.mTransparency *= (0.212671f * effect.mTransparent.r +
                                         0.715160f * effect.mTransparent.g +
                                         0.072169f * effect.mTransparent.b);

                effect.mTransparent.a = 1.f;

                mat.AddProperty(&effect.mTransparent, 1, AI_MATKEY_COLOR_TRANSPARENT);
            } else {
                effect.mTransparency *= effect.mTransparent.a;
            }

            if (effect.mInvertTransparency) {
                effect.mTransparency = 1.f - effect.mTransparency;
            }

            // Is the material finally transparent ?
            if (effect.mHasTransparency || effect.mTransparency < 1.f) {
                mat.AddProperty(&effect.mTransparency, 1, AI_MATKEY_OPACITY);
            }
        }

        // add textures, if given
        if (!effect.mTexAmbient.mName.empty()) {
            // It is merely a light-map
            AddTexture(mat, pParser, effect, effect.mTexAmbient, aiTextureType_LIGHTMAP);
        }

        if (!effect.mTexEmissive.mName.empty())
            AddTexture(mat, pParser, effect, effect.mTexEmissive, aiTextureType_EMISSIVE);

        if (!effect.mTexSpecular.mName.empty())
            AddTexture(mat, pParser, effect, effect.mTexSpecular, aiTextureType_SPECULAR);

        if (!effect.mTexDiffuse.mName.empty())
            AddTexture(mat, pParser, effect, effect.mTexDiffuse, aiTextureType_DIFFUSE);

        if (!effect.mTexBump.mName.empty())
            AddTexture(mat, pParser, effect, effect.mTexBump, aiTextureType_NORMALS);

        if (!effect.mTexTransparent.mName.empty())
            AddTexture(mat, pParser, effect, effect.mTexTransparent, aiTextureType_OPACITY);

        if (!effect.mTexReflective.mName.empty())
            AddTexture(mat, pParser, effect, effect.mTexReflective, aiTextureType_REFLECTION);
    }
}

// ------------------------------------------------------------------------------------------------
// Constructs materials from the collada material definitions
void ColladaLoader::BuildMaterials(ColladaParser &pParser, aiScene * /*pScene*/) {
    newMats.reserve(pParser.mMaterialLibrary.size());

    for (auto matIt = pParser.mMaterialLibrary.begin();
            matIt != pParser.mMaterialLibrary.end(); ++matIt) {
        const Material &material = matIt->second;
        // a material is only a reference to an effect
        auto effIt = pParser.mEffectLibrary.find(material.mEffect);
        if (effIt == pParser.mEffectLibrary.end())
            continue;
        Effect &effect = effIt->second;

        // create material
        auto *mat = new aiMaterial;
        aiString name(material.mName.empty() ? matIt->first : material.mName);
        mat->AddProperty(&name, AI_MATKEY_NAME);

        // store the material
        mMaterialIndexByName[matIt->first] = newMats.size();
        newMats.emplace_back(&effect, mat);
    }
    // ScenePreprocessor generates a default material automatically if none is there.
    // All further code here in this loader works well without a valid material so
    // we can safely let it to ScenePreprocessor.
}

// ------------------------------------------------------------------------------------------------
// Resolves the texture name for the given effect texture entry and loads the texture data
aiString ColladaLoader::FindFilenameForEffectTexture(const ColladaParser &pParser,
        const Effect &pEffect, const std::string &pName) {
    aiString result;

    // recurse through the param references until we end up at an image
    std::string name = pName;
    while (true) {
        // the given string is a param entry. Find it
        auto it = pEffect.mParams.find(name);
        // if not found, we're at the end of the recursion. The resulting string should be the image ID
        if (it == pEffect.mParams.end())
            break;

        // else recurse on
        name = it->second.mReference;
    }

    // find the image referred by this name in the image library of the scene
    auto imIt = pParser.mImageLibrary.find(name);
    if (imIt == pParser.mImageLibrary.end()) {
        ASSIMP_LOG_WARN("Collada: Unable to resolve effect texture entry \"", pName, "\", ended up at ID \"", name, "\".");

        //set default texture file name
        result.Set(name + ".jpg");
        ColladaParser::UriDecodePath(result);
        return result;
    }

    // if this is an embedded texture image setup an aiTexture for it
    if (!imIt->second.mImageData.empty()) {
        auto *tex = new aiTexture();

        // Store embedded texture name reference
        tex->mFilename.Set(imIt->second.mFileName.c_str());
        result.Set(imIt->second.mFileName);

        // setup format hint
        if (imIt->second.mEmbeddedFormat.length() >= HINTMAXTEXTURELEN) {
            ASSIMP_LOG_WARN("Collada: texture format hint is too long, truncating to 3 characters");
        }
        strncpy(tex->achFormatHint, imIt->second.mEmbeddedFormat.c_str(), 3);

        // and copy texture data
        tex->mHeight = 0;
        tex->mWidth = static_cast<unsigned int>(imIt->second.mImageData.size());
        tex->pcData = (aiTexel *)new char[tex->mWidth];
        memcpy(tex->pcData, &imIt->second.mImageData[0], tex->mWidth);

        // and add this texture to the list
        mTextures.push_back(tex);
        return result;
    }

    if (imIt->second.mFileName.empty()) {
        throw DeadlyImportError("Collada: Invalid texture, no data or file reference given");
    }

    result.Set(imIt->second.mFileName);

    return result;
}

// ------------------------------------------------------------------------------------------------
// Reads a string value from an accessor and its data array.
const std::string &ColladaLoader::ReadString(const Accessor &pAccessor, const Data &pData, size_t pIndex) const {
    size_t pos = pAccessor.mStride * pIndex + pAccessor.mOffset;
    ai_assert(pos < pData.mStrings.size());
    return pData.mStrings[pos];
}

// ------------------------------------------------------------------------------------------------
// Collects all nodes into the given array
void ColladaLoader::CollectNodes(const aiNode *pNode, std::vector<const aiNode *> &poNodes) const {
    poNodes.push_back(pNode);
    for (size_t a = 0; a < pNode->mNumChildren; ++a) {
        CollectNodes(pNode->mChildren[a], poNodes);
    }
}

// ------------------------------------------------------------------------------------------------
// Finds a node in the collada scene by the given name
const Node *ColladaLoader::FindNode(const Node *pNode, const std::string &pName) const {
    if (pNode->mName == pName || pNode->mID == pName)
        return pNode;

    for (auto a : pNode->mChildren) {
        const Collada::Node *node = FindNode(a, pName);
        if (node) {
            return node;
        }
    }

    return nullptr;
}

// ------------------------------------------------------------------------------------------------
// Finds a node in the collada scene by the given SID
const Node *ColladaLoader::FindNodeBySID(const Node *pNode, const std::string &pSID) const {
    if (nullptr == pNode) {
        return nullptr;
    }

    if (pNode->mSID == pSID) {
        return pNode;
    }

    for (auto a : pNode->mChildren) {
        const Collada::Node *node = FindNodeBySID(a, pSID);
        if (node) {
            return node;
        }
    }

    return nullptr;
}

// ------------------------------------------------------------------------------------------------
// Finds a proper unique name for a node derived from the collada-node's properties.
// The name must be unique for proper node-bone association.
std::string ColladaLoader::FindNameForNode(const Node *pNode) {
    // If explicitly requested, just use the collada name.
    if (useColladaName) {
        if (!pNode->mName.empty()) {
            return pNode->mName;
        } else {
            return format() << "$ColladaAutoName$_" << mNodeNameCounter++;
        }
    } else {
        // Now setup the name of the assimp node. The collada name might not be
        // unique, so we use the collada ID.
        if (!pNode->mID.empty())
            return pNode->mID;
        else if (!pNode->mSID.empty())
            return pNode->mSID;
        else {
            // No need to worry. Unnamed nodes are no problem at all, except
            // if cameras or lights need to be assigned to them.
            return format() << "$ColladaAutoName$_" << mNodeNameCounter++;
        }
    }
}

} // Namespace Assimp

#endif // !! ASSIMP_BUILD_NO_COLLADA_IMPORTER