/*
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/** @file  FBXConverter.cpp
 *  @brief Implementation of the FBX DOM -> aiScene converter
 */

#ifndef ASSIMP_BUILD_NO_FBX_IMPORTER

#include "FBXConverter.h"
#include "FBXParser.h"
#include "FBXMeshGeometry.h"
#include "FBXDocument.h"
#include "FBXUtil.h"
#include "FBXProperties.h"
#include "FBXImporter.h"
#include <assimp/StringComparison.h>

#include <assimp/scene.h>

#include <tuple>
#include <memory>
#include <iterator>
#include <vector>
#include <sstream>
#include <iomanip>

namespace Assimp {
namespace FBX {

using namespace Util;

#define MAGIC_NODE_TAG "_$AssimpFbx$"

#define CONVERT_FBX_TIME(time) static_cast<double>(time) / 46186158000L

FBXConverter::FBXConverter( aiScene* out, const Document& doc )
: defaultMaterialIndex()
, out( out )
, doc( doc ) {
    // animations need to be converted first since this will
    // populate the node_anim_chain_bits map, which is needed
    // to determine which nodes need to be generated.
    ConvertAnimations();
    ConvertRootNode();

    if ( doc.Settings().readAllMaterials ) {
        // unfortunately this means we have to evaluate all objects
        for( const ObjectMap::value_type& v : doc.Objects() ) {

            const Object* ob = v.second->Get();
            if ( !ob ) {
                continue;
            }

            const Material* mat = dynamic_cast<const Material*>( ob );
            if ( mat ) {

                if ( materials_converted.find( mat ) == materials_converted.end() ) {
                    ConvertMaterial( *mat, 0 );
                }
            }
        }
    }

    ConvertGlobalSettings();
    TransferDataToScene();

    // if we didn't read any meshes set the AI_SCENE_FLAGS_INCOMPLETE
    // to make sure the scene passes assimp's validation. FBX files
    // need not contain geometry (i.e. camera animations, raw armatures).
    if ( out->mNumMeshes == 0 ) {
        out->mFlags |= AI_SCENE_FLAGS_INCOMPLETE;
    }
}


FBXConverter::~FBXConverter() {
    std::for_each( meshes.begin(), meshes.end(), Util::delete_fun<aiMesh>() );
    std::for_each( materials.begin(), materials.end(), Util::delete_fun<aiMaterial>() );
    std::for_each( animations.begin(), animations.end(), Util::delete_fun<aiAnimation>() );
    std::for_each( lights.begin(), lights.end(), Util::delete_fun<aiLight>() );
    std::for_each( cameras.begin(), cameras.end(), Util::delete_fun<aiCamera>() );
    std::for_each( textures.begin(), textures.end(), Util::delete_fun<aiTexture>() );
}

void FBXConverter::ConvertRootNode() {
    out->mRootNode = new aiNode();
    out->mRootNode->mName.Set( "RootNode" );

    // root has ID 0
    ConvertNodes( 0L, *out->mRootNode );
}

void FBXConverter::ConvertNodes( uint64_t id, aiNode& parent, const aiMatrix4x4& parent_transform ) {
    const std::vector<const Connection*>& conns = doc.GetConnectionsByDestinationSequenced( id, "Model" );

    std::vector<aiNode*> nodes;
    nodes.reserve( conns.size() );

    std::vector<aiNode*> nodes_chain;
    std::vector<aiNode*> post_nodes_chain;

    try {
        for( const Connection* con : conns ) {

            // ignore object-property links
            if ( con->PropertyName().length() ) {
                continue;
            }

            const Object* const object = con->SourceObject();
            if ( nullptr == object ) {
                FBXImporter::LogWarn( "failed to convert source object for Model link" );
                continue;
            }

            const Model* const model = dynamic_cast<const Model*>( object );

            if ( nullptr != model ) {
                nodes_chain.clear();
                post_nodes_chain.clear();

                aiMatrix4x4 new_abs_transform = parent_transform;

                // even though there is only a single input node, the design of
                // assimp (or rather: the complicated transformation chain that
                // is employed by fbx) means that we may need multiple aiNode's
                // to represent a fbx node's transformation.
                GenerateTransformationNodeChain( *model, nodes_chain, post_nodes_chain );

                ai_assert( nodes_chain.size() );

                std::string original_name = FixNodeName( model->Name() );

                // check if any of the nodes in the chain has the name the fbx node
                // is supposed to have. If there is none, add another node to
                // preserve the name - people might have scripts etc. that rely
                // on specific node names.
                aiNode* name_carrier = NULL;
                for( aiNode* prenode : nodes_chain ) {
                    if ( !strcmp( prenode->mName.C_Str(), original_name.c_str() ) ) {
                        name_carrier = prenode;
                        break;
                    }
                }

                if ( !name_carrier ) {
                    NodeNameCache::const_iterator it = mNodeNames.find(original_name);
                    if ( it != mNodeNames.end() ) {
                        original_name = original_name + std::string( "001" );
                    }

                    mNodeNames.insert( original_name );
                    nodes_chain.push_back( new aiNode( original_name ) );
                } else {
                    original_name = nodes_chain.back()->mName.C_Str();
                }

                //setup metadata on newest node
                SetupNodeMetadata( *model, *nodes_chain.back() );

                // link all nodes in a row
                aiNode* last_parent = &parent;
                for( aiNode* prenode : nodes_chain ) {
                    ai_assert( prenode );

                    if ( last_parent != &parent ) {
                        last_parent->mNumChildren = 1;
                        last_parent->mChildren = new aiNode*[ 1 ];
                        last_parent->mChildren[ 0 ] = prenode;
                    }

                    prenode->mParent = last_parent;
                    last_parent = prenode;

                    new_abs_transform *= prenode->mTransformation;
                }

                // attach geometry
                ConvertModel( *model, *nodes_chain.back(), new_abs_transform );

                // check if there will be any child nodes
                const std::vector<const Connection*>& child_conns
                    = doc.GetConnectionsByDestinationSequenced( model->ID(), "Model" );

                // if so, link the geometric transform inverse nodes
                // before we attach any child nodes
                if (child_conns.size()) {
                    for( aiNode* postnode : post_nodes_chain ) {
                        ai_assert( postnode );

                        if ( last_parent != &parent ) {
                            last_parent->mNumChildren = 1;
                            last_parent->mChildren = new aiNode*[ 1 ];
                            last_parent->mChildren[ 0 ] = postnode;
                        }

                        postnode->mParent = last_parent;
                        last_parent = postnode;

                        new_abs_transform *= postnode->mTransformation;
                    }
                } else {
                    // free the nodes we allocated as we don't need them
                    Util::delete_fun<aiNode> deleter;
                    std::for_each(
                        post_nodes_chain.begin(),
                        post_nodes_chain.end(),
                        deleter
                    );
                }

                // attach sub-nodes (if any)
                ConvertNodes( model->ID(), *last_parent, new_abs_transform );

                if ( doc.Settings().readLights ) {
                    ConvertLights( *model, original_name );
                }

                if ( doc.Settings().readCameras ) {
                    ConvertCameras( *model, original_name );
                }

                nodes.push_back( nodes_chain.front() );
                nodes_chain.clear();
            }
        }

        if ( nodes.size() ) {
            parent.mChildren = new aiNode*[ nodes.size() ]();
            parent.mNumChildren = static_cast<unsigned int>( nodes.size() );

            std::swap_ranges( nodes.begin(), nodes.end(), parent.mChildren );
        }
    }
    catch ( std::exception& ) {
        Util::delete_fun<aiNode> deleter;
        std::for_each( nodes.begin(), nodes.end(), deleter );
        std::for_each( nodes_chain.begin(), nodes_chain.end(), deleter );
        std::for_each( post_nodes_chain.begin(), post_nodes_chain.end(), deleter );
    }
}


void FBXConverter::ConvertLights( const Model& model, const std::string &orig_name ) {
    const std::vector<const NodeAttribute*>& node_attrs = model.GetAttributes();
    for( const NodeAttribute* attr : node_attrs ) {
        const Light* const light = dynamic_cast<const Light*>( attr );
        if ( light ) {
            ConvertLight( *light, orig_name );
        }
    }
}

void FBXConverter::ConvertCameras( const Model& model, const std::string &orig_name ) {
    const std::vector<const NodeAttribute*>& node_attrs = model.GetAttributes();
    for( const NodeAttribute* attr : node_attrs ) {
        const Camera* const cam = dynamic_cast<const Camera*>( attr );
        if ( cam ) {
            ConvertCamera( *cam, orig_name );
        }
    }
}

void FBXConverter::ConvertLight( const Light& light, const std::string &orig_name ) {
    lights.push_back( new aiLight() );
    aiLight* const out_light = lights.back();

    out_light->mName.Set( orig_name );

    const float intensity = light.Intensity() / 100.0f;
    const aiVector3D& col = light.Color();

    out_light->mColorDiffuse = aiColor3D( col.x, col.y, col.z );
    out_light->mColorDiffuse.r *= intensity;
    out_light->mColorDiffuse.g *= intensity;
    out_light->mColorDiffuse.b *= intensity;

    out_light->mColorSpecular = out_light->mColorDiffuse;

    //lights are defined along negative y direction
    out_light->mPosition = aiVector3D(0.0f);
    out_light->mDirection = aiVector3D(0.0f, -1.0f, 0.0f);
    out_light->mUp = aiVector3D(0.0f, 0.0f, -1.0f);

    switch ( light.LightType() )
    {
    case Light::Type_Point:
        out_light->mType = aiLightSource_POINT;
        break;

    case Light::Type_Directional:
        out_light->mType = aiLightSource_DIRECTIONAL;
        break;

    case Light::Type_Spot:
        out_light->mType = aiLightSource_SPOT;
        out_light->mAngleOuterCone = AI_DEG_TO_RAD( light.OuterAngle() );
        out_light->mAngleInnerCone = AI_DEG_TO_RAD( light.InnerAngle() );
        break;

    case Light::Type_Area:
        FBXImporter::LogWarn( "cannot represent area light, set to UNDEFINED" );
        out_light->mType = aiLightSource_UNDEFINED;
        break;

    case Light::Type_Volume:
        FBXImporter::LogWarn( "cannot represent volume light, set to UNDEFINED" );
        out_light->mType = aiLightSource_UNDEFINED;
        break;
    default:
        ai_assert( false );
    }

    float decay = light.DecayStart();
    switch ( light.DecayType() )
    {
    case Light::Decay_None:
        out_light->mAttenuationConstant = decay;
        out_light->mAttenuationLinear = 0.0f;
        out_light->mAttenuationQuadratic = 0.0f;
        break;
    case Light::Decay_Linear:
        out_light->mAttenuationConstant = 0.0f;
        out_light->mAttenuationLinear = 2.0f / decay;
        out_light->mAttenuationQuadratic = 0.0f;
        break;
    case Light::Decay_Quadratic:
        out_light->mAttenuationConstant = 0.0f;
        out_light->mAttenuationLinear = 0.0f;
        out_light->mAttenuationQuadratic = 2.0f / (decay * decay);
        break;
    case Light::Decay_Cubic:
        FBXImporter::LogWarn( "cannot represent cubic attenuation, set to Quadratic" );
        out_light->mAttenuationQuadratic = 1.0f;
        break;
    default:
        ai_assert( false );
    }
}

void FBXConverter::ConvertCamera( const Camera& cam, const std::string &orig_name )
{
    cameras.push_back( new aiCamera() );
    aiCamera* const out_camera = cameras.back();

    out_camera->mName.Set( orig_name );

    out_camera->mAspect = cam.AspectWidth() / cam.AspectHeight();

    //cameras are defined along positive x direction
    out_camera->mPosition = cam.Position();
    out_camera->mLookAt = ( cam.InterestPosition() - out_camera->mPosition ).Normalize();
    out_camera->mUp = cam.UpVector();

    out_camera->mHorizontalFOV = AI_DEG_TO_RAD( cam.FieldOfView() );
    out_camera->mClipPlaneNear = cam.NearPlane();
    out_camera->mClipPlaneFar = cam.FarPlane();
}

void FBXConverter::GetUniqueName( const std::string &name, std::string &uniqueName )
{
    int i = 0;
    uniqueName = name;
    while (mNodeNames.find(uniqueName) != mNodeNames.end())
    {
        ++i;
        std::stringstream ext;
        ext << name << std::setfill('0') << std::setw(3) << i;
        uniqueName = ext.str();
    }
    mNodeNames.insert(uniqueName);
}


const char* FBXConverter::NameTransformationComp( TransformationComp comp ) {
    switch ( comp ) {
        case TransformationComp_Translation:
            return "Translation";
        case TransformationComp_RotationOffset:
            return "RotationOffset";
        case TransformationComp_RotationPivot:
            return "RotationPivot";
        case TransformationComp_PreRotation:
            return "PreRotation";
        case TransformationComp_Rotation:
            return "Rotation";
        case TransformationComp_PostRotation:
            return "PostRotation";
        case TransformationComp_RotationPivotInverse:
            return "RotationPivotInverse";
        case TransformationComp_ScalingOffset:
            return "ScalingOffset";
        case TransformationComp_ScalingPivot:
            return "ScalingPivot";
        case TransformationComp_Scaling:
            return "Scaling";
        case TransformationComp_ScalingPivotInverse:
            return "ScalingPivotInverse";
        case TransformationComp_GeometricScaling:
            return "GeometricScaling";
        case TransformationComp_GeometricRotation:
            return "GeometricRotation";
        case TransformationComp_GeometricTranslation:
            return "GeometricTranslation";
        case TransformationComp_GeometricScalingInverse:
            return "GeometricScalingInverse";
        case TransformationComp_GeometricRotationInverse:
            return "GeometricRotationInverse";
        case TransformationComp_GeometricTranslationInverse:
            return "GeometricTranslationInverse";
        case TransformationComp_MAXIMUM: // this is to silence compiler warnings
        default:
            break;
    }

    ai_assert( false );

    return nullptr;
}

const char* FBXConverter::NameTransformationCompProperty( TransformationComp comp ) {
    switch ( comp ) {
        case TransformationComp_Translation:
            return "Lcl Translation";
        case TransformationComp_RotationOffset:
            return "RotationOffset";
        case TransformationComp_RotationPivot:
            return "RotationPivot";
        case TransformationComp_PreRotation:
            return "PreRotation";
        case TransformationComp_Rotation:
            return "Lcl Rotation";
        case TransformationComp_PostRotation:
            return "PostRotation";
        case TransformationComp_RotationPivotInverse:
            return "RotationPivotInverse";
        case TransformationComp_ScalingOffset:
            return "ScalingOffset";
        case TransformationComp_ScalingPivot:
            return "ScalingPivot";
        case TransformationComp_Scaling:
            return "Lcl Scaling";
        case TransformationComp_ScalingPivotInverse:
            return "ScalingPivotInverse";
        case TransformationComp_GeometricScaling:
            return "GeometricScaling";
        case TransformationComp_GeometricRotation:
            return "GeometricRotation";
        case TransformationComp_GeometricTranslation:
            return "GeometricTranslation";
        case TransformationComp_GeometricScalingInverse:
            return "GeometricScalingInverse";
        case TransformationComp_GeometricRotationInverse:
            return "GeometricRotationInverse";
        case TransformationComp_GeometricTranslationInverse:
            return "GeometricTranslationInverse";
        case TransformationComp_MAXIMUM: // this is to silence compiler warnings
            break;
    }

    ai_assert( false );

    return nullptr;
}

aiVector3D FBXConverter::TransformationCompDefaultValue( TransformationComp comp )
{
    // XXX a neat way to solve the never-ending special cases for scaling
    // would be to do everything in log space!
    return comp == TransformationComp_Scaling ? aiVector3D( 1.f, 1.f, 1.f ) : aiVector3D();
}

void FBXConverter::GetRotationMatrix( Model::RotOrder mode, const aiVector3D& rotation, aiMatrix4x4& out )
{
    if ( mode == Model::RotOrder_SphericXYZ ) {
        FBXImporter::LogError( "Unsupported RotationMode: SphericXYZ" );
        out = aiMatrix4x4();
        return;
    }

    const float angle_epsilon = 1e-6f;

    out = aiMatrix4x4();

    bool is_id[ 3 ] = { true, true, true };

    aiMatrix4x4 temp[ 3 ];
    if ( std::fabs( rotation.z ) > angle_epsilon ) {
        aiMatrix4x4::RotationZ( AI_DEG_TO_RAD( rotation.z ), temp[ 2 ] );
        is_id[ 2 ] = false;
    }
    if ( std::fabs( rotation.y ) > angle_epsilon ) {
        aiMatrix4x4::RotationY( AI_DEG_TO_RAD( rotation.y ), temp[ 1 ] );
        is_id[ 1 ] = false;
    }
    if ( std::fabs( rotation.x ) > angle_epsilon ) {
        aiMatrix4x4::RotationX( AI_DEG_TO_RAD( rotation.x ), temp[ 0 ] );
        is_id[ 0 ] = false;
    }

    int order[ 3 ] = { -1, -1, -1 };

    // note: rotation order is inverted since we're left multiplying as is usual in assimp
    switch ( mode )
    {
    case Model::RotOrder_EulerXYZ:
        order[ 0 ] = 2;
        order[ 1 ] = 1;
        order[ 2 ] = 0;
        break;

    case Model::RotOrder_EulerXZY:
        order[ 0 ] = 1;
        order[ 1 ] = 2;
        order[ 2 ] = 0;
        break;

    case Model::RotOrder_EulerYZX:
        order[ 0 ] = 0;
        order[ 1 ] = 2;
        order[ 2 ] = 1;
        break;

    case Model::RotOrder_EulerYXZ:
        order[ 0 ] = 2;
        order[ 1 ] = 0;
        order[ 2 ] = 1;
        break;

    case Model::RotOrder_EulerZXY:
        order[ 0 ] = 1;
        order[ 1 ] = 0;
        order[ 2 ] = 2;
        break;

    case Model::RotOrder_EulerZYX:
        order[ 0 ] = 0;
        order[ 1 ] = 1;
        order[ 2 ] = 2;
        break;

    default:
        ai_assert( false );
        break;
    }

    ai_assert( order[ 0 ] >= 0 );
    ai_assert( order[ 0 ] <= 2 );
    ai_assert( order[ 1 ] >= 0 );
    ai_assert( order[ 1 ] <= 2 );
    ai_assert( order[ 2 ] >= 0 );
    ai_assert( order[ 2 ] <= 2 );

    if ( !is_id[ order[ 0 ] ] ) {
        out = temp[ order[ 0 ] ];
    }

    if ( !is_id[ order[ 1 ] ] ) {
        out = out * temp[ order[ 1 ] ];
    }

    if ( !is_id[ order[ 2 ] ] ) {
        out = out * temp[ order[ 2 ] ];
    }
}

bool FBXConverter::NeedsComplexTransformationChain( const Model& model )
{
    const PropertyTable& props = model.Props();
    bool ok;

    const float zero_epsilon = 1e-6f;
    const aiVector3D all_ones(1.0f, 1.0f, 1.0f);
    for ( size_t i = 0; i < TransformationComp_MAXIMUM; ++i ) {
        const TransformationComp comp = static_cast< TransformationComp >( i );

        if ( comp == TransformationComp_Rotation || comp == TransformationComp_Scaling || comp == TransformationComp_Translation ) {
            continue;
        }

        bool scale_compare = ( comp == TransformationComp_GeometricScaling || comp == TransformationComp_Scaling );

        const aiVector3D& v = PropertyGet<aiVector3D>( props, NameTransformationCompProperty( comp ), ok );
        if ( ok && scale_compare ) {
            if ( (v - all_ones).SquareLength() > zero_epsilon ) {
                return true;
            }
        } else if ( ok ) {
            if ( v.SquareLength() > zero_epsilon ) {
                return true;
            }
        }
    }

    return false;
}

std::string FBXConverter::NameTransformationChainNode( const std::string& name, TransformationComp comp )
{
    return name + std::string( MAGIC_NODE_TAG ) + "_" + NameTransformationComp( comp );
}

void FBXConverter::GenerateTransformationNodeChain( const Model& model, std::vector<aiNode*>& output_nodes,
        std::vector<aiNode*>& post_output_nodes ) {
    const PropertyTable& props = model.Props();
    const Model::RotOrder rot = model.RotationOrder();

    bool ok;

    aiMatrix4x4 chain[ TransformationComp_MAXIMUM ];
    std::fill_n( chain, static_cast<unsigned int>( TransformationComp_MAXIMUM ), aiMatrix4x4() );

    // generate transformation matrices for all the different transformation components
    const float zero_epsilon = 1e-6f;
    const aiVector3D all_ones(1.0f, 1.0f, 1.0f);
    bool is_complex = false;

    const aiVector3D& PreRotation = PropertyGet<aiVector3D>( props, "PreRotation", ok );
    if ( ok && PreRotation.SquareLength() > zero_epsilon ) {
        is_complex = true;

        GetRotationMatrix( Model::RotOrder::RotOrder_EulerXYZ, PreRotation, chain[ TransformationComp_PreRotation ] );
    }

    const aiVector3D& PostRotation = PropertyGet<aiVector3D>( props, "PostRotation", ok );
    if ( ok && PostRotation.SquareLength() > zero_epsilon ) {
        is_complex = true;

        GetRotationMatrix( Model::RotOrder::RotOrder_EulerXYZ, PostRotation, chain[ TransformationComp_PostRotation ] );
    }

    const aiVector3D& RotationPivot = PropertyGet<aiVector3D>( props, "RotationPivot", ok );
    if ( ok && RotationPivot.SquareLength() > zero_epsilon ) {
        is_complex = true;

        aiMatrix4x4::Translation( RotationPivot, chain[ TransformationComp_RotationPivot ] );
        aiMatrix4x4::Translation( -RotationPivot, chain[ TransformationComp_RotationPivotInverse ] );
    }

    const aiVector3D& RotationOffset = PropertyGet<aiVector3D>( props, "RotationOffset", ok );
    if ( ok && RotationOffset.SquareLength() > zero_epsilon ) {
        is_complex = true;

        aiMatrix4x4::Translation( RotationOffset, chain[ TransformationComp_RotationOffset ] );
    }

    const aiVector3D& ScalingOffset = PropertyGet<aiVector3D>( props, "ScalingOffset", ok );
    if ( ok && ScalingOffset.SquareLength() > zero_epsilon ) {
        is_complex = true;

        aiMatrix4x4::Translation( ScalingOffset, chain[ TransformationComp_ScalingOffset ] );
    }

    const aiVector3D& ScalingPivot = PropertyGet<aiVector3D>( props, "ScalingPivot", ok );
    if ( ok && ScalingPivot.SquareLength() > zero_epsilon ) {
        is_complex = true;

        aiMatrix4x4::Translation( ScalingPivot, chain[ TransformationComp_ScalingPivot ] );
        aiMatrix4x4::Translation( -ScalingPivot, chain[ TransformationComp_ScalingPivotInverse ] );
    }

    const aiVector3D& Translation = PropertyGet<aiVector3D>( props, "Lcl Translation", ok );
    if ( ok && Translation.SquareLength() > zero_epsilon ) {
        aiMatrix4x4::Translation( Translation, chain[ TransformationComp_Translation ] );
    }

    const aiVector3D& Scaling = PropertyGet<aiVector3D>( props, "Lcl Scaling", ok );
    if ( ok && (Scaling - all_ones).SquareLength() > zero_epsilon ) {
        aiMatrix4x4::Scaling( Scaling, chain[ TransformationComp_Scaling ] );
    }

    const aiVector3D& Rotation = PropertyGet<aiVector3D>( props, "Lcl Rotation", ok );
    if ( ok && Rotation.SquareLength() > zero_epsilon ) {
        GetRotationMatrix( rot, Rotation, chain[ TransformationComp_Rotation ] );
    }

    const aiVector3D& GeometricScaling = PropertyGet<aiVector3D>( props, "GeometricScaling", ok );
    if ( ok && (GeometricScaling - all_ones).SquareLength() > zero_epsilon ) {
        is_complex = true;
        aiMatrix4x4::Scaling( GeometricScaling, chain[ TransformationComp_GeometricScaling ] );
        aiVector3D GeometricScalingInverse = GeometricScaling;
        bool canscale = true;
        for (unsigned int i = 0; i < 3; ++i) {
            if ( std::fabs( GeometricScalingInverse[i] ) > zero_epsilon ) {
                GeometricScalingInverse[i] = 1.0f / GeometricScaling[i];
            } else {
                FBXImporter::LogError( "cannot invert geometric scaling matrix with a 0.0 scale component" );
                canscale = false;
                break;
            }
        }
        if (canscale) {
            aiMatrix4x4::Scaling( GeometricScalingInverse, chain[ TransformationComp_GeometricScalingInverse ] );
        }
    }

    const aiVector3D& GeometricRotation = PropertyGet<aiVector3D>( props, "GeometricRotation", ok );
    if ( ok && GeometricRotation.SquareLength() > zero_epsilon ) {
        is_complex = true;
        GetRotationMatrix( rot, GeometricRotation, chain[ TransformationComp_GeometricRotation ] );
        GetRotationMatrix( rot, GeometricRotation, chain[ TransformationComp_GeometricRotationInverse ] );
        chain[ TransformationComp_GeometricRotationInverse ].Inverse();
    }

    const aiVector3D& GeometricTranslation = PropertyGet<aiVector3D>( props, "GeometricTranslation", ok );
    if ( ok && GeometricTranslation.SquareLength() > zero_epsilon ) {
        is_complex = true;
        aiMatrix4x4::Translation( GeometricTranslation, chain[ TransformationComp_GeometricTranslation ] );
        aiMatrix4x4::Translation( -GeometricTranslation, chain[ TransformationComp_GeometricTranslationInverse ] );
    }

    // is_complex needs to be consistent with NeedsComplexTransformationChain()
    // or the interplay between this code and the animation converter would
    // not be guaranteed.
    ai_assert( NeedsComplexTransformationChain( model ) == is_complex );

    std::string name = FixNodeName( model.Name() );

    // now, if we have more than just Translation, Scaling and Rotation,
    // we need to generate a full node chain to accommodate for assimp's
    // lack to express pivots and offsets.
    if ( is_complex && doc.Settings().preservePivots ) {
        FBXImporter::LogInfo( "generating full transformation chain for node: " + name );

        // query the anim_chain_bits dictionary to find out which chain elements
        // have associated node animation channels. These can not be dropped
        // even if they have identity transform in bind pose.
        NodeAnimBitMap::const_iterator it = node_anim_chain_bits.find( name );
        const unsigned int anim_chain_bitmask = ( it == node_anim_chain_bits.end() ? 0 : ( *it ).second );

        unsigned int bit = 0x1;
        for ( size_t i = 0; i < TransformationComp_MAXIMUM; ++i, bit <<= 1 ) {
            const TransformationComp comp = static_cast<TransformationComp>( i );

            if ( chain[ i ].IsIdentity() && ( anim_chain_bitmask & bit ) == 0 ) {
                continue;
            }

            if ( comp == TransformationComp_PostRotation  ) {
                chain[ i ] = chain[ i ].Inverse();
            }

            aiNode* nd = new aiNode();
            nd->mName.Set( NameTransformationChainNode( name, comp ) );
            nd->mTransformation = chain[ i ];

            // geometric inverses go in a post-node chain
            if ( comp == TransformationComp_GeometricScalingInverse ||
                 comp == TransformationComp_GeometricRotationInverse ||
                 comp == TransformationComp_GeometricTranslationInverse
            ) {
                post_output_nodes.push_back( nd );
            } else {
                output_nodes.push_back( nd );
            }
        }

        ai_assert( output_nodes.size() );
        return;
    }

    // else, we can just multiply the matrices together
    aiNode* nd = new aiNode();
    output_nodes.push_back( nd );
    std::string uniqueName;
    GetUniqueName( name, uniqueName );

    nd->mName.Set( uniqueName );

    for (const auto &transform : chain) {
        nd->mTransformation = nd->mTransformation * transform;
    }
}

void FBXConverter::SetupNodeMetadata( const Model& model, aiNode& nd )
{
    const PropertyTable& props = model.Props();
    DirectPropertyMap unparsedProperties = props.GetUnparsedProperties();

    // create metadata on node
    const std::size_t numStaticMetaData = 2;
    aiMetadata* data = aiMetadata::Alloc( static_cast<unsigned int>(unparsedProperties.size() + numStaticMetaData) );
    nd.mMetaData = data;
    int index = 0;

    // find user defined properties (3ds Max)
    data->Set( index++, "UserProperties", aiString( PropertyGet<std::string>( props, "UDP3DSMAX", "" ) ) );
    // preserve the info that a node was marked as Null node in the original file.
    data->Set( index++, "IsNull", model.IsNull() ? true : false );

    // add unparsed properties to the node's metadata
    for( const DirectPropertyMap::value_type& prop : unparsedProperties ) {
        // Interpret the property as a concrete type
        if ( const TypedProperty<bool>* interpreted = prop.second->As<TypedProperty<bool> >() ) {
            data->Set( index++, prop.first, interpreted->Value() );
        } else if ( const TypedProperty<int>* interpreted = prop.second->As<TypedProperty<int> >() ) {
            data->Set( index++, prop.first, interpreted->Value() );
        } else if ( const TypedProperty<uint64_t>* interpreted = prop.second->As<TypedProperty<uint64_t> >() ) {
            data->Set( index++, prop.first, interpreted->Value() );
        } else if ( const TypedProperty<float>* interpreted = prop.second->As<TypedProperty<float> >() ) {
            data->Set( index++, prop.first, interpreted->Value() );
        } else if ( const TypedProperty<std::string>* interpreted = prop.second->As<TypedProperty<std::string> >() ) {
            data->Set( index++, prop.first, aiString( interpreted->Value() ) );
        } else if ( const TypedProperty<aiVector3D>* interpreted = prop.second->As<TypedProperty<aiVector3D> >() ) {
            data->Set( index++, prop.first, interpreted->Value() );
        } else {
            ai_assert( false );
        }
    }
}

void FBXConverter::ConvertModel( const Model& model, aiNode& nd, const aiMatrix4x4& node_global_transform )
{
    const std::vector<const Geometry*>& geos = model.GetGeometry();

    std::vector<unsigned int> meshes;
    meshes.reserve( geos.size() );

    for( const Geometry* geo : geos ) {

        const MeshGeometry* const mesh = dynamic_cast< const MeshGeometry* >( geo );
        if ( mesh ) {
            const std::vector<unsigned int>& indices = ConvertMesh( *mesh, model, node_global_transform, nd);
            std::copy( indices.begin(), indices.end(), std::back_inserter( meshes ) );
        }
        else {
            FBXImporter::LogWarn( "ignoring unrecognized geometry: " + geo->Name() );
        }
    }

    if ( meshes.size() ) {
        nd.mMeshes = new unsigned int[ meshes.size() ]();
        nd.mNumMeshes = static_cast< unsigned int >( meshes.size() );

        std::swap_ranges( meshes.begin(), meshes.end(), nd.mMeshes );
    }
}

std::vector<unsigned int> FBXConverter::ConvertMesh( const MeshGeometry& mesh, const Model& model,
    const aiMatrix4x4& node_global_transform, aiNode& nd)
{
    std::vector<unsigned int> temp;

    MeshMap::const_iterator it = meshes_converted.find( &mesh );
    if ( it != meshes_converted.end() ) {
        std::copy( ( *it ).second.begin(), ( *it ).second.end(), std::back_inserter( temp ) );
        return temp;
    }

    const std::vector<aiVector3D>& vertices = mesh.GetVertices();
    const std::vector<unsigned int>& faces = mesh.GetFaceIndexCounts();
    if ( vertices.empty() || faces.empty() ) {
        FBXImporter::LogWarn( "ignoring empty geometry: " + mesh.Name() );
        return temp;
    }

    // one material per mesh maps easily to aiMesh. Multiple material
    // meshes need to be split.
    const MatIndexArray& mindices = mesh.GetMaterialIndices();
    if ( doc.Settings().readMaterials && !mindices.empty() ) {
        const MatIndexArray::value_type base = mindices[ 0 ];
        for( MatIndexArray::value_type index : mindices ) {
            if ( index != base ) {
                return ConvertMeshMultiMaterial( mesh, model, node_global_transform, nd);
            }
        }
    }

    // faster code-path, just copy the data
    temp.push_back( ConvertMeshSingleMaterial( mesh, model, node_global_transform, nd) );
    return temp;
}

aiMesh* FBXConverter::SetupEmptyMesh( const MeshGeometry& mesh, aiNode& nd)
{
    aiMesh* const out_mesh = new aiMesh();
    meshes.push_back( out_mesh );
    meshes_converted[ &mesh ].push_back( static_cast<unsigned int>( meshes.size() - 1 ) );

    // set name
    std::string name = mesh.Name();
    if ( name.substr( 0, 10 ) == "Geometry::" ) {
        name = name.substr( 10 );
    }

    if ( name.length() ) {
        out_mesh->mName.Set( name );
    }
    else
    {
        out_mesh->mName = nd.mName;
    }

    return out_mesh;
}

unsigned int FBXConverter::ConvertMeshSingleMaterial( const MeshGeometry& mesh, const Model& model,
    const aiMatrix4x4& node_global_transform, aiNode& nd)
{
    const MatIndexArray& mindices = mesh.GetMaterialIndices();
    aiMesh* const out_mesh = SetupEmptyMesh(mesh, nd);

    const std::vector<aiVector3D>& vertices = mesh.GetVertices();
    const std::vector<unsigned int>& faces = mesh.GetFaceIndexCounts();

    // copy vertices
    out_mesh->mNumVertices = static_cast<unsigned int>( vertices.size() );
    out_mesh->mVertices = new aiVector3D[ vertices.size() ];
    std::copy( vertices.begin(), vertices.end(), out_mesh->mVertices );

    // generate dummy faces
    out_mesh->mNumFaces = static_cast<unsigned int>( faces.size() );
    aiFace* fac = out_mesh->mFaces = new aiFace[ faces.size() ]();

    unsigned int cursor = 0;
    for( unsigned int pcount : faces ) {
        aiFace& f = *fac++;
        f.mNumIndices = pcount;
        f.mIndices = new unsigned int[ pcount ];
        switch ( pcount )
        {
        case 1:
            out_mesh->mPrimitiveTypes |= aiPrimitiveType_POINT;
            break;
        case 2:
            out_mesh->mPrimitiveTypes |= aiPrimitiveType_LINE;
            break;
        case 3:
            out_mesh->mPrimitiveTypes |= aiPrimitiveType_TRIANGLE;
            break;
        default:
            out_mesh->mPrimitiveTypes |= aiPrimitiveType_POLYGON;
            break;
        }
        for ( unsigned int i = 0; i < pcount; ++i ) {
            f.mIndices[ i ] = cursor++;
        }
    }

    // copy normals
    const std::vector<aiVector3D>& normals = mesh.GetNormals();
    if ( normals.size() ) {
        ai_assert( normals.size() == vertices.size() );

        out_mesh->mNormals = new aiVector3D[ vertices.size() ];
        std::copy( normals.begin(), normals.end(), out_mesh->mNormals );
    }

    // copy tangents - assimp requires both tangents and bitangents (binormals)
    // to be present, or neither of them. Compute binormals from normals
    // and tangents if needed.
    const std::vector<aiVector3D>& tangents = mesh.GetTangents();
    const std::vector<aiVector3D>* binormals = &mesh.GetBinormals();

    if ( tangents.size() ) {
        std::vector<aiVector3D> tempBinormals;
        if ( !binormals->size() ) {
            if ( normals.size() ) {
                tempBinormals.resize( normals.size() );
                for ( unsigned int i = 0; i < tangents.size(); ++i ) {
                    tempBinormals[ i ] = normals[ i ] ^ tangents[ i ];
                }

                binormals = &tempBinormals;
            }
            else {
                binormals = NULL;
            }
        }

        if ( binormals ) {
            ai_assert( tangents.size() == vertices.size() );
            ai_assert( binormals->size() == vertices.size() );

            out_mesh->mTangents = new aiVector3D[ vertices.size() ];
            std::copy( tangents.begin(), tangents.end(), out_mesh->mTangents );

            out_mesh->mBitangents = new aiVector3D[ vertices.size() ];
            std::copy( binormals->begin(), binormals->end(), out_mesh->mBitangents );
        }
    }

    // copy texture coords
    for ( unsigned int i = 0; i < AI_MAX_NUMBER_OF_TEXTURECOORDS; ++i ) {
        const std::vector<aiVector2D>& uvs = mesh.GetTextureCoords( i );
        if ( uvs.empty() ) {
            break;
        }

        aiVector3D* out_uv = out_mesh->mTextureCoords[ i ] = new aiVector3D[ vertices.size() ];
        for( const aiVector2D& v : uvs ) {
            *out_uv++ = aiVector3D( v.x, v.y, 0.0f );
        }

        out_mesh->mNumUVComponents[ i ] = 2;
    }

    // copy vertex colors
    for ( unsigned int i = 0; i < AI_MAX_NUMBER_OF_COLOR_SETS; ++i ) {
        const std::vector<aiColor4D>& colors = mesh.GetVertexColors( i );
        if ( colors.empty() ) {
            break;
        }

        out_mesh->mColors[ i ] = new aiColor4D[ vertices.size() ];
        std::copy( colors.begin(), colors.end(), out_mesh->mColors[ i ] );
    }

    if ( !doc.Settings().readMaterials || mindices.empty() ) {
        FBXImporter::LogError( "no material assigned to mesh, setting default material" );
        out_mesh->mMaterialIndex = GetDefaultMaterial();
    }
    else {
        ConvertMaterialForMesh( out_mesh, model, mesh, mindices[ 0 ] );
    }

    if ( doc.Settings().readWeights && mesh.DeformerSkin() != NULL ) {
        ConvertWeights( out_mesh, model, mesh, node_global_transform, NO_MATERIAL_SEPARATION );
    }

    return static_cast<unsigned int>( meshes.size() - 1 );
}

std::vector<unsigned int> FBXConverter::ConvertMeshMultiMaterial( const MeshGeometry& mesh, const Model& model,
    const aiMatrix4x4& node_global_transform, aiNode& nd)
{
    const MatIndexArray& mindices = mesh.GetMaterialIndices();
    ai_assert( mindices.size() );

    std::set<MatIndexArray::value_type> had;
    std::vector<unsigned int> indices;

    for( MatIndexArray::value_type index : mindices ) {
        if ( had.find( index ) == had.end() ) {

            indices.push_back( ConvertMeshMultiMaterial( mesh, model, index, node_global_transform, nd) );
            had.insert( index );
        }
    }

    return indices;
}

unsigned int FBXConverter::ConvertMeshMultiMaterial( const MeshGeometry& mesh, const Model& model,
    MatIndexArray::value_type index,
    const aiMatrix4x4& node_global_transform,
    aiNode& nd)
{
    aiMesh* const out_mesh = SetupEmptyMesh(mesh, nd);

    const MatIndexArray& mindices = mesh.GetMaterialIndices();
    const std::vector<aiVector3D>& vertices = mesh.GetVertices();
    const std::vector<unsigned int>& faces = mesh.GetFaceIndexCounts();

    const bool process_weights = doc.Settings().readWeights && mesh.DeformerSkin() != NULL;

    unsigned int count_faces = 0;
    unsigned int count_vertices = 0;

    // count faces
    std::vector<unsigned int>::const_iterator itf = faces.begin();
    for ( MatIndexArray::const_iterator it = mindices.begin(),
        end = mindices.end(); it != end; ++it, ++itf )
    {
        if ( ( *it ) != index ) {
            continue;
        }
        ++count_faces;
        count_vertices += *itf;
    }

    ai_assert( count_faces );
    ai_assert( count_vertices );

    // mapping from output indices to DOM indexing, needed to resolve weights
    std::vector<unsigned int> reverseMapping;

    if ( process_weights ) {
        reverseMapping.resize( count_vertices );
    }

    // allocate output data arrays, but don't fill them yet
    out_mesh->mNumVertices = count_vertices;
    out_mesh->mVertices = new aiVector3D[ count_vertices ];

    out_mesh->mNumFaces = count_faces;
    aiFace* fac = out_mesh->mFaces = new aiFace[ count_faces ]();


    // allocate normals
    const std::vector<aiVector3D>& normals = mesh.GetNormals();
    if ( normals.size() ) {
        ai_assert( normals.size() == vertices.size() );
        out_mesh->mNormals = new aiVector3D[ vertices.size() ];
    }

    // allocate tangents, binormals.
    const std::vector<aiVector3D>& tangents = mesh.GetTangents();
    const std::vector<aiVector3D>* binormals = &mesh.GetBinormals();
    std::vector<aiVector3D> tempBinormals;

    if ( tangents.size() ) {
        if ( !binormals->size() ) {
            if ( normals.size() ) {
                // XXX this computes the binormals for the entire mesh, not only
                // the part for which we need them.
                tempBinormals.resize( normals.size() );
                for ( unsigned int i = 0; i < tangents.size(); ++i ) {
                    tempBinormals[ i ] = normals[ i ] ^ tangents[ i ];
                }

                binormals = &tempBinormals;
            }
            else {
                binormals = NULL;
            }
        }

        if ( binormals ) {
            ai_assert( tangents.size() == vertices.size() && binormals->size() == vertices.size() );

            out_mesh->mTangents = new aiVector3D[ vertices.size() ];
            out_mesh->mBitangents = new aiVector3D[ vertices.size() ];
        }
    }

    // allocate texture coords
    unsigned int num_uvs = 0;
    for ( unsigned int i = 0; i < AI_MAX_NUMBER_OF_TEXTURECOORDS; ++i, ++num_uvs ) {
        const std::vector<aiVector2D>& uvs = mesh.GetTextureCoords( i );
        if ( uvs.empty() ) {
            break;
        }

        out_mesh->mTextureCoords[ i ] = new aiVector3D[ vertices.size() ];
        out_mesh->mNumUVComponents[ i ] = 2;
    }

    // allocate vertex colors
    unsigned int num_vcs = 0;
    for ( unsigned int i = 0; i < AI_MAX_NUMBER_OF_COLOR_SETS; ++i, ++num_vcs ) {
        const std::vector<aiColor4D>& colors = mesh.GetVertexColors( i );
        if ( colors.empty() ) {
            break;
        }

        out_mesh->mColors[ i ] = new aiColor4D[ vertices.size() ];
    }

    unsigned int cursor = 0, in_cursor = 0;

    itf = faces.begin();
    for ( MatIndexArray::const_iterator it = mindices.begin(),
        end = mindices.end(); it != end; ++it, ++itf )
    {
        const unsigned int pcount = *itf;
        if ( ( *it ) != index ) {
            in_cursor += pcount;
            continue;
        }

        aiFace& f = *fac++;

        f.mNumIndices = pcount;
        f.mIndices = new unsigned int[ pcount ];
        switch ( pcount )
        {
        case 1:
            out_mesh->mPrimitiveTypes |= aiPrimitiveType_POINT;
            break;
        case 2:
            out_mesh->mPrimitiveTypes |= aiPrimitiveType_LINE;
            break;
        case 3:
            out_mesh->mPrimitiveTypes |= aiPrimitiveType_TRIANGLE;
            break;
        default:
            out_mesh->mPrimitiveTypes |= aiPrimitiveType_POLYGON;
            break;
        }
        for ( unsigned int i = 0; i < pcount; ++i, ++cursor, ++in_cursor ) {
            f.mIndices[ i ] = cursor;

            if ( reverseMapping.size() ) {
                reverseMapping[ cursor ] = in_cursor;
            }

            out_mesh->mVertices[ cursor ] = vertices[ in_cursor ];

            if ( out_mesh->mNormals ) {
                out_mesh->mNormals[ cursor ] = normals[ in_cursor ];
            }

            if ( out_mesh->mTangents ) {
                out_mesh->mTangents[ cursor ] = tangents[ in_cursor ];
                out_mesh->mBitangents[ cursor ] = ( *binormals )[ in_cursor ];
            }

            for ( unsigned int j = 0; j < num_uvs; ++j ) {
                const std::vector<aiVector2D>& uvs = mesh.GetTextureCoords( j );
                out_mesh->mTextureCoords[ j ][ cursor ] = aiVector3D( uvs[ in_cursor ].x, uvs[ in_cursor ].y, 0.0f );
            }

            for ( unsigned int j = 0; j < num_vcs; ++j ) {
                const std::vector<aiColor4D>& cols = mesh.GetVertexColors( j );
                out_mesh->mColors[ j ][ cursor ] = cols[ in_cursor ];
            }
        }
    }

    ConvertMaterialForMesh( out_mesh, model, mesh, index );

    if ( process_weights ) {
        ConvertWeights( out_mesh, model, mesh, node_global_transform, index, &reverseMapping );
    }

    return static_cast<unsigned int>( meshes.size() - 1 );
}

void FBXConverter::ConvertWeights( aiMesh* out, const Model& model, const MeshGeometry& geo,
    const aiMatrix4x4& node_global_transform ,
    unsigned int materialIndex,
    std::vector<unsigned int>* outputVertStartIndices  )
{
    ai_assert( geo.DeformerSkin() );

    std::vector<size_t> out_indices;
    std::vector<size_t> index_out_indices;
    std::vector<size_t> count_out_indices;

    const Skin& sk = *geo.DeformerSkin();

    std::vector<aiBone*> bones;
    bones.reserve( sk.Clusters().size() );

    const bool no_mat_check = materialIndex == NO_MATERIAL_SEPARATION;
    ai_assert( no_mat_check || outputVertStartIndices );

    try {

        for( const Cluster* cluster : sk.Clusters() ) {
            ai_assert( cluster );

            const WeightIndexArray& indices = cluster->GetIndices();

            if ( indices.empty() ) {
                continue;
            }

            const MatIndexArray& mats = geo.GetMaterialIndices();

            bool ok = false;

            const size_t no_index_sentinel = std::numeric_limits<size_t>::max();

            count_out_indices.clear();
            index_out_indices.clear();
            out_indices.clear();

            // now check if *any* of these weights is contained in the output mesh,
            // taking notes so we don't need to do it twice.
            for( WeightIndexArray::value_type index : indices ) {

                unsigned int count = 0;
                const unsigned int* const out_idx = geo.ToOutputVertexIndex( index, count );
                // ToOutputVertexIndex only returns NULL if index is out of bounds
                // which should never happen
                ai_assert( out_idx != NULL );

                index_out_indices.push_back( no_index_sentinel );
                count_out_indices.push_back( 0 );

                for ( unsigned int i = 0; i < count; ++i ) {
                    if ( no_mat_check || static_cast<size_t>( mats[ geo.FaceForVertexIndex( out_idx[ i ] ) ] ) == materialIndex ) {

                        if ( index_out_indices.back() == no_index_sentinel ) {
                            index_out_indices.back() = out_indices.size();

                        }

                        if ( no_mat_check ) {
                            out_indices.push_back( out_idx[ i ] );
                        }
                        else {
                            // this extra lookup is in O(logn), so the entire algorithm becomes O(nlogn)
                            const std::vector<unsigned int>::iterator it = std::lower_bound(
                                outputVertStartIndices->begin(),
                                outputVertStartIndices->end(),
                                out_idx[ i ]
                                );

                            out_indices.push_back( std::distance( outputVertStartIndices->begin(), it ) );
                        }

                        ++count_out_indices.back();
                        ok = true;
                    }
                }
            }

            // if we found at least one, generate the output bones
            // XXX this could be heavily simplified by collecting the bone
            // data in a single step.
            if ( ok ) {
                ConvertCluster( bones, model, *cluster, out_indices, index_out_indices,
                    count_out_indices, node_global_transform );
            }
        }
    }
    catch ( std::exception& ) {
        std::for_each( bones.begin(), bones.end(), Util::delete_fun<aiBone>() );
        throw;
    }

    if ( bones.empty() ) {
        return;
    }

    out->mBones = new aiBone*[ bones.size() ]();
    out->mNumBones = static_cast<unsigned int>( bones.size() );

    std::swap_ranges( bones.begin(), bones.end(), out->mBones );
}

void FBXConverter::ConvertCluster( std::vector<aiBone*>& bones, const Model& /*model*/, const Cluster& cl,
        std::vector<size_t>& out_indices,
        std::vector<size_t>& index_out_indices,
        std::vector<size_t>& count_out_indices,
        const aiMatrix4x4& node_global_transform )
{

    aiBone* const bone = new aiBone();
    bones.push_back( bone );

    bone->mName = FixNodeName( cl.TargetNode()->Name() );

    bone->mOffsetMatrix = cl.TransformLink();
    bone->mOffsetMatrix.Inverse();

    bone->mOffsetMatrix = bone->mOffsetMatrix * node_global_transform;

    bone->mNumWeights = static_cast<unsigned int>( out_indices.size() );
    aiVertexWeight* cursor = bone->mWeights = new aiVertexWeight[ out_indices.size() ];

    const size_t no_index_sentinel = std::numeric_limits<size_t>::max();
    const WeightArray& weights = cl.GetWeights();

    const size_t c = index_out_indices.size();
    for ( size_t i = 0; i < c; ++i ) {
        const size_t index_index = index_out_indices[ i ];

        if ( index_index == no_index_sentinel ) {
            continue;
        }

        const size_t cc = count_out_indices[ i ];
        for ( size_t j = 0; j < cc; ++j ) {
            aiVertexWeight& out_weight = *cursor++;

            out_weight.mVertexId = static_cast<unsigned int>( out_indices[ index_index + j ] );
            out_weight.mWeight = weights[ i ];
        }
    }
}

void FBXConverter::ConvertMaterialForMesh( aiMesh* out, const Model& model, const MeshGeometry& geo,
    MatIndexArray::value_type materialIndex )
{
    // locate source materials for this mesh
    const std::vector<const Material*>& mats = model.GetMaterials();
    if ( static_cast<unsigned int>( materialIndex ) >= mats.size() || materialIndex < 0 ) {
        FBXImporter::LogError( "material index out of bounds, setting default material" );
        out->mMaterialIndex = GetDefaultMaterial();
        return;
    }

    const Material* const mat = mats[ materialIndex ];
    MaterialMap::const_iterator it = materials_converted.find( mat );
    if ( it != materials_converted.end() ) {
        out->mMaterialIndex = ( *it ).second;
        return;
    }

    out->mMaterialIndex = ConvertMaterial( *mat, &geo );
    materials_converted[ mat ] = out->mMaterialIndex;
}

unsigned int FBXConverter::GetDefaultMaterial()
{
    if ( defaultMaterialIndex ) {
        return defaultMaterialIndex - 1;
    }

    aiMaterial* out_mat = new aiMaterial();
    materials.push_back( out_mat );

    const aiColor3D diffuse = aiColor3D( 0.8f, 0.8f, 0.8f );
    out_mat->AddProperty( &diffuse, 1, AI_MATKEY_COLOR_DIFFUSE );

    aiString s;
    s.Set( AI_DEFAULT_MATERIAL_NAME );

    out_mat->AddProperty( &s, AI_MATKEY_NAME );

    defaultMaterialIndex = static_cast< unsigned int >( materials.size() );
    return defaultMaterialIndex - 1;
}


unsigned int FBXConverter::ConvertMaterial( const Material& material, const MeshGeometry* const mesh )
{
    const PropertyTable& props = material.Props();

    // generate empty output material
    aiMaterial* out_mat = new aiMaterial();
    materials_converted[ &material ] = static_cast<unsigned int>( materials.size() );

    materials.push_back( out_mat );

    aiString str;

    // strip Material:: prefix
    std::string name = material.Name();
    if ( name.substr( 0, 10 ) == "Material::" ) {
        name = name.substr( 10 );
    }

    // set material name if not empty - this could happen
    // and there should be no key for it in this case.
    if ( name.length() ) {
        str.Set( name );
        out_mat->AddProperty( &str, AI_MATKEY_NAME );
    }

    // shading stuff and colors
    SetShadingPropertiesCommon( out_mat, props );

    // texture assignments
    SetTextureProperties( out_mat, material.Textures(), mesh );
    SetTextureProperties( out_mat, material.LayeredTextures(), mesh );

    return static_cast<unsigned int>( materials.size() - 1 );
}

unsigned int FBXConverter::ConvertVideo( const Video& video )
{
    // generate empty output texture
    aiTexture* out_tex = new aiTexture();
    textures.push_back( out_tex );

    // assuming the texture is compressed
    out_tex->mWidth = static_cast<unsigned int>( video.ContentLength() ); // total data size
    out_tex->mHeight = 0; // fixed to 0

    // steal the data from the Video to avoid an additional copy
    out_tex->pcData = reinterpret_cast<aiTexel*>( const_cast<Video&>( video ).RelinquishContent() );

    // try to extract a hint from the file extension
    const std::string& filename = video.FileName().empty() ? video.RelativeFilename() : video.FileName();
    std::string ext = BaseImporter::GetExtension( filename );

    if ( ext == "jpeg" ) {
        ext = "jpg";
    }

    if ( ext.size() <= 3 ) {
        memcpy( out_tex->achFormatHint, ext.c_str(), ext.size() );
    }

    out_tex->mFilename.Set(video.FileName().c_str());

    return static_cast<unsigned int>( textures.size() - 1 );
}

aiString FBXConverter::GetTexturePath(const Texture* tex)
{
    aiString path;
    path.Set(tex->RelativeFilename());

    const Video* media = tex->Media();
    if (media != nullptr) {
        bool textureReady = false; //tells if our texture is ready (if it was loaded or if it was found)
        unsigned int index;

        VideoMap::const_iterator it = textures_converted.find(media);
        if (it != textures_converted.end()) {
            index = (*it).second;
            textureReady = true;
        }
        else {
            if (media->ContentLength() > 0) {
                index = ConvertVideo(*media);
                textures_converted[media] = index;
                textureReady = true;
            }
        }

        // setup texture reference string (copied from ColladaLoader::FindFilenameForEffectTexture), if the texture is ready
        if (doc.Settings().useLegacyEmbeddedTextureNaming) {
            if (textureReady) {
                // TODO: check the possibility of using the flag "AI_CONFIG_IMPORT_FBX_EMBEDDED_TEXTURES_LEGACY_NAMING"
                // In FBX files textures are now stored internally by Assimp with their filename included
                // Now Assimp can lookup through the loaded textures after all data is processed
                // We need to load all textures before referencing them, as FBX file format order may reference a texture before loading it
                // This may occur on this case too, it has to be studied
                path.data[0] = '*';
                path.length = 1 + ASSIMP_itoa10(path.data + 1, MAXLEN - 1, index);
            }
        }
    }

    return path;
}

void FBXConverter::TrySetTextureProperties( aiMaterial* out_mat, const TextureMap& textures,
    const std::string& propName,
    aiTextureType target, const MeshGeometry* const mesh )
{
    TextureMap::const_iterator it = textures.find( propName );
    if ( it == textures.end() ) {
        return;
    }

    const Texture* const tex = ( *it ).second;
    if ( tex != 0 )
    {
        aiString path = GetTexturePath(tex);
        out_mat->AddProperty( &path, _AI_MATKEY_TEXTURE_BASE, target, 0 );

        aiUVTransform uvTrafo;
        // XXX handle all kinds of UV transformations
        uvTrafo.mScaling = tex->UVScaling();
        uvTrafo.mTranslation = tex->UVTranslation();
        out_mat->AddProperty( &uvTrafo, 1, _AI_MATKEY_UVTRANSFORM_BASE, target, 0 );

        const PropertyTable& props = tex->Props();

        int uvIndex = 0;

        bool ok;
        const std::string& uvSet = PropertyGet<std::string>( props, "UVSet", ok );
        if ( ok ) {
            // "default" is the name which usually appears in the FbxFileTexture template
            if ( uvSet != "default" && uvSet.length() ) {
                // this is a bit awkward - we need to find a mesh that uses this
                // material and scan its UV channels for the given UV name because
                // assimp references UV channels by index, not by name.

                // XXX: the case that UV channels may appear in different orders
                // in meshes is unhandled. A possible solution would be to sort
                // the UV channels alphabetically, but this would have the side
                // effect that the primary (first) UV channel would sometimes
                // be moved, causing trouble when users read only the first
                // UV channel and ignore UV channel assignments altogether.

                const unsigned int matIndex = static_cast<unsigned int>( std::distance( materials.begin(),
                    std::find( materials.begin(), materials.end(), out_mat )
                    ) );


                uvIndex = -1;
                if ( !mesh )
                {
                    for( const MeshMap::value_type& v : meshes_converted ) {
                        const MeshGeometry* const mesh = dynamic_cast<const MeshGeometry*> ( v.first );
                        if ( !mesh ) {
                            continue;
                        }

                        const MatIndexArray& mats = mesh->GetMaterialIndices();
                        if ( std::find( mats.begin(), mats.end(), matIndex ) == mats.end() ) {
                            continue;
                        }

                        int index = -1;
                        for ( unsigned int i = 0; i < AI_MAX_NUMBER_OF_TEXTURECOORDS; ++i ) {
                            if ( mesh->GetTextureCoords( i ).empty() ) {
                                break;
                            }
                            const std::string& name = mesh->GetTextureCoordChannelName( i );
                            if ( name == uvSet ) {
                                index = static_cast<int>( i );
                                break;
                            }
                        }
                        if ( index == -1 ) {
                            FBXImporter::LogWarn( "did not find UV channel named " + uvSet + " in a mesh using this material" );
                            continue;
                        }

                        if ( uvIndex == -1 ) {
                            uvIndex = index;
                        }
                        else {
                            FBXImporter::LogWarn( "the UV channel named " + uvSet +
                                " appears at different positions in meshes, results will be wrong" );
                        }
                    }
                }
                else
                {
                    int index = -1;
                    for ( unsigned int i = 0; i < AI_MAX_NUMBER_OF_TEXTURECOORDS; ++i ) {
                        if ( mesh->GetTextureCoords( i ).empty() ) {
                            break;
                        }
                        const std::string& name = mesh->GetTextureCoordChannelName( i );
                        if ( name == uvSet ) {
                            index = static_cast<int>( i );
                            break;
                        }
                    }
                    if ( index == -1 ) {
                        FBXImporter::LogWarn( "did not find UV channel named " + uvSet + " in a mesh using this material" );
                    }

                    if ( uvIndex == -1 ) {
                        uvIndex = index;
                    }
                }

                if ( uvIndex == -1 ) {
                    FBXImporter::LogWarn( "failed to resolve UV channel " + uvSet + ", using first UV channel" );
                    uvIndex = 0;
                }
            }
        }

        out_mat->AddProperty( &uvIndex, 1, _AI_MATKEY_UVWSRC_BASE, target, 0 );
    }
}

void FBXConverter::TrySetTextureProperties( aiMaterial* out_mat, const LayeredTextureMap& layeredTextures,
        const std::string& propName,
        aiTextureType target, const MeshGeometry* const mesh ) {
    LayeredTextureMap::const_iterator it = layeredTextures.find( propName );
    if ( it == layeredTextures.end() ) {
        return;
    }

    int texCount = (*it).second->textureCount();
    
    // Set the blend mode for layered textures
	int blendmode= (*it).second->GetBlendMode();
	out_mat->AddProperty(&blendmode,1,_AI_MATKEY_TEXOP_BASE,target,0);

	for(int texIndex = 0; texIndex < texCount; texIndex++){
    
        const Texture* const tex = ( *it ).second->getTexture(texIndex);

        aiString path = GetTexturePath(tex);
        out_mat->AddProperty( &path, _AI_MATKEY_TEXTURE_BASE, target, texIndex );

        aiUVTransform uvTrafo;
        // XXX handle all kinds of UV transformations
        uvTrafo.mScaling = tex->UVScaling();
        uvTrafo.mTranslation = tex->UVTranslation();
        out_mat->AddProperty( &uvTrafo, 1, _AI_MATKEY_UVTRANSFORM_BASE, target, texIndex );

        const PropertyTable& props = tex->Props();

        int uvIndex = 0;

        bool ok;
        const std::string& uvSet = PropertyGet<std::string>( props, "UVSet", ok );
        if ( ok ) {
            // "default" is the name which usually appears in the FbxFileTexture template
            if ( uvSet != "default" && uvSet.length() ) {
                // this is a bit awkward - we need to find a mesh that uses this
                // material and scan its UV channels for the given UV name because
                // assimp references UV channels by index, not by name.

                // XXX: the case that UV channels may appear in different orders
                // in meshes is unhandled. A possible solution would be to sort
                // the UV channels alphabetically, but this would have the side
                // effect that the primary (first) UV channel would sometimes
                // be moved, causing trouble when users read only the first
                // UV channel and ignore UV channel assignments altogether.

                const unsigned int matIndex = static_cast<unsigned int>( std::distance( materials.begin(),
                    std::find( materials.begin(), materials.end(), out_mat )
                    ) );

                uvIndex = -1;
                if ( !mesh )
                {
                    for( const MeshMap::value_type& v : meshes_converted ) {
                        const MeshGeometry* const mesh = dynamic_cast<const MeshGeometry*> ( v.first );
                        if ( !mesh ) {
                            continue;
                        }

                        const MatIndexArray& mats = mesh->GetMaterialIndices();
                        if ( std::find( mats.begin(), mats.end(), matIndex ) == mats.end() ) {
                            continue;
                        }

                        int index = -1;
                        for ( unsigned int i = 0; i < AI_MAX_NUMBER_OF_TEXTURECOORDS; ++i ) {
                            if ( mesh->GetTextureCoords( i ).empty() ) {
                                break;
                            }
                            const std::string& name = mesh->GetTextureCoordChannelName( i );
                            if ( name == uvSet ) {
                                index = static_cast<int>( i );
                                break;
                            }
                        }
                        if ( index == -1 ) {
                            FBXImporter::LogWarn( "did not find UV channel named " + uvSet + " in a mesh using this material" );
                            continue;
                        }

                        if ( uvIndex == -1 ) {
                            uvIndex = index;
                        }
                        else {
                            FBXImporter::LogWarn( "the UV channel named " + uvSet +
                                " appears at different positions in meshes, results will be wrong" );
                        }
                    }
                }
                else
                {
                    int index = -1;
                    for ( unsigned int i = 0; i < AI_MAX_NUMBER_OF_TEXTURECOORDS; ++i ) {
                        if ( mesh->GetTextureCoords( i ).empty() ) {
                            break;
                        }
                        const std::string& name = mesh->GetTextureCoordChannelName( i );
                        if ( name == uvSet ) {
                            index = static_cast<int>( i );
                            break;
                        }
                    }
                    if ( index == -1 ) {
                        FBXImporter::LogWarn( "did not find UV channel named " + uvSet + " in a mesh using this material" );
                    }

                    if ( uvIndex == -1 ) {
                        uvIndex = index;
                    }
                }

                if ( uvIndex == -1 ) {
                    FBXImporter::LogWarn( "failed to resolve UV channel " + uvSet + ", using first UV channel" );
                    uvIndex = 0;
                }
            }
        }

        out_mat->AddProperty( &uvIndex, 1, _AI_MATKEY_UVWSRC_BASE, target, texIndex );
    }
}

void FBXConverter::SetTextureProperties( aiMaterial* out_mat, const TextureMap& textures, const MeshGeometry* const mesh )
{
    TrySetTextureProperties( out_mat, textures, "DiffuseColor", aiTextureType_DIFFUSE, mesh );
    TrySetTextureProperties( out_mat, textures, "AmbientColor", aiTextureType_AMBIENT, mesh );
    TrySetTextureProperties( out_mat, textures, "EmissiveColor", aiTextureType_EMISSIVE, mesh );
    TrySetTextureProperties( out_mat, textures, "SpecularColor", aiTextureType_SPECULAR, mesh );
    TrySetTextureProperties( out_mat, textures, "SpecularFactor", aiTextureType_SPECULAR, mesh);
    TrySetTextureProperties( out_mat, textures, "TransparentColor", aiTextureType_OPACITY, mesh );
    TrySetTextureProperties( out_mat, textures, "ReflectionColor", aiTextureType_REFLECTION, mesh );
    TrySetTextureProperties( out_mat, textures, "DisplacementColor", aiTextureType_DISPLACEMENT, mesh );
    TrySetTextureProperties( out_mat, textures, "NormalMap", aiTextureType_NORMALS, mesh );
    TrySetTextureProperties( out_mat, textures, "Bump", aiTextureType_HEIGHT, mesh );
    TrySetTextureProperties( out_mat, textures, "ShininessExponent", aiTextureType_SHININESS, mesh );
}

void FBXConverter::SetTextureProperties( aiMaterial* out_mat, const LayeredTextureMap& layeredTextures, const MeshGeometry* const mesh )
{
    TrySetTextureProperties( out_mat, layeredTextures, "DiffuseColor", aiTextureType_DIFFUSE, mesh );
    TrySetTextureProperties( out_mat, layeredTextures, "AmbientColor", aiTextureType_AMBIENT, mesh );
    TrySetTextureProperties( out_mat, layeredTextures, "EmissiveColor", aiTextureType_EMISSIVE, mesh );
    TrySetTextureProperties( out_mat, layeredTextures, "SpecularColor", aiTextureType_SPECULAR, mesh );
    TrySetTextureProperties( out_mat, layeredTextures, "SpecularFactor", aiTextureType_SPECULAR, mesh);
    TrySetTextureProperties( out_mat, layeredTextures, "TransparentColor", aiTextureType_OPACITY, mesh );
    TrySetTextureProperties( out_mat, layeredTextures, "ReflectionColor", aiTextureType_REFLECTION, mesh );
    TrySetTextureProperties( out_mat, layeredTextures, "DisplacementColor", aiTextureType_DISPLACEMENT, mesh );
    TrySetTextureProperties( out_mat, layeredTextures, "NormalMap", aiTextureType_NORMALS, mesh );
    TrySetTextureProperties( out_mat, layeredTextures, "Bump", aiTextureType_HEIGHT, mesh );
    TrySetTextureProperties( out_mat, layeredTextures, "ShininessExponent", aiTextureType_SHININESS, mesh );
}

aiColor3D FBXConverter::GetColorPropertyFactored( const PropertyTable& props, const std::string& colorName,
    const std::string& factorName, bool& result, bool useTemplate )
{
    result = true;

    bool ok;
    aiVector3D BaseColor = PropertyGet<aiVector3D>( props, colorName, ok, useTemplate );
    if ( ! ok ) {
        result = false;
        return aiColor3D( 0.0f, 0.0f, 0.0f );
    }

    // if no factor name, return the colour as is
    if ( factorName.empty() ) {
        return aiColor3D( BaseColor.x, BaseColor.y, BaseColor.z );
    }

    // otherwise it should be multiplied by the factor, if found.
    float factor = PropertyGet<float>( props, factorName, ok, useTemplate );
    if ( ok ) {
        BaseColor *= factor;
    }
    return aiColor3D( BaseColor.x, BaseColor.y, BaseColor.z );
}

aiColor3D FBXConverter::GetColorPropertyFromMaterial( const PropertyTable& props, const std::string& baseName,
    bool& result )
{
    return GetColorPropertyFactored( props, baseName + "Color", baseName + "Factor", result, true );
}

aiColor3D FBXConverter::GetColorProperty( const PropertyTable& props, const std::string& colorName,
    bool& result, bool useTemplate )
{
    result = true;
    bool ok;
    const aiVector3D& ColorVec = PropertyGet<aiVector3D>( props, colorName, ok, useTemplate );
    if ( ! ok ) {
        result = false;
        return aiColor3D( 0.0f, 0.0f, 0.0f );
    }
    return aiColor3D( ColorVec.x, ColorVec.y, ColorVec.z );
}

void FBXConverter::SetShadingPropertiesCommon( aiMaterial* out_mat, const PropertyTable& props )
{
    // Set shading properties.
    // Modern FBX Files have two separate systems for defining these,
    // with only the more comprehensive one described in the property template.
    // Likely the other values are a legacy system,
    // which is still always exported by the official FBX SDK.
    //
    // Blender's FBX import and export mostly ignore this legacy system,
    // and as we only support recent versions of FBX anyway, we can do the same.
    bool ok;

    const aiColor3D& Diffuse = GetColorPropertyFromMaterial( props, "Diffuse", ok );
    if ( ok ) {
        out_mat->AddProperty( &Diffuse, 1, AI_MATKEY_COLOR_DIFFUSE );
    }

    const aiColor3D& Emissive = GetColorPropertyFromMaterial( props, "Emissive", ok );
    if ( ok ) {
        out_mat->AddProperty( &Emissive, 1, AI_MATKEY_COLOR_EMISSIVE );
    }

    const aiColor3D& Ambient = GetColorPropertyFromMaterial( props, "Ambient", ok );
    if ( ok ) {
        out_mat->AddProperty( &Ambient, 1, AI_MATKEY_COLOR_AMBIENT );
    }

    // we store specular factor as SHININESS_STRENGTH, so just get the color
    const aiColor3D& Specular = GetColorProperty( props, "SpecularColor", ok, true );
    if ( ok ) {
        out_mat->AddProperty( &Specular, 1, AI_MATKEY_COLOR_SPECULAR );
    }

    // and also try to get SHININESS_STRENGTH
    const float SpecularFactor = PropertyGet<float>( props, "SpecularFactor", ok, true );
    if ( ok ) {
        out_mat->AddProperty( &SpecularFactor, 1, AI_MATKEY_SHININESS_STRENGTH );
    }

    // and the specular exponent
    const float ShininessExponent = PropertyGet<float>( props, "ShininessExponent", ok );
    if ( ok ) {
        out_mat->AddProperty( &ShininessExponent, 1, AI_MATKEY_SHININESS );
    }

    // TransparentColor / TransparencyFactor... gee thanks FBX :rolleyes:
    const aiColor3D& Transparent = GetColorPropertyFactored( props, "TransparentColor", "TransparencyFactor", ok );
    float CalculatedOpacity = 1.0f;
    if ( ok ) {
        out_mat->AddProperty( &Transparent, 1, AI_MATKEY_COLOR_TRANSPARENT );
        // as calculated by FBX SDK 2017:
        CalculatedOpacity = 1.0f - ((Transparent.r + Transparent.g + Transparent.b) / 3.0f);
    }

    // use of TransparencyFactor is inconsistent.
    // Maya always stores it as 1.0,
    // so we can't use it to set AI_MATKEY_OPACITY.
    // Blender is more sensible and stores it as the alpha value.
    // However both the FBX SDK and Blender always write an additional
    // legacy "Opacity" field, so we can try to use that.
    //
    // If we can't find it,
    // we can fall back to the value which the FBX SDK calculates
    // from transparency colour (RGB) and factor (F) as
    // 1.0 - F*((R+G+B)/3).
    //
    // There's no consistent way to interpret this opacity value,
    // so it's up to clients to do the correct thing.
    const float Opacity = PropertyGet<float>( props, "Opacity", ok );
    if ( ok ) {
        out_mat->AddProperty( &Opacity, 1, AI_MATKEY_OPACITY );
    }
    else if ( CalculatedOpacity != 1.0 ) {
        out_mat->AddProperty( &CalculatedOpacity, 1, AI_MATKEY_OPACITY );
    }

    // reflection color and factor are stored separately
    const aiColor3D& Reflection = GetColorProperty( props, "ReflectionColor", ok, true );
    if ( ok ) {
        out_mat->AddProperty( &Reflection, 1, AI_MATKEY_COLOR_REFLECTIVE );
    }

    float ReflectionFactor = PropertyGet<float>( props, "ReflectionFactor", ok, true );
    if ( ok ) {
        out_mat->AddProperty( &ReflectionFactor, 1, AI_MATKEY_REFLECTIVITY );
    }

    const float BumpFactor = PropertyGet<float>(props, "BumpFactor", ok);
    if (ok) {
        out_mat->AddProperty(&BumpFactor, 1, AI_MATKEY_BUMPSCALING);
    }

    const float DispFactor = PropertyGet<float>(props, "DisplacementFactor", ok);
    if (ok) {
        out_mat->AddProperty(&DispFactor, 1, "$mat.displacementscaling", 0, 0);
    }
}


double FBXConverter::FrameRateToDouble( FileGlobalSettings::FrameRate fp, double customFPSVal ) {
    switch ( fp ) {
        case FileGlobalSettings::FrameRate_DEFAULT:
            return 1.0;

        case FileGlobalSettings::FrameRate_120:
            return 120.0;

        case FileGlobalSettings::FrameRate_100:
            return 100.0;

        case FileGlobalSettings::FrameRate_60:
            return 60.0;

        case FileGlobalSettings::FrameRate_50:
            return 50.0;

        case FileGlobalSettings::FrameRate_48:
            return 48.0;

        case FileGlobalSettings::FrameRate_30:
        case FileGlobalSettings::FrameRate_30_DROP:
            return 30.0;

        case FileGlobalSettings::FrameRate_NTSC_DROP_FRAME:
        case FileGlobalSettings::FrameRate_NTSC_FULL_FRAME:
            return 29.9700262;

        case FileGlobalSettings::FrameRate_PAL:
            return 25.0;

        case FileGlobalSettings::FrameRate_CINEMA:
            return 24.0;

        case FileGlobalSettings::FrameRate_1000:
            return 1000.0;

        case FileGlobalSettings::FrameRate_CINEMA_ND:
            return 23.976;

        case FileGlobalSettings::FrameRate_CUSTOM:
            return customFPSVal;

        case FileGlobalSettings::FrameRate_MAX: // this is to silence compiler warnings
            break;
    }

    ai_assert( false );

    return -1.0f;
}


void FBXConverter::ConvertAnimations()
{
    // first of all determine framerate
    const FileGlobalSettings::FrameRate fps = doc.GlobalSettings().TimeMode();
    const float custom = doc.GlobalSettings().CustomFrameRate();
    anim_fps = FrameRateToDouble( fps, custom );

    const std::vector<const AnimationStack*>& animations = doc.AnimationStacks();
    for( const AnimationStack* stack : animations ) {
        ConvertAnimationStack( *stack );
    }
}

std::string FBXConverter::FixNodeName( const std::string& name ) {
    // strip Model:: prefix, avoiding ambiguities (i.e. don't strip if
    // this causes ambiguities, well possible between empty identifiers,
    // such as "Model::" and ""). Make sure the behaviour is consistent
    // across multiple calls to FixNodeName().
    if ( name.substr( 0, 7 ) == "Model::" ) {
        std::string temp = name.substr( 7 );
        return temp;
    }

    return name;
}

void FBXConverter::ConvertAnimationStack( const AnimationStack& st )
{
    const AnimationLayerList& layers = st.Layers();
    if ( layers.empty() ) {
        return;
    }

    aiAnimation* const anim = new aiAnimation();
    animations.push_back( anim );

    // strip AnimationStack:: prefix
    std::string name = st.Name();
    if ( name.substr( 0, 16 ) == "AnimationStack::" ) {
        name = name.substr( 16 );
    }
    else if ( name.substr( 0, 11 ) == "AnimStack::" ) {
        name = name.substr( 11 );
    }

    anim->mName.Set( name );

    // need to find all nodes for which we need to generate node animations -
    // it may happen that we need to merge multiple layers, though.
    NodeMap node_map;

    // reverse mapping from curves to layers, much faster than querying
    // the FBX DOM for it.
    LayerMap layer_map;

    const char* prop_whitelist[] = {
        "Lcl Scaling",
        "Lcl Rotation",
        "Lcl Translation"
    };

    for( const AnimationLayer* layer : layers ) {
        ai_assert( layer );

        const AnimationCurveNodeList& nodes = layer->Nodes( prop_whitelist, 3 );
        for( const AnimationCurveNode* node : nodes ) {
            ai_assert( node );

            const Model* const model = dynamic_cast<const Model*>( node->Target() );
            // this can happen - it could also be a NodeAttribute (i.e. for camera animations)
            if ( !model ) {
                continue;
            }

            const std::string& name = FixNodeName( model->Name() );
            node_map[ name ].push_back( node );

            layer_map[ node ] = layer;
        }
    }

    // generate node animations
    std::vector<aiNodeAnim*> node_anims;

    double min_time = 1e10;
    double max_time = -1e10;

    int64_t start_time = st.LocalStart();
    int64_t stop_time = st.LocalStop();
    bool has_local_startstop = start_time != 0 || stop_time != 0;
    if ( !has_local_startstop ) {
        // no time range given, so accept every keyframe and use the actual min/max time
        // the numbers are INT64_MIN/MAX, the 20000 is for safety because GenerateNodeAnimations uses an epsilon of 10000
        start_time = -9223372036854775807ll + 20000;
        stop_time = 9223372036854775807ll - 20000;
    }

    try {
        for( const NodeMap::value_type& kv : node_map ) {
            GenerateNodeAnimations( node_anims,
                kv.first,
                kv.second,
                layer_map,
                start_time, stop_time,
                max_time,
                min_time );
        }
    }
    catch ( std::exception& ) {
        std::for_each( node_anims.begin(), node_anims.end(), Util::delete_fun<aiNodeAnim>() );
        throw;
    }

    if ( node_anims.size() ) {
        anim->mChannels = new aiNodeAnim*[ node_anims.size() ]();
        anim->mNumChannels = static_cast<unsigned int>( node_anims.size() );

        std::swap_ranges( node_anims.begin(), node_anims.end(), anim->mChannels );
    }
    else {
        // empty animations would fail validation, so drop them
        delete anim;
        animations.pop_back();
        FBXImporter::LogInfo( "ignoring empty AnimationStack (using IK?): " + name );
        return;
    }

    double start_time_fps = has_local_startstop ? (CONVERT_FBX_TIME(start_time) * anim_fps) : min_time;
    double stop_time_fps = has_local_startstop ? (CONVERT_FBX_TIME(stop_time) * anim_fps) : max_time;

    // adjust relative timing for animation
    for ( unsigned int c = 0; c < anim->mNumChannels; c++ ) {
        aiNodeAnim* channel = anim->mChannels[ c ];
        for ( uint32_t i = 0; i < channel->mNumPositionKeys; i++ )
            channel->mPositionKeys[ i ].mTime -= start_time_fps;
        for ( uint32_t i = 0; i < channel->mNumRotationKeys; i++ )
            channel->mRotationKeys[ i ].mTime -= start_time_fps;
        for ( uint32_t i = 0; i < channel->mNumScalingKeys; i++ )
            channel->mScalingKeys[ i ].mTime -= start_time_fps;
    }

    // for some mysterious reason, mDuration is simply the maximum key -- the
    // validator always assumes animations to start at zero.
    anim->mDuration = stop_time_fps - start_time_fps;
    anim->mTicksPerSecond = anim_fps;
}

#ifdef ASSIMP_BUILD_DEBUG
// ------------------------------------------------------------------------------------------------
// sanity check whether the input is ok
static void validateAnimCurveNodes( const std::vector<const AnimationCurveNode*>& curves,
    bool strictMode ) {
    const Object* target( NULL );
    for( const AnimationCurveNode* node : curves ) {
        if ( !target ) {
            target = node->Target();
        }
        if ( node->Target() != target ) {
            FBXImporter::LogWarn( "Node target is nullptr type." );
        }
        if ( strictMode ) {
            ai_assert( node->Target() == target );
        }
    }
}
#endif // ASSIMP_BUILD_DEBUG

// ------------------------------------------------------------------------------------------------
void FBXConverter::GenerateNodeAnimations( std::vector<aiNodeAnim*>& node_anims,
    const std::string& fixed_name,
    const std::vector<const AnimationCurveNode*>& curves,
    const LayerMap& layer_map,
    int64_t start, int64_t stop,
    double& max_time,
    double& min_time )
{

    NodeMap node_property_map;
    ai_assert( curves.size() );

#ifdef ASSIMP_BUILD_DEBUG
    validateAnimCurveNodes( curves, doc.Settings().strictMode );
#endif
    const AnimationCurveNode* curve_node = NULL;
    for( const AnimationCurveNode* node : curves ) {
        ai_assert( node );

        if ( node->TargetProperty().empty() ) {
            FBXImporter::LogWarn( "target property for animation curve not set: " + node->Name() );
            continue;
        }

        curve_node = node;
        if ( node->Curves().empty() ) {
            FBXImporter::LogWarn( "no animation curves assigned to AnimationCurveNode: " + node->Name() );
            continue;
        }

        node_property_map[ node->TargetProperty() ].push_back( node );
    }

    ai_assert( curve_node );
    ai_assert( curve_node->TargetAsModel() );

    const Model& target = *curve_node->TargetAsModel();

    // check for all possible transformation components
    NodeMap::const_iterator chain[ TransformationComp_MAXIMUM ];

    bool has_any = false;
    bool has_complex = false;

    for ( size_t i = 0; i < TransformationComp_MAXIMUM; ++i ) {
        const TransformationComp comp = static_cast<TransformationComp>( i );

        // inverse pivots don't exist in the input, we just generate them
        if ( comp == TransformationComp_RotationPivotInverse || comp == TransformationComp_ScalingPivotInverse ) {
            chain[ i ] = node_property_map.end();
            continue;
        }

        chain[ i ] = node_property_map.find( NameTransformationCompProperty( comp ) );
        if ( chain[ i ] != node_property_map.end() ) {

            // check if this curves contains redundant information by looking
            // up the corresponding node's transformation chain.
            if ( doc.Settings().optimizeEmptyAnimationCurves &&
                IsRedundantAnimationData( target, comp, ( *chain[ i ] ).second ) ) {

                FBXImporter::LogDebug( "dropping redundant animation channel for node " + target.Name() );
                continue;
            }

            has_any = true;

            if ( comp != TransformationComp_Rotation && comp != TransformationComp_Scaling && comp != TransformationComp_Translation )
            {
                has_complex = true;
            }
        }
    }

    if ( !has_any ) {
        FBXImporter::LogWarn( "ignoring node animation, did not find any transformation key frames" );
        return;
    }

    // this needs to play nicely with GenerateTransformationNodeChain() which will
    // be invoked _later_ (animations come first). If this node has only rotation,
    // scaling and translation _and_ there are no animated other components either,
    // we can use a single node and also a single node animation channel.
    if ( !has_complex && !NeedsComplexTransformationChain( target ) ) {

        aiNodeAnim* const nd = GenerateSimpleNodeAnim( fixed_name, target, chain,
            node_property_map.end(),
            layer_map,
            start, stop,
            max_time,
            min_time,
            true // input is TRS order, assimp is SRT
            );

        ai_assert( nd );
        if ( nd->mNumPositionKeys == 0 && nd->mNumRotationKeys == 0 && nd->mNumScalingKeys == 0 ) {
            delete nd;
        }
        else {
            node_anims.push_back( nd );
        }
        return;
    }

    // otherwise, things get gruesome and we need separate animation channels
    // for each part of the transformation chain. Remember which channels
    // we generated and pass this information to the node conversion
    // code to avoid nodes that have identity transform, but non-identity
    // animations, being dropped.
    unsigned int flags = 0, bit = 0x1;
    for ( size_t i = 0; i < TransformationComp_MAXIMUM; ++i, bit <<= 1 ) {
        const TransformationComp comp = static_cast<TransformationComp>( i );

        if ( chain[ i ] != node_property_map.end() ) {
            flags |= bit;

            ai_assert( comp != TransformationComp_RotationPivotInverse );
            ai_assert( comp != TransformationComp_ScalingPivotInverse );

            const std::string& chain_name = NameTransformationChainNode( fixed_name, comp );

            aiNodeAnim* na = nullptr;
            switch ( comp )
            {
            case TransformationComp_Rotation:
            case TransformationComp_PreRotation:
            case TransformationComp_PostRotation:
            case TransformationComp_GeometricRotation:
                na = GenerateRotationNodeAnim( chain_name,
                    target,
                    ( *chain[ i ] ).second,
                    layer_map,
                    start, stop,
                    max_time,
                    min_time );

                break;

            case TransformationComp_RotationOffset:
            case TransformationComp_RotationPivot:
            case TransformationComp_ScalingOffset:
            case TransformationComp_ScalingPivot:
            case TransformationComp_Translation:
            case TransformationComp_GeometricTranslation:
                na = GenerateTranslationNodeAnim( chain_name,
                    target,
                    ( *chain[ i ] ).second,
                    layer_map,
                    start, stop,
                    max_time,
                    min_time );

                // pivoting requires us to generate an implicit inverse channel to undo the pivot translation
                if ( comp == TransformationComp_RotationPivot ) {
                    const std::string& invName = NameTransformationChainNode( fixed_name,
                        TransformationComp_RotationPivotInverse );

                    aiNodeAnim* const inv = GenerateTranslationNodeAnim( invName,
                        target,
                        ( *chain[ i ] ).second,
                        layer_map,
                        start, stop,
                        max_time,
                        min_time,
                        true );

                    ai_assert( inv );
                    if ( inv->mNumPositionKeys == 0 && inv->mNumRotationKeys == 0 && inv->mNumScalingKeys == 0 ) {
                        delete inv;
                    }
                    else {
                        node_anims.push_back( inv );
                    }

                    ai_assert( TransformationComp_RotationPivotInverse > i );
                    flags |= bit << ( TransformationComp_RotationPivotInverse - i );
                }
                else if ( comp == TransformationComp_ScalingPivot ) {
                    const std::string& invName = NameTransformationChainNode( fixed_name,
                        TransformationComp_ScalingPivotInverse );

                    aiNodeAnim* const inv = GenerateTranslationNodeAnim( invName,
                        target,
                        ( *chain[ i ] ).second,
                        layer_map,
                        start, stop,
                        max_time,
                        min_time,
                        true );

                    ai_assert( inv );
                    if ( inv->mNumPositionKeys == 0 && inv->mNumRotationKeys == 0 && inv->mNumScalingKeys == 0 ) {
                        delete inv;
                    }
                    else {
                        node_anims.push_back( inv );
                    }

                    ai_assert( TransformationComp_RotationPivotInverse > i );
                    flags |= bit << ( TransformationComp_RotationPivotInverse - i );
                }

                break;

            case TransformationComp_Scaling:
            case TransformationComp_GeometricScaling:
                na = GenerateScalingNodeAnim( chain_name,
                    target,
                    ( *chain[ i ] ).second,
                    layer_map,
                    start, stop,
                    max_time,
                    min_time );

                break;

            default:
                ai_assert( false );
            }

            ai_assert( na );
            if ( na->mNumPositionKeys == 0 && na->mNumRotationKeys == 0 && na->mNumScalingKeys == 0 ) {
                delete na;
            }
            else {
                node_anims.push_back( na );
            }
            continue;
        }
    }

    node_anim_chain_bits[ fixed_name ] = flags;
}

bool FBXConverter::IsRedundantAnimationData( const Model& target,
        TransformationComp comp,
        const std::vector<const AnimationCurveNode*>& curves ) {
    ai_assert( curves.size() );

    // look for animation nodes with
    //  * sub channels for all relevant components set
    //  * one key/value pair per component
    //  * combined values match up the corresponding value in the bind pose node transformation
    // only such nodes are 'redundant' for this function.

    if ( curves.size() > 1 ) {
        return false;
    }

    const AnimationCurveNode& nd = *curves.front();
    const AnimationCurveMap& sub_curves = nd.Curves();

    const AnimationCurveMap::const_iterator dx = sub_curves.find( "d|X" );
    const AnimationCurveMap::const_iterator dy = sub_curves.find( "d|Y" );
    const AnimationCurveMap::const_iterator dz = sub_curves.find( "d|Z" );

    if ( dx == sub_curves.end() || dy == sub_curves.end() || dz == sub_curves.end() ) {
        return false;
    }

    const KeyValueList& vx = ( *dx ).second->GetValues();
    const KeyValueList& vy = ( *dy ).second->GetValues();
    const KeyValueList& vz = ( *dz ).second->GetValues();

    if ( vx.size() != 1 || vy.size() != 1 || vz.size() != 1 ) {
        return false;
    }

    const aiVector3D dyn_val = aiVector3D( vx[ 0 ], vy[ 0 ], vz[ 0 ] );
    const aiVector3D& static_val = PropertyGet<aiVector3D>( target.Props(),
        NameTransformationCompProperty( comp ),
        TransformationCompDefaultValue( comp )
        );

    const float epsilon = 1e-6f;
    return ( dyn_val - static_val ).SquareLength() < epsilon;
}


aiNodeAnim* FBXConverter::GenerateRotationNodeAnim( const std::string& name,
    const Model& target,
    const std::vector<const AnimationCurveNode*>& curves,
    const LayerMap& layer_map,
    int64_t start, int64_t stop,
    double& max_time,
    double& min_time )
{
    std::unique_ptr<aiNodeAnim> na( new aiNodeAnim() );
    na->mNodeName.Set( name );

    ConvertRotationKeys( na.get(), curves, layer_map, start, stop, max_time, min_time, target.RotationOrder() );

    // dummy scaling key
    na->mScalingKeys = new aiVectorKey[ 1 ];
    na->mNumScalingKeys = 1;

    na->mScalingKeys[ 0 ].mTime = 0.;
    na->mScalingKeys[ 0 ].mValue = aiVector3D( 1.0f, 1.0f, 1.0f );

    // dummy position key
    na->mPositionKeys = new aiVectorKey[ 1 ];
    na->mNumPositionKeys = 1;

    na->mPositionKeys[ 0 ].mTime = 0.;
    na->mPositionKeys[ 0 ].mValue = aiVector3D();

    return na.release();
}

aiNodeAnim* FBXConverter::GenerateScalingNodeAnim( const std::string& name,
    const Model& /*target*/,
    const std::vector<const AnimationCurveNode*>& curves,
    const LayerMap& layer_map,
    int64_t start, int64_t stop,
    double& max_time,
    double& min_time )
{
    std::unique_ptr<aiNodeAnim> na( new aiNodeAnim() );
    na->mNodeName.Set( name );

    ConvertScaleKeys( na.get(), curves, layer_map, start, stop, max_time, min_time );

    // dummy rotation key
    na->mRotationKeys = new aiQuatKey[ 1 ];
    na->mNumRotationKeys = 1;

    na->mRotationKeys[ 0 ].mTime = 0.;
    na->mRotationKeys[ 0 ].mValue = aiQuaternion();

    // dummy position key
    na->mPositionKeys = new aiVectorKey[ 1 ];
    na->mNumPositionKeys = 1;

    na->mPositionKeys[ 0 ].mTime = 0.;
    na->mPositionKeys[ 0 ].mValue = aiVector3D();

    return na.release();
}

aiNodeAnim* FBXConverter::GenerateTranslationNodeAnim( const std::string& name,
        const Model& /*target*/,
        const std::vector<const AnimationCurveNode*>& curves,
        const LayerMap& layer_map,
        int64_t start, int64_t stop,
        double& max_time,
        double& min_time,
        bool inverse ) {
    std::unique_ptr<aiNodeAnim> na( new aiNodeAnim() );
    na->mNodeName.Set( name );

    ConvertTranslationKeys( na.get(), curves, layer_map, start, stop, max_time, min_time );

    if ( inverse ) {
        for ( unsigned int i = 0; i < na->mNumPositionKeys; ++i ) {
            na->mPositionKeys[ i ].mValue *= -1.0f;
        }
    }

    // dummy scaling key
    na->mScalingKeys = new aiVectorKey[ 1 ];
    na->mNumScalingKeys = 1;

    na->mScalingKeys[ 0 ].mTime = 0.;
    na->mScalingKeys[ 0 ].mValue = aiVector3D( 1.0f, 1.0f, 1.0f );

    // dummy rotation key
    na->mRotationKeys = new aiQuatKey[ 1 ];
    na->mNumRotationKeys = 1;

    na->mRotationKeys[ 0 ].mTime = 0.;
    na->mRotationKeys[ 0 ].mValue = aiQuaternion();

    return na.release();
}

aiNodeAnim* FBXConverter::GenerateSimpleNodeAnim( const std::string& name,
    const Model& target,
    NodeMap::const_iterator chain[ TransformationComp_MAXIMUM ],
    NodeMap::const_iterator iter_end,
    const LayerMap& layer_map,
    int64_t start, int64_t stop,
    double& max_time,
    double& min_time,
    bool reverse_order )

{
    std::unique_ptr<aiNodeAnim> na( new aiNodeAnim() );
    na->mNodeName.Set( name );

    const PropertyTable& props = target.Props();

    // need to convert from TRS order to SRT?
    if ( reverse_order ) {

        aiVector3D def_scale = PropertyGet( props, "Lcl Scaling", aiVector3D( 1.f, 1.f, 1.f ) );
        aiVector3D def_translate = PropertyGet( props, "Lcl Translation", aiVector3D( 0.f, 0.f, 0.f ) );
        aiVector3D def_rot = PropertyGet( props, "Lcl Rotation", aiVector3D( 0.f, 0.f, 0.f ) );

        KeyFrameListList scaling;
        KeyFrameListList translation;
        KeyFrameListList rotation;

        if ( chain[ TransformationComp_Scaling ] != iter_end ) {
            scaling = GetKeyframeList( ( *chain[ TransformationComp_Scaling ] ).second, start, stop );
        }

        if ( chain[ TransformationComp_Translation ] != iter_end ) {
            translation = GetKeyframeList( ( *chain[ TransformationComp_Translation ] ).second, start, stop );
        }

        if ( chain[ TransformationComp_Rotation ] != iter_end ) {
            rotation = GetKeyframeList( ( *chain[ TransformationComp_Rotation ] ).second, start, stop );
        }

        KeyFrameListList joined;
        joined.insert( joined.end(), scaling.begin(), scaling.end() );
        joined.insert( joined.end(), translation.begin(), translation.end() );
        joined.insert( joined.end(), rotation.begin(), rotation.end() );

        const KeyTimeList& times = GetKeyTimeList( joined );

        aiQuatKey* out_quat = new aiQuatKey[ times.size() ];
        aiVectorKey* out_scale = new aiVectorKey[ times.size() ];
        aiVectorKey* out_translation = new aiVectorKey[ times.size() ];

        if ( times.size() )
        {
            ConvertTransformOrder_TRStoSRT( out_quat, out_scale, out_translation,
                scaling,
                translation,
                rotation,
                times,
                max_time,
                min_time,
                target.RotationOrder(),
                def_scale,
                def_translate,
                def_rot );
        }

        // XXX remove duplicates / redundant keys which this operation did
        // likely produce if not all three channels were equally dense.

        na->mNumScalingKeys = static_cast<unsigned int>( times.size() );
        na->mNumRotationKeys = na->mNumScalingKeys;
        na->mNumPositionKeys = na->mNumScalingKeys;

        na->mScalingKeys = out_scale;
        na->mRotationKeys = out_quat;
        na->mPositionKeys = out_translation;
    }
    else {

        // if a particular transformation is not given, grab it from
        // the corresponding node to meet the semantics of aiNodeAnim,
        // which requires all of rotation, scaling and translation
        // to be set.
        if ( chain[ TransformationComp_Scaling ] != iter_end ) {
            ConvertScaleKeys( na.get(), ( *chain[ TransformationComp_Scaling ] ).second,
                layer_map,
                start, stop,
                max_time,
                min_time );
        }
        else {
            na->mScalingKeys = new aiVectorKey[ 1 ];
            na->mNumScalingKeys = 1;

            na->mScalingKeys[ 0 ].mTime = 0.;
            na->mScalingKeys[ 0 ].mValue = PropertyGet( props, "Lcl Scaling",
                aiVector3D( 1.f, 1.f, 1.f ) );
        }

        if ( chain[ TransformationComp_Rotation ] != iter_end ) {
            ConvertRotationKeys( na.get(), ( *chain[ TransformationComp_Rotation ] ).second,
                layer_map,
                start, stop,
                max_time,
                min_time,
                target.RotationOrder() );
        }
        else {
            na->mRotationKeys = new aiQuatKey[ 1 ];
            na->mNumRotationKeys = 1;

            na->mRotationKeys[ 0 ].mTime = 0.;
            na->mRotationKeys[ 0 ].mValue = EulerToQuaternion(
                PropertyGet( props, "Lcl Rotation", aiVector3D( 0.f, 0.f, 0.f ) ),
                target.RotationOrder() );
        }

        if ( chain[ TransformationComp_Translation ] != iter_end ) {
            ConvertTranslationKeys( na.get(), ( *chain[ TransformationComp_Translation ] ).second,
                layer_map,
                start, stop,
                max_time,
                min_time );
        }
        else {
            na->mPositionKeys = new aiVectorKey[ 1 ];
            na->mNumPositionKeys = 1;

            na->mPositionKeys[ 0 ].mTime = 0.;
            na->mPositionKeys[ 0 ].mValue = PropertyGet( props, "Lcl Translation",
                aiVector3D( 0.f, 0.f, 0.f ) );
        }

    }
    return na.release();
}

FBXConverter::KeyFrameListList FBXConverter::GetKeyframeList( const std::vector<const AnimationCurveNode*>& nodes, int64_t start, int64_t stop )
{
    KeyFrameListList inputs;
    inputs.reserve( nodes.size() * 3 );

    //give some breathing room for rounding errors
    int64_t adj_start = start - 10000;
    int64_t adj_stop = stop + 10000;

    for( const AnimationCurveNode* node : nodes ) {
        ai_assert( node );

        const AnimationCurveMap& curves = node->Curves();
        for( const AnimationCurveMap::value_type& kv : curves ) {

            unsigned int mapto;
            if ( kv.first == "d|X" ) {
                mapto = 0;
            }
            else if ( kv.first == "d|Y" ) {
                mapto = 1;
            }
            else if ( kv.first == "d|Z" ) {
                mapto = 2;
            }
            else {
                FBXImporter::LogWarn( "ignoring scale animation curve, did not recognize target component" );
                continue;
            }

            const AnimationCurve* const curve = kv.second;
            ai_assert( curve->GetKeys().size() == curve->GetValues().size() && curve->GetKeys().size() );

            //get values within the start/stop time window
            std::shared_ptr<KeyTimeList> Keys( new KeyTimeList() );
            std::shared_ptr<KeyValueList> Values( new KeyValueList() );
            const size_t count = curve->GetKeys().size();
            Keys->reserve( count );
            Values->reserve( count );
            for (size_t n = 0; n < count; n++ )
            {
                int64_t k = curve->GetKeys().at( n );
                if ( k >= adj_start && k <= adj_stop )
                {
                    Keys->push_back( k );
                    Values->push_back( curve->GetValues().at( n ) );
                }
            }

            inputs.push_back( std::make_tuple( Keys, Values, mapto ) );
        }
    }
    return inputs; // pray for NRVO :-)
}


KeyTimeList FBXConverter::GetKeyTimeList( const KeyFrameListList& inputs ) {
    ai_assert( !inputs.empty() );

    // reserve some space upfront - it is likely that the key-frame lists
    // have matching time values, so max(of all key-frame lists) should
    // be a good estimate.
    KeyTimeList keys;

    size_t estimate = 0;
    for( const KeyFrameList& kfl : inputs ) {
        estimate = std::max( estimate, std::get<0>(kfl)->size() );
    }

    keys.reserve( estimate );

    std::vector<unsigned int> next_pos;
    next_pos.resize( inputs.size(), 0 );

    const size_t count = inputs.size();
    while ( true ) {

        int64_t min_tick = std::numeric_limits<int64_t>::max();
        for ( size_t i = 0; i < count; ++i ) {
            const KeyFrameList& kfl = inputs[ i ];

            if ( std::get<0>(kfl)->size() > next_pos[ i ] && std::get<0>(kfl)->at( next_pos[ i ] ) < min_tick ) {
                min_tick = std::get<0>(kfl)->at( next_pos[ i ] );
            }
        }

        if ( min_tick == std::numeric_limits<int64_t>::max() ) {
            break;
        }
        keys.push_back( min_tick );

        for ( size_t i = 0; i < count; ++i ) {
            const KeyFrameList& kfl = inputs[ i ];


            while ( std::get<0>(kfl)->size() > next_pos[ i ] && std::get<0>(kfl)->at( next_pos[ i ] ) == min_tick ) {
                ++next_pos[ i ];
            }
        }
    }

    return keys;
}

void FBXConverter::InterpolateKeys( aiVectorKey* valOut, const KeyTimeList& keys, const KeyFrameListList& inputs,
        const aiVector3D& def_value,
        double& max_time,
        double& min_time ) {
    ai_assert( !keys.empty() );
    ai_assert( nullptr != valOut );

    std::vector<unsigned int> next_pos;
    const size_t count( inputs.size() );

    next_pos.resize( inputs.size(), 0 );

    for( KeyTimeList::value_type time : keys ) {
        ai_real result[ 3 ] = { def_value.x, def_value.y, def_value.z };

        for ( size_t i = 0; i < count; ++i ) {
            const KeyFrameList& kfl = inputs[ i ];

            const size_t ksize = std::get<0>(kfl)->size();
            if (ksize == 0) {
                continue;
            }
            if ( ksize > next_pos[ i ] && std::get<0>(kfl)->at( next_pos[ i ] ) == time ) {
                ++next_pos[ i ];
            }

            const size_t id0 = next_pos[ i ]>0 ? next_pos[ i ] - 1 : 0;
            const size_t id1 = next_pos[ i ] == ksize ? ksize - 1 : next_pos[ i ];

            // use lerp for interpolation
            const KeyValueList::value_type valueA = std::get<1>(kfl)->at( id0 );
            const KeyValueList::value_type valueB = std::get<1>(kfl)->at( id1 );

            const KeyTimeList::value_type timeA = std::get<0>(kfl)->at( id0 );
            const KeyTimeList::value_type timeB = std::get<0>(kfl)->at( id1 );

            const ai_real factor = timeB == timeA ? ai_real(0.) : static_cast<ai_real>( ( time - timeA ) ) / ( timeB - timeA );
            const ai_real interpValue = static_cast<ai_real>( valueA + ( valueB - valueA ) * factor );

            result[ std::get<2>(kfl) ] = interpValue;
        }

        // magic value to convert fbx times to seconds
        valOut->mTime = CONVERT_FBX_TIME( time ) * anim_fps;

        min_time = std::min( min_time, valOut->mTime );
        max_time = std::max( max_time, valOut->mTime );

        valOut->mValue.x = result[ 0 ];
        valOut->mValue.y = result[ 1 ];
        valOut->mValue.z = result[ 2 ];

        ++valOut;
    }
}

void FBXConverter::InterpolateKeys( aiQuatKey* valOut, const KeyTimeList& keys, const KeyFrameListList& inputs,
    const aiVector3D& def_value,
    double& maxTime,
    double& minTime,
    Model::RotOrder order )
{
    ai_assert( !keys.empty() );
    ai_assert( nullptr != valOut );

    std::unique_ptr<aiVectorKey[]> temp( new aiVectorKey[ keys.size() ] );
    InterpolateKeys( temp.get(), keys, inputs, def_value, maxTime, minTime );

    aiMatrix4x4 m;

    aiQuaternion lastq;

    for ( size_t i = 0, c = keys.size(); i < c; ++i ) {

        valOut[ i ].mTime = temp[ i ].mTime;

        GetRotationMatrix( order, temp[ i ].mValue, m );
        aiQuaternion quat = aiQuaternion( aiMatrix3x3( m ) );

        // take shortest path by checking the inner product
        // http://www.3dkingdoms.com/weekly/weekly.php?a=36
        if ( quat.x * lastq.x + quat.y * lastq.y + quat.z * lastq.z + quat.w * lastq.w < 0 )
        {
            quat.x = -quat.x;
            quat.y = -quat.y;
            quat.z = -quat.z;
            quat.w = -quat.w;
        }
        lastq = quat;

        valOut[ i ].mValue = quat;
    }
}

void FBXConverter::ConvertTransformOrder_TRStoSRT( aiQuatKey* out_quat, aiVectorKey* out_scale,
    aiVectorKey* out_translation,
    const KeyFrameListList& scaling,
    const KeyFrameListList& translation,
    const KeyFrameListList& rotation,
    const KeyTimeList& times,
    double& maxTime,
    double& minTime,
    Model::RotOrder order,
    const aiVector3D& def_scale,
    const aiVector3D& def_translate,
    const aiVector3D& def_rotation )
{
    if ( rotation.size() ) {
        InterpolateKeys( out_quat, times, rotation, def_rotation, maxTime, minTime, order );
    }
    else {
        for ( size_t i = 0; i < times.size(); ++i ) {
            out_quat[ i ].mTime = CONVERT_FBX_TIME( times[ i ] ) * anim_fps;
            out_quat[ i ].mValue = EulerToQuaternion( def_rotation, order );
        }
    }

    if ( scaling.size() ) {
        InterpolateKeys( out_scale, times, scaling, def_scale, maxTime, minTime );
    }
    else {
        for ( size_t i = 0; i < times.size(); ++i ) {
            out_scale[ i ].mTime = CONVERT_FBX_TIME( times[ i ] ) * anim_fps;
            out_scale[ i ].mValue = def_scale;
        }
    }

    if ( translation.size() ) {
        InterpolateKeys( out_translation, times, translation, def_translate, maxTime, minTime );
    }
    else {
        for ( size_t i = 0; i < times.size(); ++i ) {
            out_translation[ i ].mTime = CONVERT_FBX_TIME( times[ i ] ) * anim_fps;
            out_translation[ i ].mValue = def_translate;
        }
    }

    const size_t count = times.size();
    for ( size_t i = 0; i < count; ++i ) {
        aiQuaternion& r = out_quat[ i ].mValue;
        aiVector3D& s = out_scale[ i ].mValue;
        aiVector3D& t = out_translation[ i ].mValue;

        aiMatrix4x4 mat, temp;
        aiMatrix4x4::Translation( t, mat );
        mat *= aiMatrix4x4( r.GetMatrix() );
        mat *= aiMatrix4x4::Scaling( s, temp );

        mat.Decompose( s, r, t );
    }
}

aiQuaternion FBXConverter::EulerToQuaternion( const aiVector3D& rot, Model::RotOrder order )
{
    aiMatrix4x4 m;
    GetRotationMatrix( order, rot, m );

    return aiQuaternion( aiMatrix3x3( m ) );
}

void FBXConverter::ConvertScaleKeys( aiNodeAnim* na, const std::vector<const AnimationCurveNode*>& nodes, const LayerMap& /*layers*/,
    int64_t start, int64_t stop,
    double& maxTime,
    double& minTime )
{
    ai_assert( nodes.size() );

    // XXX for now, assume scale should be blended geometrically (i.e. two
    // layers should be multiplied with each other). There is a FBX
    // property in the layer to specify the behaviour, though.

    const KeyFrameListList& inputs = GetKeyframeList( nodes, start, stop );
    const KeyTimeList& keys = GetKeyTimeList( inputs );

    na->mNumScalingKeys = static_cast<unsigned int>( keys.size() );
    na->mScalingKeys = new aiVectorKey[ keys.size() ];
    if ( keys.size() > 0 )
        InterpolateKeys( na->mScalingKeys, keys, inputs, aiVector3D( 1.0f, 1.0f, 1.0f ), maxTime, minTime );
}

void FBXConverter::ConvertTranslationKeys( aiNodeAnim* na, const std::vector<const AnimationCurveNode*>& nodes,
    const LayerMap& /*layers*/,
    int64_t start, int64_t stop,
    double& maxTime,
    double& minTime )
{
    ai_assert( nodes.size() );

    // XXX see notes in ConvertScaleKeys()
    const KeyFrameListList& inputs = GetKeyframeList( nodes, start, stop );
    const KeyTimeList& keys = GetKeyTimeList( inputs );

    na->mNumPositionKeys = static_cast<unsigned int>( keys.size() );
    na->mPositionKeys = new aiVectorKey[ keys.size() ];
    if ( keys.size() > 0 )
        InterpolateKeys( na->mPositionKeys, keys, inputs, aiVector3D( 0.0f, 0.0f, 0.0f ), maxTime, minTime );
}

void FBXConverter::ConvertRotationKeys( aiNodeAnim* na, const std::vector<const AnimationCurveNode*>& nodes,
    const LayerMap& /*layers*/,
    int64_t start, int64_t stop,
    double& maxTime,
    double& minTime,
    Model::RotOrder order )
{
    ai_assert( nodes.size() );

    // XXX see notes in ConvertScaleKeys()
    const std::vector< KeyFrameList >& inputs = GetKeyframeList( nodes, start, stop );
    const KeyTimeList& keys = GetKeyTimeList( inputs );

    na->mNumRotationKeys = static_cast<unsigned int>( keys.size() );
    na->mRotationKeys = new aiQuatKey[ keys.size() ];
    if (!keys.empty()) {
        InterpolateKeys(na->mRotationKeys, keys, inputs, aiVector3D(0.0f, 0.0f, 0.0f), maxTime, minTime, order);
    }
}

void FBXConverter::ConvertGlobalSettings() {
    if (nullptr == out) {
        return;
    }

    out->mMetaData = aiMetadata::Alloc(1);
    unsigned int index(0);
    const double unitScalFactor(doc.GlobalSettings().UnitScaleFactor());
    out->mMetaData->Set(index, "UnitScaleFactor", unitScalFactor);
}

void FBXConverter::TransferDataToScene()
{
    ai_assert( !out->mMeshes );
    ai_assert( !out->mNumMeshes );

    // note: the trailing () ensures initialization with NULL - not
    // many C++ users seem to know this, so pointing it out to avoid
    // confusion why this code works.

    if ( meshes.size() ) {
        out->mMeshes = new aiMesh*[ meshes.size() ]();
        out->mNumMeshes = static_cast<unsigned int>( meshes.size() );

        std::swap_ranges( meshes.begin(), meshes.end(), out->mMeshes );
    }

    if ( materials.size() ) {
        out->mMaterials = new aiMaterial*[ materials.size() ]();
        out->mNumMaterials = static_cast<unsigned int>( materials.size() );

        std::swap_ranges( materials.begin(), materials.end(), out->mMaterials );
    }

    if ( animations.size() ) {
        out->mAnimations = new aiAnimation*[ animations.size() ]();
        out->mNumAnimations = static_cast<unsigned int>( animations.size() );

        std::swap_ranges( animations.begin(), animations.end(), out->mAnimations );
    }

    if ( lights.size() ) {
        out->mLights = new aiLight*[ lights.size() ]();
        out->mNumLights = static_cast<unsigned int>( lights.size() );

        std::swap_ranges( lights.begin(), lights.end(), out->mLights );
    }

    if ( cameras.size() ) {
        out->mCameras = new aiCamera*[ cameras.size() ]();
        out->mNumCameras = static_cast<unsigned int>( cameras.size() );

        std::swap_ranges( cameras.begin(), cameras.end(), out->mCameras );
    }

    if ( textures.size() ) {
        out->mTextures = new aiTexture*[ textures.size() ]();
        out->mNumTextures = static_cast<unsigned int>( textures.size() );

        std::swap_ranges( textures.begin(), textures.end(), out->mTextures );
    }
}

// ------------------------------------------------------------------------------------------------
void ConvertToAssimpScene(aiScene* out, const Document& doc)
{
    FBXConverter converter(out,doc);
}

} // !FBX
} // !Assimp

#endif