assimp.assimp/code/AssetLib/glTF2/glTF2Exporter.cpp

/*
Open Asset Import Library (assimp)
----------------------------------------------------------------------

Copyright (c) 2006-2021, assimp team


All rights reserved.

Redistribution and use of this software in source and binary forms,
with or without modification, are permitted provided that the
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* Redistributions of source code must retain the above
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following disclaimer.

* Redistributions in binary form must reproduce the above
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contributors may be used to endorse or promote products
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"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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*/
#ifndef ASSIMP_BUILD_NO_EXPORT
#ifndef ASSIMP_BUILD_NO_GLTF_EXPORTER

#include "AssetLib/glTF2/glTF2Exporter.h"
#include "AssetLib/glTF2/glTF2AssetWriter.h"
#include "PostProcessing/SplitLargeMeshes.h"

#include <assimp/commonMetaData.h>
#include <assimp/Exceptional.h>
#include <assimp/StringComparison.h>
#include <assimp/ByteSwapper.h>
#include <assimp/SceneCombiner.h>
#include <assimp/version.h>
#include <assimp/IOSystem.hpp>
#include <assimp/Exporter.hpp>
#include <assimp/material.h>
#include <assimp/scene.h>

// Header files, standard library.
#include <memory>
#include <limits>
#include <inttypes.h>

using namespace rapidjson;

using namespace Assimp;
using namespace glTF2;

namespace Assimp {

    // ------------------------------------------------------------------------------------------------
    // Worker function for exporting a scene to GLTF. Prototyped and registered in Exporter.cpp
    void ExportSceneGLTF2(const char* pFile, IOSystem* pIOSystem, const aiScene* pScene, const ExportProperties* pProperties)
    {
        // invoke the exporter
        glTF2Exporter exporter(pFile, pIOSystem, pScene, pProperties, false);
    }

    // ------------------------------------------------------------------------------------------------
    // Worker function for exporting a scene to GLB. Prototyped and registered in Exporter.cpp
    void ExportSceneGLB2(const char* pFile, IOSystem* pIOSystem, const aiScene* pScene, const ExportProperties* pProperties)
    {
        // invoke the exporter
        glTF2Exporter exporter(pFile, pIOSystem, pScene, pProperties, true);
    }

} // end of namespace Assimp

glTF2Exporter::glTF2Exporter(const char* filename, IOSystem* pIOSystem, const aiScene* pScene,
    const ExportProperties* pProperties, bool isBinary)
    : mFilename(filename)
    , mIOSystem(pIOSystem)
    , mScene(pScene)
    , mProperties(pProperties)
    , mAsset(new Asset(pIOSystem))
{
    // Always on as our triangulation process is aware of this type of encoding
    mAsset->extensionsUsed.FB_ngon_encoding = true;

    if (isBinary) {
        mAsset->SetAsBinary();
    }

    ExportMetadata();

    ExportMaterials();

    if (mScene->mRootNode) {
        ExportNodeHierarchy(mScene->mRootNode);
    }

    ExportMeshes();
    MergeMeshes();

    ExportScene();

    ExportAnimations();

    // export extras
    if(mProperties->HasPropertyCallback("extras"))
    {
        std::function<void*(void*)> ExportExtras = mProperties->GetPropertyCallback("extras");
        mAsset->extras = (rapidjson::Value*)ExportExtras(0);
    }

    AssetWriter writer(*mAsset);

    if (isBinary) {
        writer.WriteGLBFile(filename);
    } else {
        writer.WriteFile(filename);
    }
}

glTF2Exporter::~glTF2Exporter() {
    // empty
}

/*
 * Copy a 4x4 matrix from struct aiMatrix to typedef mat4.
 * Also converts from row-major to column-major storage.
 */
static void CopyValue(const aiMatrix4x4& v, mat4& o) {
    o[ 0] = v.a1; o[ 1] = v.b1; o[ 2] = v.c1; o[ 3] = v.d1;
    o[ 4] = v.a2; o[ 5] = v.b2; o[ 6] = v.c2; o[ 7] = v.d2;
    o[ 8] = v.a3; o[ 9] = v.b3; o[10] = v.c3; o[11] = v.d3;
    o[12] = v.a4; o[13] = v.b4; o[14] = v.c4; o[15] = v.d4;
}

static void CopyValue(const aiMatrix4x4& v, aiMatrix4x4& o) {
    memcpy(&o, &v, sizeof(aiMatrix4x4));
}

static void IdentityMatrix4(mat4& o) {
    o[ 0] = 1; o[ 1] = 0; o[ 2] = 0; o[ 3] = 0;
    o[ 4] = 0; o[ 5] = 1; o[ 6] = 0; o[ 7] = 0;
    o[ 8] = 0; o[ 9] = 0; o[10] = 1; o[11] = 0;
    o[12] = 0; o[13] = 0; o[14] = 0; o[15] = 1;
}

template<typename T>
void SetAccessorRange(Ref<Accessor> acc, void* data, size_t count,
	unsigned int numCompsIn, unsigned int numCompsOut)
{
	ai_assert(numCompsOut <= numCompsIn);

	// Allocate and initialize with large values.
	for (unsigned int i = 0 ; i < numCompsOut ; i++) {
		acc->min.push_back( std::numeric_limits<double>::max());
		acc->max.push_back(-std::numeric_limits<double>::max());
	}

	size_t totalComps = count * numCompsIn;
	T* buffer_ptr = static_cast<T*>(data);
	T* buffer_end = buffer_ptr + totalComps;

	// Search and set extreme values.
	for (; buffer_ptr < buffer_end ; buffer_ptr += numCompsIn) {
		for (unsigned int j = 0 ; j < numCompsOut ; j++) {
			double valueTmp = buffer_ptr[j];

			// Gracefully tolerate rogue NaN's in buffer data
			// Any NaNs/Infs introduced in accessor bounds will end up in
			// document and prevent rapidjson from writing out valid JSON
			if (!std::isfinite(valueTmp)) {
				continue;
			}

			if (valueTmp < acc->min[j]) {
				acc->min[j] = valueTmp;
			}
			if (valueTmp > acc->max[j]) {
				acc->max[j] = valueTmp;
			}
		}
	}
}

inline void SetAccessorRange(ComponentType compType, Ref<Accessor> acc, void* data,
		size_t count, unsigned int numCompsIn, unsigned int numCompsOut)
{
	switch (compType) {
		case ComponentType_SHORT:
			SetAccessorRange<short>(acc, data, count, numCompsIn, numCompsOut);
			return;
		case ComponentType_UNSIGNED_SHORT:
			SetAccessorRange<unsigned short>(acc, data, count, numCompsIn, numCompsOut);
			return;
		case ComponentType_UNSIGNED_INT:
			SetAccessorRange<unsigned int>(acc, data, count, numCompsIn, numCompsOut);
			return;
		case ComponentType_FLOAT:
			SetAccessorRange<float>(acc, data, count, numCompsIn, numCompsOut);
			return;
		case ComponentType_BYTE:
			SetAccessorRange<int8_t>(acc, data, count, numCompsIn, numCompsOut);
			return;
		case ComponentType_UNSIGNED_BYTE:
			SetAccessorRange<uint8_t>(acc, data, count, numCompsIn, numCompsOut);
			return;
	}
}

// compute the (data-dataBase), store the non-zero data items
template <typename T>
size_t NZDiff(void *data, void *dataBase, size_t count, unsigned int numCompsIn, unsigned int numCompsOut, void *&outputNZDiff, void *&outputNZIdx) {
    std::vector<T> vNZDiff;
    std::vector<unsigned short> vNZIdx;
    size_t totalComps = count * numCompsIn;
    T *bufferData_ptr = static_cast<T *>(data);
    T *bufferData_end = bufferData_ptr + totalComps;
    T *bufferBase_ptr = static_cast<T *>(dataBase);

    // Search and set extreme values.
    for (short idx = 0; bufferData_ptr < bufferData_end; idx += 1, bufferData_ptr += numCompsIn) {
        bool bNonZero = false;

        //for the data, check any component Non Zero
        for (unsigned int j = 0; j < numCompsOut; j++) {
            double valueData = bufferData_ptr[j];
            double valueBase = bufferBase_ptr ? bufferBase_ptr[j] : 0;
            if ((valueData - valueBase) != 0) {
                bNonZero = true;
                break;
            }
        }

        //all zeros, continue
        if (!bNonZero)
            continue;

        //non zero, store the data
        for (unsigned int j = 0; j < numCompsOut; j++) {
            T valueData = bufferData_ptr[j];
            T valueBase = bufferBase_ptr ? bufferBase_ptr[j] : 0;
            vNZDiff.push_back(valueData - valueBase);
        }
        vNZIdx.push_back(idx);
    }

    //avoid all-0, put 1 item
    if (vNZDiff.size() == 0) {
        for (unsigned int j = 0; j < numCompsOut; j++)
            vNZDiff.push_back(0);
        vNZIdx.push_back(0);
    }

    //process data
    outputNZDiff = new T[vNZDiff.size()];
    memcpy(outputNZDiff, vNZDiff.data(), vNZDiff.size() * sizeof(T));

    outputNZIdx = new unsigned short[vNZIdx.size()];
    memcpy(outputNZIdx, vNZIdx.data(), vNZIdx.size() * sizeof(unsigned short));
    return vNZIdx.size();
}

inline size_t NZDiff(ComponentType compType, void *data, void *dataBase, size_t count, unsigned int numCompsIn, unsigned int numCompsOut, void *&nzDiff, void *&nzIdx) {
    switch (compType) {
    case ComponentType_SHORT:
        return NZDiff<short>(data, dataBase, count, numCompsIn, numCompsOut, nzDiff, nzIdx);
    case ComponentType_UNSIGNED_SHORT:
        return NZDiff<unsigned short>(data, dataBase, count, numCompsIn, numCompsOut, nzDiff, nzIdx);
    case ComponentType_UNSIGNED_INT:
        return NZDiff<unsigned int>(data, dataBase, count, numCompsIn, numCompsOut, nzDiff, nzIdx);
    case ComponentType_FLOAT:
        return NZDiff<float>(data, dataBase, count, numCompsIn, numCompsOut, nzDiff, nzIdx);
    case ComponentType_BYTE:
        return NZDiff<int8_t>(data, dataBase, count, numCompsIn, numCompsOut, nzDiff, nzIdx);
    case ComponentType_UNSIGNED_BYTE:
        return NZDiff<uint8_t>(data, dataBase, count, numCompsIn, numCompsOut, nzDiff, nzIdx);
    }
    return 0;
}

inline Ref<Accessor> ExportDataSparse(Asset &a, std::string &meshName, Ref<Buffer> &buffer,
        size_t count, void *data, AttribType::Value typeIn, AttribType::Value typeOut, ComponentType compType, BufferViewTarget target = BufferViewTarget_NONE, void *dataBase = 0) {
    if (!count || !data) {
        return Ref<Accessor>();
    }

    unsigned int numCompsIn = AttribType::GetNumComponents(typeIn);
    unsigned int numCompsOut = AttribType::GetNumComponents(typeOut);
    unsigned int bytesPerComp = ComponentTypeSize(compType);

    // accessor
    Ref<Accessor> acc = a.accessors.Create(a.FindUniqueID(meshName, "accessor"));

    // if there is a basic data vector
    if (dataBase) {
        size_t base_offset = buffer->byteLength;
        size_t base_padding = base_offset % bytesPerComp;
        base_offset += base_padding;
        size_t base_length = count * numCompsOut * bytesPerComp;
        buffer->Grow(base_length + base_padding);

        Ref<BufferView> bv = a.bufferViews.Create(a.FindUniqueID(meshName, "view"));
        bv->buffer = buffer;
        bv->byteOffset = base_offset;
        bv->byteLength = base_length; //! The target that the WebGL buffer should be bound to.
        bv->byteStride = 0;
        bv->target = target;
        acc->bufferView = bv;
        acc->WriteData(count, dataBase, numCompsIn * bytesPerComp);
    }
    acc->byteOffset = 0;
    acc->componentType = compType;
    acc->count = count;
    acc->type = typeOut;

    if (data) {
        void *nzDiff = 0, *nzIdx = 0;
        size_t nzCount = NZDiff(compType, data, dataBase, count, numCompsIn, numCompsOut, nzDiff, nzIdx);
        acc->sparse.reset(new Accessor::Sparse);
        acc->sparse->count = nzCount;

        //indices
        unsigned int bytesPerIdx = sizeof(unsigned short);
        size_t indices_offset = buffer->byteLength;
        size_t indices_padding = indices_offset % bytesPerIdx;
        indices_offset += indices_padding;
        size_t indices_length = nzCount * 1 * bytesPerIdx;
        buffer->Grow(indices_length + indices_padding);

        Ref<BufferView> indicesBV = a.bufferViews.Create(a.FindUniqueID(meshName, "view"));
        indicesBV->buffer = buffer;
        indicesBV->byteOffset = indices_offset;
        indicesBV->byteLength = indices_length;
        indicesBV->byteStride = 0;
        acc->sparse->indices = indicesBV;
        acc->sparse->indicesType = ComponentType_UNSIGNED_SHORT;
        acc->sparse->indicesByteOffset = 0;
        acc->WriteSparseIndices(nzCount, nzIdx, 1 * bytesPerIdx);

        //values
        size_t values_offset = buffer->byteLength;
        size_t values_padding = values_offset % bytesPerComp;
        values_offset += values_padding;
        size_t values_length = nzCount * numCompsOut * bytesPerComp;
        buffer->Grow(values_length + values_padding);

        Ref<BufferView> valuesBV = a.bufferViews.Create(a.FindUniqueID(meshName, "view"));
        valuesBV->buffer = buffer;
        valuesBV->byteOffset = values_offset;
        valuesBV->byteLength = values_length;
        valuesBV->byteStride = 0;
        acc->sparse->values = valuesBV;
        acc->sparse->valuesByteOffset = 0;
        acc->WriteSparseValues(nzCount, nzDiff, numCompsIn * bytesPerComp);

        //clear
        delete[] (char*)nzDiff;
        delete[] (char*)nzIdx;
    }
    return acc;
}
inline Ref<Accessor> ExportData(Asset& a, std::string& meshName, Ref<Buffer>& buffer,
    size_t count, void* data, AttribType::Value typeIn, AttribType::Value typeOut, ComponentType compType, BufferViewTarget target = BufferViewTarget_NONE)
{
    if (!count || !data) {
        return Ref<Accessor>();
    }

    unsigned int numCompsIn = AttribType::GetNumComponents(typeIn);
    unsigned int numCompsOut = AttribType::GetNumComponents(typeOut);
    unsigned int bytesPerComp = ComponentTypeSize(compType);

    size_t offset = buffer->byteLength;
    // make sure offset is correctly byte-aligned, as required by spec
    size_t padding = offset % bytesPerComp;
    offset += padding;
    size_t length = count * numCompsOut * bytesPerComp;
    buffer->Grow(length + padding);

    // bufferView
    Ref<BufferView> bv = a.bufferViews.Create(a.FindUniqueID(meshName, "view"));
    bv->buffer = buffer;
    bv->byteOffset = offset;
    bv->byteLength = length; //! The target that the WebGL buffer should be bound to.
    bv->byteStride = 0;
    bv->target = target;

    // accessor
    Ref<Accessor> acc = a.accessors.Create(a.FindUniqueID(meshName, "accessor"));
    acc->bufferView = bv;
    acc->byteOffset = 0;
    acc->componentType = compType;
    acc->count = count;
    acc->type = typeOut;

    // calculate min and max values
	SetAccessorRange(compType, acc, data, count, numCompsIn, numCompsOut);

    // copy the data
    acc->WriteData(count, data, numCompsIn*bytesPerComp);

    return acc;
}

inline void SetSamplerWrap(SamplerWrap& wrap, aiTextureMapMode map)
{
    switch (map) {
        case aiTextureMapMode_Clamp:
            wrap = SamplerWrap::Clamp_To_Edge;
            break;
        case aiTextureMapMode_Mirror:
            wrap = SamplerWrap::Mirrored_Repeat;
            break;
        case aiTextureMapMode_Wrap:
        case aiTextureMapMode_Decal:
        default:
            wrap = SamplerWrap::Repeat;
            break;
    };
}

void glTF2Exporter::GetTexSampler(const aiMaterial& mat, Ref<Texture> texture, aiTextureType tt, unsigned int slot)
{
    aiString aId;
    std::string id;
    if (aiGetMaterialString(&mat, AI_MATKEY_GLTF_MAPPINGID(tt, slot), &aId) == AI_SUCCESS) {
        id = aId.C_Str();
    }

    if (Ref<Sampler> ref = mAsset->samplers.Get(id.c_str())) {
        texture->sampler = ref;
    } else {
        id = mAsset->FindUniqueID(id, "sampler");

        texture->sampler = mAsset->samplers.Create(id.c_str());

        aiTextureMapMode mapU, mapV;
        SamplerMagFilter filterMag;
        SamplerMinFilter filterMin;

        if (aiGetMaterialInteger(&mat, AI_MATKEY_MAPPINGMODE_U(tt, slot), (int*)&mapU) == AI_SUCCESS) {
            SetSamplerWrap(texture->sampler->wrapS, mapU);
        }

        if (aiGetMaterialInteger(&mat, AI_MATKEY_MAPPINGMODE_V(tt, slot), (int*)&mapV) == AI_SUCCESS) {
            SetSamplerWrap(texture->sampler->wrapT, mapV);
        }

        if (aiGetMaterialInteger(&mat, AI_MATKEY_GLTF_MAPPINGFILTER_MAG(tt, slot), (int*)&filterMag) == AI_SUCCESS) {
            texture->sampler->magFilter = filterMag;
        }

        if (aiGetMaterialInteger(&mat, AI_MATKEY_GLTF_MAPPINGFILTER_MIN(tt, slot), (int*)&filterMin) == AI_SUCCESS) {
            texture->sampler->minFilter = filterMin;
        }

        aiString name;
        if (aiGetMaterialString(&mat, AI_MATKEY_GLTF_MAPPINGNAME(tt, slot), &name) == AI_SUCCESS) {
            texture->sampler->name = name.C_Str();
        }
    }
}

void glTF2Exporter::GetMatTexProp(const aiMaterial& mat, unsigned int& prop, const char* propName, aiTextureType tt, unsigned int slot)
{
    std::string textureKey = std::string(_AI_MATKEY_TEXTURE_BASE) + "." + propName;

    mat.Get(textureKey.c_str(), tt, slot, prop);
}

void glTF2Exporter::GetMatTexProp(const aiMaterial& mat, float& prop, const char* propName, aiTextureType tt, unsigned int slot)
{
    std::string textureKey = std::string(_AI_MATKEY_TEXTURE_BASE) + "." + propName;

    mat.Get(textureKey.c_str(), tt, slot, prop);
}

void glTF2Exporter::GetMatTex(const aiMaterial& mat, Ref<Texture>& texture, unsigned int &texCoord, aiTextureType tt, unsigned int slot = 0)
{
    if (mat.GetTextureCount(tt) > 0) {
        aiString tex;

        // Read texcoord (UV map index)
        mat.Get(AI_MATKEY_UVWSRC(tt, slot), texCoord);

        if (mat.Get(AI_MATKEY_TEXTURE(tt, slot), tex) == AI_SUCCESS) {
            std::string path = tex.C_Str();

            if (path.size() > 0) {
                std::map<std::string, unsigned int>::iterator it = mTexturesByPath.find(path);
                if (it != mTexturesByPath.end()) {
                    texture = mAsset->textures.Get(it->second);
                }

                bool useBasisUniversal = false;
                if (!texture) {
                    std::string texId = mAsset->FindUniqueID("", "texture");
                    texture = mAsset->textures.Create(texId);
                    mTexturesByPath[path] = texture.GetIndex();

                    std::string imgId = mAsset->FindUniqueID("", "image");
                    texture->source = mAsset->images.Create(imgId);

                    const aiTexture* curTex = mScene->GetEmbeddedTexture(path.c_str());
                    if (curTex != nullptr) { // embedded
                        texture->source->name = curTex->mFilename.C_Str();

                        //basisu: embedded ktx2, bu
                        if (curTex->achFormatHint[0]) {
                            std::string mimeType = "image/";
                            if(memcmp(curTex->achFormatHint, "jpg", 3) == 0)
                                mimeType += "jpeg";
                            else if(memcmp(curTex->achFormatHint, "ktx", 3) == 0) {
                                useBasisUniversal = true;
                                mimeType += "ktx";
                            }
                            else if(memcmp(curTex->achFormatHint, "kx2", 3) == 0) {
                                useBasisUniversal = true;
                                mimeType += "ktx2";
                            }
                            else if(memcmp(curTex->achFormatHint, "bu", 2) == 0) {
                                useBasisUniversal = true;
                                mimeType += "basis";
                            }
                            else
                                mimeType += curTex->achFormatHint;
                            texture->source->mimeType = mimeType;
                        }

                        // The asset has its own buffer, see Image::SetData
                        //basisu: "image/ktx2", "image/basis" as is
                        texture->source->SetData(reinterpret_cast<uint8_t *>(curTex->pcData), curTex->mWidth, *mAsset);
                    }
                    else {
                        texture->source->uri = path;
                        if(texture->source->uri.find(".ktx")!=std::string::npos ||
                           texture->source->uri.find(".basis")!=std::string::npos)
                        {
                            useBasisUniversal = true;
                        }
                    }

                    //basisu
                    if(useBasisUniversal) {
                        mAsset->extensionsUsed.KHR_texture_basisu = true;
                        mAsset->extensionsRequired.KHR_texture_basisu = true;
                    }

                    GetTexSampler(mat, texture, tt, slot);
                }
            }
        }
    }
}

void glTF2Exporter::GetMatTex(const aiMaterial& mat, TextureInfo& prop, aiTextureType tt, unsigned int slot = 0)
{
    Ref<Texture>& texture = prop.texture;

    GetMatTex(mat, texture, prop.texCoord, tt, slot);

    //if (texture) {
    //    GetMatTexProp(mat, prop.texCoord, "texCoord", tt, slot);
    //}
}

void glTF2Exporter::GetMatTex(const aiMaterial& mat, NormalTextureInfo& prop, aiTextureType tt, unsigned int slot = 0)
{
    Ref<Texture>& texture = prop.texture;

    GetMatTex(mat, texture, prop.texCoord, tt, slot);

    if (texture) {
        //GetMatTexProp(mat, prop.texCoord, "texCoord", tt, slot);
        GetMatTexProp(mat, prop.scale, "scale", tt, slot);
    }
}

void glTF2Exporter::GetMatTex(const aiMaterial& mat, OcclusionTextureInfo& prop, aiTextureType tt, unsigned int slot = 0)
{
    Ref<Texture>& texture = prop.texture;

    GetMatTex(mat, texture, prop.texCoord, tt, slot);

    if (texture) {
        //GetMatTexProp(mat, prop.texCoord, "texCoord", tt, slot);
        GetMatTexProp(mat, prop.strength, "strength", tt, slot);
    }
}

aiReturn glTF2Exporter::GetMatColor(const aiMaterial& mat, vec4& prop, const char* propName, int type, int idx) const
{
    aiColor4D col;
    aiReturn result = mat.Get(propName, type, idx, col);

    if (result == AI_SUCCESS) {
        prop[0] = col.r; prop[1] = col.g; prop[2] = col.b; prop[3] = col.a;
    }

    return result;
}

aiReturn glTF2Exporter::GetMatColor(const aiMaterial& mat, vec3& prop, const char* propName, int type, int idx) const
{
    aiColor3D col;
    aiReturn result = mat.Get(propName, type, idx, col);

    if (result == AI_SUCCESS) {
        prop[0] = col.r;
        prop[1] = col.g;
        prop[2] = col.b;
    }

    return result;
}

bool glTF2Exporter::GetMatSpecGloss(const aiMaterial &mat, glTF2::PbrSpecularGlossiness &pbrSG) {
    bool result = false;
    // If has Glossiness, a Specular Color or Specular Texture, use the KHR_materials_pbrSpecularGlossiness extension
    // NOTE: This extension is being considered for deprecation (Dec 2020), may be replaced by KHR_material_specular

    if (mat.Get(AI_MATKEY_GLOSSINESS_FACTOR, pbrSG.glossinessFactor) == AI_SUCCESS) {
        result = true;
    } else {
        // Don't have explicit glossiness, convert from pbr roughness or legacy shininess
        float shininess;
        if (mat.Get(AI_MATKEY_ROUGHNESS_FACTOR, shininess) == AI_SUCCESS) {
            pbrSG.glossinessFactor = 1.0f - shininess; // Extension defines this way
        } else if (mat.Get(AI_MATKEY_SHININESS, shininess) == AI_SUCCESS) {
            pbrSG.glossinessFactor = shininess / 1000;
        }
    }

    if (GetMatColor(mat, pbrSG.specularFactor, AI_MATKEY_COLOR_SPECULAR) == AI_SUCCESS) {
        result = true;
    }
    // Add any appropriate textures
    GetMatTex(mat, pbrSG.specularGlossinessTexture, aiTextureType_SPECULAR);

    result = result || pbrSG.specularGlossinessTexture.texture;

    if (result) {
        // Likely to always have diffuse
        GetMatTex(mat, pbrSG.diffuseTexture, aiTextureType_DIFFUSE);
        GetMatColor(mat, pbrSG.diffuseFactor, AI_MATKEY_COLOR_DIFFUSE);
    }

    return result;
}

bool glTF2Exporter::GetMatSheen(const aiMaterial &mat, glTF2::MaterialSheen &sheen) {
    // Return true if got any valid Sheen properties or textures
    if (GetMatColor(mat, sheen.sheenColorFactor, AI_MATKEY_SHEEN_COLOR_FACTOR) != aiReturn_SUCCESS)
        return false;

    // Default Sheen color factor {0,0,0} disables Sheen, so do not export
    if (sheen.sheenColorFactor == defaultSheenFactor)
        return false;

    mat.Get(AI_MATKEY_SHEEN_ROUGHNESS_FACTOR, sheen.sheenRoughnessFactor);

    GetMatTex(mat, sheen.sheenColorTexture, AI_MATKEY_SHEEN_COLOR_TEXTURE);
    GetMatTex(mat, sheen.sheenRoughnessTexture, AI_MATKEY_SHEEN_ROUGHNESS_TEXTURE);

    return true;
}

bool glTF2Exporter::GetMatClearcoat(const aiMaterial &mat, glTF2::MaterialClearcoat &clearcoat) {
    if (mat.Get(AI_MATKEY_CLEARCOAT_FACTOR, clearcoat.clearcoatFactor) != aiReturn_SUCCESS) {
        return false;
    }

    // Clearcoat factor of zero disables Clearcoat, so do not export
    if (clearcoat.clearcoatFactor == 0.0f)
        return false;

    mat.Get(AI_MATKEY_CLEARCOAT_ROUGHNESS_FACTOR, clearcoat.clearcoatRoughnessFactor);

    GetMatTex(mat, clearcoat.clearcoatTexture, AI_MATKEY_CLEARCOAT_TEXTURE);
    GetMatTex(mat, clearcoat.clearcoatRoughnessTexture, AI_MATKEY_CLEARCOAT_ROUGHNESS_TEXTURE);
    GetMatTex(mat, clearcoat.clearcoatNormalTexture, AI_MATKEY_CLEARCOAT_NORMAL_TEXTURE);

    return true;
}

bool glTF2Exporter::GetMatTransmission(const aiMaterial &mat, glTF2::MaterialTransmission &transmission) {
    bool result = mat.Get(AI_MATKEY_TRANSMISSION_FACTOR, transmission.transmissionFactor) == aiReturn_SUCCESS;
    GetMatTex(mat, transmission.transmissionTexture, AI_MATKEY_TRANSMISSION_TEXTURE);
    return result || transmission.transmissionTexture.texture;
}

void glTF2Exporter::ExportMaterials()
{
    aiString aiName;
    for (unsigned int i = 0; i < mScene->mNumMaterials; ++i) {
        ai_assert(mScene->mMaterials[i] != nullptr);

        const aiMaterial & mat = *(mScene->mMaterials[i]);

        std::string id = "material_" + ai_to_string(i);

        Ref<Material> m = mAsset->materials.Create(id);

        std::string name;
        if (mat.Get(AI_MATKEY_NAME, aiName) == AI_SUCCESS) {
            name = aiName.C_Str();
        }
        name = mAsset->FindUniqueID(name, "material");

        m->name = name;

        GetMatTex(mat, m->pbrMetallicRoughness.baseColorTexture, aiTextureType_BASE_COLOR);

        if (!m->pbrMetallicRoughness.baseColorTexture.texture) {
            //if there wasn't a baseColorTexture defined in the source, fallback to any diffuse texture
            GetMatTex(mat, m->pbrMetallicRoughness.baseColorTexture, aiTextureType_DIFFUSE);
        }

        GetMatTex(mat, m->pbrMetallicRoughness.metallicRoughnessTexture, AI_MATKEY_GLTF_PBRMETALLICROUGHNESS_METALLICROUGHNESS_TEXTURE);

        if (GetMatColor(mat, m->pbrMetallicRoughness.baseColorFactor, AI_MATKEY_BASE_COLOR) != AI_SUCCESS) {
            // if baseColorFactor wasn't defined, then the source is likely not a metallic roughness material.
            //a fallback to any diffuse color should be used instead
            GetMatColor(mat, m->pbrMetallicRoughness.baseColorFactor, AI_MATKEY_COLOR_DIFFUSE);
        }

        if (mat.Get(AI_MATKEY_METALLIC_FACTOR, m->pbrMetallicRoughness.metallicFactor) != AI_SUCCESS) {
            //if metallicFactor wasn't defined, then the source is likely not a PBR file, and the metallicFactor should be 0
            m->pbrMetallicRoughness.metallicFactor = 0;
        }

        // get roughness if source is gltf2 file
        if (mat.Get(AI_MATKEY_ROUGHNESS_FACTOR, m->pbrMetallicRoughness.roughnessFactor) != AI_SUCCESS) {
            // otherwise, try to derive and convert from specular + shininess values
            aiColor4D specularColor;
            ai_real shininess;

            if (
                mat.Get(AI_MATKEY_COLOR_SPECULAR, specularColor) == AI_SUCCESS &&
                mat.Get(AI_MATKEY_SHININESS, shininess) == AI_SUCCESS
            ) {
                // convert specular color to luminance
                float specularIntensity = specularColor[0] * 0.2125f + specularColor[1] * 0.7154f + specularColor[2] * 0.0721f;
                //normalize shininess (assuming max is 1000) with an inverse exponentional curve
                float normalizedShininess = std::sqrt(shininess / 1000);

                //clamp the shininess value between 0 and 1
                normalizedShininess = std::min(std::max(normalizedShininess, 0.0f), 1.0f);
                // low specular intensity values should produce a rough material even if shininess is high.
                normalizedShininess = normalizedShininess * specularIntensity;

                m->pbrMetallicRoughness.roughnessFactor = 1 - normalizedShininess;
            }
        }

        GetMatTex(mat, m->normalTexture, aiTextureType_NORMALS);
        GetMatTex(mat, m->occlusionTexture, aiTextureType_LIGHTMAP);
        GetMatTex(mat, m->emissiveTexture, aiTextureType_EMISSIVE);
        GetMatColor(mat, m->emissiveFactor, AI_MATKEY_COLOR_EMISSIVE);

        mat.Get(AI_MATKEY_TWOSIDED, m->doubleSided);
        mat.Get(AI_MATKEY_GLTF_ALPHACUTOFF, m->alphaCutoff);

        float opacity;
        aiString alphaMode;

        if (mat.Get(AI_MATKEY_OPACITY, opacity) == AI_SUCCESS) {
            if (opacity < 1) {
                m->alphaMode = "BLEND";
                m->pbrMetallicRoughness.baseColorFactor[3] *= opacity;
            }
        }
        if (mat.Get(AI_MATKEY_GLTF_ALPHAMODE, alphaMode) == AI_SUCCESS) {
            m->alphaMode = alphaMode.C_Str();
        }

        {
            // KHR_materials_pbrSpecularGlossiness extension
            // NOTE: This extension is being considered for deprecation (Dec 2020)
            PbrSpecularGlossiness pbrSG;
            if (GetMatSpecGloss(mat, pbrSG)) {
                mAsset->extensionsUsed.KHR_materials_pbrSpecularGlossiness = true;
                m->pbrSpecularGlossiness = Nullable<PbrSpecularGlossiness>(pbrSG);
            }
        }

        // glTFv2 is either PBR or Unlit
        aiShadingMode shadingMode = aiShadingMode_PBR_BRDF;
        mat.Get(AI_MATKEY_SHADING_MODEL, shadingMode);
        if (shadingMode == aiShadingMode_Unlit) {
            mAsset->extensionsUsed.KHR_materials_unlit = true;
            m->unlit = true;
        } else {
            // These extensions are not compatible with KHR_materials_unlit or KHR_materials_pbrSpecularGlossiness
            if (!m->pbrSpecularGlossiness.isPresent) {
                // Sheen
                MaterialSheen sheen;
                if (GetMatSheen(mat, sheen)) {
                    mAsset->extensionsUsed.KHR_materials_sheen = true;
                    m->materialSheen = Nullable<MaterialSheen>(sheen);
                }

                MaterialClearcoat clearcoat;
                if (GetMatClearcoat(mat, clearcoat)) {
                    mAsset->extensionsUsed.KHR_materials_clearcoat = true;
                    m->materialClearcoat = Nullable<MaterialClearcoat>(clearcoat);
                }

                MaterialTransmission transmission;
                if (GetMatTransmission(mat, transmission)) {
                    mAsset->extensionsUsed.KHR_materials_transmission = true;
                    m->materialTransmission = Nullable<MaterialTransmission>(transmission);
                }
            }
        }
    }
}

/*
 * Search through node hierarchy and find the node containing the given meshID.
 * Returns true on success, and false otherwise.
 */
bool FindMeshNode(Ref<Node> &nodeIn, Ref<Node> &meshNode, const std::string &meshID) {
    for (unsigned int i = 0; i < nodeIn->meshes.size(); ++i) {
        if (meshID.compare(nodeIn->meshes[i]->id) == 0) {
            meshNode = nodeIn;
            return true;
        }
    }

    for (unsigned int i = 0; i < nodeIn->children.size(); ++i) {
        if(FindMeshNode(nodeIn->children[i], meshNode, meshID)) {
            return true;
        }
    }

    return false;
}

/*
 * Find the root joint of the skeleton.
 * Starts will any joint node and traces up the tree,
 * until a parent is found that does not have a jointName.
 * Returns the first parent Ref<Node> found that does not have a jointName.
 */
Ref<Node> FindSkeletonRootJoint(Ref<Skin>& skinRef)
{
    Ref<Node> startNodeRef;
    Ref<Node> parentNodeRef;

    // Arbitrarily use the first joint to start the search.
    startNodeRef = skinRef->jointNames[0];
    parentNodeRef = skinRef->jointNames[0];

    do {
        startNodeRef = parentNodeRef;
        parentNodeRef = startNodeRef->parent;
    } while (!parentNodeRef->jointName.empty());

    return parentNodeRef;
}

void ExportSkin(Asset& mAsset, const aiMesh* aimesh, Ref<Mesh>& meshRef, Ref<Buffer>& bufferRef, Ref<Skin>& skinRef, std::vector<aiMatrix4x4>& inverseBindMatricesData)
{
    if (aimesh->mNumBones < 1) {
        return;
    }

    // Store the vertex joint and weight data.
    const size_t NumVerts( aimesh->mNumVertices );
    vec4* vertexJointData = new vec4[ NumVerts ];
    vec4* vertexWeightData = new vec4[ NumVerts ];
    int* jointsPerVertex = new int[ NumVerts ];
    for (size_t i = 0; i < NumVerts; ++i) {
        jointsPerVertex[i] = 0;
        for (size_t j = 0; j < 4; ++j) {
            vertexJointData[i][j] = 0;
            vertexWeightData[i][j] = 0;
        }
    }

    for (unsigned int idx_bone = 0; idx_bone < aimesh->mNumBones; ++idx_bone) {
        const aiBone* aib = aimesh->mBones[idx_bone];

        // aib->mName   =====>  skinRef->jointNames
        // Find the node with id = mName.
        Ref<Node> nodeRef = mAsset.nodes.Get(aib->mName.C_Str());
        nodeRef->jointName = nodeRef->name;

        unsigned int jointNamesIndex = 0;
        bool addJointToJointNames = true;
        for ( unsigned int idx_joint = 0; idx_joint < skinRef->jointNames.size(); ++idx_joint) {
            if (skinRef->jointNames[idx_joint]->jointName.compare(nodeRef->jointName) == 0) {
                addJointToJointNames = false;
                jointNamesIndex = idx_joint;
            }
        }

        if (addJointToJointNames) {
            skinRef->jointNames.push_back(nodeRef);

            // aib->mOffsetMatrix   =====>  skinRef->inverseBindMatrices
            aiMatrix4x4 tmpMatrix4;
            CopyValue(aib->mOffsetMatrix, tmpMatrix4);
            inverseBindMatricesData.push_back(tmpMatrix4);
            jointNamesIndex = static_cast<unsigned int>(inverseBindMatricesData.size() - 1);
        }

        // aib->mWeights   =====>  vertexWeightData
        for (unsigned int idx_weights = 0; idx_weights < aib->mNumWeights; ++idx_weights) {
            unsigned int vertexId = aib->mWeights[idx_weights].mVertexId;
            float vertWeight      = aib->mWeights[idx_weights].mWeight;

            // A vertex can only have at most four joint weights. Ignore all others.
            if (jointsPerVertex[vertexId] > 3) {
                continue;
            }

            vertexJointData[vertexId][jointsPerVertex[vertexId]] = static_cast<float>(jointNamesIndex);
            vertexWeightData[vertexId][jointsPerVertex[vertexId]] = vertWeight;

            jointsPerVertex[vertexId] += 1;
        }

    } // End: for-loop mNumMeshes

    Mesh::Primitive& p = meshRef->primitives.back();
    Ref<Accessor> vertexJointAccessor = ExportData(mAsset, skinRef->id, bufferRef, aimesh->mNumVertices, vertexJointData, AttribType::VEC4, AttribType::VEC4, ComponentType_FLOAT);
    if ( vertexJointAccessor ) {
        size_t offset = vertexJointAccessor->bufferView->byteOffset;
        size_t bytesLen = vertexJointAccessor->bufferView->byteLength;
        unsigned int s_bytesPerComp= ComponentTypeSize(ComponentType_UNSIGNED_SHORT);
        unsigned int bytesPerComp = ComponentTypeSize(vertexJointAccessor->componentType);
        size_t s_bytesLen = bytesLen * s_bytesPerComp / bytesPerComp;
        Ref<Buffer> buf = vertexJointAccessor->bufferView->buffer;
        uint8_t* arrys = new uint8_t[bytesLen];
        unsigned int i = 0;
        for ( unsigned int j = 0; j <= bytesLen; j += bytesPerComp ){
            size_t len_p = offset + j;
            float f_value = *(float *)&buf->GetPointer()[len_p];
            unsigned short c = static_cast<unsigned short>(f_value);
            memcpy(&arrys[i*s_bytesPerComp], &c, s_bytesPerComp);
            ++i;
        }
        buf->ReplaceData_joint(offset, bytesLen, arrys, bytesLen);
        vertexJointAccessor->componentType = ComponentType_UNSIGNED_SHORT;
        vertexJointAccessor->bufferView->byteLength = s_bytesLen;

        p.attributes.joint.push_back( vertexJointAccessor );
        delete[] arrys;
    }

    Ref<Accessor> vertexWeightAccessor = ExportData(mAsset, skinRef->id, bufferRef, aimesh->mNumVertices,
            vertexWeightData, AttribType::VEC4, AttribType::VEC4, ComponentType_FLOAT);
    if ( vertexWeightAccessor ) {
        p.attributes.weight.push_back( vertexWeightAccessor );
    }
    delete[] jointsPerVertex;
    delete[] vertexWeightData;
    delete[] vertexJointData;
}

void glTF2Exporter::ExportMeshes()
{
    typedef decltype(aiFace::mNumIndices) IndicesType;

    std::string fname = std::string(mFilename);
    std::string bufferIdPrefix = fname.substr(0, fname.rfind(".gltf"));
    std::string bufferId = mAsset->FindUniqueID("", bufferIdPrefix.c_str());

    Ref<Buffer> b = mAsset->GetBodyBuffer();
    if (!b) {
       b = mAsset->buffers.Create(bufferId);
    }

    //----------------------------------------
    // Initialize variables for the skin
    bool createSkin = false;
    for (unsigned int idx_mesh = 0; idx_mesh < mScene->mNumMeshes; ++idx_mesh) {
        const aiMesh* aim = mScene->mMeshes[idx_mesh];
        if(aim->HasBones()) {
            createSkin = true;
            break;
        }
    }

    Ref<Skin> skinRef;
    std::string skinName = mAsset->FindUniqueID("skin", "skin");
    std::vector<aiMatrix4x4> inverseBindMatricesData;
    if(createSkin) {
        skinRef = mAsset->skins.Create(skinName);
        skinRef->name = skinName;
    }
    //----------------------------------------

	for (unsigned int idx_mesh = 0; idx_mesh < mScene->mNumMeshes; ++idx_mesh) {
		const aiMesh* aim = mScene->mMeshes[idx_mesh];

        std::string name = aim->mName.C_Str();

        std::string meshId = mAsset->FindUniqueID(name, "mesh");
        Ref<Mesh> m = mAsset->meshes.Create(meshId);
        m->primitives.resize(1);
        Mesh::Primitive& p = m->primitives.back();

        m->name = name;

        p.material = mAsset->materials.Get(aim->mMaterialIndex);
        p.ngonEncoded = (aim->mPrimitiveTypes & aiPrimitiveType_NGONEncodingFlag) != 0;

		/******************* Vertices ********************/
		Ref<Accessor> v = ExportData(*mAsset, meshId, b, aim->mNumVertices, aim->mVertices, AttribType::VEC3, AttribType::VEC3, ComponentType_FLOAT, BufferViewTarget_ARRAY_BUFFER);
		if (v) p.attributes.position.push_back(v);

		/******************** Normals ********************/
        // Normalize all normals as the validator can emit a warning otherwise
        if ( nullptr != aim->mNormals) {
            for ( auto i = 0u; i < aim->mNumVertices; ++i ) {
                aim->mNormals[ i ].NormalizeSafe();
            }
        }

		Ref<Accessor> n = ExportData(*mAsset, meshId, b, aim->mNumVertices, aim->mNormals, AttribType::VEC3, AttribType::VEC3, ComponentType_FLOAT, BufferViewTarget_ARRAY_BUFFER);
        if (n) p.attributes.normal.push_back(n);

		/************** Texture coordinates **************/
        for (int i = 0; i < AI_MAX_NUMBER_OF_TEXTURECOORDS; ++i) {
			if (!aim->HasTextureCoords(i))
				continue;

            // Flip UV y coords
            if (aim -> mNumUVComponents[i] > 1) {
                for (unsigned int j = 0; j < aim->mNumVertices; ++j) {
                    aim->mTextureCoords[i][j].y = 1 - aim->mTextureCoords[i][j].y;
                }
            }

            if (aim->mNumUVComponents[i] > 0) {
                AttribType::Value type = (aim->mNumUVComponents[i] == 2) ? AttribType::VEC2 : AttribType::VEC3;

				Ref<Accessor> tc = ExportData(*mAsset, meshId, b, aim->mNumVertices, aim->mTextureCoords[i], AttribType::VEC3, type, ComponentType_FLOAT, BufferViewTarget_ARRAY_BUFFER);
				if (tc) p.attributes.texcoord.push_back(tc);
			}
		}

		/*************** Vertex colors ****************/
		for (unsigned int indexColorChannel = 0; indexColorChannel < aim->GetNumColorChannels(); ++indexColorChannel) {
			Ref<Accessor> c = ExportData(*mAsset, meshId, b, aim->mNumVertices, aim->mColors[indexColorChannel], AttribType::VEC4, AttribType::VEC4, ComponentType_FLOAT, BufferViewTarget_ARRAY_BUFFER);
			if (c)
				p.attributes.color.push_back(c);
		}

		/*************** Vertices indices ****************/
		if (aim->mNumFaces > 0) {
			std::vector<IndicesType> indices;
			unsigned int nIndicesPerFace = aim->mFaces[0].mNumIndices;
            indices.resize(aim->mNumFaces * nIndicesPerFace);
            for (size_t i = 0; i < aim->mNumFaces; ++i) {
                for (size_t j = 0; j < nIndicesPerFace; ++j) {
                    indices[i*nIndicesPerFace + j] = IndicesType(aim->mFaces[i].mIndices[j]);
                }
            }

			p.indices = ExportData(*mAsset, meshId, b, indices.size(), &indices[0], AttribType::SCALAR, AttribType::SCALAR, ComponentType_UNSIGNED_INT, BufferViewTarget_ELEMENT_ARRAY_BUFFER);
		}

        switch (aim->mPrimitiveTypes) {
            case aiPrimitiveType_POLYGON:
                p.mode = PrimitiveMode_TRIANGLES; break; // TODO implement this
            case aiPrimitiveType_LINE:
                p.mode = PrimitiveMode_LINES; break;
            case aiPrimitiveType_POINT:
                p.mode = PrimitiveMode_POINTS; break;
            default: // aiPrimitiveType_TRIANGLE
                p.mode = PrimitiveMode_TRIANGLES;
        }

        /*************** Skins ****************/
        if(aim->HasBones()) {
            ExportSkin(*mAsset, aim, m, b, skinRef, inverseBindMatricesData);
        }

        /*************** Targets for blendshapes ****************/
        if (aim->mNumAnimMeshes > 0) {
            bool bUseSparse = this->mProperties->HasPropertyBool("GLTF2_SPARSE_ACCESSOR_EXP") &&
                              this->mProperties->GetPropertyBool("GLTF2_SPARSE_ACCESSOR_EXP");
            bool bIncludeNormal = this->mProperties->HasPropertyBool("GLTF2_TARGET_NORMAL_EXP") &&
                                  this->mProperties->GetPropertyBool("GLTF2_TARGET_NORMAL_EXP");
            bool bExportTargetNames = this->mProperties->HasPropertyBool("GLTF2_TARGETNAMES_EXP") &&
                              this->mProperties->GetPropertyBool("GLTF2_TARGETNAMES_EXP");

            p.targets.resize(aim->mNumAnimMeshes);
            for (unsigned int am = 0; am < aim->mNumAnimMeshes; ++am) {
                aiAnimMesh *pAnimMesh = aim->mAnimMeshes[am];
                if (bExportTargetNames)
                    m->targetNames.push_back(pAnimMesh->mName.data);
                // position
                if (pAnimMesh->HasPositions()) {
                    // NOTE: in gltf it is the diff stored
                    aiVector3D *pPositionDiff = new aiVector3D[pAnimMesh->mNumVertices];
                    for (unsigned int vt = 0; vt < pAnimMesh->mNumVertices; ++vt) {
                        pPositionDiff[vt] = pAnimMesh->mVertices[vt] - aim->mVertices[vt];
                    }
                    Ref<Accessor> vec;
                    if (bUseSparse) {
                        vec = ExportDataSparse(*mAsset, meshId, b,
                                pAnimMesh->mNumVertices, pPositionDiff,
                                AttribType::VEC3, AttribType::VEC3, ComponentType_FLOAT);
                    } else {
                        vec = ExportData(*mAsset, meshId, b,
                                pAnimMesh->mNumVertices, pPositionDiff,
                                AttribType::VEC3, AttribType::VEC3, ComponentType_FLOAT);
                    }
                    if (vec) {
                        p.targets[am].position.push_back(vec);
                    }
                    delete[] pPositionDiff;
                }

                // normal
                if (pAnimMesh->HasNormals() && bIncludeNormal) {
                    aiVector3D *pNormalDiff = new aiVector3D[pAnimMesh->mNumVertices];
                    for (unsigned int vt = 0; vt < pAnimMesh->mNumVertices; ++vt) {
                        pNormalDiff[vt] = pAnimMesh->mNormals[vt] - aim->mNormals[vt];
                    }
                    Ref<Accessor> vec;
                    if (bUseSparse) {
                        vec = ExportDataSparse(*mAsset, meshId, b,
                                pAnimMesh->mNumVertices, pNormalDiff,
                                AttribType::VEC3, AttribType::VEC3, ComponentType_FLOAT);
                    } else {
                        vec = ExportData(*mAsset, meshId, b,
                                pAnimMesh->mNumVertices, pNormalDiff,
                                AttribType::VEC3, AttribType::VEC3, ComponentType_FLOAT);
                    }
                    if (vec) {
                        p.targets[am].normal.push_back(vec);
                    }
                    delete[] pNormalDiff;
                }

                // tangent?
            }
        }
    }

    //----------------------------------------
    // Finish the skin
    // Create the Accessor for skinRef->inverseBindMatrices
    bool bAddCustomizedProperty = this->mProperties->HasPropertyBool("GLTF2_CUSTOMIZE_PROPERTY");
    if (createSkin) {
        mat4* invBindMatrixData = new mat4[inverseBindMatricesData.size()];
        for ( unsigned int idx_joint = 0; idx_joint < inverseBindMatricesData.size(); ++idx_joint) {
            CopyValue(inverseBindMatricesData[idx_joint], invBindMatrixData[idx_joint]);
        }

        Ref<Accessor> invBindMatrixAccessor = ExportData(*mAsset, skinName, b,
                static_cast<unsigned int>(inverseBindMatricesData.size()),
            invBindMatrixData, AttribType::MAT4, AttribType::MAT4, ComponentType_FLOAT);
        if (invBindMatrixAccessor) {
            skinRef->inverseBindMatrices = invBindMatrixAccessor;
        }

        // Identity Matrix   =====>  skinRef->bindShapeMatrix
        // Temporary. Hard-coded identity matrix here
        skinRef->bindShapeMatrix.isPresent = bAddCustomizedProperty;
        IdentityMatrix4(skinRef->bindShapeMatrix.value);

        // Find nodes that contain a mesh with bones and add "skeletons" and "skin" attributes to those nodes.
        Ref<Node> rootNode = mAsset->nodes.Get(unsigned(0));
        Ref<Node> meshNode;
        for (unsigned int meshIndex = 0; meshIndex < mAsset->meshes.Size(); ++meshIndex) {
            Ref<Mesh> mesh = mAsset->meshes.Get(meshIndex);
            bool hasBones = false;
            for (unsigned int i = 0; i < mesh->primitives.size(); ++i) {
                if (!mesh->primitives[i].attributes.weight.empty()) {
                    hasBones = true;
                    break;
                }
            }
            if (!hasBones) {
                continue;
            }
            std::string meshID = mesh->id;
            FindMeshNode(rootNode, meshNode, meshID);
            Ref<Node> rootJoint = FindSkeletonRootJoint(skinRef);
            if(bAddCustomizedProperty)
                meshNode->skeletons.push_back(rootJoint);
            meshNode->skin = skinRef;
        }
        delete[] invBindMatrixData;
    }
}

// Merges a node's multiple meshes (with one primitive each) into one mesh with multiple primitives
void glTF2Exporter::MergeMeshes()
{
    for (unsigned int n = 0; n < mAsset->nodes.Size(); ++n) {
        Ref<Node> node = mAsset->nodes.Get(n);

        unsigned int nMeshes = static_cast<unsigned int>(node->meshes.size());

        //skip if it's 1 or less meshes per node
        if (nMeshes > 1) {
            Ref<Mesh> firstMesh = node->meshes.at(0);

            //loop backwards to allow easy removal of a mesh from a node once it's merged
            for (unsigned int m = nMeshes - 1; m >= 1; --m) {
                Ref<Mesh> mesh = node->meshes.at(m);

                //append this mesh's primitives to the first mesh's primitives
                firstMesh->primitives.insert(
                    firstMesh->primitives.end(),
                    mesh->primitives.begin(),
                    mesh->primitives.end()
                );

                //remove the mesh from the list of meshes
                unsigned int removedIndex = mAsset->meshes.Remove(mesh->id.c_str());

                //find the presence of the removed mesh in other nodes
                for (unsigned int nn = 0; nn < mAsset->nodes.Size(); ++nn) {
                    Ref<Node> curNode = mAsset->nodes.Get(nn);

                    for (unsigned int mm = 0; mm < curNode->meshes.size(); ++mm) {
                        Ref<Mesh> &meshRef = curNode->meshes.at(mm);
                        unsigned int meshIndex = meshRef.GetIndex();

                        if (meshIndex == removedIndex) {
                            curNode->meshes.erase(curNode->meshes.begin() + mm);
                        } else if (meshIndex > removedIndex) {
                            Ref<Mesh> newMeshRef = mAsset->meshes.Get(meshIndex - 1);

                            meshRef = newMeshRef;
                        }
                    }
                }
            }

            //since we were looping backwards, reverse the order of merged primitives to their original order
            std::reverse(firstMesh->primitives.begin() + 1, firstMesh->primitives.end());
        }
    }
}

/*
 * Export the root node of the node hierarchy.
 * Calls ExportNode for all children.
 */
unsigned int glTF2Exporter::ExportNodeHierarchy(const aiNode* n)
{
    Ref<Node> node = mAsset->nodes.Create(mAsset->FindUniqueID(n->mName.C_Str(), "node"));

    node->name = n->mName.C_Str();

    if (!n->mTransformation.IsIdentity()) {
        node->matrix.isPresent = true;
        CopyValue(n->mTransformation, node->matrix.value);
    }

    for (unsigned int i = 0; i < n->mNumMeshes; ++i) {
        node->meshes.push_back(mAsset->meshes.Get(n->mMeshes[i]));
    }

    for (unsigned int i = 0; i < n->mNumChildren; ++i) {
        unsigned int idx = ExportNode(n->mChildren[i], node);
        node->children.push_back(mAsset->nodes.Get(idx));
    }

    return node.GetIndex();
}

/*
 * Export node and recursively calls ExportNode for all children.
 * Since these nodes are not the root node, we also export the parent Ref<Node>
 */
unsigned int glTF2Exporter::ExportNode(const aiNode* n, Ref<Node>& parent)
{
    std::string name = mAsset->FindUniqueID(n->mName.C_Str(), "node");
    Ref<Node> node = mAsset->nodes.Create(name);

    node->parent = parent;
    node->name = name;

    if (!n->mTransformation.IsIdentity()) {
		if (mScene->mNumAnimations > 0 || (mProperties && mProperties->HasPropertyBool("GLTF2_NODE_IN_TRS"))) {
			aiQuaternion quaternion;
			n->mTransformation.Decompose(*reinterpret_cast<aiVector3D *>(&node->scale.value), quaternion, *reinterpret_cast<aiVector3D *>(&node->translation.value));

			aiVector3D vector(static_cast<ai_real>(1.0f), static_cast<ai_real>(1.0f), static_cast<ai_real>(1.0f));
			if (!reinterpret_cast<aiVector3D *>(&node->scale.value)->Equal(vector)) {
				node->scale.isPresent = true;
			}
			if (!reinterpret_cast<aiVector3D *>(&node->translation.value)->Equal(vector)) {
				node->translation.isPresent = true;
			}
			node->rotation.isPresent = true;
			node->rotation.value[0] = quaternion.x;
			node->rotation.value[1] = quaternion.y;
			node->rotation.value[2] = quaternion.z;
			node->rotation.value[3] = quaternion.w;
			node->matrix.isPresent = false;
		} else {
			node->matrix.isPresent = true;
			CopyValue(n->mTransformation, node->matrix.value);
		}
    }

    for (unsigned int i = 0; i < n->mNumMeshes; ++i) {
        node->meshes.push_back(mAsset->meshes.Get(n->mMeshes[i]));
    }

    for (unsigned int i = 0; i < n->mNumChildren; ++i) {
        unsigned int idx = ExportNode(n->mChildren[i], node);
        node->children.push_back(mAsset->nodes.Get(idx));
    }

    return node.GetIndex();
}


void glTF2Exporter::ExportScene()
{
    // Use the name of the scene if specified
    const std::string sceneName = (mScene->mName.length > 0) ? mScene->mName.C_Str() : "defaultScene";

    // Ensure unique
    Ref<Scene> scene = mAsset->scenes.Create(mAsset->FindUniqueID(sceneName, ""));

    // root node will be the first one exported (idx 0)
    if (mAsset->nodes.Size() > 0) {
        scene->nodes.push_back(mAsset->nodes.Get(0u));
    }

    // set as the default scene
    mAsset->scene = scene;
}

void glTF2Exporter::ExportMetadata()
{
    AssetMetadata& asset = mAsset->asset;
    asset.version = "2.0";

    char buffer[256];
    ai_snprintf(buffer, 256, "Open Asset Import Library (assimp v%d.%d.%x)",
        aiGetVersionMajor(), aiGetVersionMinor(), aiGetVersionRevision());

    asset.generator = buffer;

    // Copyright
	aiString copyright_str;
	if (mScene->mMetaData != nullptr && mScene->mMetaData->Get(AI_METADATA_SOURCE_COPYRIGHT, copyright_str)) {
        asset.copyright = copyright_str.C_Str();
	}
}

inline Ref<Accessor> GetSamplerInputRef(Asset& asset, std::string& animId, Ref<Buffer>& buffer, std::vector<float>& times)
{
    return ExportData(asset, animId, buffer, (unsigned int)times.size(), &times[0], AttribType::SCALAR, AttribType::SCALAR, ComponentType_FLOAT);
}

inline void ExtractTranslationSampler(Asset& asset, std::string& animId, Ref<Buffer>& buffer, const aiNodeAnim* nodeChannel, float ticksPerSecond, Animation::Sampler& sampler)
{
    const unsigned int numKeyframes = nodeChannel->mNumPositionKeys;

    std::vector<float> times(numKeyframes);
    std::vector<float> values(numKeyframes * 3);
    for (unsigned int i = 0; i < numKeyframes; ++i) {
        const aiVectorKey& key = nodeChannel->mPositionKeys[i];
        // mTime is measured in ticks, but GLTF time is measured in seconds, so convert.
        times[i] = static_cast<float>(key.mTime / ticksPerSecond);
        values[(i * 3) + 0] = key.mValue.x;
        values[(i * 3) + 1] = key.mValue.y;
        values[(i * 3) + 2] = key.mValue.z;
    }

    sampler.input = GetSamplerInputRef(asset, animId, buffer, times);
    sampler.output = ExportData(asset, animId, buffer, numKeyframes, &values[0], AttribType::VEC3, AttribType::VEC3, ComponentType_FLOAT);
    sampler.interpolation = Interpolation_LINEAR;
}

inline void ExtractScaleSampler(Asset& asset, std::string& animId, Ref<Buffer>& buffer, const aiNodeAnim* nodeChannel, float ticksPerSecond, Animation::Sampler& sampler)
{
    const unsigned int numKeyframes = nodeChannel->mNumScalingKeys;

    std::vector<float> times(numKeyframes);
    std::vector<float> values(numKeyframes * 3);
    for (unsigned int i = 0; i < numKeyframes; ++i) {
        const aiVectorKey& key = nodeChannel->mScalingKeys[i];
        // mTime is measured in ticks, but GLTF time is measured in seconds, so convert.
        times[i] = static_cast<float>(key.mTime / ticksPerSecond);
        values[(i * 3) + 0] = key.mValue.x;
        values[(i * 3) + 1] = key.mValue.y;
        values[(i * 3) + 2] = key.mValue.z;
    }

    sampler.input = GetSamplerInputRef(asset, animId, buffer, times);
    sampler.output = ExportData(asset, animId, buffer, numKeyframes, &values[0], AttribType::VEC3, AttribType::VEC3, ComponentType_FLOAT);
    sampler.interpolation = Interpolation_LINEAR;
}

inline void ExtractRotationSampler(Asset& asset, std::string& animId, Ref<Buffer>& buffer, const aiNodeAnim* nodeChannel, float ticksPerSecond, Animation::Sampler& sampler)
{
    const unsigned int numKeyframes = nodeChannel->mNumRotationKeys;

    std::vector<float> times(numKeyframes);
    std::vector<float> values(numKeyframes * 4);
    for (unsigned int i = 0; i < numKeyframes; ++i) {
        const aiQuatKey& key = nodeChannel->mRotationKeys[i];
        // mTime is measured in ticks, but GLTF time is measured in seconds, so convert.
        times[i] = static_cast<float>(key.mTime / ticksPerSecond);
        values[(i * 4) + 0] = key.mValue.x;
        values[(i * 4) + 1] = key.mValue.y;
        values[(i * 4) + 2] = key.mValue.z;
        values[(i * 4) + 3] = key.mValue.w;
    }

    sampler.input = GetSamplerInputRef(asset, animId, buffer, times);
    sampler.output = ExportData(asset, animId, buffer, numKeyframes, &values[0], AttribType::VEC4, AttribType::VEC4, ComponentType_FLOAT);
    sampler.interpolation = Interpolation_LINEAR;
}

static void AddSampler(Ref<Animation>& animRef, Ref<Node>& nodeRef, Animation::Sampler& sampler, AnimationPath path)
{
      Animation::Channel channel;
      channel.sampler = static_cast<int>(animRef->samplers.size());
      channel.target.path = path;
      channel.target.node = nodeRef;
      animRef->channels.push_back(channel);
      animRef->samplers.push_back(sampler);
}

void glTF2Exporter::ExportAnimations()
{
    Ref<Buffer> bufferRef = mAsset->buffers.Get(unsigned (0));

    for (unsigned int i = 0; i < mScene->mNumAnimations; ++i) {
        const aiAnimation* anim = mScene->mAnimations[i];
        const float ticksPerSecond = static_cast<float>(anim->mTicksPerSecond);

        std::string nameAnim = "anim";
        if (anim->mName.length > 0) {
            nameAnim = anim->mName.C_Str();
        }
        Ref<Animation> animRef = mAsset->animations.Create(nameAnim);
        animRef->name = nameAnim;

        for (unsigned int channelIndex = 0; channelIndex < anim->mNumChannels; ++channelIndex) {
            const aiNodeAnim* nodeChannel = anim->mChannels[channelIndex];

            std::string name = nameAnim + "_" + ai_to_string(channelIndex);
            name = mAsset->FindUniqueID(name, "animation");

            Ref<Node> animNode = mAsset->nodes.Get(nodeChannel->mNodeName.C_Str());

            if (nodeChannel->mNumPositionKeys > 0)
            {
                Animation::Sampler translationSampler;
                ExtractTranslationSampler(*mAsset, name, bufferRef, nodeChannel, ticksPerSecond, translationSampler);
                AddSampler(animRef, animNode, translationSampler, AnimationPath_TRANSLATION);
            }

            if (nodeChannel->mNumRotationKeys > 0)
            {
                Animation::Sampler rotationSampler;
                ExtractRotationSampler(*mAsset, name, bufferRef, nodeChannel, ticksPerSecond, rotationSampler);
                AddSampler(animRef, animNode, rotationSampler, AnimationPath_ROTATION);
            }

            if (nodeChannel->mNumScalingKeys > 0)
            {
                Animation::Sampler scaleSampler;
                ExtractScaleSampler(*mAsset, name, bufferRef, nodeChannel, ticksPerSecond, scaleSampler);
                AddSampler(animRef, animNode, scaleSampler, AnimationPath_SCALE);
            }
        }

        // Assimp documentation staes this is not used (not implemented)
        // for (unsigned int channelIndex = 0; channelIndex < anim->mNumMeshChannels; ++channelIndex) {
        //     const aiMeshAnim* meshChannel = anim->mMeshChannels[channelIndex];
        // }

    } // End: for-loop mNumAnimations
}


#endif // ASSIMP_BUILD_NO_GLTF_EXPORTER
#endif // ASSIMP_BUILD_NO_EXPORT