assimp/code/glTFExporter.cpp

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

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All rights reserved.

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* Redistributions in binary form must reproduce the above
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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 "glTFExporter.h"

#include "Exceptional.h"
#include "StringComparison.h"
#include "ByteSwapper.h"

#include "SplitLargeMeshes.h"
#include "SceneCombiner.h"

#include <assimp/version.h>
#include <assimp/IOSystem.hpp>
#include <assimp/Exporter.hpp>
#include <assimp/material.h>
#include <assimp/scene.h>

// Header files, standart library.
#include <memory>
#include <inttypes.h>
#include <iostream>

#include "glTFAssetWriter.h"

#ifdef ASSIMP_IMPORTER_GLTF_USE_OPEN3DGC
	// Header files, Open3DGC.
#	include <Open3DGC/o3dgcSC3DMCEncoder.h>
#endif

using namespace rapidjson;

using namespace Assimp;
using namespace glTF;

namespace Assimp {

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

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

} // end of namespace Assimp



glTFExporter::glTFExporter(const char* filename, IOSystem* pIOSystem, const aiScene* pScene,
                           const ExportProperties* pProperties, bool isBinary)
    : mFilename(filename)
    , mIOSystem(pIOSystem)
    , mProperties(pProperties)
{
    aiScene* sceneCopy_tmp;
    SceneCombiner::CopyScene(&sceneCopy_tmp, pScene);
    std::unique_ptr<aiScene> sceneCopy(sceneCopy_tmp);

    SplitLargeMeshesProcess_Triangle tri_splitter;
    tri_splitter.SetLimit(0xffff);
    tri_splitter.Execute(sceneCopy.get());

    SplitLargeMeshesProcess_Vertex vert_splitter;
    vert_splitter.SetLimit(0xffff);
    vert_splitter.Execute(sceneCopy.get());

    mScene = sceneCopy.get();

    std::unique_ptr<Asset> asset();
    mAsset.reset( new glTF::Asset( pIOSystem ) );

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

    ExportMetadata();

    //for (unsigned int i = 0; i < pScene->mNumCameras; ++i) {}

    //for (unsigned int i = 0; i < pScene->mNumLights; ++i) {}

    ExportMaterials();

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

    ExportMeshes();

    //for (unsigned int i = 0; i < pScene->mNumTextures; ++i) {}

    ExportScene();

    ExportAnimations();

    ExportSkins();

    glTF::AssetWriter writer(*mAsset);

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


static void CopyValue(const aiMatrix4x4& v, glTF::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 IdentityMatrix4(glTF::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;
}

inline Ref<Accessor> ExportData(Asset& a, std::string& meshName, Ref<Buffer>& buffer,
    unsigned int count, void* data, AttribType::Value typeIn, AttribType::Value typeOut, ComponentType compType, bool isIndices = false)
{
    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;
    size_t length = count * numCompsOut * bytesPerComp;
    buffer->Grow(length);

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

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

    // calculate min and max values
    {
        // Allocate and initialize with large values.
        float float_MAX = 10000000000000;
        for (int i = 0 ; i < numCompsOut ; i++) {
            acc->min.push_back( float_MAX);
            acc->max.push_back(-float_MAX);
        }

        // Search and set extreme values.
        float valueTmp;
        for (int i = 0 ; i < count       ; i++) {
        for (int j = 0 ; j < numCompsOut ; j++) {

            if (numCompsOut == 1) {
              valueTmp = static_cast<unsigned short*>(data)[i];
            } else {
              valueTmp = static_cast<aiVector3D*>(data)[i][j];
            }

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

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

    return acc;
}

namespace {
    void GetMatScalar(const aiMaterial* mat, float& val, const char* propName, int type, int idx) {
        if (mat->Get(propName, type, idx, val) == AI_SUCCESS) {}
    }
}

void glTFExporter::GetTexSampler(const aiMaterial* mat, glTF::TexProperty& prop)
{
    std::string samplerId = mAsset->FindUniqueID("", "sampler");
    prop.texture->sampler = mAsset->samplers.Create(samplerId);

    aiTextureMapMode mapU, mapV;
    aiGetMaterialInteger(mat,AI_MATKEY_MAPPINGMODE_U_DIFFUSE(0),(int*)&mapU);
    aiGetMaterialInteger(mat,AI_MATKEY_MAPPINGMODE_V_DIFFUSE(0),(int*)&mapV);

    switch (mapU) {
        case aiTextureMapMode_Wrap:
            prop.texture->sampler->wrapS = SamplerWrap_Repeat;
            break;
        case aiTextureMapMode_Clamp:
            prop.texture->sampler->wrapS = SamplerWrap_Clamp_To_Edge;
            break;
        case aiTextureMapMode_Mirror:
            prop.texture->sampler->wrapS = SamplerWrap_Mirrored_Repeat;
            break;
        case aiTextureMapMode_Decal:
        default:
            prop.texture->sampler->wrapS = SamplerWrap_Repeat;
            break;
    };

    switch (mapV) {
        case aiTextureMapMode_Wrap:
            prop.texture->sampler->wrapT = SamplerWrap_Repeat;
            break;
        case aiTextureMapMode_Clamp:
            prop.texture->sampler->wrapT = SamplerWrap_Clamp_To_Edge;
            break;
        case aiTextureMapMode_Mirror:
            prop.texture->sampler->wrapT = SamplerWrap_Mirrored_Repeat;
            break;
        case aiTextureMapMode_Decal:
        default:
            prop.texture->sampler->wrapT = SamplerWrap_Repeat;
            break;
    };

    // Hard coded Texture filtering options because I do not know where to find them in the aiMaterial.
    prop.texture->sampler->magFilter = SamplerMagFilter_Linear;
    prop.texture->sampler->minFilter = SamplerMinFilter_Linear;
}

void glTFExporter::GetMatColorOrTex(const aiMaterial* mat, glTF::TexProperty& prop, const char* propName, int type, int idx, aiTextureType tt)
{
    aiString tex;
    aiColor4D col;
    if (mat->GetTextureCount(tt) > 0) {
        if (mat->Get(AI_MATKEY_TEXTURE(tt, 0), tex) == AI_SUCCESS) {
            std::string path = tex.C_Str();

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

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

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

                    if (path[0] == '*') { // embedded
                        aiTexture* tex = mScene->mTextures[atoi(&path[1])];

                        uint8_t* data = reinterpret_cast<uint8_t*>(tex->pcData);
                        prop.texture->source->SetData(data, tex->mWidth, *mAsset);

                        if (tex->achFormatHint[0]) {
                            std::string mimeType = "image/";
                            mimeType += (memcmp(tex->achFormatHint, "jpg", 3) == 0) ? "jpeg" : tex->achFormatHint;
                            prop.texture->source->mimeType = mimeType;
                        }
                    }
                    else {
                        prop.texture->source->uri = path;
                    }

                    GetTexSampler(mat, prop);
                }
            }
        }
    }

    if (mat->Get(propName, type, idx, col) == AI_SUCCESS) {
        prop.color[0] = col.r; prop.color[1] = col.g; prop.color[2] = col.b; prop.color[3] = col.a;
    }
}


void glTFExporter::ExportMaterials()
{
    aiString aiName;
    for (unsigned int i = 0; i < mScene->mNumMaterials; ++i) {
        const aiMaterial* mat = mScene->mMaterials[i];


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

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

        GetMatColorOrTex(mat, m->ambient, AI_MATKEY_COLOR_AMBIENT, aiTextureType_AMBIENT);
        GetMatColorOrTex(mat, m->diffuse, AI_MATKEY_COLOR_DIFFUSE, aiTextureType_DIFFUSE);
        GetMatColorOrTex(mat, m->specular, AI_MATKEY_COLOR_SPECULAR, aiTextureType_SPECULAR);
        GetMatColorOrTex(mat, m->emission, AI_MATKEY_COLOR_EMISSIVE, aiTextureType_EMISSIVE);

        m->transparent = mat->Get(AI_MATKEY_OPACITY, m->transparency) == aiReturn_SUCCESS && m->transparency != 1.0;

        GetMatScalar(mat, m->shininess, AI_MATKEY_SHININESS);
    }
}

void glTFExporter::ExportMeshes()
{
    // Not for
    //     using IndicesType = decltype(aiFace::mNumIndices);
    // But yes for
    //     using IndicesType = unsigned short;
    // because "ComponentType_UNSIGNED_SHORT" used for indices. And it's a maximal type according to glTF specification.
    typedef unsigned short IndicesType;

    // Variables needed for compression. BEGIN.
    // Indices, not pointers - because pointer to buffer is changing while writing to it.
    size_t idx_srcdata_begin;// Index of buffer before writing mesh data. Also, index of begin of coordinates array in buffer.
    size_t idx_srcdata_normal = SIZE_MAX;// Index of begin of normals array in buffer. SIZE_MAX - mean that mesh has no normals.
    std::vector<size_t> idx_srcdata_tc;// Array of indices. Every index point to begin of texture coordinates array in buffer.
    size_t idx_srcdata_ind;// Index of begin of coordinates indices array in buffer.
    bool comp_allow;// Point that data of current mesh can be compressed.
    // Variables needed for compression. END.

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

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

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

		// Check if compressing requested and mesh can be encoded.
#ifdef ASSIMP_IMPORTER_GLTF_USE_OPEN3DGC
		comp_allow = mProperties->GetPropertyBool("extensions.Open3DGC.use", false);
#else
		comp_allow = false;
#endif

		if(comp_allow && (aim->mPrimitiveTypes == aiPrimitiveType_TRIANGLE) && (aim->mNumVertices > 0) && (aim->mNumFaces > 0))
		{
			idx_srcdata_tc.clear();
			idx_srcdata_tc.reserve(AI_MAX_NUMBER_OF_TEXTURECOORDS);
		}
		else
		{
			std::string msg;

			if(aim->mPrimitiveTypes != aiPrimitiveType_TRIANGLE)
				msg = "all primitives of the mesh must be a triangles.";
			else
				msg = "mesh must has vertices and faces.";

			DefaultLogger::get()->warn("GLTF: can not use Open3DGC-compression: " + msg);
            comp_allow = false;
		}

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

        p.material = mAsset->materials.Get(aim->mMaterialIndex);

		/******************* Vertices ********************/
		// If compression is used then you need parameters of uncompressed region: begin and size. At this step "begin" is stored.
		if(comp_allow) idx_srcdata_begin = b->byteLength;

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

		/******************** Normals ********************/
		if(comp_allow && (aim->mNormals > 0)) idx_srcdata_normal = b->byteLength;// Store index of normals array.

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

		/************** Texture coordinates **************/
        for (int i = 0; i < AI_MAX_NUMBER_OF_TEXTURECOORDS; ++i) {
            // 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;

				if(comp_allow) idx_srcdata_tc.push_back(b->byteLength);// Store index of texture coordinates array.

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

		/*************** Vertices indices ****************/
		idx_srcdata_ind = b->byteLength;// Store index of indices array.

		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] = uint16_t(aim->mFaces[i].mIndices[j]);
                }
            }

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

        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;
        }

		/****************** Compression ******************/
		///TODO: animation: weights, joints.
		if(comp_allow)
		{
#ifdef ASSIMP_IMPORTER_GLTF_USE_OPEN3DGC
			// Only one type of compression supported at now - Open3DGC.
			//
			o3dgc::BinaryStream bs;
			o3dgc::SC3DMCEncoder<IndicesType> encoder;
			o3dgc::IndexedFaceSet<IndicesType> comp_o3dgc_ifs;
			o3dgc::SC3DMCEncodeParams comp_o3dgc_params;

			//
			// Fill data for encoder.
			//
			// Quantization
			unsigned quant_coord = mProperties->GetPropertyInteger("extensions.Open3DGC.quantization.POSITION", 12);
			unsigned quant_normal = mProperties->GetPropertyInteger("extensions.Open3DGC.quantization.NORMAL", 10);
			unsigned quant_texcoord = mProperties->GetPropertyInteger("extensions.Open3DGC.quantization.TEXCOORD", 10);

			// Prediction
			o3dgc::O3DGCSC3DMCPredictionMode prediction_position = o3dgc::O3DGC_SC3DMC_PARALLELOGRAM_PREDICTION;
			o3dgc::O3DGCSC3DMCPredictionMode prediction_normal =  o3dgc::O3DGC_SC3DMC_SURF_NORMALS_PREDICTION;
			o3dgc::O3DGCSC3DMCPredictionMode prediction_texcoord = o3dgc::O3DGC_SC3DMC_PARALLELOGRAM_PREDICTION;

			// IndexedFacesSet: "Crease angle", "solid", "convex" are set to default.
			comp_o3dgc_ifs.SetCCW(true);
			comp_o3dgc_ifs.SetIsTriangularMesh(true);
			comp_o3dgc_ifs.SetNumFloatAttributes(0);
			// Coordinates
			comp_o3dgc_params.SetCoordQuantBits(quant_coord);
			comp_o3dgc_params.SetCoordPredMode(prediction_position);
			comp_o3dgc_ifs.SetNCoord(aim->mNumVertices);
			comp_o3dgc_ifs.SetCoord((o3dgc::Real* const)&b->GetPointer()[idx_srcdata_begin]);
			// Normals
			if(idx_srcdata_normal != SIZE_MAX)
			{
				comp_o3dgc_params.SetNormalQuantBits(quant_normal);
				comp_o3dgc_params.SetNormalPredMode(prediction_normal);
				comp_o3dgc_ifs.SetNNormal(aim->mNumVertices);
				comp_o3dgc_ifs.SetNormal((o3dgc::Real* const)&b->GetPointer()[idx_srcdata_normal]);
			}

			// Texture coordinates
			for(size_t num_tc = 0; num_tc < idx_srcdata_tc.size(); num_tc++)
			{
				size_t num = comp_o3dgc_ifs.GetNumFloatAttributes();

				comp_o3dgc_params.SetFloatAttributeQuantBits(num, quant_texcoord);
				comp_o3dgc_params.SetFloatAttributePredMode(num, prediction_texcoord);
				comp_o3dgc_ifs.SetNFloatAttribute(num, aim->mNumVertices);// number of elements.
				comp_o3dgc_ifs.SetFloatAttributeDim(num, aim->mNumUVComponents[num_tc]);// components per element: aiVector3D => x * float
				comp_o3dgc_ifs.SetFloatAttributeType(num, o3dgc::O3DGC_IFS_FLOAT_ATTRIBUTE_TYPE_TEXCOORD);
				comp_o3dgc_ifs.SetFloatAttribute(num, (o3dgc::Real* const)&b->GetPointer()[idx_srcdata_tc[num_tc]]);
				comp_o3dgc_ifs.SetNumFloatAttributes(num + 1);
			}

			// Coordinates indices
			comp_o3dgc_ifs.SetNCoordIndex(aim->mNumFaces);
			comp_o3dgc_ifs.SetCoordIndex((IndicesType* const)&b->GetPointer()[idx_srcdata_ind]);
			// Prepare to enconding
			comp_o3dgc_params.SetNumFloatAttributes(comp_o3dgc_ifs.GetNumFloatAttributes());
			if(mProperties->GetPropertyBool("extensions.Open3DGC.binary", true))
				comp_o3dgc_params.SetStreamType(o3dgc::O3DGC_STREAM_TYPE_BINARY);
			else
				comp_o3dgc_params.SetStreamType(o3dgc::O3DGC_STREAM_TYPE_ASCII);

			comp_o3dgc_ifs.ComputeMinMax(o3dgc::O3DGC_SC3DMC_MAX_ALL_DIMS);
			//
			// Encoding
			//
			encoder.Encode(comp_o3dgc_params, comp_o3dgc_ifs, bs);
			// Replace data in buffer.
			b->ReplaceData(idx_srcdata_begin, b->byteLength - idx_srcdata_begin, bs.GetBuffer(), bs.GetSize());
			//
			// Add information about extension to mesh.
			//
			// Create extension structure.
			Mesh::SCompression_Open3DGC* ext = new Mesh::SCompression_Open3DGC;

			// Fill it.
			ext->Buffer = b->id;
			ext->Offset = idx_srcdata_begin;
			ext->Count = b->byteLength - idx_srcdata_begin;
			ext->Binary = mProperties->GetPropertyBool("extensions.Open3DGC.binary");
			ext->IndicesCount = comp_o3dgc_ifs.GetNCoordIndex() * 3;
			ext->VerticesCount = comp_o3dgc_ifs.GetNCoord();
			// And assign to mesh.
			m->Extension.push_back(ext);
#endif
		}// if(comp_allow)
	}// for (unsigned int i = 0; i < mScene->mNumMeshes; ++i)
}

unsigned int glTFExporter::ExportNode(const aiNode* n)
{
    Ref<Node> node = mAsset->nodes.Create(mAsset->FindUniqueID(n->mName.C_Str(), "node"));

    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->children.push_back(mAsset->nodes.Get(idx));
    }

    return node.GetIndex();
}


void glTFExporter::ExportScene()
{
    const char* sceneName = "defaultScene";
    Ref<Scene> scene = mAsset->scenes.Create(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 glTFExporter::ExportMetadata()
{
    glTF::AssetMetadata& asset = mAsset->asset;
    asset.version = 1;

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

    asset.generator = buffer;
}


inline Ref<Accessor> ExportAnimationData(Asset& a, std::string& animId, Ref<Buffer>& buffer,
    unsigned int count, void* data, AttribType::Value typeIn, AttribType::Value typeOut, ComponentType compType)
{
    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;
    size_t length = count * numCompsOut * bytesPerComp;
    buffer->Grow(length);

    // bufferView
    Ref<BufferView> bv = a.bufferViews.Create(a.FindUniqueID(animId, "view"));
    bv->buffer = buffer;
    bv->byteOffset = unsigned(offset);
    bv->byteLength = length; //! The target that the WebGL buffer should be bound to.
    // bv->target = isIndices ? BufferViewTarget_ELEMENT_ARRAY_BUFFER : BufferViewTarget_ARRAY_BUFFER;
    bv->target = BufferViewTarget_ARRAY_BUFFER;

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

    // calculate min and max values
    {
        // Allocate and initialize with large values.
        float float_MAX = 10000000000000;
        for (int i = 0 ; i < numCompsOut ; i++) {
            acc->min.push_back( float_MAX);
            acc->max.push_back(-float_MAX);
        }

        // Search and set extreme values.
        float valueTmp;
        for (int i = 0 ; i < count       ; i++) {
        for (int j = 0 ; j < numCompsOut ; j++) {

            if (numCompsOut == 1) {
              valueTmp = static_cast<unsigned short*>(data)[i];
            } else {
              valueTmp = static_cast<aiVector3D*>(data)[i][j];
            }

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

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

    return acc;
}


inline void ExtractAnimationData(Asset& mAsset, std::string& animId, Ref<Animation>& animRef, Ref<Buffer>& buffer, const aiNodeAnim* nodeChannel)
{
    // Loop over the data and check to see if it exactly matches an existing buffer.
    //    If yes, then reference the existing corresponding accessor.
    //    Otherwise, add to the buffer and create a new accessor.

    //-------------------------------------------------------
    // Extract TIME parameter data.
    // Check if the timeStamps are the same for mPositionKeys, mRotationKeys, and mScalingKeys.
    if(nodeChannel->mNumPositionKeys > 0) {
        std::cout<< "Parameters.TIME\n";
        typedef float TimeType;
        std::vector<TimeType> timeData;
        timeData.resize(nodeChannel->mNumPositionKeys);
        for (size_t i = 0; i < nodeChannel->mNumPositionKeys; ++i) {
            timeData[i] = nodeChannel->mPositionKeys[i].mTime;  // Check if we have to cast type here. e.g. uint16_t()
        }

        Ref<Accessor> timeAccessor = ExportAnimationData(mAsset, animId, buffer, nodeChannel->mNumPositionKeys, &timeData[0], AttribType::SCALAR, AttribType::SCALAR, ComponentType_FLOAT);
        if (timeAccessor) animRef->Parameters.TIME = timeAccessor;
    }

    //-------------------------------------------------------
    // Extract translation parameter data
    if(nodeChannel->mNumPositionKeys > 0) {
        C_STRUCT aiVector3D* translationData = new aiVector3D[nodeChannel->mNumPositionKeys];
        for (size_t i = 0; i < nodeChannel->mNumPositionKeys; ++i) {
            translationData[i] = nodeChannel->mPositionKeys[i].mValue;
        }

        Ref<Accessor> tranAccessor = ExportAnimationData(mAsset, animId, buffer, nodeChannel->mNumPositionKeys, translationData, AttribType::VEC3, AttribType::VEC3, ComponentType_FLOAT);
        if (tranAccessor) animRef->Parameters.translation = tranAccessor;
    }

    //-------------------------------------------------------
    // Extract scale parameter data
    if(nodeChannel->mNumScalingKeys > 0) {
        C_STRUCT aiVector3D* scaleData = new aiVector3D[nodeChannel->mNumScalingKeys];
        for (size_t i = 0; i < nodeChannel->mNumScalingKeys; ++i) {
            scaleData[i] = nodeChannel->mScalingKeys[i].mValue;
        }

        Ref<Accessor> scaleAccessor = ExportAnimationData(mAsset, animId, buffer, nodeChannel->mNumScalingKeys, scaleData, AttribType::VEC3, AttribType::VEC3, ComponentType_FLOAT);
        if (scaleAccessor) animRef->Parameters.scale = scaleAccessor;
    }

    //-------------------------------------------------------
    // Extract rotation parameter data
    if(nodeChannel->mNumRotationKeys > 0) {
        C_STRUCT aiQuaternion* rotationData = new aiQuaternion[nodeChannel->mNumRotationKeys];
        for (size_t i = 0; i < nodeChannel->mNumRotationKeys; ++i) {
            rotationData[i] = nodeChannel->mRotationKeys[i].mValue;
        }

        Ref<Accessor> rotAccessor = ExportAnimationData(mAsset, animId, buffer, nodeChannel->mNumRotationKeys, rotationData, AttribType::VEC4, AttribType::VEC4, ComponentType_FLOAT);
        if (rotAccessor) animRef->Parameters.rotation = rotAccessor;
    }
}




void glTFExporter::ExportAnimations()
{
    Ref<Buffer> bufferRef = mAsset->buffers.Get(unsigned (0));
    std::cout<<"GetBodyBuffer " << bufferRef << "\n";

    std::cout<<"mNumAnimations " << mScene->mNumAnimations << "\n";
    for (unsigned int i = 0; i < mScene->mNumAnimations; ++i) {
        const aiAnimation* anim = mScene->mAnimations[i];

        std::string nameAnim = "anim";
        if (anim->mName.length > 0) {
            nameAnim = anim->mName.C_Str();
        }

        std::cout<<"mNumChannels " << anim->mNumChannels << "\n";
        for (unsigned int channelIndex = 0; channelIndex < anim->mNumChannels; ++channelIndex) {
            const aiNodeAnim* nodeChannel = anim->mChannels[channelIndex];

            // It appears that assimp stores this type of animation as multiple animations.
            // where each aiNodeAnim in mChannels animates a specific node.
            std::string name = nameAnim + "_" + std::to_string(channelIndex);
            name = mAsset->FindUniqueID(name, "animation");
            Ref<Animation> animRef = mAsset->animations.Create(name);
            std::cout<<"channelName " << name << "\n";

            /******************* Parameters ********************/
            ExtractAnimationData(*mAsset, name, animRef, bufferRef, nodeChannel);

            for (unsigned int j = 0; j < 3; ++j) {
                std::string channelType;
                int channelSize;
                switch (j) {
                    case 0:
                        channelType = "rotation";
                        channelSize = nodeChannel->mNumRotationKeys;
                        break;
                    case 1:
                        channelType = "scale";
                        channelSize = nodeChannel->mNumScalingKeys;
                        break;
                    case 2:
                        channelType = "translation";
                        channelSize = nodeChannel->mNumPositionKeys;
                        break;
                }

                if (channelSize < 1) { continue; }

                std::cout<<"channelType " << channelType << "\n";

                Animation::AnimChannel tmpAnimChannel;
                Animation::AnimSampler tmpAnimSampler;

                tmpAnimChannel.sampler = name + "_" + channelType;
                tmpAnimChannel.target.path = channelType;
                tmpAnimSampler.output = channelType;
                tmpAnimSampler.id = name + "_" + channelType;

                std::cout<<"nodeChannel->mNodeName.C_Str() " << nodeChannel->mNodeName.C_Str() << "\n";
                tmpAnimChannel.target.id = mAsset->nodes.Get(nodeChannel->mNodeName.C_Str());
                std::cout<<"tmpAnimChannel.target.id " << tmpAnimChannel.target.id << "\n";

                tmpAnimSampler.input = "TIME";
                tmpAnimSampler.interpolation = "LINEAR";

                animRef->Channels.push_back(tmpAnimChannel);
                animRef->Samplers.push_back(tmpAnimSampler);
            }

        }

        std::cout<<"mNumMeshChannels " << anim->mNumMeshChannels << "\n";
        for (unsigned int channelIndex = 0; channelIndex < anim->mNumMeshChannels; ++channelIndex) {
            const aiMeshAnim* meshChannel = anim->mMeshChannels[channelIndex];
        }

    } // End: for-loop mNumAnimations
}



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

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

        if(!aim->HasBones()) { continue; } // skip to next mesh if no bones exist.

        std::string skinName = aim->mName.C_Str();
        skinName = mAsset->FindUniqueID(skinName, "skin");
        Ref<Skin> skinRef = mAsset->skins.Create(skinName);
        skinRef->name = skinName;

        mat4* inverseBindMatricesData = new mat4[aim->mNumBones];

        for (unsigned int idx_bone = 0; idx_bone < aim->mNumBones; ++idx_bone) {
            const aiBone* aib = aim->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 = "joint_" + std::to_string(idx_bone);
            skinRef->jointNames.push_back("joint_" + std::to_string(idx_bone));
            std::cout << "Node->id " << nodeRef->id << "\n";

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


            // aib->mOffsetMatrix   =====>  skinRef->inverseBindMatrices
            CopyValue(aib->mOffsetMatrix, inverseBindMatricesData[idx_bone]);

            // aib->mNumWeights;
            // aib->mWeights;

        } // End: for-loop mNumMeshes

        Ref<Accessor> invBindMatrixAccessor = ExportAnimationData(*mAsset, skinName, bufferRef, aim->mNumBones, inverseBindMatricesData, AttribType::MAT4, AttribType::MAT4, ComponentType_FLOAT);
        if (invBindMatrixAccessor) skinRef->inverseBindMatrices = invBindMatrixAccessor;

    } // End: for-loop mNumMeshes
}




#endif // ASSIMP_BUILD_NO_GLTF_EXPORTER
#endif // ASSIMP_BUILD_NO_EXPORT