assimp.assimp/code/glTF2Importer.cpp

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

Copyright (c) 2006-2018, 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
following conditions are met:

* Redistributions of source code must retain the above
copyright notice, this list of conditions and the
following disclaimer.

* Redistributions in binary form must reproduce the above
copyright notice, this list of conditions and the
following disclaimer in the documentation and/or other
materials provided with the distribution.

* Neither the name of the assimp team, nor the names of its
contributors may be used to endorse or promote products
derived from this software without specific prior
written permission of the assimp team.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

----------------------------------------------------------------------
*/

#ifndef ASSIMP_BUILD_NO_GLTF_IMPORTER

#include "glTF2Importer.h"
#include <assimp/StringComparison.h>
#include <assimp/StringUtils.h>

#include <assimp/Importer.hpp>
#include <assimp/scene.h>
#include <assimp/ai_assert.h>
#include <assimp/DefaultLogger.hpp>
#include <assimp/importerdesc.h>
#include <assimp/CreateAnimMesh.h>

#include <memory>

#include "MakeVerboseFormat.h"

#include "glTF2Asset.h"
// This is included here so WriteLazyDict<T>'s definition is found.
#include "glTF2AssetWriter.h"
#include <rapidjson/document.h>
#include <rapidjson/rapidjson.h>

using namespace Assimp;
using namespace glTF2;

namespace {
    // generate bitangents from normals and tangents according to spec
    struct Tangent {
        aiVector3D xyz;
        ai_real w;
    };
} // namespace

//
// glTF2Importer
//

static const aiImporterDesc desc = {
    "glTF2 Importer",
    "",
    "",
    "",
    aiImporterFlags_SupportTextFlavour | aiImporterFlags_SupportBinaryFlavour | aiImporterFlags_LimitedSupport | aiImporterFlags_Experimental,
    0,
    0,
    0,
    0,
    "gltf glb"
};

glTF2Importer::glTF2Importer()
: BaseImporter()
, meshOffsets()
, embeddedTexIdxs()
, mScene( NULL ) {
    // empty
}

glTF2Importer::~glTF2Importer() {
    // empty
}

const aiImporterDesc* glTF2Importer::GetInfo() const
{
    return &desc;
}

bool glTF2Importer::CanRead(const std::string& pFile, IOSystem* pIOHandler, bool /* checkSig */) const
{
    const std::string &extension = GetExtension(pFile);

    if (extension != "gltf" && extension != "glb")
        return false;

    if (pIOHandler) {
        glTF2::Asset asset(pIOHandler);
        asset.Load(pFile, extension == "glb");
        std::string version = asset.asset.version;
        return !version.empty() && version[0] == '2';
    }

    return false;
}

static aiTextureMapMode ConvertWrappingMode(SamplerWrap gltfWrapMode)
{
    switch (gltfWrapMode) {
        case SamplerWrap::Mirrored_Repeat:
            return aiTextureMapMode_Mirror;

        case SamplerWrap::Clamp_To_Edge:
            return aiTextureMapMode_Clamp;

        case SamplerWrap::UNSET:
        case SamplerWrap::Repeat:
        default:
            return aiTextureMapMode_Wrap;
    }
}

//static void CopyValue(const glTF2::vec3& v, aiColor3D& out)
//{
//    out.r = v[0]; out.g = v[1]; out.b = v[2];
//}

static void CopyValue(const glTF2::vec4& v, aiColor4D& out)
{
    out.r = v[0]; out.g = v[1]; out.b = v[2]; out.a = v[3];
}

/*static void CopyValue(const glTF2::vec4& v, aiColor3D& out)
{
    out.r = v[0]; out.g = v[1]; out.b = v[2];
}*/

static void CopyValue(const glTF2::vec3& v, aiColor4D& out)
{
    out.r = v[0]; out.g = v[1]; out.b = v[2]; out.a = 1.0;
}

static void CopyValue(const glTF2::vec3& v, aiVector3D& out)
{
    out.x = v[0]; out.y = v[1]; out.z = v[2];
}

static void CopyValue(const glTF2::vec4& v, aiQuaternion& out)
{
    out.x = v[0]; out.y = v[1]; out.z = v[2]; out.w = v[3];
}

static void CopyValue(const glTF2::mat4& v, aiMatrix4x4& o)
{
    o.a1 = v[ 0]; o.b1 = v[ 1]; o.c1 = v[ 2]; o.d1 = v[ 3];
    o.a2 = v[ 4]; o.b2 = v[ 5]; o.c2 = v[ 6]; o.d2 = v[ 7];
    o.a3 = v[ 8]; o.b3 = v[ 9]; o.c3 = v[10]; o.d3 = v[11];
    o.a4 = v[12]; o.b4 = v[13]; o.c4 = v[14]; o.d4 = v[15];
}

inline void SetMaterialColorProperty(Asset& /*r*/, vec4& prop, aiMaterial* mat, const char* pKey, unsigned int type, unsigned int idx)
{
    aiColor4D col;
    CopyValue(prop, col);
    mat->AddProperty(&col, 1, pKey, type, idx);
}

inline void SetMaterialColorProperty(Asset& /*r*/, vec3& prop, aiMaterial* mat, const char* pKey, unsigned int type, unsigned int idx)
{
    aiColor4D col;
    CopyValue(prop, col);
    mat->AddProperty(&col, 1, pKey, type, idx);
}

inline void SetMaterialTextureProperty(std::vector<int>& embeddedTexIdxs, Asset& /*r*/, glTF2::TextureInfo prop, aiMaterial* mat, aiTextureType texType, unsigned int texSlot = 0)
{
    if (prop.texture && prop.texture->source) {
        aiString uri(prop.texture->source->uri);

        int texIdx = embeddedTexIdxs[prop.texture->source.GetIndex()];
        if (texIdx != -1) { // embedded
            // setup texture reference string (copied from ColladaLoader::FindFilenameForEffectTexture)
            uri.data[0] = '*';
            uri.length = 1 + ASSIMP_itoa10(uri.data + 1, MAXLEN - 1, texIdx);
        }

        mat->AddProperty(&uri, AI_MATKEY_TEXTURE(texType, texSlot));
        mat->AddProperty(&prop.texCoord, 1, _AI_MATKEY_GLTF_TEXTURE_TEXCOORD_BASE, texType, texSlot);

        if (prop.texture->sampler) {
            Ref<Sampler> sampler = prop.texture->sampler;

            aiString name(sampler->name);
            aiString id(sampler->id);

            mat->AddProperty(&name, AI_MATKEY_GLTF_MAPPINGNAME(texType, texSlot));
            mat->AddProperty(&id, AI_MATKEY_GLTF_MAPPINGID(texType, texSlot));

            aiTextureMapMode wrapS = ConvertWrappingMode(sampler->wrapS);
            aiTextureMapMode wrapT = ConvertWrappingMode(sampler->wrapT);
            mat->AddProperty(&wrapS, 1, AI_MATKEY_MAPPINGMODE_U(texType, texSlot));
            mat->AddProperty(&wrapT, 1, AI_MATKEY_MAPPINGMODE_V(texType, texSlot));

            if (sampler->magFilter != SamplerMagFilter::UNSET) {
                mat->AddProperty(&sampler->magFilter, 1, AI_MATKEY_GLTF_MAPPINGFILTER_MAG(texType, texSlot));
            }

            if (sampler->minFilter != SamplerMinFilter::UNSET) {
                mat->AddProperty(&sampler->minFilter, 1, AI_MATKEY_GLTF_MAPPINGFILTER_MIN(texType, texSlot));
            }
        }
    }
}

inline void SetMaterialTextureProperty(std::vector<int>& embeddedTexIdxs, Asset& r, glTF2::NormalTextureInfo& prop, aiMaterial* mat, aiTextureType texType, unsigned int texSlot = 0)
{
    SetMaterialTextureProperty( embeddedTexIdxs, r, (glTF2::TextureInfo) prop, mat, texType, texSlot );

    if (prop.texture && prop.texture->source) {
         mat->AddProperty(&prop.scale, 1, AI_MATKEY_GLTF_TEXTURE_SCALE(texType, texSlot));
    }
}

inline void SetMaterialTextureProperty(std::vector<int>& embeddedTexIdxs, Asset& r, glTF2::OcclusionTextureInfo& prop, aiMaterial* mat, aiTextureType texType, unsigned int texSlot = 0)
{
    SetMaterialTextureProperty( embeddedTexIdxs, r, (glTF2::TextureInfo) prop, mat, texType, texSlot );

    if (prop.texture && prop.texture->source) {
        mat->AddProperty(&prop.strength, 1, AI_MATKEY_GLTF_TEXTURE_STRENGTH(texType, texSlot));
    }
}

static aiMaterial* ImportMaterial(std::vector<int>& embeddedTexIdxs, Asset& r, Material& mat)
{
    aiMaterial* aimat = new aiMaterial();

   if (!mat.name.empty()) {
        aiString str(mat.name);

        aimat->AddProperty(&str, AI_MATKEY_NAME);
    }

    SetMaterialColorProperty(r, mat.pbrMetallicRoughness.baseColorFactor, aimat, AI_MATKEY_COLOR_DIFFUSE);
    SetMaterialColorProperty(r, mat.pbrMetallicRoughness.baseColorFactor, aimat, AI_MATKEY_GLTF_PBRMETALLICROUGHNESS_BASE_COLOR_FACTOR);

    SetMaterialTextureProperty(embeddedTexIdxs, r, mat.pbrMetallicRoughness.baseColorTexture, aimat, aiTextureType_DIFFUSE);
    SetMaterialTextureProperty(embeddedTexIdxs, r, mat.pbrMetallicRoughness.baseColorTexture, aimat, AI_MATKEY_GLTF_PBRMETALLICROUGHNESS_BASE_COLOR_TEXTURE);

    SetMaterialTextureProperty(embeddedTexIdxs, r, mat.pbrMetallicRoughness.metallicRoughnessTexture, aimat, AI_MATKEY_GLTF_PBRMETALLICROUGHNESS_METALLICROUGHNESS_TEXTURE);

    aimat->AddProperty(&mat.pbrMetallicRoughness.metallicFactor, 1, AI_MATKEY_GLTF_PBRMETALLICROUGHNESS_METALLIC_FACTOR);
    aimat->AddProperty(&mat.pbrMetallicRoughness.roughnessFactor, 1, AI_MATKEY_GLTF_PBRMETALLICROUGHNESS_ROUGHNESS_FACTOR);

    float roughnessAsShininess = (1 - mat.pbrMetallicRoughness.roughnessFactor) * 1000;
    aimat->AddProperty(&roughnessAsShininess, 1, AI_MATKEY_SHININESS);

    SetMaterialTextureProperty(embeddedTexIdxs, r, mat.normalTexture, aimat, aiTextureType_NORMALS);
    SetMaterialTextureProperty(embeddedTexIdxs, r, mat.occlusionTexture, aimat, aiTextureType_LIGHTMAP);
    SetMaterialTextureProperty(embeddedTexIdxs, r, mat.emissiveTexture, aimat, aiTextureType_EMISSIVE);
    SetMaterialColorProperty(r, mat.emissiveFactor, aimat, AI_MATKEY_COLOR_EMISSIVE);

    aimat->AddProperty(&mat.doubleSided, 1, AI_MATKEY_TWOSIDED);

    aiString alphaMode(mat.alphaMode);
    aimat->AddProperty(&alphaMode, AI_MATKEY_GLTF_ALPHAMODE);
    aimat->AddProperty(&mat.alphaCutoff, 1, AI_MATKEY_GLTF_ALPHACUTOFF);

    //pbrSpecularGlossiness
    if (mat.pbrSpecularGlossiness.isPresent) {
        PbrSpecularGlossiness &pbrSG = mat.pbrSpecularGlossiness.value;

        aimat->AddProperty(&mat.pbrSpecularGlossiness.isPresent, 1, AI_MATKEY_GLTF_PBRSPECULARGLOSSINESS);
        SetMaterialColorProperty(r, pbrSG.diffuseFactor, aimat, AI_MATKEY_COLOR_DIFFUSE);
        SetMaterialColorProperty(r, pbrSG.specularFactor, aimat, AI_MATKEY_COLOR_SPECULAR);

        float glossinessAsShininess = pbrSG.glossinessFactor * 1000.0f;
        aimat->AddProperty(&glossinessAsShininess, 1, AI_MATKEY_SHININESS);
        aimat->AddProperty(&pbrSG.glossinessFactor, 1, AI_MATKEY_GLTF_PBRSPECULARGLOSSINESS_GLOSSINESS_FACTOR);

        SetMaterialTextureProperty(embeddedTexIdxs, r, pbrSG.diffuseTexture, aimat, aiTextureType_DIFFUSE);

        SetMaterialTextureProperty(embeddedTexIdxs, r, pbrSG.specularGlossinessTexture, aimat, aiTextureType_SPECULAR);
    }
    if (mat.unlit) {
        aimat->AddProperty(&mat.unlit, 1, AI_MATKEY_GLTF_UNLIT);
    }

    return aimat;
}

void glTF2Importer::ImportMaterials(glTF2::Asset& r)
{
    const unsigned int numImportedMaterials = unsigned(r.materials.Size());
    Material defaultMaterial;

    mScene->mNumMaterials = numImportedMaterials + 1;
    mScene->mMaterials = new aiMaterial*[mScene->mNumMaterials];
    mScene->mMaterials[numImportedMaterials] = ImportMaterial(embeddedTexIdxs, r, defaultMaterial);

    for (unsigned int i = 0; i < numImportedMaterials; ++i) {
       mScene->mMaterials[i] = ImportMaterial(embeddedTexIdxs, r, r.materials[i]);
    }
}


static inline void SetFace(aiFace& face, int a)
{
    face.mNumIndices = 1;
    face.mIndices = new unsigned int[1];
    face.mIndices[0] = a;
}

static inline void SetFace(aiFace& face, int a, int b)
{
    face.mNumIndices = 2;
    face.mIndices = new unsigned int[2];
    face.mIndices[0] = a;
    face.mIndices[1] = b;
}

static inline void SetFace(aiFace& face, int a, int b, int c)
{
    face.mNumIndices = 3;
    face.mIndices = new unsigned int[3];
    face.mIndices[0] = a;
    face.mIndices[1] = b;
    face.mIndices[2] = c;
}

#ifdef ASSIMP_BUILD_DEBUG
static inline bool CheckValidFacesIndices(aiFace* faces, unsigned nFaces, unsigned nVerts)
{
    for (unsigned i = 0; i < nFaces; ++i) {
        for (unsigned j = 0; j < faces[i].mNumIndices; ++j) {
            unsigned idx = faces[i].mIndices[j];
            if (idx >= nVerts)
                return false;
        }
    }
    return true;
}
#endif // ASSIMP_BUILD_DEBUG

void glTF2Importer::ImportMeshes(glTF2::Asset& r)
{
    std::vector<aiMesh*> meshes;

    unsigned int k = 0;

    for (unsigned int m = 0; m < r.meshes.Size(); ++m) {
        Mesh& mesh = r.meshes[m];

        meshOffsets.push_back(k);
        k += unsigned(mesh.primitives.size());

        for (unsigned int p = 0; p < mesh.primitives.size(); ++p) {
            Mesh::Primitive& prim = mesh.primitives[p];

            aiMesh* aim = new aiMesh();
            meshes.push_back(aim);

            aim->mName = mesh.name.empty() ? mesh.id : mesh.name;

            if (mesh.primitives.size() > 1) {
                size_t& len = aim->mName.length;
                aim->mName.data[len] = '-';
                len += 1 + ASSIMP_itoa10(aim->mName.data + len + 1, unsigned(MAXLEN - len - 1), p);
            }

            switch (prim.mode) {
                case PrimitiveMode_POINTS:
                    aim->mPrimitiveTypes |= aiPrimitiveType_POINT;
                    break;

                case PrimitiveMode_LINES:
                case PrimitiveMode_LINE_LOOP:
                case PrimitiveMode_LINE_STRIP:
                    aim->mPrimitiveTypes |= aiPrimitiveType_LINE;
                    break;

                case PrimitiveMode_TRIANGLES:
                case PrimitiveMode_TRIANGLE_STRIP:
                case PrimitiveMode_TRIANGLE_FAN:
                    aim->mPrimitiveTypes |= aiPrimitiveType_TRIANGLE;
                    break;

            }

            Mesh::Primitive::Attributes& attr = prim.attributes;

            if (attr.position.size() > 0 && attr.position[0]) {
                aim->mNumVertices = attr.position[0]->count;
                attr.position[0]->ExtractData(aim->mVertices);
            }

            if (attr.normal.size() > 0 && attr.normal[0]) {
                attr.normal[0]->ExtractData(aim->mNormals);

                // only extract tangents if normals are present
                if (attr.tangent.size() > 0 && attr.tangent[0]) {
                    // generate bitangents from normals and tangents according to spec
                    Tangent *tangents = nullptr;

                    attr.tangent[0]->ExtractData(tangents);

                    aim->mTangents = new aiVector3D[aim->mNumVertices];
                    aim->mBitangents = new aiVector3D[aim->mNumVertices];

                    for (unsigned int i = 0; i < aim->mNumVertices; ++i) {
                        aim->mTangents[i] = tangents[i].xyz;
                        aim->mBitangents[i] = (aim->mNormals[i] ^ tangents[i].xyz) * tangents[i].w;
                    }

                    delete [] tangents;
                }
            }

            for (size_t tc = 0; tc < attr.texcoord.size() && tc < AI_MAX_NUMBER_OF_TEXTURECOORDS; ++tc) {
                if (attr.texcoord[tc]->count != aim->mNumVertices) {
                    DefaultLogger::get()->warn("Texcoord stream size in mesh \"" + mesh.name +
                                               "\" does not match the vertex count");
                    continue;
                }

                attr.texcoord[tc]->ExtractData(aim->mTextureCoords[tc]);
                aim->mNumUVComponents[tc] = attr.texcoord[tc]->GetNumComponents();

                aiVector3D* values = aim->mTextureCoords[tc];
                for (unsigned int i = 0; i < aim->mNumVertices; ++i) {
                    values[i].y = 1 - values[i].y; // Flip Y coords
                }
            }

            std::vector<Mesh::Primitive::Target>& targets = prim.targets;
            if (targets.size() > 0) {
                aim->mNumAnimMeshes = (unsigned int)targets.size();
                aim->mAnimMeshes = new aiAnimMesh*[aim->mNumAnimMeshes];
                for (size_t i = 0; i < targets.size(); i++) {
                    aim->mAnimMeshes[i] = aiCreateAnimMesh(aim);
                    aiAnimMesh& aiAnimMesh = *(aim->mAnimMeshes[i]);
                    Mesh::Primitive::Target& target = targets[i];

                    if (target.position.size() > 0) {
                        aiVector3D *positionDiff = nullptr;
                        target.position[0]->ExtractData(positionDiff);
                        for(unsigned int vertexId = 0; vertexId < aim->mNumVertices; vertexId++) {
                            aiAnimMesh.mVertices[vertexId] += positionDiff[vertexId];
                        }
                        delete [] positionDiff;
                    }
                    if (target.normal.size() > 0) {
                        aiVector3D *normalDiff = nullptr;
                        target.normal[0]->ExtractData(normalDiff);
                        for(unsigned int vertexId = 0; vertexId < aim->mNumVertices; vertexId++) {
                            aiAnimMesh.mNormals[vertexId] += normalDiff[vertexId];
                        }
                        delete [] normalDiff;
                    }
                    if (target.tangent.size() > 0) {
                        Tangent *tangent = nullptr;
                        attr.tangent[0]->ExtractData(tangent);

                        aiVector3D *tangentDiff = nullptr;
                        target.tangent[0]->ExtractData(tangentDiff);

                        for (unsigned int vertexId = 0; vertexId < aim->mNumVertices; ++vertexId) {
                            tangent[vertexId].xyz += tangentDiff[vertexId];
                            aiAnimMesh.mTangents[vertexId] = tangent[vertexId].xyz;
                            aiAnimMesh.mBitangents[vertexId] = (aiAnimMesh.mNormals[vertexId] ^ tangent[vertexId].xyz) * tangent[vertexId].w;
                        }
                        delete [] tangent;
                        delete [] tangentDiff;
                    }
                    if (mesh.weights.size() > i) {
                        aiAnimMesh.mWeight = mesh.weights[i];
                    }
                }
            }


            aiFace* faces = 0;
            unsigned int nFaces = 0;

            if (prim.indices) {
                unsigned int count = prim.indices->count;

                Accessor::Indexer data = prim.indices->GetIndexer();
                ai_assert(data.IsValid());

                switch (prim.mode) {
                    case PrimitiveMode_POINTS: {
                        nFaces = count;
                        faces = new aiFace[nFaces];
                        for (unsigned int i = 0; i < count; ++i) {
                            SetFace(faces[i], data.GetUInt(i));
                        }
                        break;
                    }

                    case PrimitiveMode_LINES: {
                        nFaces = count / 2;
                        faces = new aiFace[nFaces];
                        for (unsigned int i = 0; i < count; i += 2) {
                            SetFace(faces[i / 2], data.GetUInt(i), data.GetUInt(i + 1));
                        }
                        break;
                    }

                    case PrimitiveMode_LINE_LOOP:
                    case PrimitiveMode_LINE_STRIP: {
                        nFaces = count - ((prim.mode == PrimitiveMode_LINE_STRIP) ? 1 : 0);
                        faces = new aiFace[nFaces];
                        SetFace(faces[0], data.GetUInt(0), data.GetUInt(1));
                        for (unsigned int i = 2; i < count; ++i) {
                            SetFace(faces[i - 1], faces[i - 2].mIndices[1], data.GetUInt(i));
                        }
                        if (prim.mode == PrimitiveMode_LINE_LOOP) { // close the loop
                            SetFace(faces[count - 1], faces[count - 2].mIndices[1], faces[0].mIndices[0]);
                        }
                        break;
                    }

                    case PrimitiveMode_TRIANGLES: {
                        nFaces = count / 3;
                        faces = new aiFace[nFaces];
                        for (unsigned int i = 0; i < count; i += 3) {
                            SetFace(faces[i / 3], data.GetUInt(i), data.GetUInt(i + 1), data.GetUInt(i + 2));
                        }
                        break;
                    }
                    case PrimitiveMode_TRIANGLE_STRIP: {
                        nFaces = count - 2;
                        faces = new aiFace[nFaces];
                        for (unsigned int i = 0; i < nFaces; ++i) {
                            //The ordering is to ensure that the triangles are all drawn with the same orientation
                            if ((i + 1) % 2 == 0)
                            {
                                //For even n, vertices n + 1, n, and n + 2 define triangle n
                                SetFace(faces[i], data.GetUInt(i + 1), data.GetUInt(i), data.GetUInt(i + 2));
                            }
                            else
                            {
                                //For odd n, vertices n, n+1, and n+2 define triangle n
                                SetFace(faces[i], data.GetUInt(i), data.GetUInt(i + 1), data.GetUInt(i + 2));
                            }
                        }
                        break;
                    }
                    case PrimitiveMode_TRIANGLE_FAN:
                        nFaces = count - 2;
                        faces = new aiFace[nFaces];
                        SetFace(faces[0], data.GetUInt(0), data.GetUInt(1), data.GetUInt(2));
                        for (unsigned int i = 1; i < nFaces; ++i) {
                            SetFace(faces[i], faces[0].mIndices[0], faces[i - 1].mIndices[2], data.GetUInt(i + 2));
                        }
                        break;
                }
            }
            else { // no indices provided so directly generate from counts

                // use the already determined count as it includes checks 
                unsigned int count = aim->mNumVertices;

                switch (prim.mode) {
                case PrimitiveMode_POINTS: {
                    nFaces = count;
                    faces = new aiFace[nFaces];
                    for (unsigned int i = 0; i < count; ++i) {
                        SetFace(faces[i], i);
                    }
                    break;
                }

                case PrimitiveMode_LINES: {
                    nFaces = count / 2;
                    faces = new aiFace[nFaces];
                    for (unsigned int i = 0; i < count; i += 2) {
                        SetFace(faces[i / 2], i, i + 1);
                    }
                    break;
                }

                case PrimitiveMode_LINE_LOOP:
                case PrimitiveMode_LINE_STRIP: {
                    nFaces = count - ((prim.mode == PrimitiveMode_LINE_STRIP) ? 1 : 0);
                    faces = new aiFace[nFaces];
                    SetFace(faces[0], 0, 1);
                    for (unsigned int i = 2; i < count; ++i) {
                        SetFace(faces[i - 1], faces[i - 2].mIndices[1], i);
                    }
                    if (prim.mode == PrimitiveMode_LINE_LOOP) { // close the loop
                        SetFace(faces[count - 1], faces[count - 2].mIndices[1], faces[0].mIndices[0]);
                    }
                    break;
                }

                case PrimitiveMode_TRIANGLES: {
                    nFaces = count / 3;
                    faces = new aiFace[nFaces];
                    for (unsigned int i = 0; i < count; i += 3) {
                        SetFace(faces[i / 3], i, i + 1, i + 2);
                    }
                    break;
                }
                case PrimitiveMode_TRIANGLE_STRIP: {
                    nFaces = count - 2;
                    faces = new aiFace[nFaces];
                    for (unsigned int i = 0; i < nFaces; ++i) {
                        //The ordering is to ensure that the triangles are all drawn with the same orientation
                        if ((i+1) % 2 == 0)
                        {
                            //For even n, vertices n + 1, n, and n + 2 define triangle n
                            SetFace(faces[i], i+1, i, i+2);
                        }
                        else
                        {
                            //For odd n, vertices n, n+1, and n+2 define triangle n
                            SetFace(faces[i], i, i+1, i+2);
                        }
                    }
                    break;
                }
                case PrimitiveMode_TRIANGLE_FAN:
                    nFaces = count - 2;
                    faces = new aiFace[nFaces];
                    SetFace(faces[0], 0, 1, 2);
                    for (unsigned int i = 1; i < nFaces; ++i) {
                        SetFace(faces[i], faces[0].mIndices[0], faces[i - 1].mIndices[2], i + 2);
                    }
                    break;
                }
            }

            if (faces) {
                aim->mFaces = faces;
                aim->mNumFaces = nFaces;
                ai_assert(CheckValidFacesIndices(faces, nFaces, aim->mNumVertices));
            }

            if (prim.material) {
                aim->mMaterialIndex = prim.material.GetIndex();
            }
            else {
                aim->mMaterialIndex = mScene->mNumMaterials - 1;
            }

        }
    }

    meshOffsets.push_back(k);

    CopyVector(meshes, mScene->mMeshes, mScene->mNumMeshes);
}

void glTF2Importer::ImportCameras(glTF2::Asset& r)
{
    if (!r.cameras.Size()) return;

    mScene->mNumCameras = r.cameras.Size();
    mScene->mCameras = new aiCamera*[r.cameras.Size()];

    for (size_t i = 0; i < r.cameras.Size(); ++i) {
        Camera& cam = r.cameras[i];

        aiCamera* aicam = mScene->mCameras[i] = new aiCamera();

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

        if (cam.type == Camera::Perspective) {

            aicam->mAspect        = cam.cameraProperties.perspective.aspectRatio;
            aicam->mHorizontalFOV = cam.cameraProperties.perspective.yfov * aicam->mAspect;
            aicam->mClipPlaneFar  = cam.cameraProperties.perspective.zfar;
            aicam->mClipPlaneNear = cam.cameraProperties.perspective.znear;
        }
        else {
            // assimp does not support orthographic cameras
        }
    }
}

aiNode* ImportNode(aiScene* pScene, glTF2::Asset& r, std::vector<unsigned int>& meshOffsets, glTF2::Ref<glTF2::Node>& ptr)
{
    Node& node = *ptr;

    std::string nameOrId = node.name.empty() ? node.id : node.name;

    aiNode* ainode = new aiNode(nameOrId);

    if (!node.children.empty()) {
        ainode->mNumChildren = unsigned(node.children.size());
        ainode->mChildren = new aiNode*[ainode->mNumChildren];

        for (unsigned int i = 0; i < ainode->mNumChildren; ++i) {
            aiNode* child = ImportNode(pScene, r, meshOffsets, node.children[i]);
            child->mParent = ainode;
            ainode->mChildren[i] = child;
        }
    }

    aiMatrix4x4& matrix = ainode->mTransformation;
    if (node.matrix.isPresent) {
        CopyValue(node.matrix.value, matrix);
    }
    else {
        if (node.translation.isPresent) {
            aiVector3D trans;
            CopyValue(node.translation.value, trans);
            aiMatrix4x4 t;
            aiMatrix4x4::Translation(trans, t);
            matrix = matrix * t;
        }

        if (node.rotation.isPresent) {
            aiQuaternion rot;
            CopyValue(node.rotation.value, rot);
            matrix = matrix * aiMatrix4x4(rot.GetMatrix());
        }

        if (node.scale.isPresent) {
            aiVector3D scal(1.f);
            CopyValue(node.scale.value, scal);
            aiMatrix4x4 s;
            aiMatrix4x4::Scaling(scal, s);
            matrix = matrix * s;
        }
    }

    if (!node.meshes.empty()) {
        int count = 0;
        for (size_t i = 0; i < node.meshes.size(); ++i) {
            int idx = node.meshes[i].GetIndex();
            count += meshOffsets[idx + 1] - meshOffsets[idx];
        }
        ainode->mNumMeshes = count;

        ainode->mMeshes = new unsigned int[count];

        int k = 0;
        for (size_t i = 0; i < node.meshes.size(); ++i) {
            int idx = node.meshes[i].GetIndex();
            for (unsigned int j = meshOffsets[idx]; j < meshOffsets[idx + 1]; ++j, ++k) {
                ainode->mMeshes[k] = j;
            }
        }
    }

    if (node.camera) {
        pScene->mCameras[node.camera.GetIndex()]->mName = ainode->mName;
    }

    return ainode;
}

void glTF2Importer::ImportNodes(glTF2::Asset& r)
{
    if (!r.scene) return;

    std::vector< Ref<Node> > rootNodes = r.scene->nodes;

    // The root nodes
    unsigned int numRootNodes = unsigned(rootNodes.size());
    if (numRootNodes == 1) { // a single root node: use it
        mScene->mRootNode = ImportNode(mScene, r, meshOffsets, rootNodes[0]);
    }
    else if (numRootNodes > 1) { // more than one root node: create a fake root
        aiNode* root = new aiNode("ROOT");
        root->mChildren = new aiNode*[numRootNodes];
        for (unsigned int i = 0; i < numRootNodes; ++i) {
            aiNode* node = ImportNode(mScene, r, meshOffsets, rootNodes[i]);
            node->mParent = root;
            root->mChildren[root->mNumChildren++] = node;
        }
        mScene->mRootNode = root;
    }

    //if (!mScene->mRootNode) {
    //  mScene->mRootNode = new aiNode("EMPTY");
    //}
}

void glTF2Importer::ImportEmbeddedTextures(glTF2::Asset& r)
{
    embeddedTexIdxs.resize(r.images.Size(), -1);

    int numEmbeddedTexs = 0;
    for (size_t i = 0; i < r.images.Size(); ++i) {
        if (r.images[i].HasData())
            numEmbeddedTexs += 1;
    }

    if (numEmbeddedTexs == 0)
        return;

    mScene->mTextures = new aiTexture*[numEmbeddedTexs];

    // Add the embedded textures
    for (size_t i = 0; i < r.images.Size(); ++i) {
        Image &img = r.images[i];
        if (!img.HasData()) continue;

        int idx = mScene->mNumTextures++;
        embeddedTexIdxs[i] = idx;

        aiTexture* tex = mScene->mTextures[idx] = new aiTexture();

        size_t length = img.GetDataLength();
        void* data = img.StealData();

        tex->mWidth = static_cast<unsigned int>(length);
        tex->mHeight = 0;
        tex->pcData = reinterpret_cast<aiTexel*>(data);

        if (!img.mimeType.empty()) {
            const char* ext = strchr(img.mimeType.c_str(), '/') + 1;
            if (ext) {
                if (strcmp(ext, "jpeg") == 0) ext = "jpg";

                size_t len = strlen(ext);
                if (len <= 3) {
                    strcpy(tex->achFormatHint, ext);
                }
            }
        }
    }
}

void glTF2Importer::InternReadFile(const std::string& pFile, aiScene* pScene, IOSystem* pIOHandler) {

    this->mScene = pScene;

    // read the asset file
    glTF2::Asset asset(pIOHandler);
    asset.Load(pFile, GetExtension(pFile) == "glb");

    //
    // Copy the data out
    //

    ImportEmbeddedTextures(asset);
    ImportMaterials(asset);

    ImportMeshes(asset);

    ImportCameras(asset);

    ImportNodes(asset);

    if (pScene->mNumMeshes == 0) {
        pScene->mFlags |= AI_SCENE_FLAGS_INCOMPLETE;
    }
}

#endif // ASSIMP_BUILD_NO_GLTF_IMPORTER