assimp/code/AssetLib/glTF2/glTF2Asset.h

/*
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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/** @file glTFAsset.h
 * Declares a glTF class to handle gltf/glb files
 *
 * glTF Extensions Support:
 *   KHR_materials_pbrSpecularGlossiness full
 *   KHR_materials_unlit full
 *   KHR_lights_punctual full
 */
#ifndef GLTF2ASSET_H_INC
#define GLTF2ASSET_H_INC

#ifndef ASSIMP_BUILD_NO_GLTF_IMPORTER

#include <assimp/Exceptional.h>

#include <algorithm>
#include <list>
#include <map>
#include <set>
#include <stdexcept>
#include <string>
#include <vector>

#ifndef RAPIDJSON_HAS_STDSTRING
#define RAPIDJSON_HAS_STDSTRING 1
#endif

#if (__GNUC__ == 8 && __GNUC_MINOR__ >= 0)
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wclass-memaccess"
#endif

#ifndef RAPIDJSON_NOMEMBERITERATORCLASS
#define RAPIDJSON_NOMEMBERITERATORCLASS
#endif 

#include <rapidjson/document.h>
#include <rapidjson/error/en.h>
#include <rapidjson/rapidjson.h>

#if (__GNUC__ == 8 && __GNUC_MINOR__ >= 0)
#pragma GCC diagnostic pop
#endif

#ifdef ASSIMP_API
#include <assimp/ByteSwapper.h>
#include <assimp/DefaultIOSystem.h>
#include <memory>
#else
#include <memory>
#define AI_SWAP4(p)
#define ai_assert
#endif

#if _MSC_VER > 1500 || (defined __GNUC___)
#define ASSIMP_GLTF_USE_UNORDERED_MULTIMAP
#else
#define gltf_unordered_map map
#define gltf_unordered_set set
#endif

#ifdef ASSIMP_GLTF_USE_UNORDERED_MULTIMAP
#include <unordered_map>
#include <unordered_set>
#if _MSC_VER > 1600
#define gltf_unordered_map unordered_map
#define gltf_unordered_set unordered_set
#else
#define gltf_unordered_map tr1::unordered_map
#define gltf_unordered_set tr1::unordered_set
#endif
#endif

#include <assimp/StringUtils.h>

#include "AssetLib/glTF/glTFCommon.h"

namespace glTF2 {

using glTFCommon::IOStream;
using glTFCommon::IOSystem;
using glTFCommon::shared_ptr;

using rapidjson::Document;
using rapidjson::Value;

class Asset;
class AssetWriter;

struct BufferView; // here due to cross-reference
struct Texture;
struct Skin;

using glTFCommon::mat4;
using glTFCommon::vec3;
using glTFCommon::vec4;

//! Magic number for GLB files
#define AI_GLB_MAGIC_NUMBER "glTF"
#include <assimp/pbrmaterial.h>

#ifdef ASSIMP_API
#include <assimp/Compiler/pushpack1.h>
#endif

//! For binary .glb files
//! 12-byte header (+ the JSON + a "body" data section)
struct GLB_Header {
    uint8_t magic[4]; //!< Magic number: "glTF"
    uint32_t version; //!< Version number (always 2 as of the last update)
    uint32_t length; //!< Total length of the Binary glTF, including header, scene, and body, in bytes
} PACK_STRUCT;

struct GLB_Chunk {
    uint32_t chunkLength;
    uint32_t chunkType;
} PACK_STRUCT;

#ifdef ASSIMP_API
#include <assimp/Compiler/poppack1.h>
#endif

//! Values for the GLB_Chunk::chunkType field
enum ChunkType {
    ChunkType_JSON = 0x4E4F534A,
    ChunkType_BIN = 0x004E4942
};

//! Values for the mesh primitive modes
enum PrimitiveMode {
    PrimitiveMode_POINTS = 0,
    PrimitiveMode_LINES = 1,
    PrimitiveMode_LINE_LOOP = 2,
    PrimitiveMode_LINE_STRIP = 3,
    PrimitiveMode_TRIANGLES = 4,
    PrimitiveMode_TRIANGLE_STRIP = 5,
    PrimitiveMode_TRIANGLE_FAN = 6
};

//! Values for the Accessor::componentType field
enum ComponentType {
    ComponentType_BYTE = 5120,
    ComponentType_UNSIGNED_BYTE = 5121,
    ComponentType_SHORT = 5122,
    ComponentType_UNSIGNED_SHORT = 5123,
    ComponentType_UNSIGNED_INT = 5125,
    ComponentType_FLOAT = 5126
};

inline unsigned int ComponentTypeSize(ComponentType t) {
    switch (t) {
    case ComponentType_SHORT:
    case ComponentType_UNSIGNED_SHORT:
        return 2;

    case ComponentType_UNSIGNED_INT:
    case ComponentType_FLOAT:
        return 4;

    case ComponentType_BYTE:
    case ComponentType_UNSIGNED_BYTE:
        return 1;
    default:
        throw DeadlyImportError("GLTF: Unsupported Component Type " + to_string(t));
    }
}

//! Values for the BufferView::target field
enum BufferViewTarget {
    BufferViewTarget_NONE = 0,
    BufferViewTarget_ARRAY_BUFFER = 34962,
    BufferViewTarget_ELEMENT_ARRAY_BUFFER = 34963
};

//! Values for the Sampler::magFilter field
enum class SamplerMagFilter : unsigned int {
    UNSET = 0,
    SamplerMagFilter_Nearest = 9728,
    SamplerMagFilter_Linear = 9729
};

//! Values for the Sampler::minFilter field
enum class SamplerMinFilter : unsigned int {
    UNSET = 0,
    SamplerMinFilter_Nearest = 9728,
    SamplerMinFilter_Linear = 9729,
    SamplerMinFilter_Nearest_Mipmap_Nearest = 9984,
    SamplerMinFilter_Linear_Mipmap_Nearest = 9985,
    SamplerMinFilter_Nearest_Mipmap_Linear = 9986,
    SamplerMinFilter_Linear_Mipmap_Linear = 9987
};

//! Values for the Sampler::wrapS and Sampler::wrapT field
enum class SamplerWrap : unsigned int {
    UNSET = 0,
    Clamp_To_Edge = 33071,
    Mirrored_Repeat = 33648,
    Repeat = 10497
};

//! Values for the Texture::format and Texture::internalFormat fields
enum TextureFormat {
    TextureFormat_ALPHA = 6406,
    TextureFormat_RGB = 6407,
    TextureFormat_RGBA = 6408,
    TextureFormat_LUMINANCE = 6409,
    TextureFormat_LUMINANCE_ALPHA = 6410
};

//! Values for the Texture::target field
enum TextureTarget {
    TextureTarget_TEXTURE_2D = 3553
};

//! Values for the Texture::type field
enum TextureType {
    TextureType_UNSIGNED_BYTE = 5121,
    TextureType_UNSIGNED_SHORT_5_6_5 = 33635,
    TextureType_UNSIGNED_SHORT_4_4_4_4 = 32819,
    TextureType_UNSIGNED_SHORT_5_5_5_1 = 32820
};

//! Values for the Animation::Target::path field
enum AnimationPath {
    AnimationPath_TRANSLATION,
    AnimationPath_ROTATION,
    AnimationPath_SCALE,
    AnimationPath_WEIGHTS,
};

//! Values for the Animation::Sampler::interpolation field
enum Interpolation {
    Interpolation_LINEAR,
    Interpolation_STEP,
    Interpolation_CUBICSPLINE,
};

//! Values for the Accessor::type field (helper class)
class AttribType {
public:
    enum Value { SCALAR,
        VEC2,
        VEC3,
        VEC4,
        MAT2,
        MAT3,
        MAT4 };

private:
    static const size_t NUM_VALUES = static_cast<size_t>(MAT4) + 1;

    struct Info {
        const char *name;
        unsigned int numComponents;
    };

    template <int N>
    struct data { static const Info infos[NUM_VALUES]; };

public:
    inline static Value FromString(const char *str) {
        for (size_t i = 0; i < NUM_VALUES; ++i) {
            if (strcmp(data<0>::infos[i].name, str) == 0) {
                return static_cast<Value>(i);
            }
        }
        return SCALAR;
    }

    inline static const char *ToString(Value type) {
        return data<0>::infos[static_cast<size_t>(type)].name;
    }

    inline static unsigned int GetNumComponents(Value type) {
        return data<0>::infos[static_cast<size_t>(type)].numComponents;
    }
};

// must match the order of the AttribTypeTraits::Value enum!
template <int N>
const AttribType::Info
        AttribType::data<N>::infos[AttribType::NUM_VALUES] = {
            { "SCALAR", 1 }, { "VEC2", 2 }, { "VEC3", 3 }, { "VEC4", 4 }, { "MAT2", 4 }, { "MAT3", 9 }, { "MAT4", 16 }
        };

//! A reference to one top-level object, which is valid
//! until the Asset instance is destroyed
template <class T>
class Ref {
    std::vector<T *> *vector;
    unsigned int index;

public:
    Ref() :
            vector(0),
            index(0) {}
    Ref(std::vector<T *> &vec, unsigned int idx) :
            vector(&vec),
            index(idx) {}

    inline unsigned int GetIndex() const { return index; }

    operator bool() const { return vector != 0; }

    T *operator->() { return (*vector)[index]; }

    T &operator*() { return *((*vector)[index]); }
};

//! Helper struct to represent values that might not be present
template <class T>
struct Nullable {
    T value;
    bool isPresent;

    Nullable() :
            isPresent(false) {}
    Nullable(T &val) :
            value(val),
            isPresent(true) {}
};

//! Base class for all glTF top-level objects
struct Object {
    int index; //!< The index of this object within its property container
    int oIndex; //!< The original index of this object defined in the JSON
    std::string id; //!< The globally unique ID used to reference this object
    std::string name; //!< The user-defined name of this object

    //! Objects marked as special are not exported (used to emulate the binary body buffer)
    virtual bool IsSpecial() const { return false; }

    virtual ~Object() {}

    //! Maps special IDs to another ID, where needed. Subclasses may override it (statically)
    static const char *TranslateId(Asset & /*r*/, const char *id) { return id; }
};

//
// Classes for each glTF top-level object type
//

//! A typed view into a BufferView. A BufferView contains raw binary data.
//! An accessor provides a typed view into a BufferView or a subset of a BufferView
//! similar to how WebGL's vertexAttribPointer() defines an attribute in a buffer.
struct Accessor : public Object {
    struct Sparse;

    Ref<BufferView> bufferView; //!< The ID of the bufferView. (required)
    size_t byteOffset; //!< The offset relative to the start of the bufferView in bytes. (required)
    ComponentType componentType; //!< The datatype of components in the attribute. (required)
    size_t count; //!< The number of attributes referenced by this accessor. (required)
    AttribType::Value type; //!< Specifies if the attribute is a scalar, vector, or matrix. (required)
    std::vector<double> max; //!< Maximum value of each component in this attribute.
    std::vector<double> min; //!< Minimum value of each component in this attribute.
    std::unique_ptr<Sparse> sparse;

    unsigned int GetNumComponents();
    unsigned int GetBytesPerComponent();
    unsigned int GetElementSize();

    inline uint8_t *GetPointer();

    template <class T>
    void ExtractData(T *&outData);

    void WriteData(size_t count, const void *src_buffer, size_t src_stride);
    void WriteSparseValues(size_t count, const void *src_data, size_t src_dataStride);
    void WriteSparseIndices(size_t count, const void *src_idx, size_t src_idxStride);

    //! Helper class to iterate the data
    class Indexer {
        friend struct Accessor;

        // This field is reported as not used, making it protectd is the easiest way to work around it without going to the bottom of what the problem is:
        // ../code/glTF2/glTF2Asset.h:392:19: error: private field 'accessor' is not used [-Werror,-Wunused-private-field]
    protected:
        Accessor &accessor;

    private:
        uint8_t *data;
        size_t elemSize, stride;

        Indexer(Accessor &acc);

    public:
        //! Accesses the i-th value as defined by the accessor
        template <class T>
        T GetValue(int i);

        //! Accesses the i-th value as defined by the accessor
        inline unsigned int GetUInt(int i) {
            return GetValue<unsigned int>(i);
        }

        inline bool IsValid() const {
            return data != 0;
        }
    };

    inline Indexer GetIndexer() {
        return Indexer(*this);
    }

    Accessor() {}
    void Read(Value &obj, Asset &r);

    //sparse
    struct Sparse {
        size_t count;
        ComponentType indicesType;
        Ref<BufferView> indices;
        size_t indicesByteOffset;
        Ref<BufferView> values;
        size_t valuesByteOffset;

        std::vector<uint8_t> data; //!< Actual data, which may be defaulted to an array of zeros or the original data, with the sparse buffer view applied on top of it.

        void PopulateData(size_t numBytes, uint8_t *bytes);
        void PatchData(unsigned int elementSize);
    };
};

//! A buffer points to binary geometry, animation, or skins.
struct Buffer : public Object {
    /********************* Types *********************/
public:
    enum Type {
        Type_arraybuffer,
        Type_text
    };

    /// \struct SEncodedRegion
    /// Descriptor of encoded region in "bufferView".
    struct SEncodedRegion {
        const size_t Offset; ///< Offset from begin of "bufferView" to encoded region, in bytes.
        const size_t EncodedData_Length; ///< Size of encoded region, in bytes.
        uint8_t *const DecodedData; ///< Cached encoded data.
        const size_t DecodedData_Length; ///< Size of decoded region, in bytes.
        const std::string ID; ///< ID of the region.

        /// \fn SEncodedRegion(const size_t pOffset, const size_t pEncodedData_Length, uint8_t* pDecodedData, const size_t pDecodedData_Length, const std::string pID)
        /// Constructor.
        /// \param [in] pOffset - offset from begin of "bufferView" to encoded region, in bytes.
        /// \param [in] pEncodedData_Length - size of encoded region, in bytes.
        /// \param [in] pDecodedData - pointer to decoded data array.
        /// \param [in] pDecodedData_Length - size of encoded region, in bytes.
        /// \param [in] pID - ID of the region.
        SEncodedRegion(const size_t pOffset, const size_t pEncodedData_Length, uint8_t *pDecodedData, const size_t pDecodedData_Length, const std::string pID) :
                Offset(pOffset),
                EncodedData_Length(pEncodedData_Length),
                DecodedData(pDecodedData),
                DecodedData_Length(pDecodedData_Length),
                ID(pID) {}

        /// \fn ~SEncodedRegion()
        /// Destructor.
        ~SEncodedRegion() { delete[] DecodedData; }
    };

    /******************* Variables *******************/

    //std::string uri; //!< The uri of the buffer. Can be a filepath, a data uri, etc. (required)
    size_t byteLength; //!< The length of the buffer in bytes. (default: 0)
    //std::string type; //!< XMLHttpRequest responseType (default: "arraybuffer")
    size_t capacity = 0; //!< The capacity of the buffer in bytes. (default: 0)

    Type type;

    /// \var EncodedRegion_Current
    /// Pointer to currently active encoded region.
    /// Why not decoding all regions at once and not to set one buffer with decoded data?
    /// Yes, why not? Even "accessor" point to decoded data. I mean that fields "byteOffset", "byteStride" and "count" has values which describes decoded
    /// data array. But only in range of mesh while is active parameters from "compressedData". For another mesh accessors point to decoded data too. But
    /// offset is counted for another regions is encoded.
    /// Example. You have two meshes. For every of it you have 4 bytes of data. That data compressed to 2 bytes. So, you have buffer with encoded data:
    /// M1_E0, M1_E1, M2_E0, M2_E1.
    /// After decoding you'll get:
    /// M1_D0, M1_D1, M1_D2, M1_D3, M2_D0, M2_D1, M2_D2, M2_D3.
    /// "accessors" must to use values that point to decoded data - obviously. So, you'll expect "accessors" like
    /// "accessor_0" : { byteOffset: 0, byteLength: 4}, "accessor_1" : { byteOffset: 4, byteLength: 4}
    /// but in real life you'll get:
    /// "accessor_0" : { byteOffset: 0, byteLength: 4}, "accessor_1" : { byteOffset: 2, byteLength: 4}
    /// Yes, accessor of next mesh has offset and length which mean: current mesh data is decoded, all other data is encoded.
    /// And when before you start to read data of current mesh (with encoded data of course) you must decode region of "bufferView", after read finished
    /// delete encoding mark. And after that you can repeat process: decode data of mesh, read, delete decoded data.
    ///
    /// Remark. Encoding all data at once is good in world with computers which do not has RAM limitation. So, you must use step by step encoding in
    /// exporter and importer. And, thanks to such way, there is no need to load whole file into memory.
    SEncodedRegion *EncodedRegion_Current;

private:
    shared_ptr<uint8_t> mData; //!< Pointer to the data
    bool mIsSpecial; //!< Set to true for special cases (e.g. the body buffer)

    /// \var EncodedRegion_List
    /// List of encoded regions.
    std::list<SEncodedRegion *> EncodedRegion_List;

    /******************* Functions *******************/

public:
    Buffer();
    ~Buffer();

    void Read(Value &obj, Asset &r);

    bool LoadFromStream(IOStream &stream, size_t length = 0, size_t baseOffset = 0);

    /// \fn void EncodedRegion_Mark(const size_t pOffset, const size_t pEncodedData_Length, uint8_t* pDecodedData, const size_t pDecodedData_Length, const std::string& pID)
    /// Mark region of "bufferView" as encoded. When data is request from such region then "bufferView" use decoded data.
    /// \param [in] pOffset - offset from begin of "bufferView" to encoded region, in bytes.
    /// \param [in] pEncodedData_Length - size of encoded region, in bytes.
    /// \param [in] pDecodedData - pointer to decoded data array.
    /// \param [in] pDecodedData_Length - size of encoded region, in bytes.
    /// \param [in] pID - ID of the region.
    void EncodedRegion_Mark(const size_t pOffset, const size_t pEncodedData_Length, uint8_t *pDecodedData, const size_t pDecodedData_Length, const std::string &pID);

    /// \fn void EncodedRegion_SetCurrent(const std::string& pID)
    /// Select current encoded region by ID. \sa EncodedRegion_Current.
    /// \param [in] pID - ID of the region.
    void EncodedRegion_SetCurrent(const std::string &pID);

    /// \fn bool ReplaceData(const size_t pBufferData_Offset, const size_t pBufferData_Count, const uint8_t* pReplace_Data, const size_t pReplace_Count)
    /// Replace part of buffer data. Pay attention that function work with original array of data (\ref mData) not with encoded regions.
    /// \param [in] pBufferData_Offset - index of first element in buffer from which new data will be placed.
    /// \param [in] pBufferData_Count - count of bytes in buffer which will be replaced.
    /// \param [in] pReplace_Data - pointer to array with new data for buffer.
    /// \param [in] pReplace_Count - count of bytes in new data.
    /// \return true - if successfully replaced, false if input arguments is out of range.
    bool ReplaceData(const size_t pBufferData_Offset, const size_t pBufferData_Count, const uint8_t *pReplace_Data, const size_t pReplace_Count);
    bool ReplaceData_joint(const size_t pBufferData_Offset, const size_t pBufferData_Count, const uint8_t *pReplace_Data, const size_t pReplace_Count);

    size_t AppendData(uint8_t *data, size_t length);
    void Grow(size_t amount);

    uint8_t *GetPointer() { return mData.get(); }

    void MarkAsSpecial() { mIsSpecial = true; }

    bool IsSpecial() const { return mIsSpecial; }

    std::string GetURI() { return std::string(this->id) + ".bin"; }

    static const char *TranslateId(Asset &r, const char *id);
};

//! A view into a buffer generally representing a subset of the buffer.
struct BufferView : public Object {
    Ref<Buffer> buffer; //! The ID of the buffer. (required)
    size_t byteOffset; //! The offset into the buffer in bytes. (required)
    size_t byteLength; //! The length of the bufferView in bytes. (default: 0)
    unsigned int byteStride; //!< The stride, in bytes, between attributes referenced by this accessor. (default: 0)

    BufferViewTarget target; //! The target that the WebGL buffer should be bound to.

    void Read(Value &obj, Asset &r);
    uint8_t *GetPointer(size_t accOffset);
};

struct Camera : public Object {
    enum Type {
        Perspective,
        Orthographic
    };

    Type type;

    union {
        struct {
            float aspectRatio; //!<The floating - point aspect ratio of the field of view. (0 = undefined = use the canvas one)
            float yfov; //!<The floating - point vertical field of view in radians. (required)
            float zfar; //!<The floating - point distance to the far clipping plane. (required)
            float znear; //!< The floating - point distance to the near clipping plane. (required)
        } perspective;

        struct {
            float xmag; //! The floating-point horizontal magnification of the view. (required)
            float ymag; //! The floating-point vertical magnification of the view. (required)
            float zfar; //! The floating-point distance to the far clipping plane. (required)
            float znear; //! The floating-point distance to the near clipping plane. (required)
        } ortographic;
    } cameraProperties;

    Camera() :
            type(Perspective),
            cameraProperties() {
        // empty
    }
    void Read(Value &obj, Asset &r);
};

//! A light (from KHR_lights_punctual extension)
struct Light : public Object {
    enum Type {
        Directional,
        Point,
        Spot
    };

    Type type;

    vec3 color;
    float intensity;
    Nullable<float> range;

    float innerConeAngle;
    float outerConeAngle;

    Light() {}
    void Read(Value &obj, Asset &r);
};

//! Image data used to create a texture.
struct Image : public Object {
    std::string uri; //! The uri of the image, that can be a file path, a data URI, etc.. (required)

    Ref<BufferView> bufferView;

    std::string mimeType;

    int width, height;

private:
    std::unique_ptr<uint8_t[]> mData;
    size_t mDataLength;

public:
    Image();
    void Read(Value &obj, Asset &r);

    inline bool HasData() const { return mDataLength > 0; }

    inline size_t GetDataLength() const { return mDataLength; }

    inline const uint8_t *GetData() const { return mData.get(); }

    inline uint8_t *StealData();

    inline void SetData(uint8_t *data, size_t length, Asset &r);
};

const vec4 defaultBaseColor = { 1, 1, 1, 1 };
const vec3 defaultEmissiveFactor = { 0, 0, 0 };
const vec4 defaultDiffuseFactor = { 1, 1, 1, 1 };
const vec3 defaultSpecularFactor = { 1, 1, 1 };

struct TextureInfo {
    Ref<Texture> texture;
    unsigned int index;
    unsigned int texCoord = 0;

    bool textureTransformSupported = false;
    struct TextureTransformExt {
        float offset[2];
        float rotation;
        float scale[2];
    } TextureTransformExt_t;
};

struct NormalTextureInfo : TextureInfo {
    float scale = 1;
};

struct OcclusionTextureInfo : TextureInfo {
    float strength = 1;
};

struct PbrMetallicRoughness {
    vec4 baseColorFactor;
    TextureInfo baseColorTexture;
    TextureInfo metallicRoughnessTexture;
    float metallicFactor;
    float roughnessFactor;
};

struct PbrSpecularGlossiness {
    vec4 diffuseFactor;
    vec3 specularFactor;
    float glossinessFactor;
    TextureInfo diffuseTexture;
    TextureInfo specularGlossinessTexture;

    PbrSpecularGlossiness() { SetDefaults(); }
    void SetDefaults();
};

//! The material appearance of a primitive.
struct Material : public Object {
    //PBR metallic roughness properties
    PbrMetallicRoughness pbrMetallicRoughness;

    //other basic material properties
    NormalTextureInfo normalTexture;
    OcclusionTextureInfo occlusionTexture;
    TextureInfo emissiveTexture;
    vec3 emissiveFactor;
    std::string alphaMode;
    float alphaCutoff;
    bool doubleSided;

    //extension: KHR_materials_pbrSpecularGlossiness
    Nullable<PbrSpecularGlossiness> pbrSpecularGlossiness;

    //extension: KHR_materials_unlit
    bool unlit;

    Material() { SetDefaults(); }
    void Read(Value &obj, Asset &r);
    void SetDefaults();
};

//! A set of primitives to be rendered. A node can contain one or more meshes. A node's transform places the mesh in the scene.
struct Mesh : public Object {
    typedef std::vector<Ref<Accessor>> AccessorList;

    struct Primitive {
        PrimitiveMode mode;

        struct Attributes {
            AccessorList position, normal, tangent, texcoord, color, joint, jointmatrix, weight;
        } attributes;

        Ref<Accessor> indices;

        Ref<Material> material;

        struct Target {
            AccessorList position, normal, tangent;
        };
        std::vector<Target> targets;
    };

    std::vector<Primitive> primitives;

    std::vector<float> weights;
    std::vector<std::string> targetNames;

    Mesh() {}

    /// \fn void Read(Value& pJSON_Object, Asset& pAsset_Root)
    /// Get mesh data from JSON-object and place them to root asset.
    /// \param [in] pJSON_Object - reference to pJSON-object from which data are read.
    /// \param [out] pAsset_Root - reference to root asset where data will be stored.
    void Read(Value &pJSON_Object, Asset &pAsset_Root);
};

struct CustomExtension : public Object {
    //
    // A struct containing custom extension data added to a glTF2 file
    // Has to contain Object, Array, String, Double, Uint64, and Int64 at a minimum
    // String, Double, Uint64, and Int64 are stored in the Nullables
    // Object and Array are stored in the std::vector
    //

    Nullable<std::string> mStringValue;
    Nullable<double> mDoubleValue;
    Nullable<uint64_t> mUint64Value;
    Nullable<int64_t> mInt64Value;
    Nullable<bool> mBoolValue;

    // std::vector<CustomExtension> handles both Object and Array
    Nullable<std::vector<CustomExtension>> mValues;

    operator bool() const {
        return Size();
    }

    size_t Size() const {
        if (mValues.isPresent) {
            return mValues.value.size();
        } else if (mStringValue.isPresent || mDoubleValue.isPresent || mUint64Value.isPresent || mInt64Value.isPresent || mBoolValue.isPresent) {
            return 1;
        }
        return 0;
    }

    CustomExtension() = default;

    CustomExtension(const CustomExtension& other)
        : Object(other)
        , mStringValue(other.mStringValue)
        , mDoubleValue(other.mDoubleValue)
        , mUint64Value(other.mUint64Value)
        , mInt64Value(other.mInt64Value)
        , mBoolValue(other.mBoolValue)
        , mValues(other.mValues)
    {
    }
};

struct Node : public Object {
    std::vector<Ref<Node>> children;
    std::vector<Ref<Mesh>> meshes;

    Nullable<mat4> matrix;
    Nullable<vec3> translation;
    Nullable<vec4> rotation;
    Nullable<vec3> scale;

    Ref<Camera> camera;
    Ref<Light> light;

    std::vector<Ref<Node>> skeletons; //!< The ID of skeleton nodes. Each of which is the root of a node hierarchy.
    Ref<Skin> skin; //!< The ID of the skin referenced by this node.
    std::string jointName; //!< Name used when this node is a joint in a skin.

    Ref<Node> parent; //!< This is not part of the glTF specification. Used as a helper.

    CustomExtension extensions;

    Node() {}
    void Read(Value &obj, Asset &r);
};

struct Program : public Object {
    Program() {}
    void Read(Value &obj, Asset &r);
};

struct Sampler : public Object {
    SamplerMagFilter magFilter; //!< The texture magnification filter.
    SamplerMinFilter minFilter; //!< The texture minification filter.
    SamplerWrap wrapS; //!< The texture wrapping in the S direction.
    SamplerWrap wrapT; //!< The texture wrapping in the T direction.

    Sampler() { SetDefaults(); }
    void Read(Value &obj, Asset &r);
    void SetDefaults();
};

struct Scene : public Object {
    std::vector<Ref<Node>> nodes;

    Scene() {}
    void Read(Value &obj, Asset &r);
};

struct Shader : public Object {
    Shader() {}
    void Read(Value &obj, Asset &r);
};

struct Skin : public Object {
    Nullable<mat4> bindShapeMatrix; //!< Floating-point 4x4 transformation matrix stored in column-major order.
    Ref<Accessor> inverseBindMatrices; //!< The ID of the accessor containing the floating-point 4x4 inverse-bind matrices.
    std::vector<Ref<Node>> jointNames; //!< Joint names of the joints (nodes with a jointName property) in this skin.
    std::string name; //!< The user-defined name of this object.

    Skin() {}
    void Read(Value &obj, Asset &r);
};

//! A texture and its sampler.
struct Texture : public Object {
    Ref<Sampler> sampler; //!< The ID of the sampler used by this texture. (required)
    Ref<Image> source; //!< The ID of the image used by this texture. (required)

    //TextureFormat format; //!< The texture's format. (default: TextureFormat_RGBA)
    //TextureFormat internalFormat; //!< The texture's internal format. (default: TextureFormat_RGBA)

    //TextureTarget target; //!< The target that the WebGL texture should be bound to. (default: TextureTarget_TEXTURE_2D)
    //TextureType type; //!< Texel datatype. (default: TextureType_UNSIGNED_BYTE)

    Texture() {}
    void Read(Value &obj, Asset &r);
};

struct Animation : public Object {
    struct Sampler {
        Sampler() :
                interpolation(Interpolation_LINEAR) {}

        Ref<Accessor> input; //!< Accessor reference to the buffer storing the key-frame times.
        Ref<Accessor> output; //!< Accessor reference to the buffer storing the key-frame values.
        Interpolation interpolation; //!< Type of interpolation algorithm to use between key-frames.
    };

    struct Target {
        Target() :
                path(AnimationPath_TRANSLATION) {}

        Ref<Node> node; //!< The node to animate.
        AnimationPath path; //!< The property of the node to animate.
    };

    struct Channel {
        Channel() :
                sampler(-1) {}

        int sampler; //!< The sampler index containing the animation data.
        Target target; //!< The node and property to animate.
    };

    std::vector<Sampler> samplers; //!< All the key-frame data for this animation.
    std::vector<Channel> channels; //!< Data to connect nodes to key-frames.

    Animation() {}
    void Read(Value &obj, Asset &r);
};

//! Base class for LazyDict that acts as an interface
class LazyDictBase {
public:
    virtual ~LazyDictBase() {}

    virtual void AttachToDocument(Document &doc) = 0;
    virtual void DetachFromDocument() = 0;

    virtual void WriteObjects(AssetWriter &writer) = 0;
};

template <class T>
class LazyDict;

//! (Implemented in glTFAssetWriter.h)
template <class T>
void WriteLazyDict(LazyDict<T> &d, AssetWriter &w);

//! Manages lazy loading of the glTF top-level objects, and keeps a reference to them by ID
//! It is the owner the loaded objects, so when it is destroyed it also deletes them
template <class T>
class LazyDict : public LazyDictBase {
    friend class Asset;
    friend class AssetWriter;

    typedef typename std::gltf_unordered_map<unsigned int, unsigned int> Dict;
    typedef typename std::gltf_unordered_map<std::string, unsigned int> IdDict;

    std::vector<T *> mObjs; //! The read objects
    Dict mObjsByOIndex; //! The read objects accessible by original index
    IdDict mObjsById; //! The read objects accessible by id
    const char *mDictId; //! ID of the dictionary object
    const char *mExtId; //! ID of the extension defining the dictionary
    Value *mDict; //! JSON dictionary object
    Asset &mAsset; //! The asset instance

    std::gltf_unordered_set<unsigned int> mRecursiveReferenceCheck; //! Used by Retrieve to prevent recursive lookups

    void AttachToDocument(Document &doc);
    void DetachFromDocument();

    void WriteObjects(AssetWriter &writer) { WriteLazyDict<T>(*this, writer); }

    Ref<T> Add(T *obj);

public:
    LazyDict(Asset &asset, const char *dictId, const char *extId = 0);
    ~LazyDict();

    Ref<T> Retrieve(unsigned int i);

    Ref<T> Get(unsigned int i);
    Ref<T> Get(const char *id);

    Ref<T> Create(const char *id);
    Ref<T> Create(const std::string &id) { return Create(id.c_str()); }

    unsigned int Remove(const char *id);

    inline unsigned int Size() const { return unsigned(mObjs.size()); }

    inline T &operator[](size_t i) { return *mObjs[i]; }
};

struct AssetMetadata {
    std::string copyright; //!< A copyright message suitable for display to credit the content creator.
    std::string generator; //!< Tool that generated this glTF model.Useful for debugging.

    struct {
        std::string api; //!< Specifies the target rendering API (default: "WebGL")
        std::string version; //!< Specifies the target rendering API (default: "1.0.3")
    } profile; //!< Specifies the target rendering API and version, e.g., WebGL 1.0.3. (default: {})

    std::string version; //!< The glTF format version

    void Read(Document &doc);

    AssetMetadata() :
            version("") {}
};

//
// glTF Asset class
//

//! Root object for a glTF asset
class Asset {
    typedef std::gltf_unordered_map<std::string, int> IdMap;

    template <class T>
    friend class LazyDict;

    friend struct Buffer; // To access OpenFile

    friend class AssetWriter;

private:
    IOSystem *mIOSystem;

    std::string mCurrentAssetDir;

    size_t mSceneLength;
    size_t mBodyOffset, mBodyLength;

    std::vector<LazyDictBase *> mDicts;

    IdMap mUsedIds;

    Ref<Buffer> mBodyBuffer;

    Asset(Asset &);
    Asset &operator=(const Asset &);

public:
    //! Keeps info about the enabled extensions
    struct Extensions {
        bool KHR_materials_pbrSpecularGlossiness;
        bool KHR_materials_unlit;
        bool KHR_lights_punctual;
        bool KHR_texture_transform;
    } extensionsUsed;

    //! Keeps info about the required extensions
    struct RequiredExtensions {
        bool KHR_draco_mesh_compression;
    } extensionsRequired;

    AssetMetadata asset;
    Value* extras = nullptr;

    // Dictionaries for each type of object

    LazyDict<Accessor> accessors;
    LazyDict<Animation> animations;
    LazyDict<Buffer> buffers;
    LazyDict<BufferView> bufferViews;
    LazyDict<Camera> cameras;
    LazyDict<Light> lights;
    LazyDict<Image> images;
    LazyDict<Material> materials;
    LazyDict<Mesh> meshes;
    LazyDict<Node> nodes;
    LazyDict<Sampler> samplers;
    LazyDict<Scene> scenes;
    LazyDict<Skin> skins;
    LazyDict<Texture> textures;

    Ref<Scene> scene;

public:
    Asset(IOSystem *io = 0) :
            mIOSystem(io),
            asset(),
            accessors(*this, "accessors"),
            animations(*this, "animations"),
            buffers(*this, "buffers"),
            bufferViews(*this, "bufferViews"),
            cameras(*this, "cameras"),
            lights(*this, "lights", "KHR_lights_punctual"),
            images(*this, "images"),
            materials(*this, "materials"),
            meshes(*this, "meshes"),
            nodes(*this, "nodes"),
            samplers(*this, "samplers"),
            scenes(*this, "scenes"),
            skins(*this, "skins"),
            textures(*this, "textures") {
        memset(&extensionsUsed, 0, sizeof(extensionsUsed));
        memset(&extensionsRequired, 0, sizeof(extensionsRequired));
    }

    //! Main function
    void Load(const std::string &file, bool isBinary = false);

    //! Enables binary encoding on the asset
    void SetAsBinary();

    //! Search for an available name, starting from the given strings
    std::string FindUniqueID(const std::string &str, const char *suffix);

    Ref<Buffer> GetBodyBuffer() { return mBodyBuffer; }

private:
    void ReadBinaryHeader(IOStream &stream, std::vector<char> &sceneData);

    void ReadExtensionsUsed(Document &doc);
    void ReadExtensionsRequired(Document &doc);

    IOStream *OpenFile(std::string path, const char *mode, bool absolute = false);
};

} // namespace glTF2

// Include the implementation of the methods
#include "glTF2Asset.inl"

#endif // ASSIMP_BUILD_NO_GLTF_IMPORTER

#endif // GLTF2ASSET_H_INC