ReFuel.Gltf/ReFuel.Gltf/GlbStructures.cs

using System;
using System.IO;
using System.Runtime.InteropServices;

namespace ReFuel.Gltf
{
    [StructLayout(LayoutKind.Explicit, Size = 12)]
    public struct GlbHeader
    {
        [FieldOffset(0)]
        public int Signature;
        [FieldOffset(4)]
        public int Version;
        [FieldOffset(8)]
        public int Length;

        public const int SIGNATURE_VALUE = 0x46546C67; // "glTF"

        public static unsafe bool Read(Stream str, out GlbHeader header)
        {
            header = default;
            int len;

            fixed (GlbHeader* pheader = &header)
                len = str.Read(new Span<byte>(pheader, sizeof(GlbHeader)));

            if (len != sizeof(GlbHeader))
                return false;
            else if (header.Signature == GlbHeader.SIGNATURE_VALUE)
                return true;
            else
                return false;
        }
    }

    [StructLayout(LayoutKind.Explicit, Size = 8)]
    public struct GlbChunk
    {
        [FieldOffset(0)]
        public int Size;
        [FieldOffset(4)]
        public GlbChunkType Type;

        public static unsafe bool Read(Stream str, out GlbChunk chunk)
        
        {
            chunk = default;

            fixed (GlbChunk* pchunk = &chunk)
                return str.Read(new Span<byte>(pchunk, sizeof(GlbChunk))) == sizeof(GlbChunk);
        }
    }

    public enum GlbChunkType : int
    {
        Json = 0x4E4F534A,
        Bin = 0x004E4942,
    }
}