martinsm

using System;
using System.Reflection;
using System.Reflection.Emit;
using System.Collections.Generic;
using System.Runtime.InteropServices;

namespace OpenGL
{
    static class GL
    {
        public static unsafe class Private
        {
            [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
            public delegate void glCullFace(int mode);
            public static glCullFace CullFace;

            [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
            public delegate void glFrontFace(int mode);
            public static glFrontFace FrontFace;
        }
    }

    static class Loader
    {
        static IntPtr opengl;

        public static void Load()
        {
            opengl = Native.LoadLibrary("opengl32.dll");

            foreach (var field in typeof(OpenGL.GL.Private).GetFields())
            {
                Type type = field.FieldType;
                string name = type.Name;

                IntPtr ptr = Native.wglGetProcAddress(name);
                if (ptr == IntPtr.Zero)
                {
                    ptr = Native.GetProcAddress(opengl, name);
                }

                field.SetValue(null, GetDelegate(ptr, type));
            }
        }

        public static void Unload()
        {
            foreach (var field in typeof(OpenGL.GL.Private).GetFields())
            {
                field.SetValue(null, null);
            }
            Native.FreeLibrary(opengl);
        }

        static object GetDelegate(IntPtr ptr, Type type)
        {
            //return Convert.ChangeType(Marshal.GetDelegateForFunctionPointer(ptr, type), type);

            var invoke = type.GetMethod("Invoke");
            var retType = invoke.ReturnType;
            var parameters = invoke.GetParameters();
            var argCount = parameters.Length;
            var argTypes = new Type[argCount];

            for (int i = 0; i < argCount; i++)
            {
                argTypes[i] = parameters[i].ParameterType;
            }

            var method = new DynamicMethod(type.Name + "_Method", retType, argTypes, typeof(Loader), true);
            var il = method.GetILGenerator();

            if (argCount > 0) il.Emit(OpCodes.Ldarg_0);
            if (argCount > 1) il.Emit(OpCodes.Ldarg_1);
            if (argCount > 2) il.Emit(OpCodes.Ldarg_2);
            if (argCount > 3) il.Emit(OpCodes.Ldarg_3);
            for (int i = 4; i < argCount; i++)
            {
                il.Emit(OpCodes.Ldarg_S, i);
            }
            if (sizeof(int) == IntPtr.Size)
            {
                il.Emit(OpCodes.Ldc_I4, ptr.ToInt32());
            }
            else
            {
                il.Emit(OpCodes.Ldc_I8, ptr.ToInt64());
            }
            il.EmitCalli(OpCodes.Calli, CallingConvention.Cdecl, retType, argTypes);

#if DEBUG
            if (type != typeof(OpenGL.GL.Private.glGetError))
            {
                var check = typeof(Loader).GetMethod("CheckGLErrors", BindingFlags.Static | BindingFlags.NonPublic);
                il.EmitCall(OpCodes.Call, check, null);
            }
#endif
            il.Emit(OpCodes.Ret);

            return method.CreateDelegate(type);
        }

        static void CheckGLErrors()
        {
            var err = OpenGL.GL.GetError();
            if (err != OpenGL.GL.ErrorCode.NoError)
            {
                var errors = new List<string>(1);
                while (err != OpenGL.GL.ErrorCode.NoError)
                {
                    errors.Add(err.ToString());
                    err = OpenGL.GL.GetError();
                }
                throw new ApplicationException("OpenGL error(s): " + String.Join(", ", errors.ToArray()));
            }
        }
    }
}