public CustomCursor(Image img, uint xHot, uint yHot)
{
imgPtr = Marshal.AllocHGlobal(Marshal.SizeOf <Image> ());
Marshal.StructureToPtr(img, imgPtr, false);
this.img = img;
hnd = Glfw3.CreateCursor(imgPtr, (int)xHot, (int)yHot);
}
