void _AddPrimitiveGroupToLayer(int id, SpritePrimitiveGroup group)
        {
            SpriteLayer layer = _GetLayer(id);

            layer.Add(group);
        }
        SetIndexer <SpritePrimitiveGroup> _AddPrimitiveGroupToLayer(int id, SetIndexer <SpritePrimitiveGroup> group)
        {
            SpriteLayer layer = _GetLayer(id);

            return(layer.Add(group));
        }