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));
}