static int CompareProperty( ILayerProperty a,ILayerProperty b )
        {
            if( a.IsMissingComponent() || b.IsMissingComponent() )
            {
                return 0;
            }

            if( a.sortingLayerID != b.sortingLayerID )
            {
                return b.sortingLayerID - a.sortingLayerID;
            }
            return b.sortingOrder - a.sortingOrder;
        }