public static int CompareTo(object obj1, object obj2)
        {
            ICanvasData data1 = obj1 as ICanvasData;
            ICanvasData data2 = obj2 as ICanvasData;

            if (data1.Layer > data2.Layer)
            {
                return 1;
            }
            if (data1.Layer < data2.Layer)
            {
                return -1;
            }

            if (data1.Z > data2.Z)
            {
                return 1;
            }
            if (data1.Z < data2.Z)
            {
                return -1;
            }

            if (data1.Canvas.Z > data2.Canvas.Z)
            {
                return 1;
            }
            if (data1.Canvas.Z < data2.Canvas.Z)
            {
                return -1;
            }

            return 0;
        }