private function zsort():void
        {
            var observer:Vector3D = new Vector3D();
            observer.x = root.transform.perspectiveProjection.projectionCenter.x;
            observer.y = root.transform.perspectiveProjection.projectionCenter.y;
            observer.z = -root.transform.perspectiveProjection.focalLength;

            var start:Point = root.local3DToGlobal(observer);
            var g:Graphics = graphics;
            g.clear();

            var sides:Array = [];
            var i:int;
            var n:int = cube.numChildren;
            for (i = 0; i < n; i++)
            {
                var side:Sprite = cube.getChildAt(i) as Sprite;
                var center:Vector3D = side.transform.getRelativeMatrix3D(root).position;

                var distance:Number = Math.sqrt(Math.pow(center.x - observer.x, 2) + Math.pow(center.y - observer.y, 2) + Math.pow(center.z - observer.z, 2));

                var end:Point = root.local3DToGlobal(center);
                g.lineStyle(2);
                g.moveTo(start.x, start.y);
                g.lineTo(end.x, end.y);
                g.endFill();
            }
        }