_empty = true;
	public RenderBox() {		// (1) convert NV2D graph to a data structure usable by Prefuse		// (2) create a new item registry		//  the item registry stores all the visual		//  representations of different graph elements		super(new ItemRegistry(new DefaultGraph(true)));		// create a new display component to show the data		setSize(400,400);		pan(350, 350);		// lets users drag nodes around on screen (Display class method)		addControlListener(new MouseController());		addControlListener(new DragControl());        addControlListener(new PanControl());        addControlListener(new ZoomControl());	}