this.overlays = new ArrayList<Overlay>();
this.availableLiveMouseHandlers = new ArrayList<AbstractMouseHandler>();
this.zoomHandler = new ZoomHandler();
this.availableLiveMouseHandlers.add(zoomHandler);
PanHandler panHandler = new PanHandler();
int panMask = InputEvent.CTRL_MASK;
// for MacOSX we can't use the CTRL key for mouse drags, see: