public void mouseClicked(MouseEvent e) {
         if ((e.getModifiers() & MouseEvent.MOUSE_PRESSED) != 0) {
            if ((e.getModifiers() & InputEvent.BUTTON1_MASK) != 0) {
                int userToolModeFlag = documentViewController
                        .getDocumentViewModel().getViewToolMode();
                // zoom in
                if (userToolModeFlag == DocumentViewModel.DISPLAY_TOOL_ZOOM_IN) {
                    documentViewController.setZoomIn(e.getPoint());
                }
                // zoom out.
                else if (userToolModeFlag == DocumentViewModel.DISPLAY_TOOL_ZOOM_OUT) {
                    documentViewController.setZoomOut(e.getPoint());
                }
            }
        }
    }