if (w == 0 || h == 0 || !component.isShowing())
if (w <= 0 || h <= 0 || !component.isShowing())
  public synchronized void addDirtyRegion(JComponent component, int x, int y,                                          int w, int h)  {    if (w == 0 || h == 0 || !component.isShowing())      return;    Rectangle r = new Rectangle(x, y, w, h);    if (dirtyComponents.containsKey(component))      r = r.union((Rectangle)dirtyComponents.get(component));    else      insertInRepaintOrder(component);    dirtyComponents.put(component, r);    if (! repaintWorker.isLive())      {        repaintWorker.setLive(true);        SwingUtilities.invokeLater(repaintWorker);      }  }