sclass ScreenCamStream {
  volatile Rect area = screenBounds(0);
  DoneFlag ended = new(true);
  volatile BufferedImage lastFrame;
  new AtomicLong frameCount; 

  public bool step() {
    if (ended.isDone()) false;
    catchError(ended, lambda0 shootImpl);
    true;
  }
  
  BufferedImage get() { ret lastFrame; }
  long frameCount() { ret frameCount!; }
  
  void shootImpl {
    lastFrame = shootScreen2(area);
    inc(frameCount);
  }
  
  void useScreen(int iScreen) {
    area = screenBounds_safe(iScreen);
  }
  
  void end { ended.raise(); }
}