sclass ScreenCamStream {
  volatile Rect area = screenArea();
  DoneFlag ended = new(true);

  public bool step() {
    if (ended.isDone()) false;
    catchError(ended, -> shootScreen(area));
    true;
  }
  
  void useScreen(int iScreen) {
    area = screenBounds_safe(iScreen);
  }
  
  void end { ended.raise(); }
}