sclass AnimatedImageSurface > ImageSurface {
  double fps = 20;
  
  // We start & stop the timer by setting its frequency
  // to the actual frequency or 0, respectively.
  // (Don't want to close the timer as that is permanent.)
  FlexibleRateTimer animationTimer = new(0, l0 renderFrame).pileUp(false);
  
  void renderFrame {
    var img = makeImage();
    if (img != null)
      setImage(img);
  }
  
  selfType fps aka setFPS(double fps) {
    this.fps = fps;
    swing { updateTimer(isShowing()); }
    this;
  }
  
  swappable BufferedImage makeImage() {
    ret whiteImage(10, 10);
  }
  
  *() { init(); }
  *(IF0<BufferedImage> *makeImage) { init(); }
  *(double fps, IF0<BufferedImage> *makeImage) { setFPS(fps); init(); }
  *(Freq freq, IF0<BufferedImage> *makeImage) { setFPS(freq!); init(); }
  
  void updateTimer(bool showing) {
    animationTimer.setFrequencyImmediately(showing ? fps : 0.0);
  }
  
  void init {
    setDoubleBuffered(true);
    bindToComponent(this,
      -> { animationTimer.start(); updateTimer(true); },
      -> updateTimer(false));
  }
}