// f: (int w, int h) -> BufferedImage
static ImageSurface jcanvas(O f) {
  ret jcanvas(f, 500);
}

static ImageSurface jcanvas(fO f, final int updateDelay) {
  assertAWTThread();
  final new ImageSurface is;
  final Runnable update = new Runnable {
    bool first = true;
    public void run {
      BufferedImage img = is.getImage();
      int w = is.getWidth(), h = is.getHeight();
      if (first || img.getWidth() != w || img.getHeight() != h) {
        is.setImage(asBufferedImage(callF(f, w, h)));
        first = false;
      }
    }
  };
  onResize(is, r { awtLater(is, updateDelay, update) });
  bindToComponent(is, update); // first update
  ret is;
}