// 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;
  Runnable update = r {
   BufferedImage img = is.getImage();
    int w = is.getWidth(), h = is.getHeight();
    if (img.getWidth() != w || img.getHeight() != h)
      is.setImage(asBufferedImage(callF(f, w, h)));
  };
  onResize(is, r { awtLater(is, updateDelay, update) });
  bindToComponent(is, update); // first update
  ret is;
}