static BufferedImage renderBackgroundPlusCircles_withHints(int w, int h, BackgroundPlus<CircleWithColor> s) {
  BufferedImage bi = renderBackgroundPlusCircles(w, h, s);
  Graphics2D g = imageGraphics(bi);
  for (CircleWithColor e : s.things)
    drawCircle(g, e.center.x, e.center.y, e.r, colorWithAlpha(0.5, Color.black));
  g.dispose();
  ret bi;
}