static BufferedImage renderBackgroundPlusPolys_withHints(int w, int h, BackgroundPlus<PolygonWithColor> s) {
  BufferedImage bi = renderBackgroundPlusPolys(w, h, s);
  Graphics2D g = imageGraphics(bi);
  for (PolygonWithColor e : s.things)
    drawPolygon(g, e.points, colorWithAlpha(0.5, Color.black));
  g.dispose();
  ret bi;
}