static BufferedImage renderBackgroundPlusPolys(int w, int h, BackgroundPlus<PolygonWithColor> s) {
  BufferedImage bi = newBufferedImage(w, h, toColor(s.background));
  Graphics2D g = imageGraphics(bi);
  for (PolygonWithColor e : s.things)
    fillPolygon(g, e.points, toColor(e.color));
  g.dispose();
  ret bi;
}