static BufferedImage renderBackgroundPlusLines(int w, int h, BackgroundPlus<LineWithColor> s) {
  BufferedImage bi = newBufferedImage(w, h, toColor(s.background));
  Graphics2D g = imageGraphics(bi);
  for (LineWithColor e : s.things)
    drawRoundEdgeLine(g, e.a, e.b, toColor(e.color), e.width);
  g.dispose();
  ret bi;
}