svoid testDirectlyPaintingOnJComponent(int w default 256) {
  int h = w;
  var c = //jcenteredlabel("Bla");
    new JComponent {};
  setOpaqueBackground(Color.white, c);
  jMinSize(c, w, h);
  
  var it = WeightlessShuffledIteratorWithSeed<Pt>(virtualList(w*h, i -> pt(i%w, i/w)));
  
  new Var<Graphics2D> g;
  new Flag done;
  double timeToFinish = 2; // seconds
  int pixelsPerMS = iceilRatio(w*h/100, timeToFinish);
  
  awtEvery(c, 10, -> {
    if (!g.has()) {
      g.set((Graphics2D) c.getGraphics());
      if (!g.has()) ret;
    }
  
    repeat pixelsPerMS {
      if (!it.hasNext()) {
        if (done.raise())
          print("Done painting " + nPixels(w*h));
        break;
      }
      var p = it.next();
      //print(+p);
      setPixel(g!, p, Color.black);
    }
  });
  showFrame(c);
}