static void calAddAutoLayoutSwitch(CirclesAndLines cal, final Canvas canvas, O modifyLayout, bool on) {
  calAddAutoLayoutSwitch(new Var(cal), canvas, modifyLayout, on);
}

static double calAddAutoLayoutSwitch_scale = 100;

static void calAddAutoLayoutSwitch(final Var<CirclesAndLines> cal, final Canvas canvas, final O modifyLayout, final bool on) swing {
  // dummy for getting desiredLength
  CALSpringLayout _layout = new CALSpringLayout(cal!);
  callF(modifyLayout, _layout);
  
  final JCheckBox cb = jcheckbox("Auto-Layout", on);
  final JCheckBox cb2 = jcheckbox("Center", false);
  final JSpinner lineLength = jspinner(iround(_layout.desiredLength*calAddAutoLayoutSwitch_scale), 1, 50);
  addToWindow(canvas, jcenteredline(cb, cb2, jlabel("Line length:"), lineLength));
  awtCalcEvery2(canvas, 100, new Runnable {
    CALSpringLayout layout;
    CirclesAndLines lastCAL = cal!;
    
    public void run() {
      bool x = false;
      if (isChecked(cb)) {
        if (cal! != lastCAL || layout == null) {
          lastCAL = cal!;
          layout = new CALSpringLayout(cal!);
          layout.center = false;
          callF(modifyLayout, layout);
          layout.desiredLength = intFromSpinner(lineLength)/calAddAutoLayoutSwitch_scale;
        }
        layout.step();
        x = true;
      }
      if (isChecked(cb2)) {
        calCenterStepwise(cal!, 0.1);
        x = true;
      }
      if (x) updateCanvas(canvas);
    }
  });
}