!7

static Timer timer;
static Canvas canvas;
static CALSpringLayout layout;

p-subst {
  final new CirclesAndLines cal;
  Circle a = cal.circle_autoVis("Hello", 0.2, 0.5);
  Circle b = cal.circle_autoVis("World", 0.8, 0.5);
  cal.arrow(a, "", b);
  canvas = showCAL(cal);
  layout = new CALSpringLayout(cal);
  addToWindow(canvas, jcenteredline(jbutton("Start/Stop", r {
    if (timer != null) { cancelTimer(timer); timer = null; }
    else startTimer();
  })));
}

svoid startTimer {
  timer = awtCalcEvery2(canvas, 100, r {
    layout.step();
    updateCanvas(canvas);
  });
}