static void calCenter(CirclesAndLines cal) {
  if (n == 0) ret;
  double x = 0, y = 0;
  int n = l(cal.circles);
  for (Circle c : cal.circles) {
    x += c.x; y += c.y;
  }
  calTranslate(cal, 0.5-x/n, 0.5-y/n);
}