static void calCenterStepwise(CirclesAndLines cal, double speed) {
  DoublePt c = calAverageCenter(cal);
  if (c == null) ret;
  calTranslate(cal, (0.5-c.x)*speed, (0.5-c.y)*speed);#
  if (cal.translate != null) {
    cal.translate = null;
    print("calCenterStepwise translate");
  }
}