public void update(double c1x, double c1y, double c2x, double c2y) {
    for (int i = 0; i < xs.length; i++) {
      xs[i] = bezier(i * 1. / (xs.length - 1), c1x, c2x);
      ys[i] = bezier(i * 1. / (ys.length - 1), c1y, c2y);
    }
  }
public void update(double c1x, double c1y, double c2x, double c2y)