docs: private boolean isConvex(double[] a, double[] b, double[] c) {
      // We're using factor to improve numerical contrast for small polygons.
      double area = (b[0] - a[0]) * factor * (c[1] - a[1]) - (c[0] - a[0]) * factor * (b[1] - a[1]);
      return (-1e-13 < area && area < 1e-13) ? (mdist(b, c) > mdist(a, b) + mdist(a, c)) : (area < 0);
    }