sclass RenderFrequencySample_SquareWave is RenderFrequencySample {
  public double get(Complex c, double frac) {
    double abs = c.abs();
    if (abs == 0) ret 0;
    frac = frac(frac + c.angle()/twoPi());
    ret abs * (frac < .5 ? 1 : -1);
  }
}