sclass PianoSampler2 > SlidingWindow {
  macro dprint { if (debug) printVars } bool debug;
    
  gettable L<Frequency> frequencies;
 
  *() { 
    frequencies = pianoFrequencies88();
  }
 
  long haarFeaturesChecked;
  
  // one channel
  L<Complex> measureWindow(DoubleRange window, Cl<Freq> frequencies default frequencies()) {
    int channel = 0;
    assertEquals("window length", window.length(), length());
    moveTo(window.start);
    ret map(frequencies(), f -> {
      var interval = f.interval()*sampleRate;
      int period1 = ifloor(doubleRatio(window.start, interval));
      int period2 = ifloor(doubleRatio(window.end, interval))-1;
      if (period2 <= period1) ret complex(0);
      SumOfVibrations sum = new(this, channel, period1*interval, f!, period2-period1);
      ret sum.complexSum();
    });
  }
    
  Frequency lowestFrequency() { ret first(frequencies); }
  Frequency highestFrequency() { ret last(frequencies); }
  
  int minWindowSizeForBase() {
    ret iceil(sampleRate*lowestFrequency().interval());
  }
  
  void makeSmallestWindow(IQuerySound sound) {
    this.sound = sound;
    setAudio(new SlidingWindow(channels, sampleRate, sound, 0, minWindowSizeForBase());
  }
  
  S stats() { ret renderVars(+haarFeaturesChecked); }
  
  IIntegralImage imageColumn(L<Complex> intensities) {
    int n = l(intensities);
    double[] col = new[n];
    for y to n: 
      col[n-y-1] = abs(intensities.get(y));
    double[] col2 = normalizeDoubles(col, 255);
      
    ret bwIntegralImageFromFunction(1, n, (x, y) -> ifloor(col2[y]));
  }
}