sclass PianoSampler2 > SlidingWindow {
  macro dprint { if (debug) printVars } bool debug;
    
  gettable L<Frequency> frequencies;
 
  *(int *channels, double *sampleRate, IQuerySound *sound,
    int *start, int *length) {
    init();
  }
    
  *() { init(); }
    
  void init { 
    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(ifloor(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 makeWindow(DoubleRange r) {
    start = r.start;
    length = r.length;
    grab();
  }
  
  void makeWindowAround(double t, double size) {
    double start = max(0, t-size)/2);
    makeWindow(DoubleRange(start, start+size));
  }
  
  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]));
  }
}