srecord noeq PixelSetsEqual(IPixelSet set1, IPixelSet set2) {
  // pixel sets are technically identical with differing bounds
  settable bool boundsMustBeEqual = true;
  
  gettable Pt firstDifferingPixel;
  
  bool get() {
    if (set1 == null) ret set2 == null;
    if (set2 == null) false;
    
    Rect r = set1.bounds();
    if (boundsMustBeEqual && !eq(r, set2.bounds())) false;
    
    for (int y = r.y(); y < r.y2(); y++)
      for (int x = r.x(); x < r.x2(); x++)
        if (set1.contains(x, y) != set2.contains(x, y)) {
          firstDifferingPixel = pt(x, y);
          false;
        }
        
    true;
  }
}