sclass ChessOCR_Pipeline {
  replace Segmenter with IF1<BufferedImage, L<Rect>>.
  
  // input
  transient BufferedImage inputImage;
  ChessPieceRecognizer pieceRecognizer;
  
  // internal
  SeenAndQueue<Segmenter> segmenters = new(r _runSegmenters);
  SeenAndQueue<Rect> possibleBoardPositions = new(r _processPositions);
  
  // output
  new ChessOCR_BoardsFound boardsFound;

  // input segmenters & board position proposals:
  
  void addSegmenter(Segmenter s) { segmenters.add(s); }
  void addPossiblePosition(Rect r) { possibleBoardPositions.add(r); }
  
  bool queuesEmpty() { ret segmenters.queueEmpty() && possibleBoardPositions.queueEmpty(); }
  bool idle() { ret segmenters.idle() && possibleBoardPositions.idle(); }
  
  // internal
  
  void _processPositions() {
    for (Rect r : possibleBoardPositions.queueIterator())
      boardsFound.add(setAll(pieceRecognizer.recognizeBoard(clipBufferedImage(inputImage, r)), rectInOriginalImage := r));
  }
  
  void _runSegmenters() {
    for (Segmenter seg : segmenters.queueIterator())
      possibleBoardPositions.addAll(seg.get(inputImage));
  }
  
  void cleanMeUp { // cancels the threads too
    cleanUpAll(possibleBoardPositions, segmenters);
  }
}