svoid video_scoreRect(Scorer scorer, Rect expected, Rect guessed, double tolerance) {
  if ((guessed == null) != (expected == null)) ret with scorer.addError();
  if (expected == null) ret with scorer.addOK();
  scorer.addZeroToOneError(doubleAverage(
    ptDistance(rectCenter(guessed), rectCenter(expected)),
    abs(guessed.w-expected.w),
    abs(guessed.h-expected.h))/tolerance);
}