// returns best point
static Pt bwSpiralSearch(BWImage proto, IBWImage img, float instantWinThreshold default 0.8f) {
  int leewayX = img.getWidth()-proto.getWidth();
  int leewayY = img.getHeight()-proto.getHeight();
  for (long xy : pixelSpiral_longIterator(leewayX, leewayY)) {
    int x = firstIntFromLong(xy), y = secondIntFromLong(xy);
    float sim = bwImageSectionsSimilarity2(image, proto, x, y, minSimilarity);
    if (sim >= instantWinThreshold)
      ret longToPt(xy);
    if (sim >= best) {
      bestPt = xy;
      best = sim;
    }
  }
  ret longToPtUnlessMinus1(bestPt);
}