lineMatch.js

 // For closed lines, rotate to find a suitable shared starting point.
    for (; k < n; ++k) {
      var t = coincidences.peek(points[k]);
      if (open) break;
      if (p && !linesEqual(p, t)) {
        var tInP = t.every(function(line) { return p.indexOf(line) >= 0; }),
            pInT = p.every(function(line) { return t.indexOf(line) >= 0; });
        if (tInP && !pInT) --k;
        break;
      }
      p = t;
    }

    // If no shared starting point is found for closed lines, rotate to minimum.
    if (k === n && p.length > 1) {
      var point0 = points[0];
      for (k = 0, i = 1; i < n; ++i) {
        var point = points[i];
        if (pointCompare(point0, point) > 0) point0 = point, k = i;
      }
    }