whoknows.js

for (var i = 0, m = open ? n : n + 1; i < m; ++i) {
     var point = points[(i + k) % n],
          p = coincidences.peek(point);
      if (!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) a.push(point);
        arc(a);
        if (!tInP && !pInT) arc([a[a.length - 1], point]);
        if (pInT) a = [a[a.length - 1]];
        else a = [];
      }
      if (!a.length || pointCompare(a[a.length - 1], point)) a.push(point); // skip duplicate points
      t = p;
    }