code: function vornoiRegion(line, point) {
          var len2 = line.length2();
          var dp = point.dotProduct(line);
          if (dp < 0) {
              // If the point is beyond the start of the line, it is in the
              // left vornoi region.
              return LEFT_VORNOI_REGION;
          } else if (dp > len2) {
              // If the point is beyond the end of the line, it is in the
              // right vornoi region.
              return RIGHT_VORNOI_REGION;
          } else {
              // Otherwise, it's in the middle one.
              return MIDDLE_VORNOI_REGION;
          }
      }
docs: Calculates which Vornoi region a point is on a line segment. <br>
  It is assumed that both the line and the point are relative to `(0,0)`<br>
  <pre>
  |       (0)      |
  (-1)  [S]--------------[E]  (1)
  |       (0)      |
  </pre>
  
  @ignore
  @param {Vector} line The line segment.
  @param {Vector} point The point.
  @return  {number} LEFT_VORNOI_REGION (-1) if it is the left region,
  MIDDLE_VORNOI_REGION (0) if it is the middle region,
  RIGHT_VORNOI_REGION (1) if it is the right region.