getSubringCenter(ring, vertex) {
    let rings = vertex.value.originalRings;
    let center = ring.center;
    let smallest = Number.MAX_VALUE; // Always get the smallest ring.

    for (var i = 0; i < rings.length; i++) {
      for (var j = 0; j < ring.rings.length; j++) {
        if (rings[i] === ring.rings[j].id) {
          if (ring.rings[j].getSize() < smallest) {
            center = ring.rings[j].center;
            smallest = ring.rings[j].getSize();
          }
        }
      }
    }

    return center;
  }
Gets the center of a ring contained within a bridged ring and containing a given vertex.

@param {Ring} ring A bridged ring.
@param {Vertex} vertex A vertex.
@returns {Vector2} The center of the subring that containing the vertex.