code: function cornerLine(p, quadrant, size) {
  
    switch (quadrant) {
      case Const.top_left: return new Pair(p).to(p.$add(size, size));
      case Const.top_right: return new Pair(p).to(p.$add(-size, size));
      case Const.bottom_left: return new Pair(p).to(p.$add(size, -size));
      case Const.bottom_right: return new Pair(p).to(p.$add(-size, -size));
      case Const.top: return new Pair(p).to(p.$add(0, size));
      case Const.bottom: return new Pair(p).to(p.$add(0, -size));
      case Const.left: return new Pair(p).to(p.$add(size, 0));
      default: return new Pair(p).to(p.$add(-size, 0));
    }
  }
docs: Get a line indicating the quadrant