code: function getPointersCenter(pointers) {
    var pageX = 0;
    var pageY = 0;
    var count = 0;
    forEach(pointers, function (_ref3) {
      var startX = _ref3.startX,
          startY = _ref3.startY;
      pageX += startX;
      pageY += startY;
      count += 1;
    });
    pageX /= count;
    pageY /= count;
    return {
      pageX: pageX,
      pageY: pageY
    };
  }
docs: Get the center point coordinate of a group of pointers.
  @param {Object} pointers - The target pointers.
  @returns {Object} The center point coordinate.