data() {
   return {
      displacement: {
        scale: 1
      }
    }
},

mounted() {
    // this.$nextTick()将回调延迟到下次 DOM 更新循环之后执行
    let that = this;
    this.$nextTick(() => {
      // 获取放大或缩小的区域DOM
      let matrix_box = document.querySelector(".build_matrix_box");
      matrix_box.addEventListener("touchstart", function(event) {
        var touches = event.touches;
        var events = touches[0];
        var events2 = touches[1];

        // event.preventDefault();

        // 第一个触摸点的坐标
        that.displacement.pageX = events.pageX;
        that.displacement.pageY = events.pageY;

        that.displacement.moveable = true;

        if (events2) {
          that.displacement.pageX2 = events2.pageX;
          that.displacement.pageY2 = events2.pageY;
        }

        that.displacement.originScale = that.displacement.scale || 1;
        // console.log(that.displacement);
      });
      document.addEventListener("touchmove", function(event) {
        if (!that.displacement.moveable) {
          return;
        }

        event.preventDefault();

        var touches = event.touches;
        var events = touches[0];
        var events2 = touches[1];
        // 双指移动
        if (events2) {
          // 第2个指头坐标在touchmove时候获取
          if (!that.displacement.pageX2) {
            that.displacement.pageX2 = events2.pageX;
          }
          if (!that.displacement.pageY2) {
            that.displacement.pageY2 = events2.pageY;
          }

          // 双指缩放比例计算
          var zoom =
            that.getDistance(
              {
                x: events.pageX,
                y: events.pageY
              },
              {
                x: events2.pageX,
                y: events2.pageY
              }
            ) /
            that.getDistance(
              {
                x: that.displacement.pageX,
                y: that.displacement.pageY
              },
              {
                x: that.displacement.pageX2,
                y: that.displacement.pageY2
              }
            );
          // 应用在元素上的缩放比例
          var newScale = that.displacement.originScale * zoom;
          // 最大缩放比例限制
          if (newScale > 1) {
            newScale = 1;
          }
          // 记住使用的缩放值
          that.displacement.scale = newScale;
          // 图像应用缩放效果
          // console.log(newScale);
          matrix_box.style.transform = "scale(" + newScale + ")";
          // 设置旋转元素的基点位置
          matrix_box.style.transformOrigin = "0px 0px 0px";
        }
      });
    });
  },

 methods: {
    getDistance(start, stop) {
      // Math.hypot()计算参数的平方根
      return Math.hypot(stop.x - start.x, stop.y - start.y);
    },
 }