js实现类似百度地图的缩放拖动功能

使用的前端框架为vue

采用vue的框架,通过canvas的缩放绘制和外层div的滚动条控制实现功能

滚轮事件代码

    handleScroll(e) {

      console.log(e.deltaY)

      let _this = this

      if (e.deltaY > 0 && _this.zoomtimes > 1) {

        _this.zoomtimes = (_this.zoomtimes * 10 - 2) / 10

      } else if (e.deltaY < 0) {

        _this.zoomtimes = (_this.zoomtimes * 10 + 2) / 10

      }

      this.down_x = e.clientX

      this.down_y = e.clientY

      if (e.deltaY > 0) {

        _this.direction = 1

      } else {

        _this.direction = 0

      }

      e.preventDefault()

    },

wheelxy() {

      let _this = this

      if (_this.direction == 0) {

        _this.$store.state.scroll_x = _this.$refs.imageWrapper.scrollLeft =

          (((_this.$refs.imageWrapper.clientWidth - 10) * _this.zoomtimes) /

            ((_this.$refs.imageWrapper.clientWidth - 10) *

              (_this.zoomtimes - 0.2)) -

            1) *

            (_this.down_x - 67 + _this.$refs.imageWrapper.scrollLeft) +

          _this.$refs.imageWrapper.scrollLeft

        _this.$store.state.scroll_y = _this.$refs.imageWrapper.scrollTop =

          (((_this.$refs.imageWrapper.clientHeight - 10) * _this.zoomtimes) /

            ((_this.$refs.imageWrapper.clientHeight - 10) *

              (_this.zoomtimes - 0.2)) -

            1) *

            (_this.down_y - 193 + _this.$refs.imageWrapper.scrollTop) +

          _this.$refs.imageWrapper.scrollTop

      } else {

        _this.$store.state.scroll_x = _this.$refs.imageWrapper.scrollLeft =

          (1 -

            ((_this.$refs.imageWrapper.clientWidth - 10) *

              (_this.zoomtimes + 0.2)) /

              ((_this.$refs.imageWrapper.clientWidth - 10) * _this.zoomtimes)) *

            (_this.down_x - 67 + _this.$refs.imageWrapper.scrollLeft) +

          _this.$refs.imageWrapper.scrollLeft

        _this.$store.state.scroll_y = _this.$refs.imageWrapper.scrollTop =

          (1 -

            ((_this.$refs.imageWrapper.clientHeight - 10) *

              (_this.zoomtimes + 0.2)) /

              ((_this.$refs.imageWrapper.clientHeight - 10) *

                _this.zoomtimes)) *

            (_this.down_y - 193 + _this.$refs.imageWrapper.scrollTop) +

          _this.$refs.imageWrapper.scrollTop

      }

    },

通过监听zoomtimes字段获取缩放倍数,调用canvas绘制,canvas绘制完成后调用wheelxy()函数实现定位滑动条位置为鼠标指针中心.

拖动事件代码

mouse_down(e) {

      console.log(this.$store.state.scroll_x)

      this.down_x = e.clientX

      this.down_y = e.clientY

      this.$refs.imageWrapper.scrollLeft = this.$store.state.scroll_x

      this.$refs.imageWrapper.scrollTop = this.$store.state.scroll_y

      this.mouseevent = true

    },

    mouse_move(e) {

      if (this.mouseevent) {

        let x = e.clientX - this.down_x

        let y = e.clientY - this.down_y

        this.$refs.imageWrapper.scrollLeft = this.$store.state.scroll_x - x

        this.$refs.imageWrapper.scrollTop = this.$store.state.scroll_y - y

      }

    },

    mouse_up(e) {

      this.$store.state.scroll_x = this.$refs.imageWrapper.scrollLeft

      this.$store.state.scroll_y = this.$refs.imageWrapper.scrollTop

      this.mouseevent = false

    },

拖动时注册三个事件函数,用vuex记录每次放开鼠标或缩放完成后的滚动条位置

实现方法逻辑

通过计算canvas缩放时的倍数计算出x轴和y轴的增量△x和△y,其中判断鼠标滚轮方向以使用不同的计算公式,放大时△x = ( canvas.width' / canvas.width - 1) x, 缩小时 △x = ( 1 - canvas.width / canvas.width' ) x',△y同理,而x,y轴的偏移量就是滚动条应该滚动的大小,每次叠加到上一次的数据中.

拖动时,以每次vuex记录的的滚动条位置为起点进行拖动

后续更新

通过实际测试发现,通过增量△x与△y操作的缩放拖动功能虽然能实现需求功能,但是在实际运用时发现会产生不流畅的迟钝感.

个人原本认为是因为每次移动或缩放产生的大量计算导致浏览器的canvas性能出现问题,但经过查询资料和实际测试发现,这种程度的计算远远没有达到浏览器的性能瓶颈,所以说明产生钝感的原因的核心还是算法的问题,因为算法的不细致导致了动画效果的不流畅.

在几次查询资料之后,我修改了代码的算法逻辑,新的算法和之前相比更加的丝滑,代码如下:

新滚轮事件代码

handleScroll(e) {

      let _this = this

      _this.down_xy = _this.windowToCanvas(e.clientX, e.clientY)

      let newDown_xy = {

        x: (

          (_this.down_xy.x - _this.imgX - _this.b) /

          _this.zoomtimes /

          _this.ts

        ).toFixed(2),

        y: (

          (_this.down_xy.y - _this.imgY - _this.a) /

          _this.zoomtimes /

          _this.ts

        ).toFixed(2)

      }

      if (e.deltaY > 0 && _this.zoomtimes > 1 && _this.zoomtimes < 1.1) {

        _this.zoomtimes = 1

        _this.imgX =

          (1 - _this.zoomtimes * _this.ts) * newDown_xy.x +

          (_this.down_xy.x - newDown_xy.x) -

          _this.b

        _this.imgY =

          (1 - _this.zoomtimes * _this.ts) * newDown_xy.y +

          (_this.down_xy.y - newDown_xy.y) -

          _this.a

      } else if (e.deltaY > 0 && _this.zoomtimes > 1) {

        _this.zoomtimes = (_this.zoomtimes * 10 - 1) / 10

        _this.imgX =

          (1 - _this.zoomtimes * _this.ts) * newDown_xy.x +

          (_this.down_xy.x - newDown_xy.x) -

          _this.b

        _this.imgY =

          (1 - _this.zoomtimes * _this.ts) * newDown_xy.y +

          (_this.down_xy.y - newDown_xy.y) -

          _this.a

      } else if (e.deltaY < 0) {

        _this.zoomtimes = (_this.zoomtimes * 10 + 1) / 10

        _this.imgX =

          (1 - _this.zoomtimes * _this.ts) * newDown_xy.x +

          (_this.down_xy.x - newDown_xy.x) -

          _this.b

        // (1 - _this.zoomtimes) * _this.down_xy.x - _this.b

        _this.imgY =

          (1 - _this.zoomtimes * _this.ts) * newDown_xy.y +

          (_this.down_xy.y - newDown_xy.y) -

          _this.a

        // (1 - _this.zoomtimes ) * _this.down_xy.y - _this.a

      }

      this.$store.state.move_item = ''

      e.preventDefault()

      console.info(_this.imgX, _this.imgY, 'sdsdsdsdsd')

    },

    windowToCanvas(x, y) {

      let mycanvas = document.getElementById('canvas_img')

      let box = mycanvas.getBoundingClientRect() //这个方法返回一个矩形对象，包含四个属性：left、top、right和bottom。分别表示元素各边与页面上边和左边的距离

      return {

        x: x - box.left - (box.width - mycanvas.width) / 2,

        y: y - box.top - (box.height - mycanvas.height) / 2

      }

    },

新拖动事件

mouse_down(e) {

      console.log(this.$store.state.scroll_x)

      this.mouseevent = true

      this.down_xy = this.windowToCanvas(e.clientX, e.clientY)

    },

    mouse_move(e) {

      if (this.mouseevent) {

        this.down_xyl = this.windowToCanvas(e.clientX, e.clientY)

        let x = this.down_xyl.x - this.down_xy.x,

          y = this.down_xyl.y - this.down_xy.y

        this.imgX += x

        this.imgY += y

        this.down_xy = JSON.parse(JSON.stringify(this.down_xyl))

      }

    },

    mouse_up(e) {

      if (this.mouseevent) {

        this.$store.state.move_item = ''

      }

      this.mouseevent = false

    },

其中 _this.a, _this.b, _this.ts都是这个项目中canvas的效果需求特殊定义的,比如ts变量指原图放到canvas时的比例,a,b为图片初始位置对canvas边框的距离,如果要测试的话可以先去掉不用,根据自己的情况添加