微信小程序实现裁剪图片大小

<button bindtap="uploadtap">上传图片</button>
<image style="width: 100%;" mode="widthFix" src="{{canfile_image}}"></image>
<canvas canvas-id="myCanvas" id="myCanvas" style="width:100%;height:70vh;"></canvas>
<view class="canvas_model" wx:if="{{canvas_arr.show}}" catchtouchmove="setTouchMove">
  <view class="canvas_view" style="width: {{canvas_arr.width}}px;height: {{canvas_arr.height}}px;"
  bindtouchstart="handletouchstart" bindtouchmove="handletouchmove">
    <image style="width:100%;height:100%;" src="{{canvas_arr.src}}"></image>
    <view style="{{color_status?'background: rgba(0, 0, 0, 0.6);':''}}">
      <view class="canvas_horn" style="height:{{cutting.height}}px;top:{{canvas_y}}px;">
        <view></view>
        <view></view>
        <view></view>
        <view></view>
        <view></view>
        <view></view>
        <image style="width: {{canvas_arr.width}}px;height: {{canvas_arr.height}}px;top:-{{canvas_y}}px;" src="{{canvas_arr.src}}"></image>
      </view>
    </view>
  </view>
  <view class="canvas_bar" wx:if="{{cutting.show}}">
    <view bindtap="color_tap">×</view>
    <view class="bar_tab {{color_status?'tab_cation':''}}" bindtap="color_tap" data-type="1">
      <view>浅色</view>
      <view>深色</view>
      <view></view>
    </view>
    <view bindtap="ationimg">√</view>
  </view>
</view>

 .canvas_model{width: 100%;height: 100vh;position: fixed;left: 0;top: 0;background: rgba(0, 0, 0, 0.6);z-index: 10;
display:flex;justify-content: center;padding-top: 10vh;animation:model 0.3s;}
@keyframes model{
  from { opacity: 0;transform: scale(0.5); }
  to { opacity:1;transform: scale(1); }
}
.canvas_view{float: left;position: relative;}
.canvas_view>view{width: 100%;height: 100%;position: absolute;left: 0;top: 0;background: rgba(255, 255, 255, 0.4);transition: all 0.3s;}
.canvas_horn{position: absolute;left: 0;width: 100%;overflow: hidden;}
.canvas_horn>view{width: 40rpx;height: 40rpx;position: absolute;z-index: 1;}
.canvas_horn>image{position: absolute;left: 0;top: 0;}
.canvas_horn>view:nth-child(1){border-left: 2px solid #fff;border-top: 2px solid #fff;left: 0;top: 0;}
.canvas_horn>view:nth-child(2){border-right: 2px solid #fff;border-top: 2px solid #fff;right: 0;top: 0;}
.canvas_horn>view:nth-child(3){border-left: 2px solid #fff;border-bottom:2px solid #fff;left: 0;bottom: 0;}
.canvas_horn>view:nth-child(4){border-right: 2px solid #fff;border-bottom: 2px solid #fff;right: 0;bottom: 0;}
.canvas_horn>view:nth-child(5){width: 60rpx;height: 2px;background: #fff;top: 0;left: 0;right: 0;margin: 0 auto;}
.canvas_horn>view:nth-child(6){width: 60rpx;height: 2px;background: #fff;bottom: 0;left: 0;right: 0;margin: 0 auto;}
.canvas_bar{width: 100%;height: 14vh;display: flex;align-items: center;justify-content: space-between;background: #fff;
position: absolute;left: 0;bottom: 0;animation:bartion 0.5s;}
@keyframes bartion{
  from { bottom: -14vh; }
  to { bottom: 0; }
}
.canvas_bar>view:nth-child(1),.canvas_bar>view:nth-child(3){width: 160rpx;height: 100%;display: flex;align-items: center;
justify-content: center;font-size: 44rpx;font-weight: 700;}
.bar_tab{width: 300rpx;display: flex;height: 60rpx;border-radius: 10rpx;border: 1px solid #f4f4f4;line-height: 60rpx;
position: relative;font-size: 24rpx;color: #333;}
.bar_tab>view{width: 50%;height: 100%;text-align: center;position: relative;z-index: 1;transition: all 0.3s;}
.bar_tab>view:nth-child(1){color: #fff;}
.bar_tab>view:nth-child(3){position: absolute;left: 0;top: 0;background: #0081ff;border-radius: 10rpx;z-index: 0;}
.tab_cation>view:nth-child(1){color: #000;}
.tab_cation>view:nth-child(2){color: #fff;}
.tab_cation>view:nth-child(3){left: 50%;}
#myCanvas{position: absolute;left: 0;top: -71vh;z-index: -1;opacity: 0;}

Page({
  data: {
    canvas_arr:{
      src:'',
      width:parseInt(wx.getSystemInfoSync().windowWidth * 0.9),
      height:parseInt(wx.getSystemInfoSync().windowHeight * 0.7),
      show:false
    },
    cutting:{
      height:0,
      max_y:0,
      show:false
    },
    canvas_y:0,
    color_status:false,
    canfile_image:'',
  },
  color_tap(e){
    var type = e?e.currentTarget.dataset.type:0
    if(type == 1){
      this.setData({
        color_status:!this.data.color_status
      })
    }else{
      this.data.canvas_arr.show = false
      this.data.canvas_arr.height = parseInt(wx.getSystemInfoSync().windowHeight * 0.7)
      this.data.cutting.show = false
      this.data.cutting.src = ''
      this.setData({
        canvas_arr:this.data.canvas_arr,
        cutting:this.data.cutting,
        canvas_y:0,
      })
    }
  },
  setTouchMove(e){return;},
  uploadtap(e){
    var that = this
    wx.chooseImage({
      count:1,
      success (res) {
        const tempFilePaths = res.tempFilePaths[0]
        that.data.canvas_arr.src = tempFilePaths
        wx.getImageInfo({
          src: tempFilePaths,
          success (res) {
            that.data.canvas_arr.show = true
            that.data.cutting.show = true
            that.data.cutting.height = that.data.canvas_arr.width / 2
            var height = parseInt(res.height / (res.width / that.data.canvas_arr.width))
            that.data.canvas_arr.height = height > that.data.canvas_arr.height ? that.data.canvas_arr.height : height
            that.data.cutting.max_y = that.data.canvas_arr.height - that.data.cutting.height
            that.setData({
              canvas_arr:that.data.canvas_arr
            })
            setTimeout(function () {
              that.setData({
                cutting:that.data.cutting
              })
            },500)
          }
        })
      }
    })
  },
  handletouchstart: function (e) {
    this.data.startY = e.touches[0].clientY
  },
  handletouchmove (e) {
    let currentY = e.touches[0].clientY - this.data.startY
    if(currentY > 0){
      this.setData({
        canvas_y:currentY > this.data.cutting.max_y?this.data.cutting.max_y:currentY,
      })
    }else{
      this.setData({
        canvas_y:0
      })
    }
  },
  ationimg(e){
    var that = this
    var canvas_img = wx.createCanvasContext('myCanvas')
    canvas_img.width = that.data.canvas_arr.width
    canvas_img.height = that.data.canvas_arr.height
    canvas_img.drawImage(that.data.canvas_arr.src,0,0,canvas_img.width,canvas_img.height)
    canvas_img.draw(true,(()=>{
      wx.canvasToTempFilePath({
        x: 0,
        y: that.data.canvas_y,
        width:that.data.canvas_arr.width,
        height:that.data.cutting.height,
        canvasId: 'myCanvas',
        success: function (res) {
          that.setData({
            canfile_image:res.tempFilePath
          })
          that.color_tap()
          wx.showToast({
            title: '裁剪成功~',
            icon: 'none',
            duration: 3000
          })
        }
      });
    }))
  },
})