微信小程序简单的canvas裁剪图片功能详解

<view class="cut-1-1 t-c {{cutSelect == 1? 'cut-select':''}}" data-cut="1" bindtap="selectCutType">1:1</view><view class="cut-3-4 t-c {{cutSelect == 2? 'cut-select':''}}" data-cut="2" bindtap="selectCutType">3:4</view>

<block wx:for="{{imgList}}" wx:key="{{index}}" >  <swiper-item>  <scroll-view scroll-top="{{topNum}}" scroll-y class="imgFile {{cutSelect == 1?'view-1-1':'view-3-4'}}" bindscroll="endTou">   <image src='{{item}}' mode="widthFix"></image>  </scroll-view >  </swiper-item></block>

<canvas wx:for="{{imgList}}" wx:for-index="i" canvas-id="myCanvas_{{i}}" style="width: {{width[i]?width[i]*2:750}}rpx; height: {{height[i]?height[i]*2:750}}rpx;"></canvas>

.view-1-1 { width: 750rpx; height: 750rpx; overflow: hidden;}.view-3-4 { width: 750rpx; height: 750rpx; padding: 0 94rpx; box-sizing: border-box; overflow: hidden;}canvas { position: absolute; /* display: none; */ left: -999rpx; z-index: 0;}

cutPic() { const _this = this if (this.data.cutting) {  return } let promiseList = [], ctx = [] _this.data.imgList.forEach((v, i) => {  promiseList.push(_this.draw(ctx, v, i)) }) wx.showLoading({  title: '截取中...',  icon: 'none' }) this.setData({  cutting: true }) Promise.all(promiseList).then((arr) => {  wx.setStorageSync("interimImagesList", _this.data.imgFileList)  _this.uploadPic() }, err => { }) },

//获取竖向滑动坐标 endTou(e) { const _this = this let y = 'y[' + (_this.data.currentIndex - 1) + '].top' _this.setData({  [y]: e.detail.scrollTop }) },

//绘制 draw(ctx, v, i) { const _this = this let width, height return new Promise((resolve, reject) => {  ctx[i] = wx.createCanvasContext(`myCanvas_${i}`)  wx.getImageInfo({  src: v,  success: function (res) {   width = 'width[' + i + ']'   height = 'height[' + i + ']'   var str = res.height / res.width;//图片的宽高比   _this.setData({   [width]: 375,   [height]: 375 * str   }, () => {   ctx[i].drawImage(v, 0, 0, _this.data.width[i], _this.data.height[i])   ctx[i].draw(false, () => {    setTimeout(() => {    wx.canvasToTempFilePath({//调用方法，开始截取     x: 0,     y: _this.data.y[i] ? _this.data.cutSelect == 1 ? _this.data.y[i].top : _this.data.y[i].top / 0.75 : 0,     width: 375,     height: _this.data.cutSelect == 1 ? 375 : 500,     destWidth: 375,     destHeight: _this.data.cutSelect == 1 ? 375 : 500,     canvasId: 'myCanvas_' + i,     success: function (res) {     resolve(res.tempFilePath)     console.info('canvas', res.tempFilePath)     let img = 'imgFileList[' + i + ']'     _this.setData({      [img]: res.tempFilePath     })     },     fail: function (err) {     reject(err)     console.info(err)     }    })    }, 1000) // 渲染时间   })   })  }  }) }) },