小程序压缩图片先用canvas进行压缩，压缩后再用微信api//压缩图片 getCanvasImg: function

//压缩图片

getCanvasImg: function (index,failNum, tempFilePaths,imgSize){
```
    wx.showLoading({
```
```
        title:'上传中...',
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        mask:true
```
```
    })
```
```
    var that = this;
```
```
    if (index < tempFilePaths.length){
```

        if(imgSize < 512000){  //小于的不压缩

            that.photoList.push( tempFilePaths[index-1].tempFilePath)

            that.suffix.push( tempFilePaths[index-1].tempFilePath.split('.')[1])

```
            return
```
```
        }`
```
```
    `    wx.getImageInfo({
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            src:tempFilePaths[index].tempFilePath,

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            success(respone){
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                var canvasWidth, canvasHeight;

            canvasWidth= respone.width;
              canvasHeight = respone.height;`
              //压缩比例
              // 最大尺寸限制
              var maxWidth = 1000;
              var maxHeight = 1000;
              // 目标尺寸
              var targetWidth = canvasWidth
              var targetHeight = canvasHeight;
              //等比例压缩，如果宽度大于高度，则宽度优先，否则高度优先
              if (canvasWidth > maxWidth || canvasHeight > maxHeight) {
                  if (canvasWidth / canvasHeight > 1) {
                  // 宽图片
                      targetWidth = maxWidth
                      targetHeight = Math.round(maxWidth * (canvasHeight / canvasWidth))
                  } else {
                  // 高图片
                      targetHeight = maxHeight
                      targetWidth = Math.round(maxHeight * (canvasWidth / canvasHeight))
                  }
              }
              //尝试压缩文件，创建 canvas
              var ctx = wx.createCanvasContext('attendCanvasId');
              ctx.clearRect(0,0,targetWidth,targetHeight)
              ctx.drawImage(tempFilePaths[index].tempFilePath, 0, 0, targetWidth, targetHeight);`
             ` ctx.draw()
              that.$set(that,'canvasWidth',targetWidth)
              that.$set(that,'canvasHeight',targetHeight)
              setTimeout(function () {
                  index = index + 1;//上传成功的数量，上传成功则加1
                  wx.canvasToTempFilePath({
                  canvasId: 'attendCanvasId',
                  destWidth: targetWidth,
                  destHeight: targetHeight,
                  fileType:'jpg',
                  success: function success(resP) {
                      var a = tempFilePaths[index-1].tempFilePath.split('.')[1]
                      wx.compressImage({ 
                          src: resP.tempFilePath, // 图片路径
                          quality: 95, // 压缩质量
                          success(ressss){
                              upLoadPics( [ressss.tempFilePath] ,0,'',a).then(urlS => {
                                that.sendMessae(urlS, 1);
                              }).catch((err) => {
                                console.log(err);
                              });
                          },
                      })
                  }, fail: function (e) {
                          // console.log(e,'上传失败')
                      failNum += 1;//失败数量，可以用来提示用户
                      that.getCanvasImg(inedx,failNum,tempFilePaths);
                  }
                  });
              },500)
          },
      })
  }else{
      wx.hideLoading()
  }

```
//上传图片
```
```
addPhotoFn(sourceType) {
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```
  var _this = this;
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  wx.chooseMedia({
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      count: 1,
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      sizeType: ['original'],
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      mediaType:['image'],
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      sourceType:['album', 'camera'],
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      success: function (res) {
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         _this.getCanvasImg(0,0,res.tempFiles,res.size)

```
      },fail:(err)=>{
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        console.log(err,'上传错误')

```
  	}
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  })
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},
```
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