小程序下载canvas生成图片

  save_share_img:function(img){

      var that = this;
      let { result } = that.data;

      getData.getData(
          "save_share_img",
          {
              id                : result.id,
              share_img_link    : img,
              method            : "POST"
          },
          function(data) {
              if (data.errno){
                  console.log(data.errdesc);
                  return;
              }

              result.share_img = img;
              that.setData({
                  result: result
              });

          }
      );
  },
  download:function(){
      var that = this;
      let { urls,result } = that.data;

      console.log(result);
      if (result.share_img == ''){

          // 临时图片上传cdn
          wx.uploadFile({　　　　　　　　　　　　// 需要传到cdn 才可以下载!!!!!
              url       : "https://a.xxxxx.com/xxxxx/Public/upload_more_img",
              filePath  : urls,
              name      : "file",
              success   : res => {
              },
              fail : res => {
              },
              complete: res => {
                var imgdata = JSON.parse(res.data);
                var img = imgdata.data[];
                that.save_share_img(img);
                urls = img;
              }
          })
      } else {
          urls = result.share_img;
      }

      console.log('download---start');
      console.log(urls);

      wx.downloadFile({
          url: urls,
          //url:'https://cdn.xxxxxx.net/avatar_3.png',  // canvas 生成的临时图片不可
          success: function(res) {    // 只要服务器有响应数据，就会把响应内容写入文件并进入 success 回调，业务需要自行判断是否下载到了想要的内容
              console.log(res)
              if (res.statusCode == ) {
                  wx.saveImageToPhotosAlbum({
                      filePath: res.tempFilePath,
                      success: function(res) {
                          console.log(res);
                          console.log('succ');
                          wx.showToast({
                              title: '保存图片成功!~',
                          });

                          that.setData({
                              mask_btn: ,
                              share_btn: false,
                              canvas_btn:false
                          });
                      },
                      fail: function(res) {
                          console.log(res);
                          console.log('fail');
                          wx.showToast({
                              title: '保存图片失败!~'
                          });
                      },
                      complete:function(res){
                          console.log(res);
                          console.log('complete');
                      }
                  })
              } else {
                  console.log('下载图片发生错误----');
                  wx.showToast({
                      title: '保存图片发生错误!~'
                  });
              }
          },
          fail: function(res){
              console.log('下载图片发生错误');
              console.log(res);

          }
      });

      console.log('download---over');

  },
  previewImg: function() {
    var that = this;

    wx.getSetting({
        success(res) {
            console.log('-------------');
            console.log(res);

            if (!res.authSetting['scope.writePhotosAlbum']) {　　　　　　// 获取授权!!!!
                wx.authorize({
                    scope:'scope.writePhotosAlbum',
                    success() {
                        that.download();
                        console.log('授权成功')
                    }
                });

            } else {
                that.download();
                console.log('已授权');
            }
        }
    })