图片上传，压缩方法

1、点击图片上传，拿到图片，转化base64，然后在执行图片压缩

addImg() {

  let _this = this;

  plus.gallery.pick(function (path) {

    plus.io.resolveLocalFileSystemURL(path,function (entry) {

      entry.file(function (file) {

        let files = {

          src: '',

          name: file.name

        };

        let reader = new plus.io.FileReader();

        reader.readAsDataURL(file);   // 读出base64

        reader.onloadend = function (e) {

          _this.canvasDataURL(e.target.result,{

            quality: 0.7

          },function (base64Codes) {

            files.src = base64Codes;

            _this.fileUp(files);

          });

        };

        _this.$toast.loading({

          duration: 10000,// 持续展示toast

          forbidClick: true,// 禁用背景点击

          loadingType: 'spinner',

         message: '正在上传...'

        });

      });

    });

  },function (err) {

  },null);

},

2、图片压缩的方法

canvasDataURL(path,obj,callback) {

  let img = new Image();

  img.src= path;

  img.onload= function () {

    let that = this;  //默认按比例压缩

    let w = that.width,

h = that.height,

scale = w / h;

    w = obj.width || w;

    h = obj.height || (w / scale);

    let quality = 0.7; // 默认图片质量为0.7

    //生成canvas

    let canvas = document.createElement('canvas');

    let ctx = canvas.getContext('2d');

    // 创建属性节点

    let anw = document.createAttribute('width');

    anw.nodeValue= w;

    let anh = document.createAttribute('height');

    anh.nodeValue= h;

    canvas.setAttributeNode(anw);

    canvas.setAttributeNode(anh);

    ctx.drawImage(that,0,0,w,h);

    // 图像质量

    if (obj.quality && obj.quality <= 1 && obj.quality > 0) {

      quality = obj.quality;

    }

    // quality值越小，所绘制出的图像越模糊

    let base64 = canvas.toDataURL('image/jpeg',quality);

    // 回调函数返回base64的值

    callback(base64);

  };

},