移动端 Vue+Vant 的Uploader 实现上传、压缩、旋转图片功能

 <van-uploader :after-read="onRead" accept="image/*">    <img src="./icon_input_add.png" /> </van-uploader>

data() {    return {      files: {        name: "",        type: ""      },      headerImage: null,      picValue: null,      upImgUrl,    }  },  // 组件方法 获取 流  async onRead(file) {      // console.log(file);      // console.log(file.file);      this.files.name = file.file.name; // 获取文件名      this.files.type = file.file.type; // 获取类型      this.picValue = file.file; // 文件流      this.imgPreview(this.picValue);    },    // 处理图片    imgPreview(file) {      let self = this;      let Orientation;      //去获取拍照时的信息，解决拍出来的照片旋转问题      Exif.getData(file, function () {        Orientation = Exif.getTag(this, "Orientation");      });      // 看支持不支持FileReader      if (!file || !window.FileReader) return;      if (/^image/.test(file.type)) {        // 创建一个reader        let reader = new FileReader();        // 将图片2将转成 base64 格式        reader.readAsDataURL(file);        // 读取成功后的回调        reader.onloadend = function () {          // console.log(this.result);          let result = this.result;          let img = new Image();          img.src = result;          //判断图片是否大于500K,是就直接上传，反之压缩图片          if (this.result.length <= 500 * 1024) {            self.headerImage = this.result;            self.postImg();          } else {            img.onload = function () {              let data = self.compress(img, Orientation);              self.headerImage = data;              self.postImg();            };          }        };      }    },    // 压缩图片    compress(img, Orientation) {      let canvas = document.createElement("canvas");      let ctx = canvas.getContext("2d");      //瓦片canvas      let tCanvas = document.createElement("canvas");      let tctx = tCanvas.getContext("2d");      // let initSize = img.src.length;      let width = img.width;      let height = img.height;      //如果图片大于四百万像素，计算压缩比并将大小压至400万以下      let ratio;      if ((ratio = (width * height) / 4000000) > 1) {        // console.log("大于400万像素");        ratio = Math.sqrt(ratio);        width /= ratio;        height /= ratio;      } else {        ratio = 1;      }      canvas.width = width;      canvas.height = height;      //    铺底色      ctx.fillStyle = "#fff";      ctx.fillRect(0, 0, canvas.width, canvas.height);      //如果图片像素大于100万则使用瓦片绘制      let count;      if ((count = (width * height) / 1000000) > 1) {        // console.log("超过100W像素");        count = ~~(Math.sqrt(count) + 1); //计算要分成多少块瓦片        //      计算每块瓦片的宽和高        let nw = ~~(width / count);        let nh = ~~(height / count);        tCanvas.width = nw;        tCanvas.height = nh;        for (let i = 0; i < count; i++) {          for (let j = 0; j < count; j++) {            tctx.drawImage(img, i * nw * ratio, j * nh * ratio, nw * ratio, nh * ratio, 0, 0, nw, nh);            ctx.drawImage(tCanvas, i * nw, j * nh, nw, nh);          }        }      } else {        ctx.drawImage(img, 0, 0, width, height);      }      //修复ios上传图片的时候 被旋转的问题      if (Orientation != "" && Orientation != 1) {        switch (Orientation) {          case 6: //需要顺时针（向左）90度旋转            this.rotateImg(img, "left", canvas);            break;          case 8: //需要逆时针（向右）90度旋转            this.rotateImg(img, "right", canvas);            break;          case 3: //需要180度旋转            this.rotateImg(img, "right", canvas); //转两次            this.rotateImg(img, "right", canvas);            break;        }      }      //进行最小压缩      let ndata = canvas.toDataURL("image/jpeg", 0.1);      tCanvas.width = tCanvas.height = canvas.width = canvas.height = 0;      return ndata;    },    // 旋转图片    rotateImg(img, direction, canvas) {      //最小与最大旋转方向，图片旋转4次后回到原方向      const min_step = 0;      const max_step = 3;      if (img == null) return;      //img的高度和宽度不能在img元素隐藏后获取，否则会出错      let height = img.height;      let width = img.width;      let step = 2;      if (step == null) {        step = min_step;      }      if (direction == "right") {        step++;        //旋转到原位置，即超过最大值        step > max_step && (step = min_step);      } else {        step--;        step < min_step && (step = max_step);      }      //旋转角度以弧度值为参数      let degree = (step * 90 * Math.PI) / 180;      let ctx = canvas.getContext("2d");      switch (step) {        case 0:          canvas.width = width;          canvas.height = height;          ctx.drawImage(img, 0, 0);          break;        case 1:          canvas.width = height;          canvas.height = width;          ctx.rotate(degree);          ctx.drawImage(img, 0, -height);          break;        case 2:          canvas.width = width;          canvas.height = height;          ctx.rotate(degree);          ctx.drawImage(img, -width, -height);          break;        case 3:          canvas.width = height;          canvas.height = width;          ctx.rotate(degree);          ctx.drawImage(img, -width, 0);          break;      }    },    //将base64转换为文件    dataURLtoFile(dataurl) {      var arr = dataurl.split(","),        bstr = atob(arr[1]),        n = bstr.length,        u8arr = new Uint8Array(n);      while (n--) {        u8arr[n] = bstr.charCodeAt(n);      }      return new File([u8arr], this.files.name, {        type: this.files.type      });    },    //这里写接口     async postImg() {      let file = this.dataURLtoFile(this.headerImage);      let formData = new window.FormData();      formData.append("file", file);      toast_loding(this, "图片上传中・・・");      try {        let res = await util.ajax.post(this.upImgUrl, formData, {          headers: {            "Content-Type": "multipart/form-data"          }        });      } catch (e) {        console.log(e);      }    }