<template>
 <div>
  <input type="file" id="upload" accept="image" @change="upload" />
 </div>
</template>
<script>
export default {
 data() {
  return {
   picValue:{},
   headerImage:''
  };
 },
 components: {},
 methods: {
  upload(e) {
   console.log(e);
   let files = e.target.files || e.dataTransfer.files;
   if (!files.length) return;
   this.picValue = files[0];
   this.imgPreview(this.picValue);
  },
  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
   self.Exif.getData(file, function() {
    Orientation = self.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() {
     let result = this.result;
     let img = new Image();
     img.src = result;
     //判断图片是否大于100K,是就直接上传，反之压缩图片
     if (this.result.length <= 100 * 1024) {
      self.headerImage = this.result;
      self.postImg();
     } else {
      img.onload = function() {
       let data = self.compress(img, Orientation);
       self.headerImage = data;
       self.postImg();
      };
     }
    };
   }
  },
  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;
  },
  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;
   }
  },
  postImg() {
   //这里写接口
　　　　//打印的图片base64

   console.log('this.headerImage',this.headerImage);
   //接口 axios
  }
 }
};
</script>

npm install exif-js --save

import Exif from 'exif-js'
Vue.use(Exif)
Vue.prototype.Exif = Exif