解决图片显示 Exif.js更改图片的显示方向

没什么文字直接上代码

//这是一个解决exif更改脱方向的一个js文件
// 应用前先npm install exif-js --save或者直接引入exif-js

//// 调用方法
// let baseData;
// imgExif(file,function (base){
//   baseData=base
// });

import Exif from 'exif-js' //引入exif

let u = {};
// 转换的主体方法
u.index = (file, callback) => {
  let Orientation, resultData; //图片的方向,返回的值
  //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;

  // 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;
      //判断图片是否有方向值没有直接返回base64
      if (!Orientation) {
        callback(result);
      } else {
        let img = new Image();
        img.src = result;
        //图片信息加载完转换方向
        img.onload = function () {
          resultData = u.compress(img, Orientation);
          callback(resultData);
        }
      }
    }
  }
};

//更改旋转方向
u.compress = (img, Orientation) => {
  let canvas = document.createElement("canvas"), ctx = canvas.getContext('2d'),
    tCanvas = document.createElement("canvas"), tctx = tCanvas.getContext("2d"), initSize = img.src.length,
    width = img.width, height = img.height, ratio = 1;  //声明
  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
        u.rotateImg(img, 'left', canvas);
        break;
      case 8://需要逆时针（向右）90度旋转
        u.rotateImg(img, 'right', canvas);
        break;
      case 3://需要180度旋转
        u.rotateImg(img, 'right', canvas, 2);//转两次
        break;
    }
  }
  //进行最小压缩
  let ndata = canvas.toDataURL('image/jpeg', 1);
  tCanvas.width = tCanvas.height = canvas.width = canvas.height = 0;
  return ndata;
};

//更改旋转方向
u.rotateImg = (img, direction, canvas, num) => {
  //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180度
  step = num ? num : 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;
  }
};
window.imgExif = u;

要是后台需要的是file用这个转换一下就可以了

//将base64转换为img文件
u.compress = (img, Orientation) => {
  let arr = dataurl.split(','),
    mime = arr[0].match(/:(.*?);/)[1],
    bstr = atob(arr[1]),
    n = bstr.length,
    u8arr = new Uint8Array(n);
  while (n--) {
    u8arr[n] = bstr.charCodeAt(n);
  }
  return new File([u8arr], filename, {type: mime});
};