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Here you can Sed posuere consectetur est at lobortis. Donec ullamcorper nulla non metus auctor fringilla. Maecenas sed diam eget risus varius blandit sit amet non magna. Donec id elit non mi porta gravida at eget metus. Praesent commodo cursus magna, vel scelerisque nisl consectetur et.

            
              <section class="contain">
  <h2>
    使用 JavaScript 读取 JPEG 文件中 EXIF 的 Orientation 属性,利用 canvas 根据其对应值作出旋转。
  </h2>
  <div class="demo-contain">
    <section class="output-contain">
      <div class="output">
      </div>
    </section>

    <div>
      <input type="file">
    </div>
    
    <section class="preview__contain">
      <div class="preview">
        <h3>没有处理旋转的结果:</h3>
        <img class="preview--not-rotated">
      </div>
      <div class="preview">
        <h3>2. 根据 Exif 中 Orientation 进行旋转了的结果:</h3>
        <img class="preview--rotated">
      </div>
    </section>
  </div>
</section>
            
          
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              html {
  font-size: 14px;
}

body {
  background: #232425;
  font-family: -apple-system, BlinkMacSystemFont, Helvetica, Arial, sans-serif, "Apple Color Emoji";
}

.contain {
  width: 95%;
  padding: 1rem;
  max-width: 720px;
  background: #f1f2f3;
  margin: .65rem auto;
  padding: .65rem;
  border-radius: 4px;
  
  > h2 {
    font-size: 1.2rem;
  }
}

.demo-contain {
  > .output-contain {
    font-size: 1.2rem; 
    margin-bottom: 1rem;
    border-bottom: 1px solid #c1c2c3;
    > .output {
      font-size: 1rem;
      margin-bottom: .65rem;
    }
  }
}

.preview__contain {
  display: flex;
  flex-flow: row wrap;
  flex-basis: 100%;
  align-items: flex-start;
  box-sizing: border-box;
  
  > div {
    display: flex;
    flex-basis: 50%;
    flex-flow: column nowrap;
    background: #c1c2c3;
    box-sizing: border-box;
    width: 50%;
    margin: 1rem auto; 
    align-items: center;
    
    > h3 {
      margin: 0;
      min-height: 45px;
      font-weight: normal;
      background: #f1f1f1;
      width: 100%;
      padding: .65rem;
      font-size: 1.1rem;
      box-sizing: border-box;
    }
    
    img {
      display: block;
      width: 60%;
      margin: 1rem 0;
      border: 1px solid #666666;
    }
  }
}

@media (max-width: 720px)  {
  .preview__contain {
    > div {
      flex-basis: 100%;
      img {
        max-heigth: 400px;
      }
    }
  }
}

            
          
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              ;((win, doc) => {
  const $ = (selector) => doc.querySelector(selector);
  const af2view = (af) => new Promise((resolve, reject) => resolve(new DataView(af)));
  
  const af2Base64 = (af) => {
    let base64 = btoa(
      [].reduce.call(
        new Uint8Array(af), (p,c) => p + String.fromCharCode(c), '')
    );
    return 'data:image/gif;base64,' + base64;
  }
  
  const readFile = (file) => {
    let FR = new FileReader();
    return new Promise((resolve, reject) => {
      FR.onloadend = (evt) => { resolve(evt.target.result); };
      FR.onerror = (err) => { reject(event.target.error); };
      FR.readAsArrayBuffer(file);
    })
  };
  
  const rotateCtx = (orieVal, ctx, width, height) => {
    switch (orieVal) {
      case 2: ctx.transform(-1, 0, 0, 1, width, 0); break;
      case 3: ctx.transform(-1, 0, 0, -1, width, height ); break;
      case 4: ctx.transform(1, 0, 0, -1, 0, height ); break;
      case 5: ctx.transform(0, 1, 1, 0, 0, 0); break;
      case 6: ctx.transform(0, 1, -1, 0, height , 0); break;
      case 7: ctx.transform(0, -1, -1, 0, height , width); break;
      case 8: ctx.transform(0, -1, 1, 0, 0, width); break;
      default: ctx.transform(1, 0, 0, 1, 0, 0);
     }
    return ctx;
  };
  
  const parse = (view) => {
    return new Promise((resolve, reject) => {
      let offset = 0
        , len = view.byteLength
        , APP1_offset
        , TIFF_offset
        , EXIF_offset
        , little
        , IFD0_offset
        , entries_count
        , entries_offset
        , resolve_value
      
      // SOI marker
      if (view.getUint16(0, false) != 0xFFD8) reject('不是 JPEG 文件')
      
      // APP1 marker
      while (offset < len) {
        if (view.getUint16(offset, false) == 0xFFE1) break;
        else offset += 2;
      }

      if (offset >= len) reject('没找到 APP1 标识')

      // now offset point to APP1 marker 0xFFD8
      APP1_offset = offset

      // offset + 4 point offset to EXIF Header
      EXIF_offset = APP1_offset + 4;
      
      // check if  have 'Exif' ascii string: 0x45786966
      if (view.getUint32(EXIF_offset, false) != 0x45786966)  reject('无 EXIF 信息');

      TIFF_offset = EXIF_offset + 6;

      // offset + 4 point offset to EXIF header's 0x0000 
      // offset + 4 + 2 point offset to TIFF header
      // 0x4d4d: big endian, 0x4949: little endian
      little = view.getUint16(TIFF_offset, false)  == 0x4949 ? true : false
      
      IFD0_offset = TIFF_offset + view.getUint32(TIFF_offset + 4);
      
      entries_count =  view.getUint16(IFD0_offset, little);
      entries_offset = IFD0_offset + 2;

      for (let i = 0; i < entries_count; i++ ) {
        // 0x0112's format is 3 which value format is unsigned short
        // components is 1 
        // 3 * 1 < 4 
        // so the value offset is actually value not the offset to the value
        if (view.getUint16(entries_offset + (i * 12), little) == 0x0112) {
          let resolve_value = view.getUint16(entries_offset + (i * 12) + 8, little)
          console.log(resolve_value)
          resolve(resolve_value)
        } 
      }
      reject('没有 orientation 信息')
    })
  };
  
  let $input = $('input[type="file"]')
    , $output = $('.output')
    , $preview = $('.preview--not-rotated')
    , $preview2 = $('.preview--rotated');
  
  $input.addEventListener('change', e => {
    $output.innerHTML = '';
    
    readFile(e.target.files[0])
      .then(af => {
        let base64 = af2Base64(af)
          , view = new DataView(af)
          , image = new Image()
        
       
        image.src = base64;
        image.onload = (e) => {
          let target = e.target
            , canvas = doc.createElement('canvas')
            , ctx = canvas.getContext('2d')
            , width = 1200
            , height = 1200 / target.width * target.height;
          
          canvas.width = width;
          canvas.height = height;
          // 1. 未获得 exif.orientation 值的 canvas 裁切
          ctx.drawImage(e.target, 0, 0, width, height);
          $preview.src = canvas.toDataURL();
          
          // 2.获取 exif.orientation 值之后的 canvas 裁切
          parse(view)
            .then(val => {
              $output.innerHTML = `图片 Exif 中 Orientation 值是 ${val}`;
              
              // 5, 6, 7, 8 是 1, 2, 3, 4 的镜像
              if ([5,6,7,8].indexOf(val) > -1) {
                canvas.width = height;
                canvas.height = width;
              } 
              else {
                canvas.width = width;
                canvas.height = height;
              }
            
            ctx = rotateCtx(val, ctx, width, height);
            ctx.drawImage(image, 0, 0, width, height);
            $preview2.src = canvas.toDataURL('image/jpeg', 1.0);
            
           }, message => $output.innerHTML = message)
        }
      });
  }); 
})(window, document)
            
          
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