<template>  <div>  <div style="padding:20px;">  <div class="show">  <div class="picture" :style="'backgroundImage:url('+headerImage+')'"></div>  </div>  <div style="margin-top:20px;">  <input type="file" id="upload" accept="image" @change="upload">  <label for="upload"></label>  </div>  </div>  </div> </template> <script> import Exif from 'exif-js' export default {  data () {  return {  headerImage:'',  }  },  mounted () {  },  methods: {  upload (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;  //去獲取拍照時的信息，解決拍出來的照片旋轉問題  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)) {   // 創建一個reader   let reader = new FileReader();   // 將圖片2將轉成 base64 格式   reader.readAsDataURL(file);   // 讀取成功后的回調   reader.onloadend = async function () {   let result = this.result;   let img = new Image();   img.src = result;   //判斷圖片是否大于100K,是就直接上傳，反之壓縮圖片   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();   }   }   }  }  },  postImg () {  //這里寫接口  },  rotateImg (img, direction,canvas) {  //最小與最大旋轉方向，圖片旋轉4次后回到原方向  const min_step = 0;  const max_step = 3;  if (img == null)return;  //img的高度和寬度不能在img元素隱藏后獲取，否則會出錯  let height = img.height;  let width = img.width;  let step = 2;  if (step == null) {   step = min_step;  }  if (direction == 'right') {   step++;   //旋轉到原位置，即超過最大值   step > max_step && (step = min_step);  } else {   step--;   step < min_step && (step = max_step);  }  //旋轉角度以弧度值為參數  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;  }  },  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;  //如果圖片大于四百萬像素，計算壓縮比并將大小壓至400萬以下  let ratio;  if ((ratio = width * height / 4000000) > 1) {  console.log("大于400萬像素")  ratio = Math.sqrt(ratio);  width /= ratio;  height /= ratio;  } else {  ratio = 1;  }  canvas.width = width;  canvas.height = height;  // 鋪底色  ctx.fillStyle = "#fff";  ctx.fillRect(0, 0, canvas.width, canvas.height);  //如果圖片像素大于100萬則使用瓦片繪制  let count;  if ((count = width * height / 1000000) > 1) {  console.log("超過100W像素");  count = ~~(Math.sqrt(count) + 1); //計算要分成多少塊瓦片  //  計算每塊瓦片的寬和高  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);  }  //修復ios上傳圖片的時候 被旋轉的問題  if(Orientation != "" && Orientation != 1){  switch(Orientation){   case 6://需要順時針（向左）90度旋轉   this.rotateImg(img,'left',canvas);   break;   case 8://需要逆時針（向右）90度旋轉   this.rotateImg(img,'right',canvas);   break;   case 3://需要180度旋轉   this.rotateImg(img,'right',canvas);//轉兩次   this.rotateImg(img,'right',canvas);   break;  }  }  //進行最小壓縮  let ndata = canvas.toDataURL('image/jpeg', 0.1);  console.log('壓縮前：' + initSize);  console.log('壓縮后：' + ndata.length);  console.log('壓縮率：' + ~~(100 * (initSize - ndata.length) / initSize) + "%");  tCanvas.width = tCanvas.height = canvas.width = canvas.height = 0;  return ndata;  },  } } </script> <style> *{  margin: 0;  padding: 0; } .show {  width: 100px;  height: 100px;  overflow: hidden;  position: relative;  border-radius: 50%;  border: 1px solid #d5d5d5; } .picture {  width: 100%;  height: 100%;  overflow: hidden;  background-position: center center;  background-repeat: no-repeat;  background-size: cover; } </style>