vue2实现移动端上传、预览、压缩图片解决拍照旋转问题

因为最近遇到个移动端上传头像的需求，上传到后台的数据是base64位，其中为了提高用户体验，把比较大的图片用canvas进行压缩之后再进行上传。在移动端调用拍照功能时，会发生图片旋转，为了解决这个问题引入了exif去判断拍照时的信息再去处理图片，这是个很好的插件。关于exif.js可以去他的GitHub上了解，这边直接 npm install exif-js --save   安装，然后import一下就可以使用了。以下就是源码，可以直接使用。

<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 = async 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();
  }
  }
  }
 }
 },
 postImg () {
 //这里写接口
 },
 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;
 }
 },
 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);
 console.log('压缩前：' + initSize);
 console.log('压缩后：' + ndata.length);
 console.log('压缩率：' + ~~(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>

以上所述是小编给大家介绍的vue2实现移动端上传、预览、压缩图片解决拍照旋转问题，希望对大家有所帮助，如果大家有任何疑问请给我留言，小编会及时回复大家的。在此也非常感谢大家对我们网站的支持！