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北冥有鱼网站的支持！
