因爲最近遇到個移動端上傳頭像的需求,上傳到後臺的數據是base64位,其中爲了提高用戶體驗,把比較大的圖片用canvas進行壓縮之後再進行上傳。在移動端調用拍照功能時,會發生圖片旋轉,爲了解決這個問題引入了exif去判斷拍照時的信息再去處理圖片,這是個很好的插件。關於exif.js可以去他的GitHub上了解,這邊直接npm install exif-js --save 安裝,然後import一下就可以使用了。以下就是源碼,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:'',picValue:''
}
},
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);
// 讀取成功後的回調
reader.onloadend = function () {
let result = this.result;
let img = new Image();
img.src = result;
//判斷圖片是否大於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 () {
//這裏寫接口
},
rotateImg (img, direction,canvas) {
//最小與最大旋轉方向,圖片旋轉4次後回到原方向
const min_step = 0;
const max_step = 3;
if (img == null)return;
//img的高度和寬度不能在img元素隱藏後獲取,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);
}
//旋轉角度以弧度值爲參數
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;
//如果圖片大於四百萬像素,計算壓縮比並將大小壓至400萬以下
let ratio;
if ((ratio = width * height / 4000000) > 1) {
console.log("大於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);
//如果圖片像素大於100萬則使用瓦片繪製
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('壓縮後:' + 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>