vue 实现上传前图片压缩功能

首先，因为我这边项目是迭代的，只需要添加一个压缩功能，所以我这边是从获取到file之后开始写的。

1.前端：

<el-upload action="/FileUpload" :http-request="uploadSectionFile" :show-file-list="false" style="display:inline-block" :disabled="AttachmentCategoryID==0" v-if="CanEdit">
<el-button type="primary" :disabled="AttachmentCategoryID==0">附件上传</el-button>
</el-upload>

2、return{}里定义

return{
headerImage:,
picValue:,
}

3.上传前压缩的方法

uploadSectionFile(f) { //	附件上传
let self = this;
let Orientation;
let ndata;

if(f.file.size<=1* 1024* 1024){
//判断图片是否大于1M,是就直接上传
ndata=f.file;
self.postImg(ndata);
}else{
//反之压缩图片
let reader = new FileReader();
// 将图片2将转成 base64 格式
reader.readAsDataURL(f.file);
console.log(reader)
// 读取成功后的回调
reader.onloadend = function () {
let result = this.result;
let img = new Image();
img.src = result;
img.onload = function () {
let data = self.compress(img,Orientation);
self.headerImage = data;
ndata=  self.compress(img,Orientation);

//BASE64转图片
var arr = ndata.split(','), mime = arr[0].match(/:(.*?);/)[1],
bstr = atob(arr[1]), n = bstr.length, u8arr = new Uint8Array(n);
while(n--){
u8arr
 = bstr.charCodeAt(n);
}
ndata=new File([u8arr],f.file.name, {type:mime})
self.postImg(ndata);

}
}
}
},async postImg (ndata) {
let param = new FormData(); //创建form对象
param.append('file', ndata); //通过append向form对象添加数据
let config = {
headers: {
'Content-Type': 'multipart/form-data'
}
}
try {
const response = await FileUpload(param, config)  //此处写接口对应的vue方法

if (response.Code == 200) {
this.handleFileUploadSuccess(response.Data)
}
} catch (error) {
console.log(error)}
},
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("ndata:"+ndata)

console.log('压缩率：' + ~~(100 * (initSize - ndata.length) / initSize) + "%");
tCanvas.width = tCanvas.height = canvas.width = canvas.height = 0;

return ndata;
}`