canvas因为图片资源不在同一域名下而导致的跨域污染画布的解决办法

我们要绘制一张图片，内容包括一张背景图和一个动态生成的二维码，前提是背景图是项目本身的静态资源，二维码是服务端动态生成的，二者不在同一域名下。

解决办法：把所有图片都重定向同一个域名下：

let count = 0;
let bgImg = document.creatElement('img');
let qrImg = document.creatElement('img');
bgImg.src = redirectUrl('x.png');
qrImg.src = redirectUrl('y.png');
[bgImg, qrImg].forEach((e) => {
    e.onload = () => {
        count ++;
        if (count === 2) {
            drawerImg(bgImg, qrImg);  
        }
    }
})
function redirectUrl (url) {
    return 'https://xxx/view?fileUrl=' + encodeURIComponent(url);
}
function drawerImg (imgContent, qrContent, scaleBy = 2) {
    let {bgImgW, bgImgH} = {375, 800};
    let {qrx, qry, qrw, qrh} = {20, 700, 50, 50};
    let Canvas = document.createElement('canvas');
    let ctx = Canvas.getContext("2d");
    Canvas.width = bgImgW * scaleBy;
    Canvas.height= bgImgH * scaleBy;
    ctx.drawImage(imgContent, 0, 0, bgImgW * scaleBy, bgImgH * scaleBy);
    ctx.drawImage(qrContent, qrx * scaleBy, qry * scaleBy, qrw * scaleBy, qrh * scaleBy);
    
    let nodeI = document.createElement("img");
    nodeI.src = Canvas.toDataURL();
    document.body.appendChild(nodeI)
}