Using html2canvas to generate shared images, CDN images do not show the problem

qwer 2021-04-07 21:41:06
using html2canvas html canvas generate


background

Generate shared images , Contains the text and text returned by the back end , The picture is cdn resources . Start using html2canvas when , Using local images , No problem generating screenshots .

Code implementation

import html2canvas from 'html2canvas';
const shareContent = document.getElementById("capture"); // The content area to generate the screenshot 
(window.html2canvas || html2canvas)(shareContent, {
useCORS: true, // Allow cross-domain + Set up <img crossOrigin="Anonymous" />
scrollY: 0,
scrollX: 0,
height:shareContent.offsetHeight - 2,
}).then((canvas) => {
console.log(" Generate the whole picture ");
setUrl(canvas.toDataURL("image/png", 1))
})
 Copy code 

problem

But instead cdn Resource time , stay ios Random on the device The screenshot is empty 、 The picture can't show the situation .

Solution

Because using local images , No such problem , So the front end is taking pictures cdn Resource time ,

  1. Convert resources asynchronously to base64
  2. take base64 Assign a value to img label
  3. Finally, execute the code to generate the screenshot

After the test, the problem is solved

Code implementation

  1. You need to load more than one cdn picture , So use Promise Processing multiple cdn Turn the picture into base64
// Pass in cdn Address 
function convertUrlToBase64(url) {
return new Promise((resolve) => {
let img = new Image();
img.crossOrigin = 'Anonymous';
img.src = url;
img.onload = function () {
let canvas = document.createElement('canvas');
canvas.width = img.width;
canvas.height = img.height;
let ctx = canvas.getContext('2d');
ctx.drawImage(img, 0, 0, img.width, img.height);
let ext = img.src.substring(img.src.lastIndexOf('.') + 1).toLowerCase();
let dataURL = canvas.toDataURL('image/' + ext);
let base64 = {
dataURL: dataURL,
type: 'image/' + ext,
ext: ext
};
resolve(base64)
}
})
}
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  1. Achieve asynchronous loading of multiple images , take base64 Assign a value to img label , Finally, execute to generate a screenshot
const bgImg = document.getElementsByClassName('photo')[0];
const avatarImg = document.getElementsByClassName('avatar')[0]
Promise.all([convertUrlToBase64(bgImg.src), convertUrlToBase64(avatarImg.src)])
.then(([base641,base642]) => {
bgImg.src = base641.dataURL;
avatarImg.src = base642.dataURL;
(window.html2canvas || html2canvas)(shareContent, {
useCORS: true,
scrollY: 0,
scrollX: 0,
height:shareContent.offsetHeight - 2,
}).then((canvas) => {
console.log(" Generate the whole picture ");
setUrl(canvas.toDataURL("image/png", 1))
Toast.hide();
})
})
 Copy code 

Conclusion

html2canvas Generate screenshots ,cdn The picture does not show that the problem has been solved perfectly .

Encountered in the process of using , When generating a screenshot , The whole text moves down , It's not settled yet , In the official view issue github.com/niklasvh/ht…

版权声明
本文为[qwer]所创,转载请带上原文链接,感谢
https://qdmana.com/2021/04/20210407213622941z.html

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