html2canvas等待图像加载 [英] html2canvas wait for images to load

问题描述

一段时间以来我一直遇到这个问题，我似乎找不到解决办法.

I'm having this problem for some time ow and I can't seem to find a solution.

我正在使用最新的html2canvas js插件来拍摄用flotcharts绘制的图表的屏幕截图，然后通过隐藏的输入提交base64屏幕截图.问题是图表的div也有一些图像，并且html2canvas在加载图像之前返回了base64字符串.我可以将setTimeout放在提交上，直到它们加载完毕，但显然chrome打开我提交的页面作为弹出窗口(这真的不行，因为我们的客户不知道如何允许弹出窗口). 所以这就是我尝试过的，但是图像没有预加载(由于html2canvas的异步特性)

I'm using the latest html2canvas js plugin to take a screenshot of chart made with flotcharts and then submit the base64 screenshot via a hidden input. The problem is the div with the chart also has some images and html2canvas return a base64 string before the images are loaded. I can put a setTimeout on the submit untill they are loaded but apparently chrome opens the page where I submitted as a popup (which is really not ok cause our clients don't know how allow popups). So this is what I tried but the images are not preloaded (because of the async nature of html2canvas)

function getPNGBase64forHtml($container) {
    var imageString;

    html2canvas($container, {
        useCORS: true,
        onrendered: function(canvas) {
            imageString = canvas.toDataURL('image/png');
        }
    });

    return imageString;
}

这也可以(虽然可以，但是不能及时加载图像):

And also this (this works ok but it doesn't load the images in time):

function getPNGBase64forHtml($container) {
    var h2canvas = html2canvas($container);
    var queue = h2canvas.parse();
    var canvas = h2canvas.render(queue);

    return canvas.toDataURL('image/png');
}

所以问题出在等待图像加载到html2canvas中，然后执行其余的东西. 如果有人可以帮助，将不胜感激，我向您致敬的先生和女士们！ :)

So the problem is with waiting till the images are loaded in html2canvas then exeuting the rest of my stuff. If anyone can please help, that would be very much appreciated, I bow to you kind sirs and madams! :)

修改:

这是我捕获的部分的html，所有这些都在打印容器div多数民众赞成中.无法捕获时间轴中的箭头(仅显示一个箭头)，因为它是图像，其他所有操作都可以:

Here is the html of the part that I capture, this all is in a print-container div thats all. The arrow (only one is showed) in the timeline-prognose doesn't get captured cause it's a image, everything else does:

<div id="timeline-outer-container">
    <div id="timeline-container" class="flot-container">
        <div id="timeline-chart" class="flot-chart">
            <canvas class="flot-base" width="888" height="335" ></canvas>
            <div class="flot-text" >
                <div class="flot-x-axis flot-x1-axis xAxis x1Axis">
                    <div class="flot-tick-label tickLabel" >Q1</div>
                    <div class="flot-tick-label tickLabel">Q2</div>
                    ...
                </div>
                <div class="flot-y-axis flot-y1-axis yAxis y1Axis">
                    <div class="flot-tick-label tickLabel">75</div>
                    <div class="flot-tick-label tickLabel">100</div>
                    ...
                </div>
            </div>
            <canvas class="flot-overlay" width="888" height="335"></canvas>
            <div class="axis-label xaxis">Zeitraum</div>
            <div class="axis-label yaxis rotate-90">Anzahl</div>
            <div id="zoom-out-button" class="timeline-zoom-button"><i class="fa fa-zoom-out"></i></div>
            <div id="zoom-in-button" class="timeline-zoom-button"><i class="fa fa-zoom-in"></i></div>
            <div id="zoom-default-button" class="timeline-zoom-button"><i class="fa fa-repeat"></i></div>
        </div>
    </div>
</div>

<div id="timeline-prognose">
    <img id="timeline-arrow-up" class="timeline-arrows" src="/portal//images/arrows/up.png" alt="">
    <img id="timeline-arrow-down" class="timeline-arrows" src="/portal//images/arrows/down.png" alt="">
</div>

推荐答案

因此，由于您使用的是远程图像，因此可以使用以下修复程序在脚本中进行一些修改:

So since you're using remotes images you can use the following fix doing some modifications in your script:

function getPNGBase64forHtml() {
    var imageString;

    html2canvas(document.body, {
        useCORS: true,
        logging : true, //Enable log (use Web Console for get Errors and Warnings)
        proxy :"html2canvasproxy.php",
        onrendered: function(canvas) {
            var img = new Image();
            img.onload = function() {
                img.onload = null;
                document.body.appendChild(img);
            };

            img.onerror = function() {
                img.onerror = null;
                if(window.console.log) {
                    window.console.log("Not loaded image from canvas.toDataURL");
                } else {
                    alert("Not loaded image from canvas.toDataURL");
                }
            };

            imageString = canvas.toDataURL('image/png');
        }
    });

    return imageString;
}

如果您使用的是php，则代理设置必须使用以下脚本: html2canvas-php-proxy

If you are using php then the proxy setting must use the following script: html2canvas-php-proxy

否则，在.NET项目中，您可以使用以下脚本资源:

Otherwise with .NET projects you can use these script resources:

带有asp-classic的html2canvas代理-vb 带有asp.net的html2canvas代理-csharp

如果您决定使用本地图像，则不会出现此错误.

If you decided to use local images this bug will not appear.

希望它对您有用，这是此html2canvas错误的原始线程 https://github .com/niklasvh/html2canvas/issues/145

Hope it works for you, here is the original thread for this html2canvas bug https://github.com/niklasvh/html2canvas/issues/145

这篇关于html2canvas等待图像加载的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！