将svg转换为png时如何包含CSS样式

问题描述

我创建了一个简单的 SVG 元素，在单击按钮时会下载到 png，我的解决方案类似于 这里

i've created a simple SVG elment that get dowbloaded to png when clicking on a button, my solution is similiar to here

基本思路是:
1.svg 到画布
2.canvas转dataUrl
3.触发从dataUrl下载

The basic idea is:
1.svg to canvas
2.canvas to dataUrl
3.trigger download from dataUrl

问题是在下载 png 文件时，它不包含应用于 svg 的 css 样式我的解决结果

注意 - 我知道通过在元素上移动样式内联"(如 here 或通过挖掘 DOM 树并使用 getComputedStyle(element,null); 的递归解决方案

NOTICE - I know there is a workingaround solution by moving the styles "inline" on the elements like here or the recursive solution by digging the DOM tree and using getComputedStyle(element,null);

问题:
1.这个问题的真正原因和解决方案是什么.
(与GPU加速有关吗?)
2.如何在使用带有 Fontface 的自定义字体时仍然克服这个问题

 <button id="btn">svg to png</button>

  <svg id="svg" width="200" height="200">
    <circle cx="50" cy="50" r="30" />
    <text class="svgTxt" x="0" y="100">Hen's SVG Image</text>
  </svg>
  <canvas id="canvas"  width="200" height="200"></canvas>

我的 CSS:

  /*adding exo2 font*/
    @font-face {
    font-family: 'exo_2black';
    src: url('./exo2font/Exo2-Black-webfont.eot');
    src: url('./exo2font/Exo2-Black-webfont.eot?#iefix') format('embedded-opentype'),
         url('./exo2font/Exo2-Black-webfont.woff') format('woff'),
         url('./exo2font/Exo2-Black-webfont.ttf') format('truetype'),
         url('./exo2font/Exo2-Black-webfont.svg#exo_2black') format('svg');
    font-weight: normal;
    font-style: normal;

}
/*change circle color depends on window size*/
@media screen and (min-width: 480px) {
    svg circle {
        fill: lightgreen;
    }
}
/*style on the svg text*/
    .svgTxt{
      font-family: 'exo_2black';
      font-size: 30px;
      fill: red;
    }

我的代码:

  //reference to elements
    var btn = document.querySelector('#btn');
    var svg = document.getElementById('svg');
    var svgTexts = svg.getElementsByTagName('text');
    var canvas = document.getElementById('canvas');
    //Style definitions for svg elements defined in stylesheets are not applied to the generated canvas. This can be patched by adding style definitions to the svg elements before calling canvg.
  //3.trigger download from dataUrl
    function triggerDownload(imgURI) {
      var evt = new MouseEvent('click', {
        view: window,
        bubbles: false,
        cancelable: true
      });

      var a = document.createElement('a');
      a.setAttribute('download', 'hen_saved_image.png');
      a.setAttribute('href', imgURI);
      a.setAttribute('target', '_blank');
      a.dispatchEvent(evt);
    }
    //btn click event
    btn.addEventListener('click', function () {
      // 1.svg to canvas
      var ctx = canvas.getContext('2d');
      var data = (new XMLSerializer()).serializeToString(svg);//serialize the svg element to string
      var DOMURL = window.URL || window.webkitURL || window;
      var img = new Image();
      var svgBlob = new Blob([data], { type: 'image/svg+xml;charset=utf-8' });//A blob object represents a chuck of bytes that holds data of a file.
      var url = DOMURL.createObjectURL(svgBlob);//creates a DOMString containing an URL representing the object given in paramete
      $('svg').append(deletedSVGText);
      img.onload = function () {
        ctx.drawImage(img, 0, 0);
        DOMURL.revokeObjectURL(url);
        // 2.canvas to dataUrl
        var imgURI = canvas
          .toDataURL('image/png')
          .replace('image/png', 'image/octet-stream');// returns a data URI containing a representation of the image in the format specified by the type parameter

        triggerDownload(imgURI);
      };
      img.src = url;
    });

推荐答案

问题一(上半场): 真正的原因是什么_{(到底GPU加速是否相关?)}

不，GPU 加速与此无关.
最广泛的原因是隐私.

No, GPU acceleration has nothing to do with it.
The broadest reason is privacy.

要使用 drawImage 绘制 svg，您必须将 svg 作为外部文档加载到 <img> 标记内.SVG 可以是一种用于资源加载的非常复杂的图像格式(它实际上可以需要任何 HTML 文档可能需要的任何类型的资源).因此，规范中已声明与