当用作背景图像时，SVG 中的 Web 动画会中断

Question

我刚刚使用在线服务为自己生成了一个基于 SVG 的加载指示器，但每次加载使用它的页面时，我都会收到来自 Chrome 的警告，通知我 SMIL 动画已被弃用，这比较讨厌。为了摆脱它，我决定研究用网络动画替换 <animate> 标签。以下是原始 SVG：

<svg width='200px' height='200px' xmlns="http://www.w3.org/2000/svg" viewBox="0 0 100 100" preserveAspectRatio="xMidYMid" class="uil-ring-alt">
  <circle cx="50" cy="50" r="40" stroke="white" fill="none" stroke-width="10" stroke-linecap="round"/>
  <circle cx="50" cy="50" r="40" stroke="#808080" fill="none" stroke-width="6" stroke-linecap="round">
    <animate attributeName="stroke-dashoffset" dur="2s" repeatCount="indefinite" from="0" to="502"/>
    <animate attributeName="stroke-dasharray" dur="2s" repeatCount="indefinite" values="150.6 100.4;1 250;150.6 100.4"/>
  </circle>
</svg>

这是我最终得到的结果：

<svg width='200px' height='200px' xmlns="http://www.w3.org/2000/svg" viewBox="0 0 100 100" preserveAspectRatio="xMidYMid" xmlns:xlink="http://www.w3.org/1999/xlink">
  <circle cx="50" cy="50" r="40" stroke="white" fill="none" stroke-width="10" stroke-linecap="round"/>
  <circle cx="50" cy="50" r="40" stroke="#808080" fill="none" stroke-width="6" stroke-linecap="round" id="line"/>
  <script type="text/javascript" xlink:href="https://cdn.rawgit.com/web-animations/web-animations-js/45d8e40300e82ff02ccfbbc78c89500de0f5616f/web-animations.min.js"></script>
  <script type="text/javascript"><![CDATA[
    var line = document.getElementById("line");
    line.animate(
      [
        {strokeDashoffset:0},
        {strokeDashoffset:502}
      ],
      { duration: 2000, iterations: Infinity }
    );
    line.animate(
      [
        {strokeDasharray:"150.6 100.4"},
        {strokeDasharray:"1 250"},
        {strokeDasharray:"150.6 100.4"}
      ],
      { duration: 2000, iterations: Infinity }
    );
  ]]></script>
</svg>

我正要为我设法使它工作而感到非常兴奋，然后当我注意到完全相同的 SVG，当用作 background-image 在 CSS，完全拒绝动画（下面的演示；请注意，我在这里使用数据 URI 内联了 SVG，但是当使用常规 URL 加载 SVG 时也会发生同样的情况）。

body:before {
  content: '';
  display: block;
  width: 200px;
  height: 200px;
  background: url('data:image/svg+xml;utf8,<svg width="200px" height="200px" xmlns="http://www.w3.org/2000/svg" viewBox="0 0 100 100" preserveAspectRatio="xMidYMid" xmlns:xlink="http://www.w3.org/1999/xlink"><circle cx="50" cy="50" r="40" stroke="white" fill="none" stroke-width="10" stroke-linecap="round"/><circle cx="50" cy="50" r="40" stroke="#808080" fill="none" stroke-width="6" stroke-linecap="round" id="line"/><script type="text/javascript" xlink:href="https://cdn.rawgit.com/web-animations/web-animations-js/45d8e40300e82ff02ccfbbc78c89500de0f5616f/web-animations.min.js"></script><script type="text/javascript"><![CDATA[var line = document.getElementById("line");line.animate([{strokeDashoffset:0},{strokeDashoffset:502}],{ duration: 2000, iterations: Infinity });line.animate([{strokeDasharray:"150.6 100.4"},{strokeDasharray:"1 250"},{strokeDasharray:"150.6 100.4"}],{ duration: 2000, iterations: Infinity });]]></script></svg>') no-repeat center center;
  background-size: contain;
}

我应该忽略警告并继续使用 SMIL 还是有办法让 Web 动画在 SVG 中工作？

Answer 1

遗憾的是，backgrounImage 属性的动画尚不支持。

While CSS Backgrounds and Borders Module Level 3 Editor’s Draft says “Animatable: no” for background-image at the time of writing, support for crossfading images in CSS appeared in Chrome 19 Canary. Until widespread support arrives this can be faked via image sprites and background-position or opacity. To animate gradients they must be the same type

您可以在以下文章中阅读更多内容：

http://oli.jp/2010/css-animatable-properties/

https://developer.mozilla.org/en-US/docs/Web/CSS/CSS_animated_properties

当用作背景图像时，SVG 中的 Web 动画会中断

Web Animation inside SVG breaks when used as a background image

javascript

css

svg

background-image

web-animations