css - IE8 web font iframe bug workarounds

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css - IE8 web font iframe bug workarounds

posted Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

css - IE8 web font iframe bug workarounds

This blog post (slightly annoying page there) (and that's not my blog by the way) describes a bizarre bug I ran into yesterday in Internet Explorer 8 only. The bug involves .EOT web fonts and <iframe> elements.

I haven't extensively researched the exact trigger for the bug, but it's basically the case that a page using a web font that loads content into an <iframe> such that the frame also uses a web font becomes "defaced" by the browser. The previously-OK text rendered with the web font suddenly shifts to awful-looking Arial or something else, sort-of on its own. Sometimes it flips back, only to degrade again on random user interactions like mouse moves.

That blog post has an example. To clarify, it's the containing page that gets messed up, not the page in the <iframe> (at least, that's the case so far in my experience).

Has anybody found a better workaround than what's suggested in that blog, which is to force a "reload" of the CSS <link> element from whence the @font-face declarations come? (I could do that but it'd be a minor pain, plus it would force me to move my font setup out of my document <head> which if I recall is a performance issue; I'll have to scrounge around and find that tidbit again.)

edit — update

OK here's a test page. Here's the main (container) page:

<!DOCTYPE html>
<html>
  <head>
    <style id='font_style'>
      @font-face {
        font-family: 'bold-display';
        src: url('DejaVuSans-Bold.eot');
      }
    </style>
    <style>
      .fancy { font-family: bold-display, "franklin gothic medium", "verdana", sans-serif; font-size: 32px; }
      iframe { width: 500px; height: 200px; }
      #floater {
        position: absolute;
        top: 100px; left: 100px;
        display: none;
      }
      #floater.showing {
        display: block;
      }
    </style>
    <script>
      function load() {
        var frame = document.createElement('iframe'),
          floater = document.getElementById('floater'),
          target = document.getElementById('target');

        frame.src = 'frame.html';
        target.appendChild(frame);
        floater.className += 'showing';
      }
      function unload() {
        var floater = document.getElementById('floater'),
          target = document.getElementById('target');
        target.innerHTML = '';
        floater.className = floater.className.replace(/showing/g, '');
      }
    </script>
  </head>
  <body>
    <div class='fancy'>Hello World</div>
    <button type='button' onclick='load()'>Click Me</button>
    <div id='floater'>
      <div id='target'></div>
      <button type='button' onclick='unload()'>Close</button>
  </body>
</html>

The frame page has the same @font-face and a dummy message.

The problem appears to have something to do with using the loaded fonts with a list of more than one alternate font. I (for no good reason) had tossed in a couple of similar more-common fonts in my "font-family" values. When I dropped them back to:

 .title { font-family: bold-display, sans-serif; }

then the problem went away (or at least it seems to have gone away so far).

Thanks to those who've helped out. To @albert, add an answer summarizing what you tried and I'll upvote you :-)

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1 Reply

深蓝 · Answer 1 · 2021-10-23T17:48:36+0000

So, there is no performance hit with the following (as long as your CSS is reasonably sized), you get to leave the <link> tag in <head>, and it works without issue, but you are still basically 'reloading' your <link> elements (though you are not doing so by resetting their url).

On the removal of the <iframe> element, simply do the following:

var sheets = document.styleSheets;
for(var s = 0, slen = sheets.length; s < slen; s++) {
    sheets[s].disabled = true;
    sheets[s].disabled = false;
}

Reloading is all I can really think of as working since it seems to be removing it in garbage collection from the <iframe>. Set up a test page that obviously only works for IE 8.

Of Note: I was originally unable to reprodcue this issue using Google web fonts, and had to specifically download a .eot font for use for this. So your work around maybe to use WOFF fonts first, and only load EOT if necessary.

Not exactly sure if this is what you were looking for, but if it's not, please clarify and I'll edit as necessary.

Update 1: The cause

So, I've narrowed down the cause of the issue. I am only able to reproduce if the following occurs (and this is a nasty one folks).

And <iframe> is contained within a parent element
The parent element's class is changed
The class does not change the display of the element it is being applied to (or really, if it does not change the overall display on the <iframe> element)

And, from what I can tell, yes, it has to be the class name. I was unable to reproduce given the same steps on the id of an element. Seriously. This one is a nasty one. I'll keep digging a bit.

Update 2: A Secondary Cause

If the <iframe> is not fully in the browser window on draw, it will not load the font within the <iframe> window, and will unload the font for the main window whenever it has to redraw the page (most notably when it is resized). This is a gnarly bug.

Update 3: What should be a solution

Instead of using display: none;, set the height and the width of the element to be 0px and the overflow: hidden;, and you'll get the same effect as display none, but it will not remove it from the DOM, thereby not redrawing the page and taking your font. My test page from before has been updated, so you can see the effect on what used to be the bug.

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css - IE8 web font iframe bug workarounds

css - IE8 web font iframe bug workarounds

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