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[RequestAnimationFrame] requestAnimationFrame use in documents whose containing elements have no CSS box

From: Boris Zbarsky <bzbarsky@MIT.EDU>
Date: Thu, 22 Dec 2011 11:30:25 -0500
Message-ID: <4EF35B21.6030602@mit.edu>
To: public-web-perf@w3.org
Consider a testcase like this:

   <iframe style="display: none"
           src="some-document-using-requestAnimationFrame">
   </iframe>

I believe that right now Gecko will not run the animation frame 
callbacks for that subdocument.  I'm guessing that WebKit will run them, 
based on brief code inspection.  What does IE do?

The reason Gecko doesn't run them is that they're tied into the general 
"animation" infrastructure, which gets turned off in any situation in 
which styles cannot be computed.  And in documents whose viewport does 
not have a useful size (because the iframe has no CSS box at all), 
that's the case in Gecko.

The obvious questions are:

1)  Does the spec allow this behavior?
2)  If not, should it?
3)  Should it require it?  (This would take a bit of thinking to define; 
the definition of what Gecko does is above: no request callbacks in a 
document whose containing element has no CSS box; there may be some 
weirdness with svg:foreignObject kids having boxes even if the 
foreignObject is display:none, of course.)

-Boris
Received on Thursday, 22 December 2011 16:31:02 UTC

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