RESOLVED INVALID208032
Animations sometimes don't start before the next requestAnimationFrame 
https://bugs.webkit.org/show_bug.cgi?id=208032
Summary Animations sometimes don't start before the next requestAnimationFrame
Simon Fraser (smfr)
Reported 2020-02-20 14:43:41 PST
Created attachment 391337 [details] Testcase Attached testcase shows that we don't always trigger animations before the next requestAnimationFrame. Chrome and Firefox do. Need two drop the testcase into LayoutTests/animations.
Attachments
Testcase (2.73 KB, text/html)
2020-02-20 14:43 PST, Simon Fraser (smfr) 		no flags
Details
This isn't reliable in WTR either (3.01 KB, text/html)
2020-02-20 15:10 PST, Simon Fraser (smfr) 		no flags
Details
Another flakey version (3.01 KB, text/html)
2020-02-20 16:02 PST, Simon Fraser (smfr) 		no flags
Details
And another (3.02 KB, text/html)
2020-02-20 16:04 PST, Simon Fraser (smfr) 		no flags
Details
View All Add attachment proposed patch, testcase, etc.
Simon Fraser (smfr)
Comment 1 2020-02-20 14:44:55 PST
One extra setTimeout(, 0) fixes this.
Simon Fraser (smfr)
Comment 2 2020-02-20 14:46:23 PST
(In reply to Simon Fraser (smfr) from comment #1) > One extra setTimeout(, 0) fixes this. Actually no. Even a rAF is super flakey.
Simon Fraser (smfr)
Comment 3 2020-02-20 15:08:41 PST
In general, it seems that we don't reliably start animations (and fire events) before the next rAF. This makes it really hard to write compatible animation code.
Radar WebKit Bug Importer
Comment 4 2020-02-20 15:09:03 PST
<rdar://problem/59646027>
Simon Fraser (smfr)
Comment 5 2020-02-20 15:10:13 PST
Created attachment 391340 [details] This isn't reliable in WTR either
Simon Fraser (smfr)
Comment 6 2020-02-20 16:00:10 PST
I found that forcing layout after the document.body.classList.remove('changed'); makes things better; we seem to batch the document.body.classList.remove('changed')/document.body.classList.add('changed') and think nothing changed.
Simon Fraser (smfr)
Comment 7 2020-02-20 16:02:29 PST
Created attachment 391351 [details] Another flakey version
Simon Fraser (smfr)
Comment 8 2020-02-20 16:04:47 PST
Created attachment 391352 [details] And another
Simon Fraser (smfr)
Comment 9 2020-02-20 16:32:41 PST
Hmm, I was testing with "CSS animations via web animations" turned off. Turn then on and things are better.
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