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Re: [csswg-drafts] [css-contain-2] content-visibility should pause css animations in subtree (#5611)

From: Chris Harrelson via GitHub <sysbot+gh@w3.org>
Date: Tue, 13 Oct 2020 20:58:52 +0000
To: public-css-archive@w3.org
Message-ID: <issue_comment.created-708005474-1602622731-sysbot+gh@w3.org>
> Is this a reason not to do option 2? I think that option 1 and 2 have all of the same difficulties since playing or paused, animations and their start times are observable.

I don't think option 2 is feasible at all, because it would mean we would have to compute style every time it changes, even while skipped, just in case it affected an animation.
 
> > I like the option (3) @flackr mentioned, because it's simple and matches what `display: none` content does.
> 
> I think option (3) is my preferred option as well as I think it's the most internally consistent and least likely to have interop issues if/when we change when we can skip style recalcs and has no hysteresis about whether the element had been previously styled.

Agree about those advantages, but the developer ergonomics *might* be better with option (1). I say only "might" because the hysteresis may be a problem for some developers due to the new race conditions.
 
> One potential wrinkle I just thought of is the interaction with Element.getAnimations. I assume that getAnimations({subtree: true}) should not enter hidden content-visibility subtrees, but presumably if you call Element.getAnimations on an element within the hidden content-visibility subtree it should because it needs to freshen the style of that element which will create an animation? Alternately perhaps getting all animations in a subtree is another performance pitfall similar to selecting all text?

I think it's ok for this to just be another performance pitfall.

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