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RE: [css3-animations] Clarifying the handling of repeated animation names

From: Sylvain Galineau <sylvaing@microsoft.com>
Date: Wed, 16 Jan 2013 23:22:15 +0000
To: Øyvind Stenhaug <oyvinds@opera.com>, "www-style@w3.org" <www-style@w3.org>
Message-ID: <3C4041FF83E1E04A986B6DC50F0178291BF45565@TK5EX14MBXC221.redmond.corp.microsoft.com>

[Øyvind Stenhaug:]
 
> On Mon, 14 Jan 2013 22:56:40 +0100, Sylvain Galineau
> <sylvaing@microsoft.com> wrote:
> 
> >
> > [Øyvind Stenhaug:]
> >>
> >> On Fri, 11 Jan 2013 19:54:23 +0100, Sylvain Galineau
> >> <sylvaing@microsoft.com> wrote:
> 
> >> > 1. If the animation shorthand runs multiple animations against the
> >> > same property, use 'last one wins' to decide which @keyframes rule
> >> > animates that property. Then only allow this one animation to update
> >> > the property *regardless of the respective durations of the
> >> > winning/losing animations*.
> >> >
> >> > 2. If the animation shorthand runs multiple animations against the
> >> > same property, use 'last one wins' to decide which @keyframes rule
> >> > animates the property *first*. Once this animation has completed, use
> >> > last-one-wins to pick the next @keyframes rule to animate the
> property
> >> > *among the losing animations that are still running*.
> 
> >> > While #1 is much simpler, I'm not sure this reflects author intent
> >> well.
> >> > It may
> >> > not even reflect the spec's original intent either; the first prose
> >> > excerpt above specifically says the last animation wins *at that
> point
> >> > in time*.
> >>
> >> For what it's worth, that wording is not the *original* one (it was
> >> changed for <https://www.w3.org/Bugs/Public/show_bug.cgi?id=14778>).
> >
> > Yes; I really meant 'the original intent of the current prose'; but
> since
> > you wrote it I'm comfortable taking your word as to what it meant :)
> 
> OK, #1 does indeed not reflect the original intent of the current prose
> (which I probably wrote with the Gecko/WebKit in mind) :)
> 
> >> Though B) might require clarifying what
> >> happens if 'animation-name' is changed. For instance, what happens if
> >> you
> >> go from 'foo 10s foo 20s' to 'foo 30s' and then to 'foo 10s foo 20s'
> >> again? Does the 20-second 'foo' get restarted? ("In order to restart an
> >> animation, it must be removed then reapplied.")
> 
> Oops, I forgot commas after the '10s' here.
> 
> > I'm not sure I follow this
> > point?http://lists.w3.org/Archives/Public/www-style/2011Apr/0352.html

> 
> In short: When you go from "animation-name: foo, foo" to "animation-name:
> foo", does that correspond to removing the first "foo", or the last?

Ah, that. First thought is that the result after the update should be 
consistent with what happens when you start with:

	animation-name foo;
	animation-duration: 10s, 4s;

i.e. the 10s foo runs.

> 
> In long: I'm thinking of the part of
> http://dev.w3.org/csswg/css3-animations/#animations a couple of paragraphs
> above the example. A more complete quote:
> 
> "Note also that changing the value of ‘animation-name’ does not
> necessarily restart an animation (e.g., if a list of animations are
> applied and one is removed from the list, only that animation will stop;
> The other animations will continue). In order to restart an animation, it
> must be removed then reapplied."
> 
> For a simpler example[*], let's say we have
> 
> <!doctype html>
> <style>
> @keyframes foo { from { margin-left: 0px; } to { margin-left: 600px; } }
> @keyframes bar { from { margin-left: 0px; } to { margin-left: 600px; } }
> p { animation-duration: 10s; animation-name: foo; }
> .first { animation-name: foo, bar; }
> .second { animation-name: bar, foo; }
> </style>
> <p>Moving right</p>
> 
> At t=5 seconds, we change the class name of the <p>. If we set it to
> "first", then there is a new animation that is "winning" and it starts
>  from the beginning, reaching 100% at t=15 seconds.

Yes, bar starts running.

> 
> On the other hand, if we set the class to "second" instead, then "foo" is
> still winning so it just carries on and reaches 100% at t=10 seconds.
> (Then, assuming alternative #2, "bar" takes over and does the last half of
> the animation all over again.)

Right.

> 
> So if all instances of 'bar' in this example is replaced by 'foo', which
> case does that correspond to?

When going from 'foo,foo' to 'foo', see above. I think it would be consistent
for the behavior to be consistent with start with 'foo' and 2 durations.

When starting with 'foo' and updating to 'foo,foo' then I would expect the
second foo to 'win' i.e. like that bar in .first.


> 
> [*] I am going the opposite way here, adding to the list rather than
> removing from it, to avoid having the issue described at
> http://lists.w3.org/Archives/Public/www-style/2011Apr/0352.html complicate
> matters.
> 
> --
> Øyvind Stenhaug
> Opera Software ASA
Received on Wednesday, 16 January 2013 23:23:15 GMT

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