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RE: Animations issues (was Re: [CSSWG] Minutes Telecon 2012-12-12)

From: Sylvain Galineau <sylvaing@microsoft.com>
Date: Thu, 20 Dec 2012 04:49:01 +0000
To: Brian Birtles <bbirtles@mozilla.com>, "www-style@w3.org" <www-style@w3.org>
Message-ID: <3C4041FF83E1E04A986B6DC50F0178291BEF86C4@TK5EX14MBXC222.redmond.corp.microsoft.com>
[Brian Birtles:]
> 
> (2012/12/20 5:50), Sylvain Galineau wrote:
> > We agreed at the time that such empty @keyframes rules would not run.
> 
> We discussed this resolution in the Web Animations call last week and
> wanted to ask for clarification on why such rules do not run.[1]
> 
> We wonder if it is worthwhile allowing such animations to run anyway for
> the following reasons:
> 
> i) If in a future version, animations can be sequenced and an animation
> with a 3s duration but no keyframes is included in a sequence, we think
> one would still expect it to delay the next animation in the sequence by
> 3s. If it takes time, it seems reasonable to also fire events.

So essentially using a @keyframes rule instead of animation-delay? This
suggests scenarios where the latter doesn't cut it. Any on your mind?

> 
> ii) In such a future scenario where sequencing and other synchronisation
> is possible, there are valid uses for empty animations--both to act as
> spacers in a sequence or simply to fire events at appropriate times for
> triggering other actions.

We could make animation delays fire their own start/end events. That leads 
us back to the previous comment.

> 
> iii) We think it is useful to distinguish timing from the animation
> effect. If such a distinction is made then events are related to timing
> and should not depend on the animation effect.

Indeed. That was my question during the call i.e. do start/end events reflect
only duration or both duration *and* interpolation? There is support for the
latter and at least two implementations support it. (Though, interestingly, 
individuals' preferences do not always reflect their browser's current 
behavior). In particular I do not think we have really argued why this is 
the better behavior for authors.

> 
> In the Web Animations model, animations with no keyframes (and even those
> with no animation effect) still occupy time and fire events for the above
> reasons. If CSS decides otherwise that's not a major problem for us: the
> CSS bindings to Web Animations will simply require that no Animation
> object is created in that case. However, for the above 3 reasons, we
> wanted to quickly query the rationale behind this decision.
> 
It's good to know it's not a major problem; it would at least seem better 
for future authors if the models aligned, however. 

The difference between IE/Firefox and Chrome suggests this has not been
an issue for content so far; we should be able to choose.


Received on Thursday, 20 December 2012 04:49:58 GMT

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