W3C home > Mailing lists > Public > www-style@w3.org > December 2015

Re: [web-animations] Fixing getAnimations()

From: Brian Birtles <bbirtles@mozilla.com>
Date: Tue, 1 Dec 2015 13:20:52 +0900
To: Kevin Doughty <socallednonflipped@gmail.com>
Cc: Rachel Nabors <rachelnabors@gmail.com>, "public-fx@w3.org" <public-fx@w3.org>, "www-style@w3.org" <www-style@w3.org>
Message-ID: <565D2024.8090808@mozilla.com>
Hi Kevin,

Thanks for your mail.

On 2015/11/30 6:31, Kevin Doughty wrote:
> Why is there a distinction between CSS transitionProperty and CSS
> animationName and script based animation id? Why are these three not one
> and the same?

All Animations have an id which is essentially Animation's name. You can 
put an id on transitions or CSS animations or script-generated 
animations and search on them.

In addition to that, transitions have a transitionProperty field so you 
can easily see what property triggered the animation, even the animation 
has been modified since (so you know how to cancel it from style).

Likewise, CSS animations also have an animationName field so you can 
tell what @keyframes rule(s) generated it. That's useful for DevTools 
and the like so they can let the author tweak the original style that 
generated the animation even if something else has changed the 
animation's id since then.

Incidentally, having those separate properties to filter on also makes 
it easy to get just transitions of the 'opacity' property without 
accidentally picking up CSS animations named 'opacity' or animations 
that script has tagged with the id 'opacity'. So while it's probably not 
strictly necessary to be able to filter on these properties, I think 
allowing that makes using getAnimations() more robust since you're more 
likely to get what you asked for.

> I do want a way to access all animations vs. a single
> keyed accessor.

I believe 'id' gives you that, although we don't have a way to set ids 
for CSS animations/transitions from markup yet, only from script.

> Something like getAnimations() and getAnimationNamed().
> But how about you let getAnimations operate on a NodeList instead of
> creating parallel API (like the subtree boolean) to do the same tasks?
> document.querySelectorAll(...).getAnimations()

That's an interesting idea. I'm not sure how much enthusiasm there is 
for extending NodeList. I think the current tendency is to use native 
Array objects rather than smart-list objects where we can.

I think extending Element and PseudoElement is a good first step, 
however. For one thing NodeList doesn't handle pseudo-elements, and if 
the extend Element, it's fairly easy to apply it to the elements in 
NodeList. We can extend NodeList later if it proves useful.

> If the user wants to recall animations they should give them a name. Too
> many conveniences make an API hard to grasp, when all one needs to do is
> loop through and filter.

I think the use cases for this API are fairly varied, e.g.

   "Does this element have anything animating its scale?"
   "Is this element at rest?"
   "Restart all the animations on this slide"

I don't think you want to require authors to go through and name all the 
animations just to do these things. Perhaps one of the differences here 
with CA is that we're operating in an environment where animations may 
be defined by many different sources such as third-party 'theme' 
stylesheets, UA styles etc.

Best regards,


> On Thu, Nov 26, 2015 at 1:38 AM, Rachel Nabors <rachelnabors@gmail.com
> <mailto:rachelnabors@gmail.com>> wrote:
>     I concur these are issues. I like the way your thinking is going.
>     photo 	
>     *Rachel Nabors*
>     Web Animation Engineer
>     w:rachelnabors.com <http://rachelnabors.com>
>     <http://twitter.com/rachelnabors>
>     <http://dribbble.com/rachelthegreat>
>     <http://plus.google.com/u/0/+RachelNabors>
>     <http://linkedin.com/in/rachelnabors>
>     ------------------------------------------------------------------------
>     Curator of Web Animation Weekly <http://www.webanimationweekly.com>
>     On Wed, Nov 25, 2015 at 6:40 PM Brian Birtles <bbirtles@mozilla.com
>     <mailto:bbirtles@mozilla.com>> wrote:
>         Hi,
>         Web Animations defines Animatable.getAnimations() (where
>         Animatable is
>         implemented by Element and a forthcoming PseudoElement
>         interface) and I
>         think we've agreed to add Document.getAnimations() as well.[1]
>         I've found two problems with the first method which I'm going to
>         call
>         Element.getAnimations() for now since PseudoElement doesn't
>         exist yet.
>         PROBLEM 1. Element.getAnimations() doesn't work on a subtree
>         Recently I was working on a presentation where I wanted to use
>         script to
>         restart all the animations in a particular slide, represented by a
>         <section> element.
>         What I really wanted to do was something like:
>             section.getAnimations().forEach(anim => anim.currentTime = 0);
>         However, Element.getAnimations() doesn't return animations from its
>         descendants (unlike querySelectorAll, getElementById, etc.).
>         To further complicate things, Document.getAnimations() *does* return
>         animations from its desendants (or will, once it is specced).
>         PROBLEM 2. getAnimations() relies too much on the order in which
>         animations are returned
>         Whenever you see code using getAnimations(), it almost always
>         looks like
>         this:
>             var anim = elem.getAnimations()[0];
>         That's really brittle. If some style is added that causes a
>         transition
>         to fire on elem, you may end up getting the wrong result.
>         Of course, you can go through all the animations returned from
>         getAnimations() and test their animationName/transitionProperty
>         attributes and make sure you get the right object, but most
>         people won't
>         bother.
>         PROPOSAL: Add some options to getAnimations()
>         At a minimum, I think we need:
>         * transitionProperty - used to filter by 'transitionProperty'
>         which is
>             only set on CSS transitions
>         * animationName - used to filter by 'animationName' which is
>         only set on
>             CSS animations
>         * id - used to filter by 'id' which may be set on script-generated
>             animations
>         * subtree - true means to fetch animations from descendents too
>         (based
>             on the Mutation Observer API)
>         It's not obvious to me what the default value of subtree should
>         be. I'd
>         say 'false' except that would prevent using the same options
>         object on
>         Document.getAnimations(). Perhaps true? Given that most people
>         will use
>         this on leaf nodes anyway, maybe that would be ok?
>         It's also not clear if we should only inspect the
>         transitionProperty on
>         CSSTransition objects, or if script-generated objects that
>         define their
>         own transitionProperty should be considered too. I guess they
>         should.
>         Likewise for animationName and CSS Animations.
>         Some usage patterns are bogus, e.g. passing subtree:false to
>         Document.getAnimations() or specifying both transitionProperty and
>         animationName (except in rare cases where script added these
>         properties), but maybe that's ok.
>         Example usage:
>             // Get the animation I just added
>             elem.style.animation = 'move 3s';
>             var anim = elem.getAnimations({ animationName: 'move' })[0];
>             // Get all transform transitions in this section
>             section.classList.add('move-in');
>             var transitions =
>               section.getAnimations({ transitionProperty: 'transform' });
>         As you can see in the first example, we still have the '[0]' thing
>         there. It's more safe now since we're only dealing with CSS
>         Animations
>         named 'move', but you could still get the wrong result and it's
>         also a
>         bit of an eyesore and pain to type.
>         I wonder if it's worth following the querySelector/querySelectorAll
>         pattern and having a pair of functions: getAnimation/getAnimations?
>         In the singular, if there were multiple matches on the same element
>         you'd return the one with the highest composite order[2] since
>         that's
>         most likely to be the one that you want. If you had multiple matches
>         within a subtree, I'm not sure: tree order or composite order.
>         Possible future extensions:
>         * Parameters to get only CSS transition or only CSS animations?
>         * Parameters to get all animations that affect certain
>         properties? e.g.
>             all animations that affect either the 'opacity' property or
>             'visibility' property.
>         These can be easily implemented using Array.filter() so there's no
>         urgency for these.
>         What do you think?
>         Brian
>         [1]
>         https://lists.w3.org/Archives/Public/public-fx/2015JulSep/0073.html
>         [2] http://w3c.github.io/web-animations/#the-effect-stack
Received on Tuesday, 1 December 2015 04:21:25 UTC

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