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Re: [csswg-drafts] [css-transitions][css-animations] Complex timing functions

From: Brian Birtles via GitHub <sysbot+gh@w3.org>
Date: Mon, 19 Sep 2016 15:09:25 +0000
To: public-css-archive@w3.org
Message-ID: <issue_comment.created-248020930-1474297748-sysbot+gh@w3.org>
Just a few thoughts here:
* I don't know how important it is to worry about discontinuities 
here. It might be that it's sufficient to handle that using keyframes 
(assuming we'll eventually add a nicer syntax for overlapping 
keyframes such as `50%+ { ... }`). Certainly if it complicates the 
syntax too much I'd suggest leaving it out.
* I like the idea of a 1d function. Solving the value for <em>t</em> 
before you can evaluate the function is a pain.
* Supporting SVG syntax sounds like overkill.
* The solution @visiblecode was moving towards seems very similar to 
[this one 
here](https://lists.w3.org/Archives/Public/public-fx/2015AprJun/0104.html)
 (item 4). Let's call it the chaining approach.
* The other major alternative being thrown around is one-big-function 
approach referenced (a) [in the web animations 
spec](http://w3c.github.io/web-animations/#issue-9e5dcac9), and (b) 
[previously proposed to 
www-style](https://lists.w3.org/Archives/Public/public-fx/2015JulSep/0037.html)
 by @AmeliaBR.
* We still do get a lot of requests for script-defined timing 
functions. I'm not sure if we will expose this to markup but I think 
in any case the proposal would be to time box them. (Also, talking 
about this over lunch with @shans, if we assume these functions are 
stateless, then we might not even need worklets for this since 
implementations could presumably just sample the function at, say, a 
~100 points and just linearly interpolate between the points although 
that wouldn't work for discontinuities which I think the <em>do</em> 
want for script-defined timing functions.)
* Spring timing functions have the additional complication that you 
really would like the duration to be calculated from the springiness 
and distance of the animation. For this I think we can probably 
exploit the fact that the default animation duration in Web Animations
 is "auto" but I believe Google might not have another proposal for 
this.

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