Re: [css-transitions-2][css-animations-2] Proposal for animation-timing keywords for half-parabola curves - facilitating correct rise/fall/bounce type animations

Requests for new timing functions are one of the top things we
should look at for the next level of these specs (so changing
subject line appropriately), but the current level of these specs it
to spec the features that are already shipping.

So changing subject line so we catch this as an issue on the next
level.

-David

On Thursday 2013-06-20 01:22 +1000, Dean Trower wrote:
> The CSS transitions/animations module currently defines for the
> animation-timing and transition-timing properties, the keywords "ease",
> "ease-in", "ease-out" and "ease-in-out" as shortcuts for cubic-bezier(...)
> with certain specific arguments.
> 
> I'D LIKE TO PROPOSE that a couple more such keywords be added to this list -
> specifically, for *parabolic* timing functions:  Representing the path
> objects take either rising, or falling, under gravity.
> 
> The reason is that making objects appear to rise, fall, or bounce under
> gravity is I'd expect a fairly common use-case for CSS animation --- but
> using any of the ease-* curves to do it will result in wrong-looking
> (unphysical) behaviour:  Such animations require parabolic timing functions
> to look correct.
> 
> Rising and falling half-parabolas (*somewhat* similar in shape to ease-out
> and ease-in respectively) are also representable using cubic bezier curves,
> specifically (assuming my math is correct):
> 
>  rise:    cubic-bezier(0.33333, 0.66667, 0.66667, 1)
>  fall:    cubic-bezier(0.33333, 0, 0.66667, 0.33333)
> 
> Having keyword shortcuts for these curves (perhaps "rise" and "fall"?) will
> facilitate the easy creation of physically-correct rise/fall/bounce
> animations, and will also make it clear at a glance, from looking at the
> CSS, just what such animations are supposed to do.  (Which certainly isn't
> the case if you use cubic-bezier(...) with numerical arguments instead).
> 
> 
> Thanks for your consideration,
> 
>  Dean Trower
> 

-- 
𝄞   L. David Baron                         http://dbaron.org/   𝄂
𝄢   Mozilla                          https://www.mozilla.org/   𝄂
             Before I built a wall I'd ask to know
             What I was walling in or walling out,
             And to whom I was like to give offense.
               - Robert Frost, Mending Wall (1914)