[web-animations] Suggestion - parabolic cubic-bezier timing function keywords

At the moment, the Web Animations draft defines only the keywords "linear", 
"ease", "ease-in", "ease-out" and "ease-in-out" as shortcuts to 
cubic-bezier(...) timing functions of certain shapes.

I'd like to suggest 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 "parabolic-rise" and 
"parabolic-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

Received on Wednesday, 26 June 2013 01:04:48 UTC