Re: [CSS-animations] animation-fill-mode on partial iteration

On Friday 2014-10-03 15:06 -0700, Estelle Weyl wrote:
> The spec and implementation are different when it comes to handling animation-fill-mode on a partial animation cycle.
> 
> Safari follows the spec.
> The implementation of FF and Blink do not follow the spec, but make more sense.
> Haven't tried IE. 
> 
> Example is at http://estelle.github.io/animation/files/halfiterationforwards.html.
> Spec is at: http://dev.w3.org/csswg/css-animations/#animation-timing-function where it reads:
> 
> Note: If animation-iteration-count is a non-integer value, the animation will stop executing partway through its animation cycle, but a forwards fill will still apply the values of the 100% keyframe, not whatever values were being applied at the time the animation stopped executing.
> 
> Basically the spec says now "no matter where you are in the animation, jump to the 100% keyframe" which is what safari does. FF and Blink stay on the keyfraome where the partial animation ended.
> 
> Safari goes to the 100% keyframe even if the last iteration is 'reverse', which seemingly conforms to the spec, but truly doesn't look right if you were on the 99% keyframe.
> 
> Is the spec going to change to reflect blink's and FF's behavior? Or should i file a bug with chrome and FF? I am hoping the spec changes.

I'm not sure why the spec says what it does; it was added as part of
the conversion of the spec to bikeshed, in:
https://dvcs.w3.org/hg/csswg/rev/cd69f7e8600c
https://dvcs.w3.org/hg/csswg/rev/3e45563964a5

Note that the first of these revisions removed prose saying
otherwise:

  # If the value for 'animation-fill-mode' is ''forwards'', then
  # after the animation ends (as determined by its
  # 'animation-iteration-count'), the animation will apply the
  # property values for the time the animation ended. When
  # 'animation-iteration-count' is an integer greater than zero, the
  # values applied will be those for the end of the last completed
  # iteration of the animation (rather than the values for the start
  # of the iteration that would be next). When
  # 'animation-iteration-count' is zero, the values applied will be
  # those that would start the first iteration (just as when
  # 'animation-fill-mode' is ''backwards'').

I'm in favor of reverting this change.

-David

-- 
𝄞   L. David Baron                         http://dbaron.org/   𝄂
𝄢   Mozilla                          https://www.mozilla.org/   𝄂
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