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Re: [csswg-drafts] [scroll-animations] ScrollTimeline fill-mode has asymmetric interaction with animation fill modes. (#4325)

From: Majid Valipour via GitHub <sysbot+gh@w3.org>
Date: Tue, 31 Mar 2020 16:08:06 +0000
To: public-css-archive@w3.org
Message-ID: <issue_comment.created-606723725-1585670885-sysbot+gh@w3.org>
@JTensai  removed the fill in this [PR](

However including in it, the fix for making the [end scroll offset inclusive](https://github.com/WICG/scroll-animations/issues/19) for Issue 19 was also removed. 

So now scroll timeline has the following behaviour:

  1. **scroll offset < start** 
       - timeline is in `before` phase (timeline.currentTime is 0)
        - animation is in `before` phase and its backward fill is activated if specified.
  2. **start <= scroll offset < end**
     -  timeline is in `active` phase (timeline.currentTime is calculated based on existing formula
     - animation phase and output is based on timeline's current time.
  3. **end >= scroll offset**  
      - timeline is in `after` phase (timeline.currenTime is timeRange)
      - animation is in `after` phase and its backward fill is activated if specified.

This has simplified the model quite a bit. But we are still considering "end scroll offset" as exclusive and at that position the timeline's is considered in after phase. So animations should have `fill:forwards` to have value in that position. This was considered bad by [Issue 19](https://github.com/WICG/scroll-animations/issues/19).

So I think we should add back that fix or add text to the spec asking people to use "fill: forward" for such animations.

GitHub Notification of comment by majido
Please view or discuss this issue at https://github.com/w3c/csswg-drafts/issues/4325#issuecomment-606723725 using your GitHub account
Received on Tuesday, 31 March 2020 16:08:09 UTC

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