[csswg-drafts] [scroll-animations-1] [web-animations-2] (#12134)

graouts has just created a new issue for https://github.com/w3c/csswg-drafts:

== [scroll-animations-1] [web-animations-2] ==
I've been looking at a [scroll-driven animation demo](https://scroll-driven-animations.style/demos/carousel-with-markers/css/) which behaves differently in Safari Technology Preview (version 217) and Chrome (version 135.0.7049.115). In this demo, small dots are meant to show which "page" is shown within the scrolling container. Each dot has an animation attached to a scroll timeline for the entire scroll container and an `animation-range` to target the subsection of that scroll container matching the given "page".

The difference in behavior between Safari Technology Preview and Chrome shows when we've scrolled all the way to the end. At this stage, all dots appear as "on" in Safari Technology Preview only. This is use to the [at progress timeline boundary](https://drafts.csswg.org/web-animations-2/#at-progress-timeline-boundary) being computed to true for _all_ animations. Indeed, as far as I can tell from the current states of the spec, we don't account for animation ranges here to see whether we are matching the end of the animation range, which is probably what we should do.

I believe Chrome does _not_ implement the notion of _at progress timeline boundary_ and in fact this demo explicitly works around this by adding a pixel to the `animation-range-end` to make sure the 100% timeline time is still yielding an active animation for the final dot.

I think we should modify how the _at progress timeline boundary_  flag is computed to account for animation ranges. That flag was originally discussed in https://github.com/w3c/csswg-drafts/issues/5223.

Cc @flackr, @bramus, @kevers-google, @andruud, @majido and @birtles.

Please view or discuss this issue at https://github.com/w3c/csswg-drafts/issues/12134 using your GitHub account


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Received on Tuesday, 29 April 2025 14:15:13 UTC