1773149 - Handle scroll animations properly when changing animation-timeline from/to none

Status: RESOLVED WORKSFORME

(Core :: CSS Transitions and Animations, defect, P3)

Description

[Boris Chiou [:boris]]

It seems we don't handle it well for the case that changing animation-timeline from timeline to none or vice versa. See [1][2]. Need to fix this bug.

[1] https://searchfox.org/mozilla-central/rev/0e3d9bfae6fdaa6cb29cbce3f25471d5708aedc3/testing/web-platform/tests/scroll-animations/css/at-scroll-timeline-dynamic.tentative.html#164-196

[2] https://searchfox.org/mozilla-central/source/testing/web-platform/meta/scroll-animations/css/at-scroll-timeline-dynamic.tentative.html.ini#53-54

Comment 1

[Boris Chiou [:boris]]

Perhaps this test failure is not related to animation-timeline from <timeline-name> to none because I notice we do remove the animation from the scroll-timeline and get an unresolved current time (so we get an null progress, and then we don't compose the style for this animation).

Comment 2

[Boris Chiou [:boris]]

This may be related to web-animations-2: https://drafts.csswg.org/web-animations/#setting-the-timeline.

Comment 3

[Boris Chiou [:boris]]

Based on Bug 1774060 comment 4, it makes more sense to cancel the CSS animation when changing the animation-timeline to none. And we shouldn't generate the CSS animation if we set animation-timeline: none initially.

Comment 4

[Boris Chiou [:boris]]

Attachment: Bug 1773149 - Discard CSSAnimations with null timeline.

The bug addresses the following cases:

1. Set animation-timeline: none initially
   -> No CSSAnimation is generated
2. Set animation-timeline: unknown-timeline initially
   -> No CSSAnimation is generated
3. Change animation-timeline from a scroll-timeline name to none
   -> The existing CSSAnimation is cancelled.
4. Change animation-timeline from a scroll-timeline name to unknown-timeline
   -> The existing CSSAnimation is cancelled.

Basically, we treat the null timeline just like what we do for @keyframes.
If there is no matched @keyframes, we don't generate the CSS animation.
Same for timeline.

Comment 5

[Boris Chiou [:boris]]

Per the spec comment: https://github.com/w3c/csswg-drafts/issues/7364#issuecomment-1155851858

For now, I'd like to rely on set-the-timeline-of-an-animation procedure to make the decision, so let's close this bug for now.