Bug 214352

Summary:

CSS Transition of inherited value sequenced across children elements

Product:

WebKit

Reporter:

Meir Cohen <meirkoen>

Component:

Animations

Assignee:

Nobody <webkit-unassigned>

Status:

NEW ---

Severity:

Critical

CC:

dino, graouts, graouts, koivisto, myfonj, simon.fraser, webkit-bug-importer

Priority:

Keywords:

BrowserCompat, InRadar

Version:

Safari 13

Hardware:

Mac

OS:

macOS 10.15

Attachments:

Description	Flags
Reduction	none

Description Meir Cohen 2020-07-15 07:21:41 PDT

Transition of inherited value, such as `text-indent`, in nested elements, is happening in sequence and not simultaneously with the transition of the parent value.

Here is a codepen demonstrates the issue: https://codepen.io/meirkoen/pen/mdVGRYj?editors=1100
On the left side you can see 3 variants of the issue.
On the right side you can see how it can be fixed - by specifying the values on the children as well.

I have tried to search the [css-transitions] https://drafts.csswg.org/css-transitions/ spec for a definition of this behaviour but I did not see one.

I've also opened an issue in csswg-drafts (https://github.com/w3c/csswg-drafts/issues/5324) to make sure that it's not an ambiguity in the spec at this section https://drafts.csswg.org/css-transitions/#starting. 

I also confirmed that it works well in Firefox

Comment 1 Radar WebKit Bug Importer 2020-07-22 07:22:18 PDT

<rdar://problem/65935293>

Comment 2 Antoine Quint 2020-07-31 05:48:05 PDT

Pretty amazing, thanks for filing Meir! There are transition events fired on each frame here.

Comment 3 Antoine Quint 2020-07-31 05:59:56 PDT

This issues reproduces with a Safari build that predates the new Web Animations engine, this is likely a bug in the CSS code that generates the Animation objects fed to Style::TreeResolver::createAnimatedElementUpdate().

Comment 4 Antoine Quint 2020-07-31 06:09:13 PDT

Created attachment 405683 [details]
Reduction

I've reduced the test further to just a color transition on <p> and nested <span> without any text-ident or display styles.

Comment 5 Antoine Quint 2020-07-31 06:09:42 PDT

This test only works correctly in Firefox, both Chrome and Safari have the wrong behavior of staggering the animations across elements.