[Webkit-unassigned] [Bug 231953] Element with position: sticks after sticking, starts to move incorrectly when scrolling

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=231953

Bruno Stasse <augus.dupin at gmail.com> changed:

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--- Comment #7 from Bruno Stasse <augus.dupin at gmail.com> ---
Created attachment 447214

  --> https://bugs.webkit.org/attachment.cgi?id=447214&action=review

Testcase2

I am also experiencing this issue on iOS 15.2. Note that I started seeing it since iOS 15. It did not happen before, so this should probably be considered a REGRESSION. As far as I can tell it only affects iOS, not macOS.

It is very problematic as elements with position: sticky do not move correctly with the scroll, they are late compared to other elements, creating jank. This makes for a very poor experience.

I created a new testcase where I think the problem is more visible. See Testcase2 and Video_testcase2.

While scrolling up and down inside the scroll container, you should only see yellow inside (the color of the spacers elements and the sticky element). What actually happens is that you see the scroll container red background because the element with position: sticky is not correctly painted at the position it should be, revealing the background.

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