[Webkit-unassigned] [Bug 257794] New: Incorrect rendering for elements with animated transforms inside container with overflow: clip

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=257794

            Bug ID: 257794
           Summary: Incorrect rendering for elements with animated
                    transforms inside container with overflow: clip
           Product: WebKit
           Version: WebKit Nightly Build
          Hardware: All
                OS: All
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Layout and Rendering
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: benjamin.larsson+wkbz at piktiv.se
                CC: bfulgham at webkit.org, simon.fraser at apple.com,
                    zalan at apple.com

Created attachment 466613

  --> https://bugs.webkit.org/attachment.cgi?id=466613&action=review

Test case

A container with overflow: clip cause problems with rendering animated elements inside it. Changing the container to overflow: hidden solves these issues. It appears that removing the animations but adding will-change: transform to the elements will also reproduce the same issue.

In the test case, the incorrectly rendered elements are thin divs used as horizontal lines, with animated position/rotation/scale.

When these lines have a border radius, then during animations they are clipped, with only the top half being rendered. This gives the appearance of some of the lines being thinner than they should. See attached image.

When the border radius is removed, the full elements are rendered, but now their positions are slightly offset vertically.

Reproduced in Safari 16.5 and nightly WebKit build 264935 on MacOS Monterey, and in Safari on iPhone.

Please see the attached test case for a demonstration. It's a largely unedited upload of the test case I used while debugging this issue in our app, so apologies if it isn't quite as clean as it could be.

-- 
You are receiving this mail because:
You are the assignee for the bug.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.webkit.org/pipermail/webkit-unassigned/attachments/20230607/a7a1ec3e/attachment-0001.htm>