[Webkit-unassigned] [Bug 266433] New: Slow forced layout and paint in browser on initial load and scroll

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=266433

            Bug ID: 266433
           Summary: Slow forced layout and paint in browser on initial
                    load and scroll
           Product: WebKit
           Version: Safari 17
          Hardware: All
                OS: All
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Layout and Rendering
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: kashdan at squareup.com
                CC: bfulgham at webkit.org, simon.fraser at apple.com,
                    zalan at apple.com

Created attachment 469043

  --> https://bugs.webkit.org/attachment.cgi?id=469043&action=review

Video of the Vuejs app while scrolling up and down

Component: Layout and Rendering, initial browser load, scrolling

OS: macOS Sonoma 14.2, Ipad 17.1
Safari: Version 17.1, 17.2

Summary: Scrolling with mouse causes white screen during layout invalidation / forced layout calculations

Steps to Reproduce:

My team fixed the bug in our production application, however I was able to replicate the issue with a small VueJS web application

1) Pull this small git repo https://github.com/wkashdan/forced-layout-app

2) npm install, npm run serve (in a current version of node, I was using 18)

3. Visit localhost:8080, you will see images render on the screen, the code randomly changes image sizes, and logs the positioning of image to force a layout invalidation and forced layout.

4. Scroll up and down in the browser, you are likely to see some white frames between paints. When using the scrollbar this does not happen. This also does not happen in chrome with either mousewheel or scrollbar. 

Result: occasional white screens frames
Expected Results: Smooth scrolling, no white screens 

Additional details:
While I was only able to replicate a few white frames in this example, it was much worse on our production application, taking sometimes 500ms to 1.5 seconds to render content on scroll. We think this was a regression however we have been unable to pinpoint a version of Safari or an OS tied to this.

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