[Webkit-unassigned] [Bug 257375] New: elem.getBoundingClientRect does not include visualViewport.offsetLeft

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=257375

            Bug ID: 257375
           Summary: elem.getBoundingClientRect does not include
                    visualViewport.offsetLeft
           Product: WebKit
           Version: WebKit Nightly Build
          Hardware: iPhone / iPad
                OS: iOS 16
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Layout and Rendering
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: bugzillawebkit at katur.de
                CC: bfulgham at webkit.org, simon.fraser at apple.com,
                    zalan at apple.com

Created attachment 466505

  --> https://bugs.webkit.org/attachment.cgi?id=466505&action=review

minimal repro of the issue

When the visual viewport is scaled and moved a getBoundingClientRect does not include visualViewport.offsetLeft.

In my minimal repro (attached and online https://www.katur.de/issues/safari_viewport-scaled_pos-fixed.html ) I check every 
second the BoundingClientRect of a base element and put its top,left value to the position of a position:fixed overlay element. 

This overlay element should cover the base element exactly.
On desktop and mobile Chrome+Firefox this works even with pinch zoom.
With mobile Safari I get an offset in the size of visualViewport.offsetLeft.

The repo has a second overlay which uses the same BoundingClientRect values but add visualViewport.offsetTop/Left value to the position.

With mobile Chrome+Firefox the "BCR overlay" is always over the base element even with pinch zoom.
With mobile Safari the "BCR+offset* overlay" is always over the base element even with pinch zoom.

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