[Webkit-unassigned] [Bug 199691] New: The whole viewport shifts down when resetting document scrollTop

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=199691

            Bug ID: 199691
           Summary: The whole viewport shifts down when resetting document
                    scrollTop
           Product: WebKit
           Version: Safari Technology Preview
          Hardware: Unspecified
                OS: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: HTML Editing
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: xidorn-webkit at upsuper.org
                CC: wenson_hsieh at apple.com

Created attachment 373876

  --> https://bugs.webkit.org/attachment.cgi?id=373876&action=review

testcase

Steps to reproduce:
1. open the attached testcase on iOS
2. tap the "Hello world" text

Expect result:
The keyboard shows up without moving the viewport.

Actual result:
The whole viewport briefly shifts down.


In this testcase, the page tries to move the text up manually (for various reasons), thus it wants to remove the scrolling on document done by the browser. But that triggers this issue.

The effect is similar to bug 198737, and this is probably the actual cause of that issue.

This is reproducible on both iOS 12 and iOS 13.

Similar to bug 198737, you can see this shift clearer via using simulators with Debug / Slow Animations enabled.

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