[Webkit-unassigned] [Bug 226689] New: visualViewport.height changes and resize events fired when viewport height is not changing

bugzilla-daemon at webkit.org bugzilla-daemon at webkit.org
Sat Jun 5 17:08:59 PDT 2021


https://bugs.webkit.org/show_bug.cgi?id=226689

            Bug ID: 226689
           Summary: visualViewport.height changes and resize events fired
                    when viewport height is not changing
           Product: WebKit
           Version: Safari 14
          Hardware: iPhone / iPad
                OS: iOS 14
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Layout and Rendering
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: john.crim at gmail.com
                CC: bfulgham at webkit.org, simon.fraser at apple.com,
                    zalan at apple.com

On iOS and iPadOS, using Safari 14 on iOS 14:

After scrolling to the bottom of the page with the on-screen keyboard displayed, while scrolling up with ones finger kept on the screen, visualViewport.height increases with scrolling while there is no change to the actual viewport height; and, many visualViewport.resize events are raised while they should not be.

This bug does not occur:
* When the on-screen keyboard is not displayed
* When scrolling down
* After the finger is removed from the screen, while scrolling up

I've create a test page which shows it clearly:

https://cdpn.io/jcrim/debug/JjWvMEo/RBAOJRxOZjnr

You can view the test page source code or edit it here:

https://codepen.io/jcrim/pen/JjWvMEo

Repro steps (on iOS or iPadOS) :
# Click on a text input to make the on-screen keyboard appear
# Scroll down to bottom of viewport
# While scrolling up from bottom of viewport, leave finger on screen (while slowly dragging down to scroll). View `visualViewport.height` and resize events to see bug.
# After releasing finger from scrolling up, notice that `visualViewport.height` changes to the correct value (matching the actual height of the layout viewport).

*The Bug* is that visualViewport resize events are occurring, and the visualViewport.height value is increasing while dragging, even though the height of the viewport is the same size.

*Expected behavior:* visualViewport.height does not increase, and visualViewport.resize events are not raised, when the actual viewport is not changing size.

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