[Webkit-unassigned] [Bug 212982] New: Viewport Unit based element clipped by Safari bottom controls

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=212982

            Bug ID: 212982
           Summary: Viewport Unit based element clipped by Safari bottom
                    controls
           Product: WebKit
           Version: Safari 13
          Hardware: iPhone / iPad
                OS: iOS 13
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Layout and Rendering
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: bokan at chromium.org
                CC: bfulgham at webkit.org, simon.fraser at apple.com,
                    zalan at apple.com

Created attachment 401460

  --> https://bugs.webkit.org/attachment.cgi?id=401460&action=review

Demonstrating the issue

Repro steps:

1. Visit https:/bokand.github.io/demo/https://bokand.github.io/demo/urlbarsize.html
2. See the second bar from the right, "viewport-unit position:fixed". This is a 99vh position:fixed element
3. Scroll down a little so that the URL bar and bottom controls start to hide, but not so much that they're fully hidden.

What should happen:
The element's height indicates that it should extend behind the bottom controls

What happens instead:
The part of the element that is behind the bottom controls isn't rendered when revealed

The value in parenthesis in the bar is the getBoundingClientRect height. Based on that value, the fixed-vh bar should be the same height as the absolute-vh bar but it appears that the fixed one is clipped out.

Once the controls are fully hidden and a resize/layout occurs, the bar becomes visible.

Note: the position-fixed bar is expected to be shorter as it getBoundingClientRect height shorter while the controls are showing.

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