[Webkit-unassigned] [Bug 210714] New: Using vmax for select <option> font-size adds a noticeable delay to all future interactive events

bugzilla-daemon at webkit.org bugzilla-daemon at webkit.org
Sat Apr 18 23:21:23 PDT 2020


https://bugs.webkit.org/show_bug.cgi?id=210714

            Bug ID: 210714
           Summary: Using vmax for select <option> font-size adds a
                    noticeable delay to all future interactive events
           Product: WebKit
           Version: Safari 13
          Hardware: iPhone / iPad
                OS: iOS 13
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: CSS
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: j at jamielinux.com

Created attachment 396894

  --> https://bugs.webkit.org/attachment.cgi?id=396894&action=review

Test case reduction

I've attached a one-file test case reduction. Interactive elements (a button in this case) are responsive to begin with. Click into the <select> dropdown and out again, and now all future button presses take a few hundred milliseconds to respond. This persists even after a page refresh; only a force refresh seems to fix it.

The delay happens to all interactive touch/click events (ie, links, buttons etc). In the test case, the button (toggling the background color) just makes it easier to appreciate the delay, but the delay also applies to opening the <select> dropdown itself.

I've put the same test case here: https://jamielinux.github.io/webkit-select-font-size-bug/

Steps to reproduce:
1. Create a <select> dropdown.
2. Style <option> font-size to any vmax value.
3. Load website. 
4. Touch events (eg, a button) are responsive.
5. Open the <select> dropdown and close it.
6. All future touch events have a delay of a few hundred milliseconds.
7. Refresh page and problem still persists.
8. Force refresh page and problem resets.

Hardware/software details:
- iPhone XS Max
- iOS 13.4.1
- Both iOS Safari & iOS Firefox

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