[Webkit-unassigned] [Bug 209968] New: Scroll position is reset when rubber banding

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=209968

            Bug ID: 209968
           Summary: Scroll position is reset when rubber banding
           Product: WebKit
           Version: Safari 13
          Hardware: iPhone / iPad
                OS: iOS 13
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Scrolling
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: ldebeasi at gmail.com

Created attachment 395378

  --> https://bugs.webkit.org/attachment.cgi?id=395378&action=review

Bug reproduction example

Rubber band/overflow scrolling on a non-body element gets reset when changing another element's transform or opacity. This does not happen when changing something else such as the element's background-color.

Steps to reproduce:

1. Open the attached reproduction file on an iOS device.
2. Tap and hold one of the cards that says "Hello World". The card that was tapped should scale down slightly.
3. While holding down on the card, scroll up a bit, then scroll down to perform the rubber band effect at the top.
4. While the rubber band effect is active, remove your pointer from the screen.
5. You should see the scroll position abruptly reset to 0 rather than ease back.
6. Tap "Alter opacity when active" and repeat steps 2-5.
7. Tap "Alter background when active" and repeat steps 2-4. You should see the scroll position ease back to 0 rather than abruptly jump back.

Expected Behavior:

When changing transform or opacity, I would expect the scroll position to ease back to 0 rather than abruptly jump back.


Tested on an iPhone 11 running iOS 13.4, but this issue appears on earlier versions of iOS 13.

I have run into this issue several times in the past. This has resulted in a few less than ideal workarounds such as https://github.com/ionic-team/ionic/blob/master/core/src/components/header/header.ios.scss#L81-L90.

Unfortunately, this issue has started to affect some of our users who are building applications with our components that transform or change opacity when active. The current workaround is to change something other than transform or opacity, but it would be great if this issue could get addressed.

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