[Webkit-unassigned] [Bug 203335] New: Horizontal gestures easily cancellable inside "touch-action: pan-y" element (preventDefault() doesn't help)

bugzilla-daemon at webkit.org bugzilla-daemon at webkit.org
Wed Oct 23 14:44:56 PDT 2019


https://bugs.webkit.org/show_bug.cgi?id=203335

            Bug ID: 203335
           Summary: Horizontal gestures easily cancellable inside
                    "touch-action: pan-y" element (preventDefault()
                    doesn't help)
           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: m at rcel.cz

Created attachment 381731

  --> https://bugs.webkit.org/attachment.cgi?id=381731&action=review

test case

I'm unable to reliably combine vertical scrolling (allowed via "touch-action: pan-y") with handling of custom horizontal gestures (pointer events). In Safari (on iOS 13.2 developer beta 4), some slow horizontal gestures are too easily cancellable by going up or down. Other browsers (Latest preview of Firefox or Chrome on other platforms) lock really fast to one axis and do not cancel gesture in progress when user moves in the direction of other axis.

Please see attached test file. The steps are:

1. Tap the yellow box and continue horizontal gesture to the right. 
2. At some point, change the gesture direction and go up or down.

On iPhone X, even when moving the box 20-50 pixels horizontally, gesture can still be canceled by going vertically (not always, but depending on gesture distance/velocity). When moving really slow, I can even go beyond 50 pixels.

As attempted in the example, calling preventDefault() from pointermove callbacks also doesn't stop scrolling in the y axis.

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