[Webkit-unassigned] [Bug 149526] New: wheel event triggered only once per touchpad touch

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=149526

            Bug ID: 149526
           Summary: wheel event triggered only once per touchpad touch
    Classification: Unclassified
           Product: WebKit
           Version: Safari 9
          Hardware: Macintosh
                OS: Mac OS X 10.11
            Status: NEW
          Severity: Critical
          Priority: P2
         Component: Event Handling
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: m.goleb+bugzilla at gmail.com

Open http://output.jsbin.com/mimiqi/ in Safari 9 and scroll using a MacBook touchpad. The counter at the top left shows how many times the wheel event is fired. In all browsers except Safari 9 (i.e. Chrome, Firefox, **even Safari 8**) the event is fired once per animation frame. Safari 9 USUALLY fires it only once per touching the touchpad, although sometimes it switches into once-per-frame mode (scroll a little in various directions and you should see it).

This will break many interactions that depend on wheel happening in every animation frame to provide a custom scroll-like UI.

Note that I can't reproduce this new broken behavior on JSFiddle which may mean it doesn't happen in iframes (the test case is identical): http://jsfiddle.net/eoxzpqn5/

Is there any chance of this getting fixed in Safari 9? Seems pretty severe to me. :(

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