[Webkit-unassigned] [Bug 47036] New: Wheel scrolls and autoscrolls should not scroll overflow:hidden

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=47036

           Summary: Wheel scrolls and autoscrolls should not scroll
                    overflow:hidden
           Product: WebKit
           Version: 528+ (Nightly build)
          Platform: PC
        OS/Version: All
            Status: ASSIGNED
          Severity: Normal
          Priority: P2
         Component: WebCore Misc.
        AssignedTo: webkit-unassigned at lists.webkit.org
        ReportedBy: pkasting at google.com
                CC: hyatt at apple.com, jamesr at chromium.org


If a ScrollView has more content than is visible in some dimension, but there is no scrollbar for that dimension, then user events such as down arrow/scroll wheel/middle-mouse-autoscroll ("pan-scroll") should not scroll it into view.  The arrow keys already don't.  This is about fixing the wheel and autoscroll code.

There is one bit of weirdness here.  Consider a scrollable page containing an iframe with overflow:hidden content.  EventHandler::handleWheelEvent() will first try to dispatch a wheel event to the inner frame.  (My patch will fix the ScrollView for this frame to correctly report that it's not scrollable.)  When that doesn't accept the event, it will then dispatch to the containing frame (the outer document).  This is how wheel scrolls scroll the whole page once a hovered element reaches the end of its scroll area.

Now consider the same case, but with middle-mouse-autoscroll.  We dispatch a mousedown event to the inner frame, which gets a chance to prevent it.  If it doesn't, the code in Node::defaultEventHandler() checks if the inner frame is scrollable.  When it's not, we terminate without doing anything.  It seems to me that it would be nice to scroll the outer page in this case.  But this raises a lot of questions.  First, should I dispatch a mousedown event to the containing frame too, like wheel events do?  Second, should I duplicate the wheel event's behavior of scrolling the outer page for scrollable inner frames that are at the end of their scroll area, or only do this for cases where the inner frames aren't scrollable at all?  Both of these seem like they could be weird.

hyatt, if you have any thoughts, I'd appreciate them...

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