[Webkit-unassigned] [Bug 136005] New: Snap offsets sometimes improperly recomputed on iOS

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=136005

           Summary: Snap offsets sometimes improperly recomputed on iOS
           Product: WebKit
           Version: 528+ (Nightly build)
          Platform: iOS
        OS/Version: Unspecified
            Status: NEW
          Severity: Enhancement
          Priority: P2
         Component: WebCore Misc.
        AssignedTo: webkit-unassigned at lists.webkit.org
        ReportedBy: wenson_hsieh at apple.com


Snap offsets are incorrectly recomputed when zooming in and when changing orientation on iOS. To reproduce, open itunes.html in the first snap point examples attachment here: https://bugs.webkit.org/show_bug.cgi?id=134283, zoom in, and then try to scroll. The scroll animation should immediately snap the scroll offset back to the previous snap point with no animation. This indicates that the snap point is retargeting to an incorrect point. Specifically, the instant snap with lack of animation is a result of the scroll velocity (received by RemoteScrollingCoordinatorProxy::adjustTargetContentOffsetForSnapping) having the wrong sign relative to the target content offset. In other words, velocity indicates we're moving in a certain direction, but the targetContentOffset is in the opposite direction.

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