[Webkit-unassigned] [Bug 32440] New: Pan scrolling is slow, jerky, buggy compared to Firefox

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=32440

           Summary: Pan scrolling is slow, jerky, buggy compared to
                    Firefox
           Product: WebKit
           Version: 528+ (Nightly build)
          Platform: PC
        OS/Version: All
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: WebCore Misc.
        AssignedTo: webkit-unassigned at lists.webkit.org
        ReportedBy: pkasting at google.com
                CC: hyatt at apple.com


The pan scrolling algorithm notes on it that it "matches Firefox'
implementation", but this is not quite true.

* The velocity calculation is the same, but WebCore scrolls every 50 ms whereas
Firefox scrolls every 20 ms.  This means WebCore's scroll is jerky and sluggish
in comparison.
* The dead zone near the center is larger on WebCore, meaning if you increase
the scroll speed by dropping the delay to 20 ms, it's not possible to achieve
as fine-grained control of scroll speed as Firefox.

There are also two other bugs:

* The center icon jumps sometimes under rapid scrolling.
* There's no accommodation for timer lag, so pages which are more complex and
take a long time to scroll feel laggy.

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