[Webkit-unassigned] [Bug 24368] New: DOM WheelEvent delta conversion innaccurate

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=24368

           Summary: DOM WheelEvent delta conversion innaccurate
           Product: WebKit
           Version: 528+ (Nightly build)
          Platform: PC
        OS/Version: All
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: HTML DOM
        AssignedTo: webkit-unassigned at lists.webkit.org
        ReportedBy: pkasting at google.com


The code in WebCore/dom/WheelEvent.cpp that calculates a wheel event's scroll
delta isn't right.  It tries to convert the provided wheelDeltaX and
wheelDeltaY by multiplying by 120 (the value of Windows' WHEEL_DELTA constant).
 But the scroll delta is supposed to be the original value supplied by Windows,
which isn't just (delta * WHEEL_DELTA), but more like (delta * WHEEL_DELTA /
SPI_GETWHEELSCROLLLINES).

There are two ways to fix.  One is to write more complex code here that
reverses everything done up in WebKit (where the native event was transformed
into a WebCore one) to recalculate the original native value.  The other way,
which is probably better, is to carry the original native delta amount along on
the WebCore event, and supply it directly to this function.

I don't know how the glue code would set this value on non-Windows OSes, but I
imagine it could make up something close to what happens now.


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