WheelEvent's deltaX/deltaY sign is wrong

Source/core/dom/WheelEvent.cpp

 /*
  * Copyright (C) 2001 Peter Kelly (pmk@post.com)
  * Copyright (C) 2001 Tobias Anton (anton@stud.fbi.fh-darmstadt.de)
  * Copyright (C) 2006 Samuel Weinig (sam.weinig@gmail.com)
  * Copyright (C) 2003, 2005, 2006, 2008, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2013 Samsung Electronics. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
@@ skipping 12 matching lines @@
 
 #include "config.h"
 #include "core/dom/WheelEvent.h"
 
 #include "core/dom/Clipboard.h"
 #include "core/dom/EventNames.h"
 #include "core/platform/PlatformWheelEvent.h"
 
 namespace WebCore {
 
+static inline double wheelTicksToPixels(double ticks)
+{
+    if (!ticks)
+        return 0;

[arv (Not doing code reviews), 2013/08/21 14:19:23]

Is it worth special casing 0? Are you concerned about -0?

[do-not-use, 2013/08/21 14:31:10]

I had an issue with a test failing because a shouldBe check that would say "got
-0 but expected 0".

shouldBe() is extremely strict:
function isResultCorrect(_actual, _expected)
{
    if (_expected === 0)
        return _actual === _expected && (1/_actual) === (1/_expected);
...
}

1/0 !== 1/-0 even though 0 === -0.

[arv (Not doing code reviews), 2013/08/21 14:52:30]

Makes sense. I think we should normalize -0 here.

Maybe a comment would be useful?

[do-not-use, 2013/08/21 15:00:36]

Done.

[arv (Not doing code reviews), 2013/08/21 15:02:53]

That comment is not very nice. How about:

// Make sure we use +0 for all zeros.

+    return -ticks * WheelEvent::TickMultiplier;
+}
+
 WheelEventInit::WheelEventInit()
     : deltaX(0)
     , deltaY(0)
     , deltaZ(0)
     , wheelDeltaX(0)
     , wheelDeltaY(0)
     , deltaMode(WheelEvent::DOM_DELTA_PIXEL)
 {
 }
 
 WheelEvent::WheelEvent()
     : m_deltaMode(DOM_DELTA_PIXEL)
     , m_directionInvertedFromDevice(false)
 {
     ScriptWrappable::init(this);
 }
 
 WheelEvent::WheelEvent(const AtomicString& type, const WheelEventInit& initializer)
     : MouseEvent(type, initializer)
-    , m_deltaX(initializer.deltaX ? initializer.deltaX : initializer.wheelDeltaX)
-    , m_deltaY(initializer.deltaY ? initializer.deltaY : initializer.wheelDeltaY)
+    , m_deltaX(initializer.deltaX ? initializer.deltaX : -initializer.wheelDeltaX)
+    , m_deltaY(initializer.deltaY ? initializer.deltaY : -initializer.wheelDeltaY)
     , m_deltaZ(initializer.deltaZ)
     , m_deltaMode(initializer.deltaMode)
 {
     ScriptWrappable::init(this);
 }
 
 WheelEvent::WheelEvent(const FloatPoint& wheelTicks, const FloatPoint& rawDelta, unsigned deltaMode,
     PassRefPtr<AbstractView> view, const IntPoint& screenLocation, const IntPoint& pageLocation,
     bool ctrlKey, bool altKey, bool shiftKey, bool metaKey, bool directionInvertedFromDevice)
     : MouseEvent(eventNames().wheelEvent,
                  true, true, view, 0, screenLocation.x(), screenLocation.y(),
                  pageLocation.x(), pageLocation.y(),
                  0, 0,
                  ctrlKey, altKey, shiftKey, metaKey, 0, 0, 0, false)
-    , m_deltaX(wheelTicks.x() * TickMultiplier)
-    , m_deltaY(wheelTicks.y() * TickMultiplier)
+    , m_deltaX(wheelTicksToPixels(wheelTicks.x()))
+    , m_deltaY(wheelTicksToPixels(wheelTicks.y()))
     , m_deltaZ(0) // FIXME: Not supported.
     , m_rawDelta(roundedIntPoint(rawDelta))
     , m_deltaMode(deltaMode)
     , m_directionInvertedFromDevice(directionInvertedFromDevice)
 {
     ScriptWrappable::init(this);
 }
 
 void WheelEvent::initWheelEvent(int rawDeltaX, int rawDeltaY, PassRefPtr<AbstractView> view,
                                 int screenX, int screenY, int pageX, int pageY,
                                 bool ctrlKey, bool altKey, bool shiftKey, bool metaKey)
 {
     if (dispatched())
         return;
 
     initUIEvent(eventNames().wheelEvent, true, true, view, 0);
 
     m_screenLocation = IntPoint(screenX, screenY);
     m_ctrlKey = ctrlKey;
     m_altKey = altKey;
     m_shiftKey = shiftKey;
     m_metaKey = metaKey;
 
-    m_deltaX = rawDeltaX * TickMultiplier;
-    m_deltaY = rawDeltaY * TickMultiplier;
+    m_deltaX = wheelTicksToPixels(rawDeltaX);
+    m_deltaY = wheelTicksToPixels(rawDeltaY);
     m_rawDelta = IntPoint(rawDeltaX, rawDeltaY);
     m_deltaMode = DOM_DELTA_PIXEL;
     m_directionInvertedFromDevice = false;
 
     initCoordinates(IntPoint(pageX, pageY));
 }
 
 void WheelEvent::initWebKitWheelEvent(int rawDeltaX, int rawDeltaY, PassRefPtr<AbstractView> view,
                                       int screenX, int screenY, int pageX, int pageY,
                                       bool ctrlKey, bool altKey, bool shiftKey, bool metaKey)
@@ skipping 37 matching lines @@
     return static_cast<WheelEvent*>(EventDispatchMediator::event());
 }
 
 bool WheelEventDispatchMediator::dispatchEvent(EventDispatcher* dispatcher) const
 {
     ASSERT(event());
     return EventDispatchMediator::dispatchEvent(dispatcher) && !event()->defaultHandled();
 }
 
 } // namespace WebCore