WheelEvent's deltaX/deltaY sign is wrong

Source/core/dom/WheelEvent.cpp

Index: Source/core/dom/WheelEvent.cpp
diff --git a/Source/core/dom/WheelEvent.cpp b/Source/core/dom/WheelEvent.cpp
index 1c000eecec2146a66df376ccae29af9f69281012..9bbc95fa51e36607a431e8bfadd0d3ec7e1687b8 100644
--- a/Source/core/dom/WheelEvent.cpp
+++ b/Source/core/dom/WheelEvent.cpp
@@ -30,6 +30,13 @@
 
 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)
@@ -49,8 +56,8 @@ WheelEvent::WheelEvent()
 
 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)
 {
@@ -65,8 +72,8 @@ WheelEvent::WheelEvent(const FloatPoint& wheelTicks, const FloatPoint& rawDelta,
                  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)
@@ -90,8 +97,8 @@ void WheelEvent::initWheelEvent(int rawDeltaX, int rawDeltaY, PassRefPtr<Abstrac
     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;