WheelEvent's deltaX/deltaY should report real amount of pixels scrolled

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 bcb3d69d1169a71cc6a9463c752cebf1e3c38cb9..f2b71f6c8488607a0c80b71b87564b45f5b3019b 100644
--- a/Source/core/dom/WheelEvent.cpp
+++ b/Source/core/dom/WheelEvent.cpp
@@ -30,14 +30,6 @@
 
 namespace WebCore {
 
-static inline double wheelTicksToPixels(double ticks)
-{
-    // Make sure we use +0 for all zeros.
-    if (!ticks)
-        return 0;
-    return -ticks * WheelEvent::TickMultiplier;
-}
-
 WheelEventInit::WheelEventInit()
     : deltaX(0)
     , deltaY(0)
@@ -60,6 +52,7 @@ WheelEvent::WheelEvent()
 
 WheelEvent::WheelEvent(const AtomicString& type, const WheelEventInit& initializer)
     : MouseEvent(type, initializer)
+    , m_wheelDelta(initializer.wheelDeltaX ? initializer.wheelDeltaX : -initializer.deltaX, initializer.wheelDeltaY ? initializer.wheelDeltaY : -initializer.deltaY)

[arv (Not doing code reviews), 2013/08/22 14:15:49]

Is this correct? What if initializer.wheelDeltaX was initialized to 0?

[do-not-use, 2013/08/22 14:46:03]

I am not sure I understand the question. If initializer.wheelDeltaX was
initialized to zero, then we will attempt to deduce its value from
initializer.deltaX if its was provided.

We need such fallback so that wheelEvent.wheelDeltaX() will return something
even though the event was initialized with the new deltaX.

[do-not-use, 2013/08/22 15:08:21]

If the caller constructs the WheelEvent from JS and provides deltaX/deltaY but
not wheelDeltaX/wheelDeltaY then we are missing information about the number of
wheel ticks (since wheelDeltaX == ticksX * TickMultiplier).

To make sure that wheelDeltaX/wheelDeltaY do not return 0 in that case, we make
the assumption that ticksX * TickMultiplier is close to -deltaX. This is not
perfect but I don't see what else we could do here.

[arv (Not doing code reviews), 2013/08/22 15:25:15]

My point was that if wheelDeltaX was initialized to 0 we treat that as false
(not present) and fall back to deltaX. There needs to be a way of knowing if it
was set to 0 or whether it is missing.

     , m_deltaX(initializer.deltaX ? initializer.deltaX : -initializer.wheelDeltaX)
     , m_deltaY(initializer.deltaY ? initializer.deltaY : -initializer.wheelDeltaY)
     , m_deltaZ(initializer.deltaZ)
@@ -76,10 +69,10 @@ WheelEvent::WheelEvent(const FloatPoint& wheelTicks, const FloatPoint& rawDelta,
                  pageLocation.x(), pageLocation.y(),
                  0, 0,
                  ctrlKey, altKey, shiftKey, metaKey, 0, 0, 0, false)
-    , m_deltaX(wheelTicksToPixels(wheelTicks.x()))
-    , m_deltaY(wheelTicksToPixels(wheelTicks.y()))
-    , m_deltaZ(0) // FIXME: Not supported.
-    , m_rawDelta(roundedIntPoint(rawDelta))
+    , m_wheelDelta(wheelTicks.x() * TickMultiplier, wheelTicks.y() * TickMultiplier)
+    , m_deltaX(-rawDelta.x())
+    , m_deltaY(-rawDelta.y())
+    , m_deltaZ(0)
     , m_deltaMode(deltaMode)
     , m_directionInvertedFromDevice(directionInvertedFromDevice)
 {
@@ -101,9 +94,9 @@ void WheelEvent::initWheelEvent(int rawDeltaX, int rawDeltaY, PassRefPtr<Abstrac
     m_shiftKey = shiftKey;
     m_metaKey = metaKey;
 
-    m_deltaX = wheelTicksToPixels(rawDeltaX);
-    m_deltaY = wheelTicksToPixels(rawDeltaY);
-    m_rawDelta = IntPoint(rawDeltaX, rawDeltaY);
+    m_wheelDelta = IntPoint(rawDeltaX * TickMultiplier, rawDeltaY * TickMultiplier);
+    m_deltaX = -rawDeltaX;
+    m_deltaY = -rawDeltaY;
     m_deltaMode = DOM_DELTA_PIXEL;
     m_directionInvertedFromDevice = false;