From Stephan Huber,

"attached you'll find some modifications to Producer, osgGA and
osgProducer to enable Mac OS X support for

+ scrollwheels,
+ mightymouse-srollballs
+ new tracking-pads with scroll feature
+ tablet-support (pressure, proximity and pointertype) (Wacom only tested)

I think there was a bug in the windows-implementation of scroll-wheel
support (wrong order of ScrollingMotion-enum, casting problem) which is
fixed now.

The scrollwheel-code is a bit klunky across platforms, some devices on
OS X can report an absolute delta in pixel-coordinates not only the
direction, so for now there is scrollingMotion (which describes the
direction) and scrolldeltax and scrolldeltay. I decided to leave the
scrollingmotion-stuff to not break old code relying on this."

src/osgGA/GUIEventAdapter.cpp

@@ -26,10 +26,14 @@ GUIEventAdapter::GUIEventAdapter():
     _Ymax(1.0),
     _mx(0.5),
     _my(0.5),
+    _pressure(0.0),
     _buttonMask(0),
     _modKeyMask(0),
-    _scrollingMotion(SCROLL_DOWN),
-    _mouseYOrientation(Y_INCREASING_DOWNWARDS)
+    _scrollingMotion(SCROLL_NONE),
+    _scrollingDeltaX(0),
+    _scrollingDeltaY(0),
+    _mouseYOrientation(Y_INCREASING_DOWNWARDS),
+    _tabletPointerType(UNKNOWN)
 {}
 
 GUIEventAdapter::GUIEventAdapter(const GUIEventAdapter& rhs):
@@ -44,10 +48,14 @@ GUIEventAdapter::GUIEventAdapter(const GUIEventAdapter& rhs):
     _Ymax(rhs._Ymax),
     _mx(rhs._mx),
     _my(rhs._my),
+    _pressure(rhs._pressure),
     _buttonMask(rhs._buttonMask),
     _modKeyMask(rhs._modKeyMask),
     _scrollingMotion(rhs._scrollingMotion),
-    _mouseYOrientation(rhs._mouseYOrientation)
+    _scrollingDeltaX(rhs._scrollingDeltaX),
+    _scrollingDeltaY(rhs._scrollingDeltaY),
+    _mouseYOrientation(rhs._mouseYOrientation),
+    _tabletPointerType(rhs._tabletPointerType)
 {}
 
 GUIEventAdapter::~GUIEventAdapter()