From Stephan Huber, "attached you'll find a proposal for handling multi-touch-events with

osgGA. My approach is to bundle all touchpoints into one custom data
structure which is attached to an GUIEventAdapter.

The current approach simulates a moving mouse for the first touch-point,
so basic manipulators do work, sort of.

I created a MultiTouchTrackballManipulator-class, one touch-point does
rotate the view, two touch-points pan and zoom the view as known from
the iphone or other similar multi-touch-devices. A double-tap (similar
to a double-click) resets the manipulator to its home-position.

The multi-touch-trackball-implementation is not the best, see it as a
first starting point. (there's a demo-video at http://vimeo.com/15017377 )"

src/osgGA/GUIEventAdapter.cpp

@@ -42,7 +42,8 @@ GUIEventAdapter::GUIEventAdapter():
     _modKeyMask(0),
     _mouseYOrientation(Y_INCREASING_DOWNWARDS),
     _scrolling(),
-    _tabletPen()
+    _tabletPen(),
+    _touchData(NULL)
 {}
 
 GUIEventAdapter::GUIEventAdapter(const GUIEventAdapter& rhs,const osg::CopyOp& copyop):
@@ -67,7 +68,8 @@ GUIEventAdapter::GUIEventAdapter(const GUIEventAdapter& rhs,const osg::CopyOp& c
     _modKeyMask(rhs._modKeyMask),
     _mouseYOrientation(rhs._mouseYOrientation),
     _scrolling(rhs._scrolling),
-    _tabletPen(rhs._tabletPen)
+    _tabletPen(rhs._tabletPen),
+    _touchData(rhs._touchData)
 {}
 
 GUIEventAdapter::~GUIEventAdapter()
@@ -107,3 +109,14 @@ const osg::Matrix GUIEventAdapter::getPenOrientation() const
     
     return ( zrot * yrot * xrot );
 }
+
+void GUIEventAdapter::addTouchPoint(unsigned int id, TouchPhase phase, float x, float y, unsigned int tapCount)
+{
+    if (!_touchData.valid()) {
+        _touchData = new TouchData();
+        setX(x);
+        setY(y);
+    }
+    
+    _touchData->addTouchPoint(id, phase, x, y, tapCount);
+}