Added osgUtil::TransformCallback to help with rigid body animation.

include/osgUtil/TransformCallback

@@ -0,0 +1,34 @@
+//C++ header 
+
+#ifndef OSGUTIL_TRANSFORMCALLBACK
+#define OSGUTIL_TRANSFORMCALLBACK 1
+
+#include <osg/Node>
+#include <osgUtil/Export>
+
+namespace osgUtil
+{
+
+class OSGUTIL_EXPORT TransformCallback : public osg::NodeCallback
+{
+
+    public:
+
+        TransformCallback(const osg::Vec3& pivot,const osg::Vec3& axis,float angularVelocity);
+
+        virtual void operator() (osg::Node* node, osg::NodeVisitor* nv);
+                
+    protected:
+    
+        float               _angular_velocity;
+        osg::Vec3           _pivot;
+        osg::Vec3           _axis;
+
+        int                 _previousTraversalNumber;
+        double              _previousTime;
+
+};
+
+};
+
+#endif

src/osgUtil/TransformCallback.cpp

@@ -0,0 +1,51 @@
+#include <osg/Transform>
+
+#include <osgUtil/TransformCallback>
+
+using namespace osgUtil;
+
+TransformCallback::TransformCallback(const osg::Vec3& pivot,const osg::Vec3& axis,float angularVelocity)
+{
+    _pivot = pivot;
+    _axis = axis;
+    _angular_velocity = angularVelocity;
+    
+    _previousTraversalNumber = -1;
+    _previousTime = -1.0;
+}
+
+void TransformCallback::operator() (osg::Node* node, osg::NodeVisitor* nv)
+{
+    osg::Transform* transform = dynamic_cast<osg::Transform*>(node);
+    if (nv && transform)
+    {
+        
+        const osg::FrameStamp* fs = nv->getFrameStamp();
+        if (!fs) return; // not frame stamp, no handle on the time so can't move.
+
+        
+        // ensure that we do not operate on this node more than
+        // once during this traversal.  This is an issue since node
+        // can be shared between multiple parents.
+        if (nv->getTraversalNumber()!=_previousTraversalNumber)
+        {
+            double newTime = fs->getReferenceTime();
+            float delta_angle = _angular_velocity*(newTime-_previousTime);
+
+            osg::Matrix mat = osg::Matrix::trans(-_pivot)*
+                              osg::Matrix::rotate(delta_angle,_axis)*
+                              osg::Matrix::trans(_pivot);
+
+
+            // update the specified transform
+            transform->preMult(mat);
+            
+            _previousTraversalNumber = nv->getTraversalNumber();
+            _previousTime = newTime;
+        }
+    }
+
+    // must call any nested node callbacks and continue subgraph traversal.
+    traverse(node,nv);
+
+}