From Chuck Seberino, "Here is a fix for the RotateCylinderDragger. This patch fixes the case where the picking direction is close to the cylinder axis. The current behavior is this:

* If the eyepoint and cylinder axis are close to parallel (given some tolerance), then it uses a plane perpendicular to the cylinder axis.
* Otherwise it uses a plane parallel to the cylinder axis oriented towards the eyepoint (previous behavior).  This gives decent behavior and is the only path that was taken in the previous code.   I kept with previous behavior and that allowed a good bit of code to be removed, simplifying things.  There is now no need for the _onCylinder flag, but since there is a public accessor, I wasn't sure how to handle it for backwards compatibility, so I left it in.  NOTE - there is no default initialized value, so if it is kept in, it should be set to 'false' to keep same behavior as before.  I am not quite sure how the _onCylinder case was supposed to behave as even forcing that path gave undesirable behavior, even with carefully controlled dragging.
"

include/osgManipulator/Projector

@@ -295,6 +295,7 @@ class OSGMANIPULATOR_EXPORT CylinderPlaneProjector : public CylinderProjector
         mutable osg::Plane _plane;
         mutable bool       _onCylinder;
         mutable osg::Vec3d _planeLineStart, _planeLineEnd;
+        mutable bool       _parallelPlane;
 };
 
 }