Cache the current position in the animation track and attempt to reuse it in the next frame.
Decent speed up for the Update phase, about 0.3 ms faster in Balmora.
Works around a compiler warning with OSG 3.4:
warning: base class 'class osg::Callback' should be explicitly initialized in the copy constructor [-Wextra]
With no default argument for osg::CopyOp&, the compiler no longer sees the function as a real copy constructor and stops warning about the missing virtual initializations.
We don't care about this warning because there is nothing interesting to initialize in the osg::NodeCallback base anyway.
A proper fix for the warning would require to inserting OSG_VERSION conditional compiling all over the place, that is as long as we are still supporting OSG 3.2.
scrawl