Since this is a temporary thing until we get fps/time stored in the context, it shouldn't be public - that just encourages other code to become reliant upon it. Can you just make it a static variable defined in SceneReader.cpp please? If you need to access it from SceneWriter.cpp too then just declare it again there - I'd rather the evil of duplicating that definition than the evil of introducing public fields we can't support going forwards...

Also note that we prefix statics with g_ and not s_.