OK. Thank you again for your answer.
Hopefully my question is of some value to others who are looking for similar information.
I guess I understand what you are saying. You would have to throw away almost all of the functionality of the SFML window class and only get the benefit of a bitmapped screen area.
The main reason I was looking at SFML is because I just noticed that SDL has come out with SDL2. I'm not even sure that SDL2 still supports a direct connection to the Linux Framebuffer. But while I was looking for stuff about it, I found a comparison of it to SFML. So I started looking at that.
One thing I really like about SFML is the fact that it is truly written in C++ and is a nice collection of classes, rather than C.
James.