When I started attempting to compile Tnl aside from changing a few "#include" statements for CEGUI all went well (as far as CEGUI went)
However I upgraded from ubuntu 14.04 which used CEGUI version 0.7.6 to ubuntu 16.04 which uses CEGUI version 0.8.4
many changes were made to CEGUI which break the Tnl code depending on CEGUI see
http://cegui.org.uk/wiki/Porting_tips_and_changes_from_0.7.X_to_0.8.X
for details.
It seems ther are going to be more changes when version 1.0 is released per google search of "porting CEGUI"
How to proceed here is not up to me, I'm just reporting what I ran into
I tried to solve the issues but only had limited success as I do not yet have the knowledge of the code needed to rewrite the affected codes