Most of the time was spent getting used to debugging C++ and spotting silly mistakes rather than understanding OO C++.
Then I foolishly thought I might have time to do a demo using QT. No such look - all kinds of very strange errors, essentially I couldn't get anything to compile. GTK was much easier (both to compile and to understand).
I will probably just look at doing a demo with the GD library instead.
Oddly - the C++ will probably have less LoC than the perl version (excluding comments and pod) - some of that because its a Second System (and so quicker/easier to design), and some is because OOP in C++ can be more concise than perl, the C++ code is a bit clearer than the perl as it relies more on using class attributes to keep state than the equivilent code which uses more data structures (partly because data structures are much easier to deal with in Perl than C++, partly because the prototypes and earlier versions were procedural rather than OO).