In general, 'classes' declarations were done with macro. I don't remember the exact code — something akin to

BEGIN_CLASS(A, Parent);
CLASS_MEMBER(a...)
END_CLASS();

The project had started before C++ existed, and the switch would be too costly. It's not just OOP part, also reflection mechanism with bindings to the homemade scripting language, and multi-platform UI library. It was a gem of its time.