And the winner is ...
Well I kept poking somewhat disinterestedly at some JNI code generator ideas. Just feeling pretty blah over-all, maybe it's the weather ... hay-fever, sleep apnoea, insomnia, all a big pita over the last few days.
I started looking into m4, and it could probably create a fairly concise definition and generator: but boy, the escaping rules and special cases are such a prick to learn it just isn't worth the effort. For all the intricacies of learning m4 there's very little pay off - it isn't a very useful tool in general and as I wont be using it all the time i'd just have to learn it all again whenever I looked at it. No thanks.
The cpp stuff is still an idea, but the definitions are clumsier than they need to be; one cannot automate the parameter passing convention inferencing which is often possible.
But the exercise did provide useful for the programme design. I took the way it worked and ported it to perl instead (now perl is a tool which is easy to learn with a massive pay-off; definitely not the one to use for every problem though). Macro processors do more work than they appear to on the surface, but after a bit of mucking about (and some fighting with weird perl inconsistencies with references and so on) I had something going. Well I suppose it's an improvement; it halved the amount of code required to do the same thing so that's gotta be better than a poke in the eye.
Because the jjmpeg binding generator is the oldest it's also the crustiest - so when i care I will look into it i'll probably replace it: it isn't a high priority since what is there does work just fine.