Sorry, i didnt want to be nosey.
A new pull request is available on Github (Enhance DEC Rainbow 100 Option Graphics #1589).
It seems i am a bit at a dead end with the NEC GDC.
Perhaps someone more knowledgeable could have a look at vector mode and the odd FIG parameters - see section BUGS in #1589
+Interaction of Upd7220 and Rainbow.cpp:
+- FIG directions / params appear to be odd (lines go 45 degrees up or down instead of straight dir.),
+- RDAT with MOD 2 is unimplemented. WDAT appears to set "m_bitmap_mod" wrongly ("2" means all pixels will be reset)
Text looks funny too (see screenshots above)
Several assembly snippets and freeware games are here (ASM in folder EX32)