I've used finalbits in c++ plugin sdk and it was working fine this way

bmap_lock..
change parts of finalbits
bmap_unlock

but there seems to be something i cannot see here, changing kinda feels like i am changing the finalbits but not writing to the real struct engine is using.

Anyway i do not really HAVE TO use finalbits, i just need change parts of bitmaps in an efficent way. pixel_to_bmapping pixel by pixel is way too slow for that, do you have any other suggestions?