After the disappointment of last night, I realised this morning that I dont need to copy the whole screen - just 21 lines of it! Knocking off 4 lines saves a fair bit, particually since I dont have to generate them either! So what this now gives me, is the whole bitmap printed from scratch and copied well in just over the lower/top boarder (when I start on the 1st line of the panel).
It also means the RAW copy can take place inside the boarder area, meaning theres no longer any problem with rendering to an offscreen buffer and blitting down.
So next thing to do tonight is to get the XeO3 scroll working again! This should be pretty easy, as its now still just a character map, albeit a 16 bit one!
I'm also pretty confident that I can get my multiplexor happening along with the BLIT well inside the boarder area, which means I would already have 16 sprites, and now just need to add loads of software ones and see what the affects like. I could also now burn sprites on the player so he could be super hi-res IF I manage to get lots of software sprites on screen. I think I could get 30+ running around....but only time will tell.
Oh...and the more I do of this, the more I realise I'm gonna need a debugger of somesort, which might mean I need to update my C64 emulator to do 65816/superCPU. Im not sure it would be able to run at full speed (because of how its written), but machines are getting faster all the time so I guess it would catch up!