Is this even possible? There are some games that seem to do this for
intro screens and messages, but I'm not sure those aren't just elaborate
tricks (32 or 40 pixel re-writes, with alternating start positions on
each line (TAZ) or maybe a REFP0/REFP1 (Sorcerer's Apprentice?) It's
not hard to re-write the GRP data with both players in double copy, or
even with one in triple and the other in double (40 pixels hi-res!)
I've done that, but it seems maybe not possible to squeeze in those last
8 pixels. I can even re-write all six bytes, but I haven't figured out
how to do it with *real* data read from memory, but only by cheating and
writing the last byte from a register that was just used for one of the
prior bytes--meaning I can do things like:
p0 p1 p0 p1 p0 p1
0 1 2 3 4 3
(dang, it went too quick for me to read then write a new bit
pattern in the last spot--I could also have put a four or a two in
there, but not a 5--just gimme *one* more register...)
The fastest way I've figure so far is to absond with the stack pointer
and hide away byte 6 long before the time critical stuff:
ldx byte6
txs
..
sta GRP0
stx GRP1
sty GRP0
tsx ;2 freaking cycles, and I need it yesterday!
stx GRP1
But that's still too slow...
Anyone know for sure? If you can find code that does this, I'd
appreciate it if you sent it to me, since I'm still without a
disassembler (and really tired of trying something that seems actually
like it might be impossible).
--
mor@xxxxxxx
http://www.crl.com/~mor/
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