> Da: Erik K Mooney <emooney1@xxxxxxxx>
> >...how could they put seven aliens per row in Atari Galaxian?
>
> Short answer: lots and lots of code :) It's an 8k game... disassembling
> the code
> shows about half of the second bank to be mostly the same section of code
> repeated over and over, except with small differences. May even be as
> much
> as a different routine for each possible combination of aliens present on
> any
> particular row.... either that or a different routine for each possible
> number of
> pixels for the leftmost alien to be offset from the left edge of the
> screen.
Ok, we're entering the twilight zone... :)
> Here's a snippet from Distella:
(...)
> LDA $87 ;3
> NOP ;2
> STA RESP0 ;3 pixel 107
> STA NUSIZ0 ;3
> LDA $88 ;3
> INY ;2
> STA RESP0 ;3 pixel 140
> STA NUSIZ0 ;3
> LDA $89 ;3
> NOP ;2
> STA RESP0 ;3 pixel 177
> STA NUSIZ0 ;3
> So, pparently,
> hitting RESP0 every 11 cycles and writing different values to NUSIZ
> allows multiple
> copies of objects (?) The vertical delay is also set, if that matters.
Well, this seems a technique that we haven't yet examined closely (and
neither used in our games/demos).
Can one draw multiple copies of a sprite hitting RESPx more than once in
the same scanline? From the source code above it seems something like that,
but I wouldn't be so sure.
Ciao,
P.
--
Archives updated once/day at http://www.biglist.com/lists/stella/archives/
Unsubscribing and other info at http://www.biglist.com/lists/stella/stella.html
