Subject: R: [stella] a thing that doesn't let me sleep... From: "Piero Cavina" <p.cavina@xxxxxxxxxxxxx> Date: Sat, 23 Aug 1997 19:19:16 +0200 |
> 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
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