RE: [stella] parallel efforts / Invaders

Subject: RE: [stella] parallel efforts / Invaders
From: Erik Mooney <emooney@xxxxxxxxxxxxxxxx>
Date: Wed, 14 Mar 2001 16:28:34 -0500
> And as far as Eckhard's code, I haven't looked at a disassembly (seeing as
> how I still have trouble reading my own 2600 assembly code), but I believe
> he is using the self-modifying playfield drawing code in RAM.  (Wasn't there
> some kind of demo posted here a while back about that?)

Hmm.. I'm not sure.  I found a post from me at
explaining how the multisprite trick could be done running the code in RAM
to disable particular sprites via self-modification.  I have here a
source and binary dated 8/25/1997 that demonstrates it, named
sprites2.bin, but can't find it if I ever posted it.

And Piero responded to that post saying that he couldn't think of any use
for it besides a formation of aliens in a vertical shooter, and we already
had many games of the type like Galaxian and Communist Mutants, so the
idea just sort of got dropped.

Looking through the rest of the posts from that month (August 1997) is
quite interesting.. my Zeldalike RPG kernel that I started and lost
interest in is there, as well as a little something called "PCMSG - Piero
Cavina's Multi-Sprite Game".  The repeating-sprite trick was first
mentioned in the post:

It appears it was me who discovered the multi-sprite trick, by
disassembling Galaxian, in the thread "A little thing that doesn't let me
sleep."  I had thought it was Eckhard's trick actually, although looks
like I discovered it, Piero explained it, Eckhard coded it, and a year
later John Saeger hit on the idea of alternating both player 0 and player
1 for even more sprites.  I programmed my invaders demo a bit after that,
but never shared it and rather forgot about it.

Archives (includes files) at
Unsub & more at

Current Thread