Re: [stella] parallel efforts / Invaders

Subject: Re: [stella] parallel efforts / Invaders
From: Erik Mooney <emooney@xxxxxxxxxxxxxxxx>
Date: Wed, 14 Mar 2001 16:44:18 -0500
Andrew wrote:

> I've had an evening's play with this code.  It is quite fascinating.
> I'm even more impressed, now that I understand essentially what is

Great, maybe you can explain it to me. :)

> And it appears that the same thing has happened here, with Space
> Invaders - although I'm sure people have been working on the perfect
> space invaders clone since day 1 ... kind of the 2600 holy grail, now
> that Pacman has been tamed.  There are probably a few more variants
> hiding in the closet.

I don't think anyone else here tried Space Invaders after my playfield-
graphics one, until Eckhard's multi-sprite version just now.  Also, some
of my problem with Space Invaders was that I never played the original
back in the day -- still haven't except for MAME.  I played the TI-99
version for many hours, though, and that's more what I tried to copy both
for the playfield and multi-sprite versions.  I had even forgotten that
the original didn't move the formation in unison until I saw Eckhard's.

> I do not plan, for the while, to take over Space Invaders.  I think that
> this sort of coding is probably still a bit beyond me.

Would you want to work on it as a joint project?  I might be able to go
back to it if I had someone else pushing me, doing some of the 'boring'
code like joystick input, and supplying alternative ideas for code.  I
particularly don't like the amount of time - 4 scanlines - that it takes
to do the self-modification of the code in RAM, and would love to see that

Thomas wrote:

> While I will play with this codes too, I won't make a complete Space Invaders.
> The kernel is the only thing which I'd like to do, that's fun.

That's exactly my problem.  Doing a seemingly-impossible kernel is fun,
especially when it's something even an NES couldn't do.  Writing joystick
code, missile movement, collision detection, score display is boring and
why I never finished either version of INV.

Eckhard wrote:
> Missiles might not be too useful anyway, since they are always set to
> display two copies like the players. But you could use the ball instead.
> That would at least allow one shot per invader row without flickering.
> You might have to limit the invader shots to come only from the last
> row of invaders though.

That's a good idea, and I think the multiple-copies problem for the
missiles was why I never went anywhere with it.  It would work to use the
ball for player bullets, as they can and must be displayed during the
invader formation, and the missiles for invader bombs, in the space below
the formation.

> Ha, my mighty invaders will eat your tiny little kindergarten-invaders
> for breakfast. ;-)

Well, mine are smaller, so I could fit about 250 of them on the screen if
I so desired :)

> But hey, I just realized that, if I changed my sprites to six pixels
> width too, I could shift the last two invaders per row,and display 11
> evenly spaced invaders that way.

Is there time to load a new graphic into A, or even to do a shift on it,
between the 9th and 10th invaders?  I don't see it, but "impossible" is a
word not to be used lightly around here...

> But since the two pixel
> shifting happens to other sprites too, when you remove some from the
> formation, this might not work in all situations. Might be worth a try
> though.

I thought I actually had the pixel shifting solved, or at least reasonably
minimized.  Also, it's only a one pixel shift, and it happens because
there are nine pixels between successive RESPx hits, but only 8 pixels
between NUSIZ copies.  Argh, I'm getting curious enough to set up the 2600
again and try this out, seeing as how the various emulators aren't perfect
with regards to the repeating-sprites...

And Andrew wrote:
> One thing that disturbed me a little bit was the recent clash with the
> 'crazy valet' program - where two brilliant programmers independantly
> decided to work on a secret project of essentially exactly the same
> game.

We've got the opposite problem here - both of us want the other person to
do Invaders :)

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