Re: [stella] parallel efforts / Invaders

Subject: Re: [stella] parallel efforts / Invaders
From: "Eckhard Stolberg" <Eckhard_Stolberg@xxxxxx>
Date: Thu, 15 Mar 2001 14:29:51 +0100
> 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...

Yes there is enough time for a second load. In fact in my version
I'm loading the graphics for player0 and player1 through two
different pointers, as I was planning to use different graphics
for every other invader at one point. And if I use Jim Nitchals'
single-cycle-precission deleay routine in ROM, I should have
plenty of time for displaying shots too.

There also is enough time to apply the shifted graphics. Remember
what you are seeing is the second player copy, so the RESPx happens
quite a few pixels away from the actual display position.

And now I remember what the problem was that I was thinking of.
If you only have one invader in a row, it will display both
of it's player copies, since from the second line on, the only
hit to RESPx happens always at the same time in the line. You
will have to special-case that, like position that player normaly
during the setup phase for that row and then don't hit RESPx
during the display.

> 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...

Well, you might want to have a closer look at the display of
your program then. Or maybe not. ;-) The invaders in the third
row for example are all shifted to the left. And on my system
and on the emulators it's two pixels. Look at my demo. The lower
invaders are 7 pixels wide and there is the one pixel gap between
two invaders, yet the second to last invader in the row is
attatched to the invader before him.

Oh BTW, I know exactly how you feel. I had to dig out my old code
yesterday too and try out the sprite shifting. I almost got it
working, but I seriously need to clean up the code before I can
post something here. I guess that's what I get for always making
fun of Andrew's commenting habbit. ;-)

So Erik, tell me why is it that I always feel challenged to
write some VCS code after reading your posts. ;-)

Ciao, Eckhard Stolberg

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