Re: [stella] parallel efforts / Invaders

Subject: Re: [stella] parallel efforts / Invaders
From: Erik Mooney <emooney@xxxxxxxxxxxxxxxx>
Date: Fri, 16 Mar 2001 02:28:11 -0500
On Thu, 15 Mar 2001 14:29:51 +0100, you wrote:

>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.

That's the part I missed; you're right.

>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 ran into that problem too.  Funny how making the code do the complex
case of 11 invaders makes it unable to do the simple case of 1 invader.

>> 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.

See, I have no idea what my own program is doing anymore. :)  Yes, I see
that now, although I don't understand why it's two pixels instead of one,
or even why there's any offset at all.  Every single invader in my demo is
drawn as a second copy of the player (NUSIZx is always 1.)

Why I didnt see it before was that I had programmed the thing with either
a full invader formation, or the same invaders missing in each row.  I
only put in the some-missing invader formation as a quick hack to show off
the routine right before posting it.

>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. ;-)

Because I've become the guru of this list, dispensing advice from on high
while not dirtying my own hands in such mortal matters anymore. :)

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