[stella] RESP & HMP quirks

Subject: [stella] RESP & HMP quirks
From: "Eric Ball" <ericball@xxxxxxxxxxxx>
Date: Fri, 29 Nov 2002 21:59:06 -0500
I've been doing some experimenting with Manuel's horizontal positioning
routine (http://www.biglist.com/lists/stella/archives/200211/msg00165.html).
I made it for one sprite only, which ruins the natural 0=left edge
positioning (for my routine 16=left edge 'cause of the missing instructions
and the SEC).

Anyway, I was playing around seeing what happens when I try to move the
sprite off the edge of the screen.  I expected the sprite to just slide off
the screen into the horizontal overscan/blanking, but instead it wraps
around!  Well, it does for a moment, then it starts jumping all over the
place.  I thought it was just a quirk with Z26, but then I tried it on a VCS
via my SuperCharger and got the same results.

Attached is a test program which demonstrates this.  Each joystick controls
one sprite.  Moving the joystick left moves the sprite left by one pixel,
right moves right one, up and down move by eight.  The first line of the
sprite is the position in binary.

The next version will have a numeric display, I promise.  I'll also add
changing NUSIZ via the fire button and some other minor tweaks.

I realize this has probably been discussed in the past, but I haven't
managed to read through the entire archive yet.  Can anyone shed some light
on what the TIA is doing?

Attachment: sprite.zip
Description: Zip compressed data

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