[Coco] GIME Scrolling Questions

[Chris Spry]

Nevermind I think. Something hit me in the afternoon to give a try with the
two GIME registers, so I reprogrammed my test program and low and behold the
idea worked.  Now I got scrolling.  Now I just need to figure out a way to
program it from shifting up a line with the scroll (the 2 registers do reset
after a full screen has scrolled by, but at the reset the screen goes back
to the normal area and then jumps up a line again....maybe if I start the
FF9D really high and lower it along with FF9E bit by bit when needed it'll
adjust and won't happen.....something to try).  I would love to get less
than 4 pixels per scroll movement if possible, but this does work for now
and if I can't it won't kill me. :)

-Chris

----- Original Message ----- 
From: "Chris Spry" <bugster at cedarcomm.com>
To: "CoCoList for Color Computer Enthusiasts" <coco at maltedmedia.com>
Sent: Monday, January 26, 2004 6:14 PM
Subject: [Coco] GIME Scrolling Questions


> Hey guys,
>
> Well I've decided to go in a bit of a different direction with MiniHog and
> will have a quick scrolling game but the gameplay is going to be different
> than originally planned.  I was messing around with the GIME scrolling
> registers quite a bit on Sunday and could not quite figure them out.  I
was
> using a standard 320x192x16 screen (HSCREEN 2). I could get the screen to
> scroll the contents from left to right by poking FF9E and FF9F rather
> seperately or together in different steps.  Usually steps of 1.  However
> when using FF9F (Horizontal Offset Register) it would scroll the screen by
> four pixels per step (Poking with a value of 0-127 sets the horizontal
> offset address in a different location at a video location x2 of the value
> being inputed).  It would work up to a point.  First off I noticed the
> oncoming screen would be shifted up by one line but would scroll fine
until
> the value going into FF9F went past 48.  Once it went past there it would
> lower the line back down and start showing a different location.  I found
> that out by actually drawing a slope across the screen and then add to
this
> slope by 4 horizontal boxes all the way to the left, adding to it to the
> right after the scroll looking like it's ascending (since the screen
shifts
> over by 4 per step).  Then after the 48 value it was as if it wasn't
taking
> my boxes anymore and just showing some of the original stuff from before.
I
> tried FF9E and it seems to work alright, except that it scrolls too much
too
> fast for what I need.  I tried combining the two poking different values
and
> getting odd results depending on what I did.  I tried to find the formula
to
> make a smooth side scrolling effect adding oncoming new screen data, but
> can't figure out what this might be if there is one.  I image that there
is
> one, especially after seeing Sock Master's scrolling/game demo.  Can
anybody
> possible help me out with this, I'd really like to get this game going in
> production again.
>
> -Chris
>
>
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