Path: chuka.playstation.co.uk!news
From: Developer Support <dev_support@interactive.sony.com>
Newsgroups: scea.yaroze.programming.2d_graphics,scee.yaroze.programming.2d_graphics
Subject: Re: Scrolling without BG ??
Date: Wed, 28 May 1997 10:22:36 +0100
Organization: Sony Computer Entertainment Europe
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George Bain wrote:
> 
> Is it possible to scroll a background without BG?  What I'am trying to do
> on the PlayStation is scroll two 160*240 images...just a simple wrap around.
> I tried some things out but I loose the image when I wrap around.  The image
> would be useless to break down into 16*16 tiles so I need another way.
> If this is not possible or anyone know of hints or tricks please let me know.
> 
> P.S. Does anyone...anyone..know how to use the system timers?
> 
> Latah....
> 
> George Bain

If you draw 4 images then you'll have no problems. Draw the first one at
your (x,y), remember to do a x %= 320, y %= 256 (or what ever your
screen resolution is). Then draw then others at (x-320,y) (x,y-256) and
(x-320,y-256) (again depends on your screen resolution). Its not ideal
but will do the job.

As for system timers there are 3 functions long StartRCnt(unsigned
long), long ResetRCnt(unsigned long) and long GetRCnt(unsigned long).
The only values that do anything in the calls are 0,1 and 2. 0 and 2
seem to be pixel counts (time to draw a pixel, or of that order, there
isn't much in the way of details on how they were set up), and 1 seems
to be a scanline count.

To use the root counters just call StartRCnt with the number you want.
ResetRCnt as necessary and GetRCnt to get a value. The value returned is
in the range 0-65535, after which the counters wrap around.

Example

#include <libps.h>

void main()
   {
   unsigned long counter;

   counter = 0;   // could also be 1 or 2

   StartRCnt(counter);
   
   while(*program terminate condition*)
      {
      ResetRCnt(counter);

      *all the code*

      printf("Time taken: %d\n",GetRCnt(counter));
      }
   }


Stuart