Subject: Scrolling problems...
From: Mark Carter <[email-masked]>
To: [email-masked]
Date: Sat, 28 Sep 1996 16:16:13 +0000

Hi,

Does anyone know the best way to do hardware scrolling...?

Now I'll explain my situation - because I guess its pretty important!

(I'm using autoback 0 and bob update off)

I've got a lowres 640x480 screen which I scroll in a 320x190 display, 
about 15 bobs including a ball, which the scrolling follows. All of 
this (including scrolling) was controlled by AMal proggies.
To begin with I was running the game at 25Hz using the following 
method:

do
   [program code taking between 0.5 and 1.5 vbls]
   Synchro:wait vbl:bob update
   rem next line makes sure that we only wait a vbl if we need to
   If less-than-2-vbls since last last loop then wait vbl
   rem I've tried removing the line above and it doesnt make the 
          display any smoother
loop

This however, is very jerky.  So I then decided to make the ball move 
at 50Hz by taking it out of the Amal bank and putting the new Amos 
code just BEFORE each Vbl.

This was even worse!  However, when I ran the program by freezing the 
scrolling amal program, all was ok.  I think the problem is that 
while EVERYTHING visible is updated in one smooth burst during the 
Bob Update command, the scrolling is done during the Synchro command. 
So, in effect, there are 2 changes to-the-eye every Vbl.

Please Help!

I hope this all made some sense!

Cheers,
        Mark

Mailto:[email-masked], [email-masked]
URL:   http://www.westmead.demon.co.uk/mark/index.htm