From:	Shawn Hargreaves <Shawn AT talula DOT demon DOT co DOT uk>
Newsgroups:	comp.os.msdos.djgpp
Subject:	Re: Scrolling using Allegro...
Date:	Tue, 9 Jun 1998 20:54:01 +0100
Organization:	None
Message-ID:	<LkbFjCAZLZf1Ewn6@talula.demon.co.uk>
References:	<6ljh31$qm0$1 AT supernews DOT com>
NNTP-Posting-Host:	talula.demon.co.uk
MIME-Version:	1.0
Lines:	23
To:	djgpp AT delorie DOT com
DJ-Gateway:	from newsgroup comp.os.msdos.djgpp

Johnny P. writes:
>I am using Allegro's scroll_screen() fxn and it works perfect when 
>scrolling vertically. When scrolling horizontally, it is very jumpy and 
>redraws incorrect parts of the image.

From allegro.txt:

   Mode-X scrolling is reliable and will work on any card. Unfortunately
   most VESA implementations can only handle horizontal scrolling in 
   four pixel increments, so smooth horizontal panning is impossible in 
   SVGA modes. This is a shame, but I can't see any way round it.

>If scrolling horizontally is a problem, would it be easier to draw all
>graphics to a 1024 X 1024 buffer (1,048,576 bytes for a 256-color
>mode--kinda large) and then blit the active section to the screen?  

That is pretty much the only possible approach, if you want to do smooth
pixel scrolling.


--
Shawn Hargreaves - shawn AT talula DOT demon DOT co DOT uk - http://www.talula.demon.co.uk/
"Miracles are nothing if you've got the wrong intentions" - Mike Keneally

- Raw text -