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From: holloway@drivax.UUCP (Bruce Holloway)
Newsgroups: comp.sys.atari.st
Subject: Re: need info on LineA and Animation programming
Message-ID: <1709@drivax.UUCP>
Date: Mon, 1-Jun-87 13:12:45 EDT
Article-I.D.: drivax.1709
Posted: Mon Jun  1 13:12:45 1987
Date-Received: Wed, 3-Jun-87 03:47:39 EDT
References: <156@xrxns.UUCP>
Reply-To: holloway@drivax.UUCP (Bruce Holloway)
Organization: Digitalis Research, Inc.
Lines: 37
Keywords: sprites, low-level graphics programming

In article <156@xrxns.UUCP> toml@xrxns.UUCP (Tom Love) writes:
>on a slightly different topic - how are you hackers out there implementing 
>animation?  using linea, or other rom/bios routines, or rolling your own?
>how reasonable is it to attempt to manage multiple display buffers as an
>assist to animation?  (might as well make use of the ram and the relocatable
>display base, as long as the result is reasonably fast and leaves time
>inbetween to update the other buffers).  or does this result in flicker or
>other undesirable side effects?

When I do animation (check out "Money", 2/87 ST-Log), I use multiple buffers,
drawn with the VDI routines (or read in from disk), and flip them. There's no
flicker - the screen base isn't changed until vertical blank. Very smooth
animation. I've never used the Line A blit routines 'cause I have no documen-
tation on them. But as I understand it, they are only a fast interface into
the VDI routines, so they don't give you anything more that using the VDI
routines would.

On my animation with GEM on the IBM/PC-AT, since you can't change the base
of video memory, I instead write over the part of the background that the
image has moved past with a filled rectangle routine (usually with a user
defined fill pattern), and then draw the new image, very fast. Not much
flicker if you do it this way...


	+-----+...+
	|%%%%%|   :	A = Old position
	|%   %|   :	B = New position
	|% B %| A :
	|%   %|   :	Write over (A - (A intersect B)) with the background
	|%%%%%|   :			pattern
	+-----+...+	Write the sprite at B

- Bruce
-- 
Bruce Holloway - Relapsed Newsaholic   {ihnp4,seismo,sun}!amdahl!drivax!holloway
"Everything should be made as complex as possible - esp. if you're paid hourly."
What Irony? 75!                      - "The Personal Diaries of Albert Einstein"
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