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From: scotty@l5comp.UUCP (Scott Turner)
Newsgroups: comp.sys.amiga
Subject: Re: Swapping graphics pages at 60Hz
Message-ID: <292@l5comp.UUCP>
Date: Fri, 10-Jul-87 01:01:51 EDT
Article-I.D.: l5comp.292
Posted: Fri Jul 10 01:01:51 1987
Date-Received: Sun, 12-Jul-87 13:55:33 EDT
References: <187@mv05.ecf.toronto.edu> <3504@well.UUCP>
Reply-To: scotty@l5comp.UUCP (Scott Turner)
Organization: L5 Computing, Edmonds, WA
Lines: 55
Summary: Come on Leo, it's BUILT IN! :)

In article <3504@well.UUCP> ewhac@well.UUCP (Leo 'Bols Ewhac' Schwab) writes:
>In article <187@mv05.ecf.toronto.edu> drascic@ecf.UUCP writes:
>>What we want to do is use the Amiga to
>>draw dynamic three dimensional, "stereo" images in the same way.  We will
>>thus need two graphics buffers, and we will need to be able to switch
>>between these 60 times a second, in sync with the screen refresh.  Is
>>this possible?
>	Yes.
>>Is it amazingly difficult?
>	No.
>
>	I like succinct responses, don't you? :-)
Well, I've been watching North all day on CNN and he doesn't seem to like them
so...

First off, the Amiga has some of the most unique video display hardware
available in a PC. It's so unique I bought one even though it came with a
Commodore label on it. (How about THAT for an advertizing campaign? "Yeah,
this computer is so good I bought it even though it's from Commodore. Why
don't you too?" ;)

The part we are concerned with here is that the DMA channels that provide the
data to the display do NOT have a built in reset mechanism. When the beam
reaches the bottom of the display they will NOT be reset back to the start of
the display.

This is where the COPPER steps in. When the beam reaches the bottom of the
display the COPPER steps in and resets the DMA registers back to the start of
the display.

If you have ever grabbed the top of the screen and yanked it down to reveal
another screen behind then you you have seen the COPPER in action. You see,
you don't have to wait till the bottom of the display to reload the DMA
registers... NOR reload them to the start of the SAME screen... This is ALSO
why two screens don't TOUCH. If you look real close you'll see a scan line or
two of blackness. These black lines are the time it takes for the copper to
switch screens. When switching at the bottom of the display there is TONS of
time though, so you shouldn't have any trouble with that.

Anyway, what I'm saying is that the Amiga already has software in it that
allows it to switch video buffers at a 60hz (or more) rate. The thing to do
is read the RKM and hardware manuals on the subject of driving the COPPER.
It also wouldn't hurt to read the items in the hardware manual about how the
display hardware works, so you know what to do with it when you figure out
the COPPER.

>	I will feed your name to my boss to be added to the list of people
>to file court-imposed restraining orders against :-) :-) :-) :-) :-) :-).
Better watch it Leo or North may point his finger at you next. :-) :-) :-)

Scott Turner
-- 
UUCP-stick: stride!l5comp!scotty | If you want to injure my goldfish just make
UUCP-auto: scotty@l5comp.UUCP    | sure I don't run up a vet bill.
GEnie: JST			 | "The bombs drop in 5 minutes" R. Reagan
		Disclaimer? I own L5 Computing. Isn't that enough?