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From: ewhac@well.UUCP (Leo 'Bols Ewhac' Schwab)
Newsgroups: comp.sys.amiga
Subject: Re: Double Buffering Glitch (attn: CATS and other Guru's)
Message-ID: <3680@well.UUCP>
Date: Wed, 5-Aug-87 03:46:24 EDT
Article-I.D.: well.3680
Posted: Wed Aug  5 03:46:24 1987
Date-Received: Sat, 8-Aug-87 12:38:42 EDT
References: <1679@cadovax.UUCP>
Reply-To: ewhac@well.UUCP (Leo 'Bols Ewhac' Schwab)
Distribution: world
Organization: Shyster and Shaft Legal Services.
Lines: 38
Summary: Use ScrollVPort()

In article <1679@cadovax.UUCP> keithd@cadovax.UUCP (Keith Doyle) writes:
>Hi gang,
>
>Included in this message is an example of a 'glitch' I've been chasing
>for some time, with no success.
>
>What I am attempting to do, is while double buffering two screens of
>data, to cause the switch by swapping the bitmap structure pointed to
>by the rastport with a secondary bitmap structure, and then do a:
>
>	Forbid();
>	MakeView(view);
>	MrgCop();
>	LoadView();
>	Permit();
>
	Hummmm.  Did you know that you can do this, and Intuition won't
mind:

	screen -> ViewPort.RasInfo -> BitMap = pointer_to_other_BitMap;
	ScrollVPort (&screen -> ViewPort);

	All you do is stuff the pointer to the bitmap structure you want,
and call ScrollVPort() on the viewport structure.  This has the added
advantage that it massages the existing copper lists in place.  MrgCop()
computes a whole new list, which I'm sure takes much longer.  Be sure you
restore the original pointer before you call CloseScreen(); I've no idea
what will happen if you don't.

	If you'd like to see ScrollVPort()-style double buffering in action,
take a look at the source code to Ing, my windows-bouncing program.  I use
it in there.

_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_
Leo L. Schwab -- The Guy in The Cape	ihnp4!ptsfa -\
 \_ -_	 Bike shrunk by popular demand,	      dual ---> !{well,unicom}!ewhac
O----^o	 But it's still the only way to fly.  hplabs / (pronounced "AE-wack")
"Work FOR?  I don't work FOR anybody!  I'm just having fun."  -- The Doctor