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From: bryce@hoser.berkeley.edu (Bryce Nesbitt)
Newsgroups: comp.sys.amiga
Subject: Re: Double Buffering
Message-ID: <21733@ucbvax.BERKELEY.EDU>
Date: Thu, 12-Nov-87 02:49:19 EST
Article-I.D.: ucbvax.21733
Posted: Thu Nov 12 02:49:19 1987
Date-Received: Sat, 14-Nov-87 16:01:57 EST
References: <7768@steinmetz.steinmetz.UUCP> <1038@sugar.UUCP>
Sender: usenet@ucbvax.BERKELEY.EDU
Lines: 57
Keywords: double buffering, vertical retrace, screens

In article <1038@> peter@sugar.UUCP (Peter da Silva) writes:
>In article <7768@>, guilford@sunbird.steinmetz (james d guilford) writes:
>
>> I looked up double buffering in the RKM.  It suggested...
>
>Why don't you just set up two screens and use ScreenToFront and ScreenToBack
>to flip them? 

Peter da Silva, multitasking terrorist.  This is quick, easy and  probably
will be compatible in the future.  But it is also a dirty, ugly
kludge that gives users headaches.  Try C= N or C= M on such a program.
Try dragging the screen.  YUCK!


*At least* put some protection in if you go this route.  Someone else
probably has a better suggestion, but how about:

	key=LockIBase(0L);
		check IntuitionBase->FirstScreen; if the same
		as yours, contine.  Else quit animating.
	UnLockIBase(key);

In the second case, post a "start animating" requester in *your*
screen.  Or maybe one in each, come to think of it.  Still a 
kludge.


It could be that many of the "better" Dbuffering techniques may
break Hedley's Highres Monitor.  (That 1000*800 monochrome monitor
shown at Comdex)  This is pure speculation, however.


This is another one that works:

Set the ViewPort->RasInfo->BitMap plane pointers to the
"other" data then MakeScreen(Screen), RethinkDisplay().
The problem with this is that it rebuilds the copperlists
and that takes a while.  (Reference: WaveBench-1 in interlace :-)

I've seen ScrollVPort() used.  This is fast but seems to have some
display trashing problems and has crashed.  Perhaphs a Forbid()?

A unique solution was used by Matt Dillon.  He had a two bitplane
display for Wiredemo.  He draws into one plane at a time, setting
the color registers to make that plane invisible at the time.
Flopping the color registers is fast.  The problem here is that two
bitplanes of data are fetched by the custom chips, I think (but am 
ot positive) that droping one bitplane will leave more cycles for
the blitter. (issue: can the blitter take advantage of free
"odd" cycles)
Other than that, it works great in practice!

|\ /|  . Ack! (NAK, SOH, EOT)
{o O} . bryce@hoser.berkeley.EDU -or- ucbvax!hoser!bryce
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