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From: bart@amiga.UUCP (Barry A. Whitebook)
Newsgroups: comp.sys.amiga
Subject: double buffering...
Message-ID: <1965@amiga.amiga.UUCP>
Date: Wed, 11-Nov-87 21:26:29 EST
Article-I.D.: amiga.1965
Posted: Wed Nov 11 21:26:29 1987
Date-Received: Sat, 14-Nov-87 06:03:02 EST
Reply-To: bart@amiga.UUCP (Barry A. Whitebook)
Followup-To: bart@amiga.UUCP (Barry A. Whitebook)
Organization: Commodore-Amiga Inc, Los Gatos, CA
Lines: 67
Keywords: double buffer

[ eat this line -- please! ]

this is amiga!bart:

regarding double buffering of animation... here is what "robo" does

----------------- begin fragment -------------------------

while( ... )
{
	Animate(&animKey, rp);
	SortGList(rp);
	DrawGList(rp,vp); 
	vp->RasInfo->BitMap = &bitmap[dispIndex]; 
	WaitTOF();
	MakeScreen(screen);	
	RethinkDisplay();
	dispIndex ^= 1;
	rp->BitMap = &bitmap[dispIndex];
}

----------------- end   fragment -------------------------

note that for a non-dualpf screen the RasInfo->Bitmap is used to remake
the copper list for this screen which has a non-layered vp. 
also note that the rp->BitMap change allows for the current DrawGlist()
call to take place in the "not-currently-displayed" bitmap. also
remember to tell gels that DBUFFER is in effect so that save/restore
works properly between bitmaps.

another way to double buffer is found in the amiga3d demo which
DOES NOT USE gels code to render into its rp->bitmaps, so it incurs less
overhead on the double buffering itself by making these calls:

----------------- begin fragment -------------------------

while( ... )
{
	Forbid();
	WaitTOF();
	WaitBlit();
	Disable();
	(&screen->ViewPort)->RasInfo = rip[frametoggle];
	ScrollVPort(&screen->ViewPort);
	Enable();
	Permit();
	frametoggle ^= 1;
}
----------------- end   fragment -------------------------

this stuffs alternate rasinfo pointers into the viewport and
lets ScrollVPort handle the pokes directly into the copper list.
NOTE CAREFULLY: the elaborate Forbid; WaitTOF; Disable; Enable; Permit;
nesting are to protect the "currently displayed" copper list from being
modified while the copper is fetching instructions from that list.

happy hacking. 

-- 
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