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From: ogden@nmsu.edu (Bill Ogden)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Animation Questions
Message-ID: <OGDEN.89Oct13114501@helios.nmsu.edu>
Date: 13 Oct 89 17:45:01 GMT
References: <3123@crdgw1.crd.ge.com> <10611@claris.com> <34698@srcsip.UUCP>
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Organization: NMSU Computer Science
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In-reply-to: mnkonar@gorby.SRC.Honeywell.COM's message of 13 Oct 89 00:06:58 GMT

In article <34698@srcsip.UUCP> mnkonar@gorby.SRC.Honeywell.COM (Murat N. Konar) writes:


>I beleive that the above code fragment will only eliminate flicker on Mac Pluses
>SEs and  maybe SE30s.  MacII variants may have monitors that have a vertical 
>blanking interval that is different than the normal 1/60 sec.  So if you synch
>up with the Tick counter, you are still out of synch with the Monitor's vertical
>retrace.  The solution appears to be to figure out which monitor you are drawing on
>(easy, see the chapter on GDevices in IM vol V), figure out what slot that monitor's
>card is in (don't know how to do that), and then synch up with that slots VBL queue
>(info for that puzzle is buried in IM vol V also, but not in digestible form).

I use GetVideoDefault to find the slot (but may NOT be the device
currently being written to!) and then set up a dummy (do nothing) 
VBL task which decrements the vblCount every vertical blank period. It
seems to work.
Here's how I do it:

VBLQElPtr 		vtrace;	/* global vertical blank task pointer */
int			vSlot;	/* global for video slot */

InstallRetracer()	/* installs the dummy vbl task in default slot */
{
	DefVideoRec	defaultScreen;

	GetVideoDefault(&defaultScreen);
	vSlot = defaultScreen.sdSlot;
  	vtrace =(VBLQElPtr) NewPtr(sizeof(VBLTask)); 
	vtrace->qType = vType;
	vtrace->vblAddr = DummyVBLTask;
	vtrace->vblCount = 3000;    /* count can be anything */
	vtrace->vblPhase = 0;
	SlotVInstall(vtrace,vSlot);
}

waitForSync()  /* call this to wait for the next vertical blank peroid */

{	int		wait;

	wait = vtrace->vblCount;
	while (vtrace->vblCount == wait); 
}

Be sure and do a SlotVRemove call when you done !!
This will only work on MacII's or later.


Bill Ogden  ogden@nmsu.edu
Computing Research Lab / Psychology Dept
New Mexico State University