Path: utzoo!attcan!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!usc!apple!portal!sv!news
From: daven@svc.portal.com (Dave Newman)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Advice on icon animation wanted
Message-ID: <1990Dec20.211549.12600@svc.portal.com>
Date: 20 Dec 90 21:15:49 GMT
References: <1116@babcock.cerc.wvu.wvnet.edu> <47444@apple.Apple.COM> <1990Dec18.220806.8816@svc.portal.com>
Sender: news@svc.portal.com
Reply-To: daven@svc.portal.com (Dave Newman)
Organization: Software Ventures Corporation.
Lines: 21

In article <1990Dec18.220806.8816@svc.portal.com>, daven@svc.portal.com writes:
> In article <47444@apple.Apple.COM> stevec@Apple.COM (Steve Christensen) writes:
> > You also can't draw from an interrupt routine because the heap may not be
> > consistent, and QuickDraw uses the Memory Manager for regions.
> 
> However, if he refrains from calls that move memory, and manages to set
> A5 to the application's A5, then there's nothing preventing him from
> persuing this route.
> 

I erred. One can not call QuickDraw from inside a VBL task for the simple
reason that QuickDraw is not reentrant. Shoule the task run while QD was
in the middle of drawing, the results are likely to be amusing at best,
or diastrous at worst.

I thank others for pointing out that the Vertical Retrace Mgr on II class
Macs can manage multiple VBL task queues, each synchronized to a different
monitor's VBL clock. This means that one can have a VBL task inform the
application when a VBL is occuring on a particular monitor.

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