Path: utzoo!attcan!cmtl01!matrox!uvm-gen!uunet!lll-winken!ames!pasteur!ucbvax!bloom-beacon!apple!lsr
From: lsr@Apple.COM (Larry Rosenstein)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Fast image changes
Keywords: Vertical Retrace Queue, Color QuickDraw
Message-ID: <478@internal.Apple.COM>
Date: 25 Jan 89 17:52:34 GMT
References: <243@usage.csd.unsw.oz>
Organization: Advanced Technology Group, Apple Computer
Lines: 23


In article <243@usage.csd.unsw.oz> grants@usage.csd.unsw.oz (Grant Sayer) writes:
>
>scan line which interrupts the picture.  Does the method of placing the
>code which swaps the images, basically a copybits operation, into the VBL
>task queue seem a viable solution.  If this is the casethen is it true

You can't actually do the CopyBits in the VBL task, because VBL tasks are
restricted in what they can do.  You can use the VBL task to indicate to
your main application when vertical blanking occurs.  The main application
would poll the flag and do the copybits when vertical blanking happens.

On a Mac II, things work a bit differently.  Since the video is handled by
each video card, the standard VBL stuff doesn't directly correspond to
vertical retraces.  Instead you have to use SlotVInstall to install the vbl
task in the queue associated with the desired screen.  You should look at
the Vertical Retrace Manager of Inside Mac volume 5 for more info.

-- 
		 Larry Rosenstein,  Object Specialist
 Apple Computer, Inc.  20525 Mariani Ave, MS 46-B  Cupertino, CA 95014
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