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From: billkatt@sol.engin.umich.edu (Steve Bollinger)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Fast image changes
Message-ID: <41153b20.a590@mag.engin.umich.edu>
Date: 25 Jan 89 22:30:00 GMT
References: <243@usage.csd.unsw.oz> <1453@ditsyda.oz> <2350@ilium.cs.swarthmore.edu>
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Reply-To: billkatt@caen.engin.umich.edu (Steve Bollinger)
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In article <2350@ilium.cs.swarthmore.edu> jackiw@ilium.UUCP (Nick Jackiw) writes:
>In article <1453@ditsyda.oz> vincent@ditsyda.oz (David A. Vincent) writes:
>> in article <243@usage.csd.unsw.oz>, grants@usage.csd.unsw.oz (Grant Sayer) says:
>> >  	I am trying to draw two images one on an offscreen pixelmap and then
>> [...]
>> >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
>> 
>> This seems viable provided that the copybits can be completed during
>> the VBL period.  
>> 
>
>Much easier is just to coordinate your copyBits with the VBL interval.  
>You can do this in Pascal by waiting for the system timer to tick, something
>which happens as a system-VBL task.
>
>	var x:longint;
>
>	Delay(1,X);	{Wait for next VBL interval}
>	Copybits(...);	{Here we go, do it fast!}

Except... He said that he was using a pixelmap (pixMap), and those are under
color quickdraw.  The VBL is fake on the Mac II and won't help reduce flicker.
You need to look in inside Mac V 5 at chapter 29 for the correct way to sync
to the REAL VBL on a Mac II.  And also you don't need to complete the operation
before the verticla blanking interval is over, you just need to keep ahead of
the scan line.

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