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From: dweisman@umiami.ir.miami.edu (Ordinary Man)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Animation
Message-ID: <1991Feb7.233344.7781@umiami.ir.miami.edu>
Date: 8 Feb 91 04:33:44 GMT
References: <9102030634.AA09598@enuxha.eas.asu.edu> <1991Feb7.093610.12594@ecmwf.co.uk>
Organization: Univ of Miami IR
Lines: 45

In article <1991Feb7.093610.12594@ecmwf.co.uk>, mab@ecmwf.co.uk (Baudoin Raoult) writes:
> In article <9102030634.AA09598@enuxha.eas.asu.edu>, trotter@ENUXHA.EAS.ASU.EDU (Russell T. Trotter) writes:
>> What is the best way to do animation if I am relying on
>> the main event loop for the updates for the motion?
>> 
>> I have tried various combinations of CopyBits(),
>> PutIcon, DrawPicture(),...etc, but they all
>> seem to be too flickery.  Am I just doing 
>> something fundamentally wrong?  
>> Thanks to all who reply!  
> 
> To avoid flickery animation, you must synchronise your CopyBits with the video spot.
> The simplest way is to use TickCount, as the tick counter is updated every 60th of
> second, each time the video spot starts to update  new screen. So just write:
> 
> 	tmp := TickCount;
> 	while tmp=Tickcount do { nothing } ;
> 	
> 	CopyBits(.....)

This is fine except for a minor detail. As it says in IM Vol. I...

"...don't rely on the tick count being incremented to a certain value, such
as testing whether it has become equal to its old value plus 1; check for
'greater than or equal to' (since an interrupt task may keep control for
more than one tick)."

So instead say:

	tmp:=TickCount;
	repeat until TickCount>=(tmp+1);

	CopyBits.....

==Dan

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