Path: utzoo!attcan!uunet!lll-winken!ames!mailrus!bbn!apple!carr
From: carr@Apple.COM (Randy Carr)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Fast image changes
Summary: VBL Tasks
Message-ID: <24792@apple.Apple.COM>
Date: 26 Jan 89 16:42:32 GMT
References: <243@usage.csd.unsw.oz> <1453@ditsyda.oz> <2350@ilium.cs.swarthmore.edu>
Organization: Apple Computer Inc, Cupertino, CA
Lines: 34

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.
>
>	Delay(1,X);	{Wait for next VBL interval}
>	Copybits(...);	{Here we go, do it fast!}
>
>Follow-ups to comp.sys.mac.programmer ONLY.  Eradicate cross-posts!
>
Well... Mac II's and other machines that use NuBus video have different vbl
times depending on the monitor used.  _Delay, on the other hand, is always in
1/60 sec intervals.  So... in order to have true vbl drawing, you must use
_SlotVInstall tasks (see the Apple Technote #221).

>+-------------------+-jackiw@cs.swarthmore.edu / !rutgers!bpa!swatsun!jackiw-+
>|  nicholas jackiw  | jackiw%campus.swarthmore.edu@swarthmr.bitnet           |
>+-------------------+-VGP/MathDept/Swarthmore College, Swarthmore, PA 19081--+

Randy Carr                                          Network Systems Development
Domain: carr@apple.com                                     Apple Computer, Inc.
UUCP:   {nsc,dual,sun,voder}!apple!carr             20525 Mariani Ave. M/S 27-O
AppleLink: CARR2                                            Cupertino, CA 95014

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