Path: utzoo!censor!geac!torsqnt!news-server.csri.toronto.edu!cs.utexas.edu!usc!apple!portal!sv!daven
From: daven@svc.portal.com
Newsgroups: comp.sys.mac.programmer
Subject: Re: Advice on icon animation wanted
Message-ID: <1990Dec18.205338.6800@svc.portal.com>
Date: 18 Dec 90 20:53:38 GMT
References: <1116@babcock.cerc.wvu.wvnet.edu>
Organization: Software Ventures
Lines: 46

In article <1116@babcock.cerc.wvu.wvnet.edu> un020070@vaxa.wvnet.edu writes:
> I am writing a program in which I am animating a lot of icons
> at one time.  I want to keep the animation smooth and clean, and
> I also want to keep everything going at a constant rate regardless
> of the processor speed, which means that I will somehow have to involve
> the tick counter.  I can think of two strategies for doing this:
> 
> #1: Have the main program be constantly thinking about the animation
> of the icons, but handle the actual animation during the video
> horizontal retrace, when the processor is interrupted and when no
> drawing is taking place on the screen.  I could have a queue of
> icons to be plotted, and plot just one during each retrace cycle.
> (I have never written a routine for the horizontal retrace interrupt,
> however, so this would mean doing some figuring.)

Using a VBL task would probably produce the smoothest animation. However,
there is an issue here I've always wondered about. With the non-color
Mac's the VBL task was tied to the vertical blanking of the B&W monitor.
With the color Mac's there is no gaurantee that this is so. I believe the
Apple 13" color monitor refreshes it's screen at a faster rate than the 60Hz
rate of the VBL task queue. So, could animation by means of a VBL task could
cause some flicker on a color monitor?

> #2: Handle the animation wholly in the main program, looking at
> the tick counter to calculate the position of an icon at any
> given time.

Probably a simplier scheme to implement. You'd be free of the restrictions
governing what a VBL task can and can't do.

> If anyone has done anything like this, I would appreciate your guidance.
> 
> Second question:  How do you draw an icon in XOR?  Is this possible
> with the easy-to-use PlotIcon, or do I have to mess with some kind
> of bit transfer?

PlotIcon calls CopyBits with SrcCopy mode, so no it can't do SrcXor. You
will have to call do the work of PlotIcon yourself, calling CopyBits
with SrcXor mode.


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   Dave Newman              |  daven@svc.portal.com        |  AppleLink: D0025
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