Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!usc!apple!keith
From: keith@Apple.COM (Keith Rollin)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Optimizing animation processing speed
Message-ID: <53054@apple.Apple.COM>
Date: 18 May 91 22:28:16 GMT
References: <1776@babcock.cerc.wvu.wvnet.edu>
Organization: Apple Computer Inc., Cupertino, CA
Lines: 34

In article <1776@babcock.cerc.wvu.wvnet.edu> un020070@vaxa.wvnet.edu writes:
>
>In this animation, I am moving icons around on the screen.  I
>have two offscreen bitmaps.  The first offscreen contains the
>background art, which is slow to draw; this way, I only have to
>draw it once.  I continually CopyBits this whole bitmap into
>the second bitmap.  I draw the icons the second bitmap, then
>copyBits the second bitmap onto the screen.  This whole process
>happens every event loop.  (Slow as this sounds, I have reason
>to believe that this is actually not the big time-consumer.)

Depending on how many icons you are moving, I can think of two
things you could do:

- if you have a small number of icons, then don't refresh the
entirety of your second buffer. Just overwrite the few icons
selectively. That way, you aren't refreshing the majority of
your second buffer that doesn't need it.

- if you have a large number of icons, then the overhead of
calling QuickDraw a large number of times my actaully slow
you down enough that a single Copybits call to copy the entire
buffer is faster. However, if your buffers are bitmaps with the
same dimensions, or PixMaps with the same dimensions and color
table information, then try using BlockMove instead of
CopyBits.


-- 
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Keith Rollin  ---  Apple Computer, Inc. 
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"But where the senses fail us, reason must step in."  - Galileo