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From: lim@iris.ucdavis.edu (Lloyd Lim)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Optimizing animation processing speed
Message-ID: <8996@ucdavis.ucdavis.edu>
Date: 18 May 91 22:26:39 GMT
References: <1776@babcock.cerc.wvu.wvnet.edu>
Sender: usenet@ucdavis.ucdavis.edu
Reply-To: lim@iris.ucdavis.edu (Lloyd Lim)
Organization: U.C. Davis - Department of Electrical Engineering and Computer Science
Lines: 57

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.)

But you can still speed it up.  Instead of copying the whole background
over, keep track of where each icon was and just copy over little squares
of the background.  You could also take all the old squares, make a region
out of them, and use that as the maskRgn in a CopyBits of the whole
background.  I'm not sure which would be faster.

>Each time I plot an icon, I GetIcon it, then draw it using copyBits,
>then ReleaseResource it.  Now, if I'm not mistaken, this doesn't
>actually purge the icon from memory, right?  If something else needs
>the memory it will write over it, but if nobody needs the memory,
>the icon will hang around until the next cycle, and GetIcon will
>just give me a handle to the icon in memory, right?

IM says:
"Given a handle to a resource, ReleaseResource releases the memory occupied by
the resource data, if any, and replaces the handle to that resource in the
resource map with NIL. The given handle will no longer be recognized as a
handle to a resource; if the Resource Manager is subsequently called to get
the released resource, a new handle will be allocated. Use this procedure
only after you're completely through with a resource."

Don't call ReleaseResource.  If the resource is purgeable, it will stick
around unless the memory is needed for something else.  Icons aren't very
big so if you're using the same ones over and over, you probably will want
to load them once, save the handles, and make them unpurgeable (but not
locked).  Then just refer to them by the handles.

>In doing the calculations for the animation, I frequently refer
>to complex data structures by handles.  Is this a particularly
>slow way of doing things?  Could I speed things up appreciably by
>locking the handles and using more Pascal WITH statements?

There isn't much to a handle dereference.  Generally, using handles
and keeping them unlocked as much as possible is a good thing to do.
If you need to refer to a field with a call that moves memory, make a local
copy of the field and use the copy in the call.  If you need to use
something larger and move memory, HGetState, HLock, and HSetState.
WITHs and/or register variables (does Pascal have those?) might help a
little.

+++
Lloyd Lim     Internet: lim@iris.eecs.ucdavis.edu
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