Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!mcnc!uvaarpa!murdoch!news
From: mil@mendel.acc.Virginia.EDU (Maria I. Lasaga)
Newsgroups: comp.sys.mac.programmer
Subject: Optimizing Copybits
Message-ID: <1990Aug2.223758.13691@murdoch.acc.Virginia.EDU>
Date: 2 Aug 90 22:37:58 GMT
Sender: news@murdoch.acc.Virginia.EDU
Distribution: usa
Organization: University of Virginia
Lines: 49



We need to optimize the speed with which copybits places a complex
image from an offscreen port to the screen.  We are working with an
SE (2.5Mb RAM), to which we have attached a 19" monitor (LaserView
by Sigma Designs).  We can't seem to get any image to be copied in
under 50-60 msec (which is about 3-4 refresh scans).  Each image to
be transferred is under 20K in size.

We are using SrcCopy.  we have defined the source rectangle in the
offscreen port to be the size of the monitor's screen size.  We have 
defined the destination rectangle to be the same size as the 
entire screen.  However, we define the clipping region to be the size
the PICT's picture frame (which is centered on both ports' portrect).
(We have also tried making the destination rectangle and the source rectangle
the same size as the PICT's picframe, and then clipping the drawing
region on the screen to the size of the picframe also.  This doesn't
make the copy procedure more efficient, since in both cases the
clipping region is the same size as the PICT's picframe.)

Because we are using a large-screen monitor, we cannot use an
accelerator board (at least, given the monitor we are using,  
since no company manufactures an accelerator with an adaptor
for our monitor).

We happened to expand RAM from 1 Meg to 2.5 Meg and surprisingly
to us, we cut down the drawing time to 1/4 of what it was before
the upgrade.  If we expanded to 4 meg, would we cut down on the
drawing time further?  (Why did additional RAM speed up the
copybits procedure in the first place?)

What more can we do?  What are we doing wrong?  We need to get
the drawing times as close to 1 refresh cycle as possible.  (This
program is for an experiment in visual perception.)

Any help would be greatly appreciated.



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Maria Lasaga
Department of Psychology
Gilmer Hall
University of Virginia
Charlottesville, Virginia 22903


e-mail:  MIL@virginia.bitnet
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