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From: lanmaint@nssdcb.gsfc.nasa.gov (Dave Yoest)
Newsgroups: comp.sys.atari.8bit
Subject: Re: Creative Computing lightpen (was Re: Atari trivia)
Message-ID: <5564@dftsrv.gsfc.nasa.gov>
Date: 5 Jun 91 10:30:46 GMT
References: <1991Jun3.002321.2267@mnemosyne.cs.du.edu> <42968@cup.portal.com>
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In article <42968@cup.portal.com>, Chris_F_Chiesa@cup.portal.com writes...
>For what it's worth, I picked up some third-party commercial light-pen at
>a local user-group flea market a couple of months ago, got it to work, and
>had the SAME experience of totally useless horizontal resolution: "picking
>a pixel +/- 40 pixels away from where you were pointing" sounds about right...
> 
>Must be the Atari hardware. :-(


I don't think it's the atari hardware because I got the atari "light 
gun" from a friend and wrote a little c program to "shoot" at the 
screen machine gun style. The gun IS a light pen and seems pretty
accurate (+-2 or 3 pixels) even from a distance of 15 feet away!

There a small algorithm necessary to map the light pen coordinates
to screen coordinates, it can be found in the technical reference
manual. If anyone needs it I would be happy to look it up and
post it. Also I would also be willing to post the C source for
MACHINE GUN (DEEP BLUE C). It's not very good from a game standpoint,
or from a C progamming standpoint (kludgey code), but it does work
and could be used to test the accuracy of your light pen hardware.

I also (once upon a time) had a KOALA lightpen with KOALA paint
for pen. When you started KOALA for pen, it would have you
"calibrate" the pen by pointing at a horizontal and then a vertical
line. It also was quite accurate once calibration was completed.



Dave Yoest
LAN M&O Section Supervisor
NASA/Goddard Space Flight Center
Greenbelt, Md. USA

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