Re: [stella] Light gun/pen

Subject: Re: [stella] Light gun/pen
From: Chris Wilkson - MCD <cwilkson@xxxxxxxxxxxxx>
Date: Tue, 30 Sep 1997 10:34:42 -0700 (PDT)
> I think it's more than that with Atari systems at least, otherwise light
> pens would not work as paint programs or pointing devices.  Such a system
> as you describe is far too crude for anything but the early pong systems
> and you wouldn't be able to differentiate between hitting one object or
> another, etc....
> The Atari 8-bit has discrete hardware registers for reading a light pen
> (light pens work better than guns for obvious reasons).  It does a fairly
> rough job on the horizontal ;)  The important thing isn't whether or not a
> light gun detects light (which will just give you on or off), it is
> finding a way for the computer to determine the X and Y coordinates of
> where the beam is hitting the TV, and THEN cross referencing this with
> your objects.

Well, I've always just kinda assumed that you would sequence the targets.
I.e. dont draw them every frame.  A well designed light gun will have a fairly
narrow field of vision, so could be pretty accurate.  I don't know how it's
implemented in the 2600 (anyone disassembled Sentinel yet? :) ), but I do know
that the gun has to be the sensor.  CRT's are output only.

And if the lightgun has a photodiode or phototransistor rather than a photo-
resistor, then it can be fast enough to sense within 20 pixels or so on the


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