[stella] Light gun/pen

Subject: [stella] Light gun/pen
From: Glenn Saunders <krishna@xxxxxxxxxxxx>
Date: Tue, 30 Sep 1997 09:52:50 -0700 (PDT)
On Tue, 30 Sep 1997, Eckhard Stolberg wrote:
> I don't have a lightgun, but I think it is the same as a paddle with a
> photo sensor instead of a potentiometer. You would read it the same way
> and it would take longer to recharge depending on how much light reaches 
> the sensor. Since the amount of light, that reaches the sensor, depends

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.

Other than Atari systems like the XEGS, 7800, or the unused capability in
the 5200, the only other systems I know of that supported a light pen/gun
were the Astrocade (at least I know it had a port for it) and the Vectrex
(which probably operated under principles similar to the earliest 1960s
style light pens which were originally used with oscilliscope monitors). 

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