Re: [stella] Light gun/pen

Subject: Re: [stella] Light gun/pen
From: Nick S Bensema <nickb@xxxxxxxxxxxx>
Date: Tue, 30 Sep 1997 12:11:41 -0700 (MST)
>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.

Using a black background and a highly-contrasted TV, and assuring either only 
one object per scanline-frame (like ancient Pong machines), or a 1/30-second 
"test cycle" that would flash the objects that could have been hit and see
which one registers on the light gun.  I think the NES did something similar;
ever notice how the screen flashes on Duck Hunt whenever you shoot the gun?

>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). 

And the NES if we want to go there.  :-)  But using Duck Hunt as evidence,
its light gun support might not have been the greatest.

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