I though Duck hunt was only interested in hit or miss, so it only flashed a 
block over the target area. If the gun saw the flash at the time it was 
supposed to be displayed, you had a hit. It didn't bother with the rest of the 
screen. You could usually see the block around the duck flash as 30fps isn't 
really that fast.

----- Original Message -----
> The "quickly flying light dot" is how the picture was drawn on a CRT,
> so it
> didn't have to do anything special. The light pen simply reported to
> the video card "I saw the dot", and the board would then store
> somewhere the
> exact x/y position that it was drawing when the pen fired. This is how
> the gun for the NES worked, as well as various other such instruments
> for other
> computers. I remember the C64 having such, also.
> 
> It probably wasn't a great idea to stand that close to a CRT for
> extended periods of time.
> 
> Michael
> 
> 
> On Mon, Sep 9, 2013 at 3:00 PM, Jack Coats <[email protected]> wrote:
> 
> > The other day I ran into my doc's about CGA displays, including the
> > lightpen input. The light pen was a photo transistor and a switch
> > that signaled the CGA board the light pen was pressing on the glass
> > screen. The CGA display actually did the scanning (with a quickly
> > flying 'light dot' to find the pen position) and reported it back to
> > the computer through the CGA display card.
> >
> > Now back to your daily dose of
> > non-bone-kives-and-bear-skin-technology.
> >
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> 
> 
> -- Michael Darrin Chaney, Sr.
> [email protected]
> http://www.michaelchaney.com/
> 
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-- 
Steven Critchfield [email protected]

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