Light Guns

[Graham]

De_Bunk's thread reminded me of something I could never figure out. How do console "Light Guns" (A la the old "Duck Hunt" game, for instance) work?

Does anyone know?

How does it know where you are aiming? I can see how the gun can feed back to the console, obviously, but how does it position itself? How does it even know which way the gun is pointed?

What am I missing here?

:confused:

Graham

[KillerX]

When you pull the trigger, the whole screen goes black except for the target area, which will be white. The gun merely has a light sensor that detects the white spot if you are aimed at it.

[Mendor]

http://en.wikipedia.org/wiki/Video_game_light_gun

[Graham]

You learn something every day!

Thanks guys.

Graham

[davidhorman]

I've only played games which use the second method (flash the whole screen and use timing and a photo-sensor in the gun to work out where it's pointing).

A friend of mine had a light-pen, which I assume used a similar method, except you touched it directly to the screen. We never got it to work though.

David

[Smackety]

So if you shoot at a light bulb or something you will always hit? I thought it detected the green color on the duck.

[Paul C. Anagnostopoulos]

Who remembers light pens?

~~ Paul

[Smackety]

Who remembers light pens?

~~ Paul

someone from 2003. It is a relic of an earlier age I guess.

[jsiv]

A friend of mine had a light-pen, which I assume used a similar method, except you touched it directly to the screen. We never got it to work though.
It's the same concept, only more timing-sensitive. The pen works by taking advantage of the fact that the point on the screen where the electron beam is focused on is slightly brighter than the rest. This triggers the pen's light sensor which in turn notifies the computer which then saves the current location of the beam to a register.

The gun is simpler because it requires no position information. If there are three ducks on the screen and you press the fire button, it simply displays three different images of a black screen with a white square in succession, the position of the square representing a particular duck. If the light sensor in the gun fires, the console just has to check which image it was displaying at the time. And yes, this usually means you can cheat by just pointing it at a bright light.

Of course, both devices rely on behavior only found on old analog CRT displays, and so aren't very relevant these days.

[Paul C. Anagnostopoulos]

I spent my undergraduate years building a graphics system. That was 1970--74, when all we had were vector displays. No such thing as raster displays yet. So the pointing devices were light pens and trackballs.

It was so tiring to use a light pen that we rigged up a spring connected to a wrist strap and hung it from the ceiling. Then the user didn't have to fight gravity quite so much.

~~ Paul

[666]

Who remembers light pens?

~~ Paul
Me! Me! On an IBM 370. We used one to point on a timeline to program where an onboard spacecraft experiment package would be switched on and off during the orbit. Circa 1972-73 before we automated the process.