MadSci Network: Computer Science

Re: how do videogame 'guns' work?

Date: Tue May 9 07:51:04 2000
Posted By: Karl Kolbus, Staff, Data processing, Mequon Consulting Corp.
Area of science: Computer Science
ID: 957190523.Cs

Hi Ambi!
I don't know how old YOU are, but Duckhunt and Hogans alley weren't even 
an idea yet when I started playing computer/arcade games. OUR generation  
was brought up on "Pong" and "Space Invaders". So, considering your 
obvious irreverence for us "Senior Citizens", I feel compelled to answer 
your questions thusly - How do video game "guns" work? Answer: Quite well, 
thank you! and "Is my theory even close? Answer: It depends on how good 
your aim is! There. Now that I've gotten that off of my chest, I'll try to 
answer your question in a little more seriously.

Basically, there are two types of "arcade" style games. Those that use an 
active matrix display, a specialized CRT, and those that don't. By active 
matrix, I'm referring to a CRT which has a matrix of photodiode 'areas' 
built into it behind the phosphor dots. So yes, you were pretty close in 
that respect. Each photodiode covers several pixels of the screen, to (1) 
reduce the manufacturing cost of the CRT, and (2) make it possible to hit 
the target. If it were done on a single pixel basis, your chances of 
making a hit would be very difficult indeed! When you fire the gun, a 
light beam, usually infrared, strikes the screen and, if the target 
happens to be in close proximity to where your beam strikes, you score a 
hit. The internal programming knows where each target is at any point in 
time, so your shot must arrive when that portion of the screen is active, 
or no hit is recorded. Additionally, the light beam is encoded, much like 
a remote control device for a television set. A particular digital code 
tells the program which 'fire' button you used - one code for a mortar 
round, another for a bazooka shot, etc. That also prevents you from 
cheating by using a laser pointer or infrared light emitting diode to fool 
the system.
Most home type games, like Nintendo and computer games, must rely on a 
different method of determining the position of the shot fired at the 
screen. The reason is simple: Television sets and computer CRT's don't 
have any sensing devices (photodiodes) built into their screens. The 
solution is equally simple: the joystick or other controller mechanism, 
functions like a computer mouse. By moving it up/down or left/right, 
corresponding pulses are sent to the game program which moves the aiming 
point to a particular position on the screen; just like your cursor. The 
program 'maps' the position of each target on the screen and, if you fire 
your gun while the game has a target mapped to the same area of the screen 
as you have aimed, you score a hit! The same type of coded signal (or a 
seperate wire from each button on your joystick) tells the game which 
weapon you used.
I hope this has helped you understand the principals behind gaming 
devices. While there are more sophisticated methods already being 
employed, they are highly specialized and very costly - definitely not for 
home use.
Happy gaming, Ambi!
Karl Kolbus - Your not-so-mad scientist.      

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