Light gun

A light gun is a pointing device for computers and a control device for arcade and video games. The first light guns appeared in the 1930s, following the development of light-sensing vacuum tubes. It was not long before the technology began appearing in arcade shooting games, beginning with the Seeburg Ray-O-Lite in 1936. These early light gun games, like modern laser tag, used small targets (usually moving) onto which a light-sensing tube was mounted; the player used a gun (usually a rifle) that emitted a beam of light when the trigger was pulled. If the beam struck the target, a "hit" was scored. Modern screen-based light guns work on the opposite principle - the sensor is built into the gun itself, and the on-screen target(s) emit light rather than the gun. The first light gun of this type was used on the MIT Whirlwind computer.

The light gun, and its descendant, the light pen, are now rarely used as computer pointing devices, because of the popularity of the mouse and changes in monitor display technology - traditional light guns can only work with standard CRT monitors.

Use in video games

The video game light gun is typically modeled on a ballistic weapon (usually a pistol) and is used for targeting objects on a video screen. With force feedback, the light gun can also simulate the recoil of the weapon.

Light guns are very popular in arcade games, but had not caught on as well in the home video game console market until after the Nintendo Entertainment System (NES), Sega Master System (SMS), Sega Mega Drive, and Super Nintendo Entertainment System (SNES) systems. Nevertheless, many home 'Pong' systems of the 70s included a pistol or gun for shooting simple targets on screen.

Traditional light guns cannot be used on the newer LCD and plasma screens, and have problems with projection screens.

The following are famous example of light guns:

* Magnavox Odyssey Shooting Gallery the first gun for a home console was in fact a big rifle, which looked very lifelike and even needed to be "cocked" after each shot
* Nintendo's NES Zapper for the NES, arguably the most popular example of the light gun
* XG-1 for Atari XE-GS
* Action Max, a console that used VHS tapes for games, solely controlled by a light gun
* Light Phaser for Sega Master System
* Super Scope for Super Nintendo, shaped like a bazooka
* Menacer for Sega Mega Drive
* Sega Lock-On, a stand-alone laser tag system
* Namco's GunCon and GunCon 2, first to read the video signal in the accessory (rather than internally in the console) and said to be highly accurate; used for PlayStation and PlayStation 2
* Dreamcast light guns for Sega Dreamcast
* Magnum Light Phaser For Spectrum / Commodore 64
* The Wii Zapper for the Wii console is designed to house the Wii Remote and Nunchuk, giving a light gun feel (although the Wii Remote itself does not use traditional light gun technology).There are also light guns for Sega Saturn, Xbox and several other console and arcade systems. Recent light gun video games include "Time Crisis 4", "Virtua Cop 3", and "The House of the Dead 4".

The Wii Remote can be seen as a successor to this technology, and it can be used relatively accurately with CRT, LCD, plasma, and projection screens. Like the NES Zapper, it is "bundled" with the system, but unlike traditional light guns, the Wii Remote serves as a primary controller. If coupled with the Nunchuk attachment, the Wii Remote allows for a potentially seamless union between first-person shooter gameplay and "light gun" implementation. Namco's GunCon 3 also uses a system similar to the Wii Remote, using 2 infrared LEDs and sensors in the gun, as opposed to the traditional light guns.

Design

The "light gun" is named because it uses light as its method of detecting where on screen the user is targeting. The name leads one to believe that the gun itself emits a beam of light, but in fact most light guns actually "receive" light through a photodiode in the gun barrel.

There are two versions of this technique that are commonly used, but the concept is the same: when the trigger of the gun is pulled, the screen is blanked out to black, and the diode begins reception. All or part of the screen is painted white in a way that allows the computer to judge where the gun is pointing, based on when the diode detects light. The user of the light gun notices little or nothing, because the period in which the screen is blank is usually only a fraction of a second ("see persistence of vision").

Sequential targets

The first detection method, used by the Zapper, involves drawing each target sequentially in white light after the screen blacks out. The computer knows that if the diode detects light as it is drawing a square (or after the screen refreshes), that is the target the gun is pointed at. Essentially, the diode tells the computer whether or not you hit something, and for n objects, the sequence of the drawing of the targets tell the computer "which" target you hit after 1 + ceil(log₂(n)) refreshes (one refresh to determine if any target at all was hit and ceil(log₂(n)) to do a binary search for the object that was hit).

An interesting side effect of this is that on poorly designed games, often a player can point the gun at a light bulb, pull the trigger and hit the first target every time. Better games account for this either by detecting if all targets appear to match or by displaying a black screen and verifying that "no" targets match.

Cathode ray timing

The second method, used by the Super Nintendo Entertainment System's Super Scope and computer light pens is more elaborate and more accurate.

The trick to this method lies in the nature of the cathode ray tube inside the video monitor (CRTs were the only affordable TV monitors in the late 1980s and early 1990s, when this method was popularized). The screen is drawn by a scanning electron beam that travels across the screen starting at the top until it hits the end, and then moves down to update the next line. This is done repeatedly until the entire screen is drawn, and appears instantaneous to the human eye as it is done very quickly.

When the player pulls the trigger, the computer (often assisted by the display circuitry) times how long it takes the electron beam to excite the phosphor at the location at which the gun is pointed. The light gun sends a signal after sensing the sudden small change in brightness of a point on the screen when the electron gun refreshes that spot. The computer then calculates the targeted position based on the monitor's horizontal refresh rate (the fixed amount of time it takes the beam to get from the left to right side of the screen). Either the computer provides a time base for the horizontal refresh rate through the controller's connector (as in the Super Scope), or the gun reads the composite video signal through a T-connector on the A/V cable (as in the GunCon 2). Once the computer knows where the gun is pointed, it can tell through collision detection if it coincides with the target or not.

Many guns of this type (including the Super Scope) ignore red light, as red phosphors have a much slower rate of decay than green or blue phosphors. As a result, some (but not all) games brighten the entire screen somewhat when the trigger is pulled in order to get a more reliable fix on the position.

Display timing is useless with plasma, LCD, and DLP, which refresh all pixels at the same time.

Combined method

Some light guns designed for sequential targeting are not timed precisely enough to get an (X, Y) reading against the video signal, but they can use a combination of the two methods. First the screen is brightened and the response time is measured as in cathode ray timing, but the computer measures only which scanline was hit and not which horizontal pixel was hit. This does not need nearly as fast a timer that pure cathode ray timing uses, on the order of 15 kHz for Y vs. 5 MHz for (X, Y) on a standard resolution display. Then using sequential targets, the game cycles among those targets on the line.

Infrared emitters

A new method was developed to compensate for display technologies other than CRT. It relies on one or several infrared light emitters placed near the screen, and one IR sensor on the muzzle of the gun. When the trigger is pressed, the gun sends the intensity of the IR beam it detects. Since this intensity depends upon both distance and relative angle to the screen, angle sensors are located in the gun. This way a trigonometric equation system is solved, and the muzzle's 3D position relative to the screen is calculated. Then, by projecting the muzzle on the screen with the measured angles the impact point is determined. An early example of this technology (though not using IR) can be seen in the NES Power Glove Accessory, which used three ultrasonic sensors serving the same function as the IR emitters used in some lightguns.

A simpler variant is commonly used in arcades, where there are no angle detectors but 4 IR sensors. However, this can prove inaccurate when shooting from certain distances and angles, since the calculation of angles and 3D position has a larger margin of error.

Other variants include 3 or more emitters with different infrared wavelengths and the same number of sensors. With this method and proper calibration three or more relative angles are obtained, thus not needing angle detectors to position the gun.

Sometimes, the sensors are placed around the screen and the emitter on the gun, but calculations are similar.

This family of methods are used for the Wii Remote, Guncon 3, [ [http://kotaku.com/gaming/reload/how-the-time-crisis-4-light-gun-works-268674.php Reload: How The Time Crisis 4 Light Gun Works ] ] and modern arcade light gun games.

Multiplayer

A game that uses more than one gun reads both triggers continuously and then, when one player pulls a gun's trigger, the game reads that gun until it knows which object was hit.

Positional guns

Positional guns are fairly common in video arcades. A positional gun is a gun mounted to the cabinet on a swivel that allows the player to aim the gun. These are often confused with light guns but work quite differently. These guns may not be removed from the cabinet like the optical counterparts, which are tethered and stored in a mounted holster. They are typically more expensive initially but easier to maintain and repair. Games that use positional guns include "Operation Wolf", "Silent Scope", the arcade version of ', "Space Gun", "Revolution X" and '. The console ports used light guns.

A positional gun is effectively an analog stick that records the position of the gun to determine where the player is aiming. The gun must be calibrated, which usually happens after powering up. Some games have mounted optical guns, such as Exidy's "Crossbow".

See also

* Light gun shooter
* List of light gun games

References