A light gun is a pointing device for computers and a control device for arcade and video games, typically shaped to resemble a pistol.
Modern screen-based light guns work by building an optical sensor into the gun, which receives its input from the light emitted by on-screen target(s). The first device of this type, the light pen, was used on the MIT Whirlwind computer.
The light gun and its ancestor the light pen are now rarely used as pointing devices due largely to the popularity of the mouse and changes in monitor display technologyâ€"conventional light guns work only with CRT monitors.
Early history
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.
These games evolved throughout subsequent decades, culminating in Sega's Periscope, the company's first successful game released in 1966, which required the player to target cardboard ships. Periscope was an early electro-mechanical game, and the first arcade game to cost a quarter per play. Sega's 1969 game Missile featured electronic sound and a moving film strip to represent the targets on a projection screen, and their 1972 game Killer Shark featured a mounted light gun that shot at targets whose movement and reactions were displayed using back image projection onto a screen. Nintendo released the Beam Gun in 1970 and the Laser Clay Shooting System in 1973, followed in 1974 by the arcade game Wild Gunman, which used video projection to display the target on the screen. In 1975, Sega released the early co-operative light gun shooters Balloon Gun and Bullet Mark.
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. The first gun for a home console was in fact a big rifle, the Magnavox Odyssey's Shooting Gallery, which looked very lifelike and even needed to be "cocked" after each shot.
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), Mega Drive/Genesis, Super Nintendo Entertainment System (SNES) systems and Atari XEGS. Many home 'Pong' systems of the 1970s included a pistol or gun for shooting simple targets on screen. Nintendo's NES Zapper for the NES is the most popular example of the light gun, and Duck Hunt its most popular game.
Traditional light guns cannot be used on the newer LCD and plasma screens, and have problems with projection screens.
There are also light guns for Sega Saturn, PlayStation and several other console and arcade systems. Recent light gun video games include Resident Evil: The Umbrella Chronicles, Time Crisis 4, Virtua Cop 3, and The House of the Dead: Overkill.
In 2007, Nintendo released the Wii Zapper for the Wii, a peripheral which is actually a plastic shell that houses both the Wii Remote and nunchuk for gun-style video games. While it does not contain any traditional light gun technology, the peripheral makes use of the Wii Remote's built-in infrared tracking system to shoot targets that correspond on-screen. Its name is a reference to the classic NES Zapper for the Nintendo Entertainment System. Sony have also released attachments that house the PlayStation Move motion controller in the form of a pistol and rifle, the latter named the Sharp Shooter.
Namco's GunCon 3 also uses an infrared optical sensor system similar to the Wii Remote.
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), then that is the target at which the gun is pointed. Essentially, the diode tells the computer whether or not the player hit something, and for n objects, the sequence of the drawing of the targets tell the computer which target the player 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).
A side effect of this is that on poorly designed games, often a player can point the gun at a light bulb or other bright light source, pull the trigger, and cause the system to falsely detect a hit on 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's green/blue pixels somewhat when the trigger is pulled in order to get a more reliable fix on the position.
Display timing is not possible with plasma, LCD, and DLP monitors, since they do not have an "off" state between refreshes. Their digital signal processing electronics also may introduce a nontrivial lag between the signal input and display output, which is not predictable because it varies between monitor models and brands and even between mode settings of a single monitor. A lag which is not very significant for player feedback may be enough to completely destroy the accuracy of a display-timing based light gun system.
Combined method
Some light guns designed for sequential targeting are not timed precisely enough to get the (X, Y) reading of the video signal, but they can use a combination of sequential targeting with cathode ray timing. 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 15Â kHz for Y vs. 5Â 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.
The Wii Remote uses an infrared video camera in the handheld controller, rather than a simple sensor.
This family of methods are used for the Wii Remote, GunCon 3, and modern arcade light gun games.
The downside of this method is that it's not as accurate as a traditional light gun. The additional IR image processing results in lag or "cursor drift", i.e. when quickly sweeping the light gun across the screen the crosshair will seem to drag slightly behind where the light gun is actually pointing.
Image capture
When the user pulls the trigger the screen is replaced for a split-second with a seemingly random display of black and white pixels, or groups of pixels (blocks). The light gun contains a fine-resolution but low pixel count digital camera with a very narrow field of view. With just a handful of the dot image pixels captured, the gun converts the small image into a binary array which allows the computer to locate the exact position the gun was pointed at. This method is compatible with any screen of any size. The size of the screen and distance to shooter is entered into the gun driver software to determine the dimensions of the random blocks/pixels to best allow rendering on the light gun CCD.
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 their 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 Silent Scope, the arcade version of Resident Evil Survivor 2, Space Gun, Revolution X, and Terminator 2: Judgment Day. Console ports sometimes use light guns.
A positional gun is essentially an analog joystick that records the position of the gun to determine where the player is aiming on the screen. The gun must be calibrated, which usually happens after powering up. Early examples of a positional gun include Sega's Sea Devil in 1972, Taito's Attack in 1976 and Cross Fire in 1977, and Nintendo's Battle Shark in 1978. Some games, however, have mounted optical guns, such as Exidy's Crossbow.
Light gun models
See also
- Light gun shooter
- List of light gun games
