Duality is a minigame in Grand Theft Auto: San Andreas, available in the form of one of the game's four arcade games. Duality arcade machines are scattered throughout interiors of buildings in San Andreas, including bars, nightclubs, 24-7 stores and Madd Dogg's Crib. This game is similar to Twins Minigame in Windows Phone.
The core mechanics of Duality in similar to Asteroids in which the player must control a ship in a 2-D space while obstacles approach the ship; the ship is capable of firing ammunition and activating its rocket booster for propulsion, both at the cost of energy represented by a green bar (which will refill after a short time without use), while also featuring a red bar to indicate the ship's health.
As opposed to simply destroying approaching objects, gameplay in Duality is centered around the concept of attaining "Black" (negative) or "White" (positive) points, represented by small and large spheres colored black and white that the player's ship may encounter:
- Larger spheres have their own gravitational force that affect movement of the player's ship; white spheres push the player away while black ones pull the player towards them. If the ship touches a large black sphere, the ship's health will deplete and eventually result in the ship exploding, ending the game; in contrast, any chance contact with the white sphere will replenish the ship's health. The player may shoot any large sphere for points — destroying a black sphere will award the player 10 "white" points while destroying a white one will award the player with 10 "black" points.
- Smaller spheres are actually indestructible pickups that replenish the ship's energy bar, but their effect on the player's score varies between black and white. Contact with a white sphere will award the player 5 "white" points, while black ones award the player 5 "black" points.
If the player has a white score, the player will lose one white point for each bullet shot, thus requiring the player employ some degree of precision to maintain their score count.
With these rules in mind, the player can choose to aim for a high "white" score or a high "black" score, each presenting slightly different challenges to the player; gameplay prioritizing white high scores tend to be easier as there is no significant penalty to destroy black spheres, gameplay prioritizing black high scores however discourage destruction of black spheres but impose no score penalty firing ammunition. It is also for this reason that the game keeps tabs for both the 10 highest "white" scores and the 10 highest "black" scores, the only minigame in the GTA series to have two hi-score lists.