A new augmented reality game can run on two Android phones, over 3G or Wi-Fi, without an additional server. The unique networking method used for the game could be quite useful for those working on disaster relief or in the military, where significant infrastructure isn't always available.

Multiplayer games on mobile devices like phones usually require remote servers for communication between devices and game hosting, says Roelof Kemp, a computer scientist at Vrije Universiteit, in Amsterdam, the Netherlands, who codeveloped the game. But the game allows phones to communicate without the cost and added complexity of maintaining this additional infrastructure, he says.

"We hope it's going to open the door for new and interesting distributed computing applications," says Kemp.

The game uses a computing middleware system, called Ibis, originally developed for high-performance, distributed computing tasks, such as image processing or astrophysics research, but which Kemp and colleagues have adapted to run on Android phones. "It allows each phone to run a lightweight communication server," says Kemp. The devices can communicate directly with the game, which is hosted on both handsets, using a 3G connection or Wi-Fi.

Known as Photoshoot, the game offers a modern-day take on the old gun-slinging shootouts of the Wild West by fusing the real world with virtual play. It's simple enough: two players walk three steps away from each other, turn and shoot. But instead of firing bullets, a player tries to shoot a photograph of his opponent, lining up the onscreen crosshairs in the camera's viewfinder with the opponent's face. Each player has up to six shots, and the first to "shoot" their opponent in the face wins.

The game was developed in response to the Android Developers Challenge 2, launched by Google to encourage the development of innovative applications for its Android phones. Consequently, the game was designed to use data fusion, bringing together many different aspects of the device's hardware in order to combine the gameplay with real events in the world.

The accelerometers and digital compass built into Android phones allow the game-- distributed on both phones--to act like the referee, making sure each player has taken three steps and doesn't turn too soon. "And to evaluate if it was a hit or a miss, we use a face-detection algorithm," says Kemp. This works even if the face is partly obscured by the other player holding their phone in front of it, he says.