Games with Reality - iPhone Game Blueprints - page 337

Planning game controls
Surprisingly, in most cases, a control system in AR games is not a major issue. Play-
ers move the camera over a virtual scene, so there is no need for special controls to
maneuver in space. Thereby, many AR shooters only have one major button: FIRE .
So, it is more interesting to know about a situation when fiducial markers are turned
into tools to manipulate a game situation.
ThereisadifferencebetweenARonmobiledevicesandsomeacademicexperiments
that use optical head-mounted displays to produce AR. The latter usually needs a
player to hold a gameboard with fiducial markers in his hands, tilting and moving it,
since the gameboard is a way to control objects and events in a game.
A very good example is Marble Game , designed by Ohan Oda and Steve Feiner
at Columbia University's Computer Graphics and User Interfaces Lab ( ht-
tp://www.youtube.com/watch?v=6AKgH4On65A ) , where players needed to guide a
ball through a maze. A special game board with ARTags was used as the physical
base for a virtual game scene. Its tilts were transformed into directions and the value
of "the speed of the ball". Such a method cannot be applied for handheld devices, as
a player cannot hold both the device and the gameboard in his hands for a long period
of time. However, some tricks with movable markers can still be done: a player may
hold the device with one hand and rotate it, or hold the fiducial marker in the other
hand and create a game-like situation. The only issue is that the standard paradigm
says that the marker is the center of a game scene, and by rotating it, you rotate the
whole scene. Since the game should be oriented towards one item rather than being
scene based. For instance, a model of a spherical antenna is used as an AR 3D pup-
pet. The fiducial can be freely rotated on a tabletop by a player, which is followed by
the rotation of the antenna on the screen. The main objective of such a game is to
catch signals from different directions. It is worth mentioning that these signals should
come from the coordinate system of the screen (view orientation) as the local coordin-
ates of the marker are not reliable; they always change their orientation on a surface.