Games with Reality - iPhone Game Blueprints - page 329

camera resolution or be destroyed by distorted perspectives. Therefore, to
play from a distance, the markers should be printed or drawn larger.
• Angle : This is critical mainly for planar graphic references. These work suc-
cessfully within the range of the angle between a device and the surface on
which a marker is attached, and it's also correlated with the distance. The
range is pretty comfortable, although if the camera is tilted to an angle great-
er than 90 degrees relative to the reference graphics, the AR may be ruined.
• Environment : For most AR games, flat and empty spaces are required as
the basis for the virtual construction. These may be tabletop surfaces (prefer-
ably without a mess!), floors, walls, and so on. There should also be the op-
portunity to place a marker. It may be hard to get a good background for
the game in crowded places such as public transportation, waiting rooms, or
even working places, because there a lot of objects around. Therefore, many
AR games can be considered as entertainment that is restricted to private
zones, such as living rooms. Only in such environments will players get the
full experience.
• Scale : In some cases, the virtual game world is bigger than its physical coun-
terpartandthiscannotbeadjustedbyplayersinthegame.Thisisbecauseof
some technical issues (for instance, the size of virtual units strongly depends
on the dimensions of the graphic marker), or there may be other reasons that
developers did not include such functionality.
• Boundaries : Ideally, an AR game should track both the fiducial marker as
the most trusted reference point, and the boundaries of the surface that it
is placed on (for instance, to determine the edges of a tabletop or its dis-
tance from walls). However, it is hard not only because of additional technic-
al issues, but also because it raises some big questions about game-level
design. For example, what should the application do with some game ele-
ments placed outside of the boundaries? The logical answer is not to display
them! But that can destroy the total balance of the game! Some sly players
begin cheating, whisking some enemies away from a desk or putting them
behind walls. A boundaries check creates a more flexible structure in game
worlds, AI, and so on, but very often, it is not an option. However, without it
game elements may float in the air because a tabletop was over; such a pic-
ture is not very realistic and players may become frustrated.
• Occlusions : Since games with a single fiducial marker do not scan their sur-
roundings to develop a 3D map, the real-time background through the cam-
era is totally flat. There cannot be an occlusion between a real object in a
scene and a virtual one, even if the real one is situated closer to the player.