LIME

Red Rover: An Interactive Video Game

Introduction

RedRover is a spatial game in which individuals equipped with small mobile devices form teams and interact in a physical environment augmented with virtual elements. This forces the participants to rely to a great extent on information provided by the mobile units and not solely on what is visible to the naked eye.

The key component of RedRover is that players share their physical location in space. Each player has a kind of radar image on their screen which is constantly updated with the locations of (connected) players as they move.

Playing the Game

First compile the RedRover code using the makefile in the examples/redRover directory. Start the game by changing to the bin directory or adding redrover.jar to your classpath, then executing:

java redRover.RedRover <config_file>

Appendix A below contains information about configuration files.

Only one instance of Red Rover can run in each LimeServer, although multiple instances can be run on the same host if you specify different ports as in java redRover.RedRover rr.gp -port 1900.

Note: RedRover places players in a virtual space where coordinates on the screen do not have a direct correlation to location in the physical workd. Although Lime1.1 has support for retrieving location information from GPS untis, RedRover does not access this information. Therefore, RedRover should always be run with engagementMode set to explicit. Further, RedRover does not support the option -engage on.

What to Expect

When the game begins, the user interface appears on your screen similar to the following, but only showing the icon for your player in the center of the screen.

The screen above shows a game involving four players on four computers--two on the red team, and two on the yellow team. The players join the game by pressing their engagement button (see below). This brings us to the nine buttons on the left side of the interface. Each of these buttons has a unique purpose during game play as described below. The first four buttons represent the current state of the GUI and thus only one of these four can be selected at any given time.

The next three buttons work like toggle switches, each controlling a distinct aspect of the game.

The last two buttons deal with looking for and finding objects while playing the game.

The first thing that you will need to do is engage so that you can communicate with the rest of the people in the game. To do this, click on the engage/disengage button. After engaging you will see the other players appear on your screen. You're now ready to play the game!

Game play proceeds as players use the features specified above to move about the map. One of the games you can play with Red Rover is a simple freeze tag where one team is it (see the configuration file). When a player from the it team tags a player on any other team, that player is frozen. A frozen player can be unfrozen by being tagged by a member of his own team.

How Red Rover Uses Lime

When an instance of Red Rover begins, two tuple spaces are created. One is the team tuple space, and one is the game tuple space. The game tuple space is used to communicate with all other agents playing the game. The team tuple space is used to communicate only with agents on the same team. There is a Lime StationaryAgent inside the Red Rover game. It is this agent that allows the players to interact with each other. There are two ways the players communicate with each other. One method is to register weak reactions on the team and/or public tuple spaces as a way of listening for information from other players. The other method is to write tuples to the team and/or public tuple spaces to share information with other players.

After the tuple spaces are set up, the agent registers one weak reaction in the team tuple space and one weak reaction in the public tuple space. These weak reactions will fire whenever a new tuple arrives that should be processed. The reactions then fire an event which is processed by the game.

After the agent registers the weak reactions, it will enter an infinite loop for writing tuples. For each iteration through the loop, the Interactor will wait to dequeue an item from its synchronized queue (the Interactor uses a queue from the Lime API -- gp.util.Queue). Once an item is available from the queue, it will be processed by wrapping it in a tuple and then writing the tuple out to the appropriate tuple space. The tuples that are written out to the tuple space contain information about the Interactor that it would like to share either with everyone or with other agent's on his team. For example, a player might place a location tuple in the tuple space. Then, as he moves, he removes his old location tuple from the tuple space (via an inp operation) and then writes his new location (via an out operation). Other players who would like to know the current location of that player would register a reaction to react to new location tuples of other players. When these reactions are fired, the players' screens are updated with the new information.

Configuration File

Note: A line starting with a pound sign (#) is a comment. 

#####################################################################
# Red Rover properties file
#
# The name of the player. 
# any string value is appropriate. 
name = Player One 

# The team name and also becomes the name of the team
# tuple space. The team name should be one of the following
# colors: blue, green, orange, purple, red or yellow
team = Red

# Specifies whether or not your team is it (in the freeze tag game). 
# Only one team should be it at any given time.
IT=true

# Optional...used to name the public tuple space. If you
# use this then make sure EVERYONE in the game is using the
# same value. The default value is "public".
publicTSName = public

# Optional...Time between network updates of movement events,
# in milliseconds. Default is 1000.
updatetime=1000

# Optional...Distance another player needs to be within in
# order to tag me. Default is 10.0
tagdistance=10.0

# The starting position in space for the player.
# default is random
# startX = 50 
# startY = 20

# The image to appear when a player's icon is clicked on. 
# Can be .gif or .jpg.  Default is none.
# picture = gp1.jpg

LIME: Linda in a Mobile Environment