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IDC 2009 – Demos 3-5 June, 2009 – Como, Italy
278
Tangible Optical Chess:
A Laser Strategy Game on an Interactive Tabletop
David Joyner
GVU Center
Georgia Institute of Technology
Atlanta, GA 30332
david.joyner@gatech.edu
Chih-Sung (Andy) Wu
Chih-Sung (Andy) Wu
GVU Center
Georgia Institute of Technology
Atlanta, GA 30332
andywu@gatech.edu
Ellen Yi-Luen Do
Ellen Yi-Luen Do
GVU Center, College of Architecture,
College of Computing
Georgia Institute of Technology
Atlanta, GA 30332
ellendo@gatech.edu
ABSTRACT
This paper presents Tangible Tracking Table, an interactive
tabletop display, and Optical Chess, a strategy game. We discuss
the design and implementation of both systems and report our
evaluation game play sessions with young adults, with a special
focus on how the Tangible Tracking Table enhances interaction
over a point-and-click interface.
Categories and Subject Descriptors
K.8.0 Games, H.5.2 interaction styles
General Terms
Design
Keywords
Game, chess, tabletop, tangible interaction
1. INTRODUCTION
This implementation of Optical Chess unites two discrete systems
into one interactive tabletop game. The Tangible Tracking Table
(TTT) is a physical table with a projected screen that uses
cameras and visual markers to track items placed on it. This
allows a game to be played on a table like board games while a
computer simulates game mechanics. To demonstrate, we chose
Optical Chess, a game that invokes the concept of laser beams
being reflected by mirrors. Laser games [2, 3, 5] and interactive
tabletops [4] are not new ideas, but this combination of the two
provides valuable insight into users' interactions with such
tabletops.
We demonstrated the game to young adults using both a point-
and-click interface and the Tangible Tracking Table, and
observed their interaction with each, noting especially the
instances where interaction with the Tracking Table differed from
interaction with the point-and-click interface. In the vast majority
of observed instances, playing the game using the Tracking Table
provided notable benefits over the point-and-click interface.
2. TANGIBLE OPTICAL CHESS
The initial design of Optical Chess resulted from analysis of
existing games and the game's four goals: (a) to be easy to learn,
(b) to be very difficult to master, (c) to be strictly strategic (no
random element), and (d) to lend itself to complex strategies that
emerge from a simple rule set. This analysis led to the
fundamental building blocks of the game: namely, that the game
will feature lasers, mirrors, and a “King” that will serve as the
target for the opponent.
The transition to an implementation on an interactive tabletop not
only allowed the game to be prototyped relatively easily, but it
also provided valuable insight into how players use the interactive
tabletop to interact with a mechanically simple game.
3. IMPLEMENTATION
Initially, the game was prototyped with a point-and-click interface
to ensure playability. Figure 1 shows the Graphical User Interface
of Optical Chess. The circles represent Kings, the slashes (\ and /)
represent Mirrors in different orientations and the triangles are
symbols for the lasers. The laser beam travels in straight-line and
changes its direction 90 degrees when deflected by a Mirror. A
right click on the chessboard would bring up several options:
add/remove Mirror, add Laser or add King in that location. Here
we see that the red player just placed a Left-Facing (\) Mirror onto
the chessboard. In this version, it allows up to four players to play
the game.
As soon as the game's viability was confirmed, a full
implementation was designed using TTT. Figure 2 shows a play
session with many physical game pieces placed on the TTT.
These tangible game pieces are placed and rotated on the tabletop
by hands. Players can observe the paths of laser beams displayed
on the TTT tabletop.
3.1 The Tangible Tracking Table
The Tangible Tracking Table is an interactive table runs on a
modified version of the reacTIVision system [1], with a library of
unique visual fiducial markers that can be attached to the base of
tangible objects, such as Chess pieces – or, in our case, the tokens
of lasers and mirrors. The table uses Diffused Illumination against
a translucent surface to enable a camera to read the fiducial
markers and recognize their identity (that is, which item is
mapped to which marker), position and angle of rotation. This
information is then passed into the simulation, and the included
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DC 2009, June 3–5, 2009, Como, Italy
Copyright 2009 ACM 978-1-60558-395-2/09/06… $5.00.
IDC 2009 – Demos 3-5 June, 2009 – Como, Italy
279
software places the pieces on a virtual game board and reacts
accordingly.
Figure 1. The GUI prototype of Optical Chess. Players use the
mouse to add chess pieces on the chessboard.
3.2 Game Software
The game software was written in C# and runs in full-screen
mode atop TTT (see Figure 2). The game is based on a simple
grid. Every piece takes up exactly one spot on the grid, and only
one piece can occupy a spot at a time. As such, the table detects
the locations of all the pieces and rounds their locations to the
nearest grid spot, aligning the pieces properly to the grid. The
rotation of the pieces is significant as well; however, the game
rules stipulate that pieces must be placed at one of only two
rotation angles, and as such the game software rounds the rotation
angles of the pieces to the nearest of these two angles.
The game software, in conjunction with the reacTIVision system,
differentiates pieces based on the identity of their fiducial
markers. There are three types of pieces, one King, one Laser and
several Mirrors, and each impacts the simulation differently.
Figure 2. Physical game pieces of Tangible Optical Chess on
the Tangible Tracking Table.
4. EVALUATION
Evaluations of both the point-and-click interface and the Tangible
Tracking Interface versions of Optical Chess have been conducted
during Open House events and informal demonstrations. More
rigorous studies of the table's impact on the game are underway,
but early observations show a difference between the point-and-
click interactions and those with the TTT. In general, the table
provided more useful feedback and allowed players to more easily
understand and plan their strategy.
The most interesting finding came from observations of how
interaction with the table was superior to interaction with the
point-and-click interface. Several problems were observed during
the play sessions with the point-and-click interface. Many players
were unsure which direction to place a mirror to achieve the result
they wanted, and often thought that laser pieces actually took up
board space. Neither issue arose during sessions with the TTT,
suggesting that players benefited from being able to see and
manipulate the three-dimensional, tangible tabletop pieces to
place them in intended positions with ease.
Overall, player interactions with the TTT were observed to be as
simple and intuitive as interacting with a standard board game.
The digital media successfully provided features - such as a
visible laser beam - which are unfeasible in an actual
implementation. The drawbacks at the expense of a standard
board game center around physical needs, and no drawbacks were
observed with regards to actual user interaction
5. DISCUSSION
While the TTT and Optical Chess provide an excellent means
with which to demonstrate one another, the true strength is in the
TTT's enhancement of player interaction with the game.
Introducing physical pieces and a physical board greatly increased
users' ability to understand and extrapolate the impact of moves
on the board compared to a point-and-click interface. More
importantly, the addition of a physical board increases the players'
enjoyment of the game, and removes many of the barriers to
gameplay in order to allow the players to focus on strategy.
6. ACKNOWLEDGEMENTS
We would like to thank Dr. Ali Mazalek and Synaesthetic Media
Lab for the support and resources to develop applications on the
interactive tabletop, and the students of the Fall 2008 Design
Games class for their feedback on the design process.
7. REFERENCES
[1] Kaltenbrunner, M. and Bencina, R., reacTIVision: A
Computer-Vision Framework for Table-Based Tangible
Interaction, In Proc. TEI07, ACM Press (2007), 69-74.
[2] Innovention Toys, Khet, http://www.khet.com/, (2007).
[3] Laser Prisms, http://www.arcadestreet.com/laser-prisms.htm
[4] Mazalek, A., Winegarden, C., Al-Hadded, T., Robinson, S.
& Wu, C., 2009, “Architales: physical/digital co-design of an
interactive story table”, In Proc. of TEI09, ACM Press
(2009), 241-248.
[5] Wilk, Stephen R. "Playing with light: A history of games
that incorporate the photon". In Optics and Photonics News,
OSA, (2007), 18 (10): 18.
