Janek Schleicher

# NAME

Games::Backgammon - Perl extension for modelling backgammon games

# SYNOPSIS

``````  use Games::Backgammon;

my \$game = Games::Backgammon->new(
position => {
whitepoints => {3 => 1, 4 => 1, 5 => 3, 6 => 3}, # ideal 40 pip position
blackpoints => {4 => 3, 5 => 5, 6 => 7},         # ideal 79 pip position
atroll      => 'black',
}
);

print "Position ID: ", \$game->position_id;
print "Checkers off from white", \$game->whitepoints('off');
print "Now you can do these moves: ", join " ", \$game->legal_moves(2,1);

[NOT IMPLEMENTED YET]

\$game->move('6-off 5-off');

print join "\n",
"Now black has a pip count of " . \$game->blackpips,
"With " . \$game->blackpoints('off') . " checkers off the game";

``````

# DESCRIPTION

This module helps modelling backgammon games. It is not basically intented to play backgammon for itself. I just wrote it to analyze (long) racings in a convenient way.

Most of the routines are just wrappers to the gnubg program of Gary Wong.

## FUNCTIONS

my \$game = Games::Backgammon->new(position => \%pos)

This creates a new backgammon game. At the moment, it's necessary to define the starting position. The reason is that I just have not yet programmed how to do the beginning roll.

Please look to the documentation of set_position for the definition of the position hash.

\$game->set_position(%pos)

Resets the backgammon game to a specific position. You can specify the position of the checkers and who is at the roll. (Of course, in future versions, I'll also add the doubling cube to the position, and the possibility of doubling before a rol).

Thus the position hash has the following outlook:

``````  position => {
whitepoints => {\$point1 => \$nr_of_white_checkers_on_point1,
\$point2 => \$nr_of_white_checkers_on_point2,
...
'bar'   => \$nr_of_white_checkers_on_the_bar},

blackpoints => {\$point1 => \$nr_of_black_checkers_on_point1,
\$point2 => \$nr_of_black_checkers_on_point2,
...
'bar'   => \$nr_of_black_checkers_on_the_bar},

atroll      => 'white'     # or 'black'
}
``````

With the `whitepoints` and <blackpoints> arguments, you can define where the checkers of each side are. The point numbers are always regarded from the player's view. So point x for white is point (25-x) for black. Please take care that black's and white's checkers are not at the same point (what would result in an error). It's also forbidden that both players have a closed board and both players have checkers on the bar. Specifying more than 15 checkers is not allowed.

Please also look also to the following example:

``````  GNU Backgammon  Position ID: sOfgEwDg8+AIBg
+13-14-15-16-17-18------19-20-21-22-23-24-+     O: gnubg
| X        X  O    |   | O  O  X          |     0 Points
| X           O    |   | O  O  X          |
| X           O    |   | O                |
|                  |   | O                |
|                  |   |                  |
v|                  |BAR|                  |     (Doppler: 1)
| O                |   | X                |
| O           X    |   | X                |
| O           X    |   | X                |
| O           X    |   | X                |     At Roll
| O     O     X    |   | X                |     0 Points
+12-11-10--9--8--7-------6--5--4--3--2--1-+     X: janek
Pip counts: O 138, X 159

This interesting position can be defined with (O is white, X is black)

position => {
whitepoints => {5 => 2, 6 => 4,  8 => 3, 13 => 5, 15 => 1},
blackpoints => {6 => 5, 8 => 4, 13 => 3, 16 => 1, 21 => 2},
atroll      => 'black'
}
``````

The number of checkers at the bar is defined with `'bar' =` \$nr_of_checkers_at_bar>,

Note, that you neither needn't nor mustn't define the checkers off the game. (They are simply calculated by the calculation of 15 - checkers still left in the game). The atroll parameter has to be either 'white' or 'black' (whether upper/lower case is unimportant) [the default is 'black'].

This method is unfortunately not explicitly tested (only via the initialization with new).

my %point = \$game->whitepoints; my \$off = \$game->whitepoints('off');

This method returns either the hash with all white points (including the checkers off the game, if there are someones) or the number of checkers at a specific point. The hash is returned when there is no argument specified, while the number of checkers is returned if the point is passed as argument. Note that points without a checker are not represented in the hash.

For further details, please read the documentation of `set_position`.

my %point = \$game->blackpoints; my \$off = \$game->blackpoints('off');

Similar to `whitepoints`.

my \$atroll = \$game->atroll;

Returns the player who is at roll

my \$id = \$game->position_id

Returns the position id of the current position from the view of the player at roll. This id is the same like generated from gnubg. Please look to the documentation of gnubg to get a detailed explanation.

\$game->legal_moves(\$n0, \$n1)

Returning a list of all legal moves in the current position with the roll (\$n0, \$n1). (just a wrapper to gnubg's GenerateMoves) A legal move is only represented by its string representation. It's already a shorted string version.

None by default.

# BUGS

Please inform me about every one you can find.

There could be problems to compile/install this module. I used gcc version 3.2 and I would recommend to have at least 2.95.

# TODO

A lot. I'm working currently on it.

Please feel free to suggest me anything you'll need. (I will do it on the top of my priority list).

My next planned steps are:

Game::Backgammon::ideal_bearoff_position(\$pips)

Returning the ideal bearoff position for a given pip count for one man

Game::Backgammon::one_checker_race(\$whitepip,\$blackpip)

Returning the chances in a one checker race for each position.

Alltough, I have not yet implemented many functions of gnubg, I have bundled whole the project with this module. I plan to implement soon many more functions, and currently I want to see whether the bundling also works with CPAN.