Working with the Checkers applet

The Checkers applet enables running a heuristic position evaluation function for the game of checkers, using the MIN-MAX algorithm. The applet provides the user interface to control the settings and the course of the game, the basic minimax algorithm, and also enforces the rules of the game (below). The applet requires Java JRE packages, and JDK to be installed on your system.

Game rules

The applet implements a variant of checkers with the following rules:

• the player with white pieces starts the game,
• pieces can move only one square, and only forward diagonally (the light squares),
• jumping by pieces must be forward; jumping backward by pieces is not allowed,
• jumping is mandatory,
• multiple jumping in one turn is allowed, which is a combination of several jumping moves, each of which is a correct jumping move,
• if there is more than one possibility of jumping, a player may choose any of them; majority jumping rule is not enforced,
• when a piece reaches the furthest rown, it becomes a king,
• a king can move backward or forward, but still only one square diagonally (the light squares)
• a king can capture both forward and backward,
• the object of the game is to deprive the opponent of the possibility to move, either by capturing all the opponent's pieces, or by blocking them,
• a draw occurs if the players perform sixty moves without jumping, or if the repeat a sequence of six moves, ie, one player moves, then the opponent moves, then the first player backtracks the last move (with a king), the opponent also backtracks her move, and the first player repeats the original move, and so does the opponent,

Heuristic function API

The interface of the heuristic function required by an applet, is described in the comment of a sample function, which can be loaded into the editor while running the applet (both Java and Javascript).

User Interface

Game modes

• 'Manual',
• 'Internal function' - a function implemented in the applet,
• 'User function 1' - the first member function,
• 'User function 2' - the second user function.

Game modes are selected separately for the top and bottom player.

Board position

It is possible to turn the board around by clicking 'Turn board around'.

The level of analysis

The box 'Level' allows you to choose the level of computation in the Min-Max algorithm.

Running tests

A series of games can be run in sequence by setting the value of 'Number of tests'.

Starting/Stopping the game

The 'Play'/'Pause' enables to run the algorithm for the preset game parameters.

Animation

The applet allows to view a simulation game in several modes:

• full - full of animation,
• fast - fast animation,
• result only - only display the terminal state of the game,
• off - no animation.

The speed of the game

Changing the speed of the game is possible using the box 'game speed'.

Event Log

In the bottom left of the applet's display area is the space for showing the events of the game. The log can be enabled ('Log' set to 'on') or disabled ('Log' set to 'off'). It is possible to record the event log on a file. To do this, select 'save' from the 'Log' menu.

Board editor

Clicking on 'Edit board' enables one to set the initial state of the game. In the course of defining this state, all pieces' color and rank can be set (box 'Color' and 'Figure').

Function Editor

The text box to the right of the applet makes it possible to write user position evaluation functions.

File Operations

During the operation of the applet up to two user functions (Java or Javascript) can be loaded and active. A user can create and use more functions, but they have to be saved to and loaded from disk files with the following operations:

• the 'Open' button to load a text file into the editor,
• the 'Save As ...' function to record the editor contents on a file.

Solutions to problems

In case of problems with compiling Java files on Windows (a 'javac' program is required when applying the user functions), the environment variable PATH must be properly set (no need to remove the defined paths, just add a new one after a semicolon). A quick guide can be found here:
http://tomasz.topa.pl/java/java-dodawanie-zmiennej-srodowiskowej-path

After adding an environment variable, restart the computer in order to load the changes. If it is still not possible to compile the file, it means that the error may be caused by the applet previously placed in the cache. Then, follow these steps:

• clear the cache of the Web browser -> (CTRL + F5) during the browser session,
• open the Java console ('Java' icon in the startmenu -> right button -> 'Java console', or in the browserL 'Tools' -> 'Java console') and type 'x' there,
• restart the browser.

Note!

In the case of errors in the applet log related to the IO access - 'acces denied', which may occur when:

• trying to view the contents of the log (method 'setText')
• using the Math package,
• JavaScript compilation,

the applet can be run from the console (command line) by entering this command:

appletviewer -J-Djava.security.policy=http://sequoia.ict.pwr.wroc.pl/~witold/ai/Checkers/java.policy.applet http://sequoia.ict.pwr.wroc.pl/~witold/ai/Checkers/