Chessmate

Chessmate is a chess engine written in C++.

It implements the rules of chess and is able to suggest a move using a minimax algoritm.

The move suggestion works as follows:

• calculate all legal moves of the current board state
• for each move, perform it, and repeat these two steps until fixed depth
• then, evaluate the current board position by
  • weighting the pieces (pawn=100, knight=300, bishop=325, rook=500, queen=900)
  • adding weights for each piece, depending on its position using a table
• calculate the board position with the maximum score and suggest the first move leading to this position

We cut out a lot of legal moves by using the alpha-beta pruning algorithm

Server

You can easily integrate this chess engine in your front end using the server that comes with chessmate.

Idea

Each game is associated with a gameID and its state is stored in a json file

Each player is associated with and playerID to prevent cheating (moves can only be performed provided the playerID)

Usage

Create Game

To create a chess game, type the following command:

path/to/server creategame

it responds with something like this:

{"gameID":6737,"success":true}

Join Game

In order to play the game you've created, players must manually join the game.

This is necessary in order to send playerID's to the players.

path/to/server joingame GAME_ID

to join with any free color or

path/to/server -pwhite joingame GAME_ID

path/to/server -pblack joingame GAME_ID

to add a player for white or black.

The server responds with

{"player":"white","playerID":4852,"success":true}

if successfull or

{"error":"game doesn't exist","success":false}

Here's a list of errors that can occur:

• game doesn't exist
  • the provided GAME_ID is not associated with an existing game
• game is full
  • both white and black players already joined the game
• player already joined
  • the specified player (white or black) already joined the game

Game State

In order to get the current game state, type:

path/to/server gamestate GAME_ID

The server responds with something like this:

{
    "gameState": {
        "FEN": "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1",
        "active":"w",
        "castle": ["K","Q","k","q"],
        "halfMoves": 1,
        "inCheck": false,
        "legalMoves": [
            "a2a3", "a2a4", "b2b3", "b2b4", "c2c3", "c2c4", "d2d3", "d2d4", "e2e3", "e2e4",
            "f2f3", "f2f4", "g2g3", "g2g4", "h2h3", "h2h4", "b1c3", "b1a3", "g1h3", "g1f3"
        ],
        "history": [],
        "status": "prepare"
    },
    "success": true
}

This is how the response can be interpreted:

• FEN: the FEN code of the current game state
• active: active player ("w" for white and "b" for black)
• castle: a list of available castles ("K" white kingside, "Q" white queenside, "k" black kingside, "q" black queenside)
• halfMoves: count of halfmoves already played
• inCheck: true if the active player is in check
• legalMoves: a complete list legal moves the active player can do (following the UCI Standard)
• history: a history of all moves already played in chronological order (UCI Standard)
• status:
  • "prepare" if at least one player hasn't joined
  • "inGame" if all players joined and the game is not over
  • "checkmate" if a player won by checkmate
  • "draw" if the game ended with a draw

Do Move

To do a move, type the following:

path/to/server domove GAME_ID PLAYER_ID MOVE

where MOVE follows the UCI Standard:

• specify start and end square (e.g. e2e4)
• for castling, use the kings origin and destination square (e.g. e1g1 for white kingside)
• for promoting, append the piece character (e.g. e7e8q)

The server responds with something like this

{"success": true}

if successfull or

{"error":"game not full","success":false}

• game not full (at least one player has not joined the game yet)
• wrong playerid provided (the playerID provided doesn't match with the active player)
• invalid move (the move is either in an invalid format or illegal)
• game over (the game already ended, either with checkmate or draw)

Installation

git clone https://github.com/fburgerdev/chessmate.git

You can locate prebuild binaries (debian) in bin/dist, or compile yourself

With Make

cd build && make config=dist -j8

Or with Visual Studio

open build/engine.sln and compile in dist config