SwiftChess

SwiftChess is a chess engine written in Swift.

Features

• Move validation
• AI with three difficulty levels
• Callbacks for check, checkmate and stalemate
• Supports castling
• Supports En Passent
• Supports pawn promotion
• Asyncronous AI move calculation

SwiftChess doesn’t provide any UI, just all of the logic required to create a chess game. The example project contains a complete UIKit UI with touch handling that you start from if you like.

Example

The example application contains a complete implementation of SwiftChess.

Run Example/Example.xcodeproj

Basic Use

Start a game

// Make a human player
let whitePlayer = Human(color: .white)

// ... or an AI Player
let blackPlayer = AIPlayer(color: .black, configuration: AIConfiguration(difficulty: .hard))

// Create a game       
let game = Game(firstPlayer: whitePlayer, secondPlayer: blackPlayer)

Make a move

if let player = game.currentPlayer as? Human {

	let currentLocation = BoardLocation(x: 4, y: 1)
	let newLocation = BoardLocation(x: 4, y: 2)

	try! player.movePiece(from: currentLocation,
                        to: newLocation)
}

Tell the AI to make a move

if let player =  game.currentPlayer as? AIPlayer {
	player.makeMoveAsync()
}

Then just wait for the callbacks!

extension GameViewController: GameDelegate {

	func gameDidMovePiece(game: Game, piece: Piece, toLocation: BoardLocation) {
        // Move piece on board
    }
    
    func gameDidRemovePiece(game: Game, piece: Piece, location: BoardLocation) {
        // Remove piece from board 
    }
    
    func gameDidTransformPiece(game: Game, piece: Piece, location: BoardLocation) {
    	// A pawn was promoted!
    }
    
    func gameWonByPlayer(game: Game, player: Player) {
    	ShowAlert("Checkmate!")
    }
    
    func gameEndedInStaleMate(game: Game) {
     	ShowAlert("Stalemate!")
    }
    
    func gameDidChangeCurrentPlayer(game: Game) {
    	// Make another move        
    }
}

Persistence

The entire state of a SwiftChess game can be converted to and initialised from a Dictionary.

Get a snapshot of the current state:

let dictionary: [String: Any] = game.dictionaryRepresentation

Initialise a game with a previous snapshot:

let game = Game(dictionary: dictionary)

The returned dictionary stores all the information required to create a ‘save game’ feature. The player colors, AI difficulty, piece positions etc.

You can serialize this to JSON, save it to disk, send it over the network etc.

Other stuff

Make a castling move

if game.board.canColorCastle(color: .white, side: .kingSide) {
	player.performCastleMove(side: .kingSide)
}

Support pawn promotion

func promotedTypeForPawn(location: BoardLocation, 
                         player: Human, 
                         possiblePromotions: [Piece.PieceType], 
                         callback: @escaping (Piece.PieceType) -> Void) {

	// Show UI for the user to select one of the possible promotion types
	// then call the handler
	
	// ...or some games just promote to a queen
	callback(.queen)
}

Author

Follow me on twitter @SteveBarnegren

License

SwiftChess is available under the MIT license. See the LICENSE file for more info.