/// <summary>
/// Function to evaluate the value of the state (Evaluation function)
/// </summary>
/// <param name="state">The state to be evaluated</param>
/// <returns>The value of the state</returns>
public int Evaluate(CheckersGameState state)
{
PieceColor winner = state.winner;
//white is winner, if ai is white, then return max_int else return min_int
if (winner == PieceColor.White)
{
return((state.aiColor == PieceColor.White) ? MAX_INT : MIN_INT);
}
//Find out that white is winner, if ai is white, then return max_int else return min_int
else if (winner == PieceColor.Black)
{
return((state.aiColor == PieceColor.White) ? MIN_INT : MAX_INT);
}
//return the custom designed evaluation function
//The states are evaluated by the difference in pieces left weighted by the number of turns that has occured
//Every 4 turns the weight of difference in pieces goes up
else
{
if (state.aiColor == PieceColor.White)
{
return((int)(state.whiteGamePieces.Count - state.blackGamePieces.Count) * (int)(1 + state.numTurnsPassed * 0.25));
}
else
{
return((int)(state.blackGamePieces.Count - state.whiteGamePieces.Count) * (int)(1 + state.numTurnsPassed * 0.25));
}
}
}
/// <summary>
/// Function called to initialize a new checkers game
/// </summary>
public void initComponent()
{
isMousePressed = false;
didAiMove = false;
currentState = new CheckersGameState(PieceColor.None);
blackButton = new Rectangle(25, 640, 150, 40);
whiteButton = new Rectangle(200, 640, 150, 40);
}
/// <summary>
/// Function that starts a new game for the player given the player color
/// </summary>
/// <param name="playerColor">Color of the player</param>
public void newGame(PieceColor playerColor)
{
Console.WriteLine("========================================================"
+ "\n NEW GAME "
+ "\n========================================================");
iterativeDepth = 0;
currentState = new CheckersGameState(playerColor);
}
/// <summary>
/// Max value search function
/// </summary>
/// <param name="state">The current state of the game</param>
/// <param name="alpha">highest alpha found</param>
/// <param name="beta">lowest beta found</param>
/// <param name="depth">depth current state is at</param>
/// <returns>The best max value</returns>
public int MaxValue(CheckersGameState state, int alpha, int beta, int depth)
{
//increase depth
depth++;
maxDepth = (depth > maxDepth) ? depth : maxDepth;
//Evaluate the state
int utilityValue = Evaluate(state);
//If the state is terminal or if the cuttoff is reached, return the value
if (utilityValue == MAX_INT || utilityValue == MIN_INT ||
depth == cutoff + iterativeDepth || (DateTime.Now - startTime).TotalSeconds > 55)
{
return(utilityValue);
}
//integer value used to determine alpha
int value = MIN_INT;
//A temporary gamestate to prevent anything in the actual game from changing
CheckersGameState tempState;
//The loop below finds every possible action from this state,
//then using the temporary state, it will do the action,
//and pass that state into the minValue function to find the largest possible value for alpha
foreach (CheckersPiece piece in state.moveablePieces)
{
state.doGamePieceAction(piece);
foreach (GameMove action in state.activeGamePiece.getPossibleMoves())
{
tempState = new CheckersGameState(state);
nodes++;
if (tempState.doTileAction(tempState.gameBoard.getTileAt(action.destinationPosition)) == true)
{
tempState.activeGamePiece.Update(tempState);
}
value = Math.Max(value, MinValue(tempState, alpha, beta, depth));
//if alpha becomes greater than or equal to beta prune the tree
if (value >= beta)
{
maxPruned++;
return(value);
}
if (alpha < value)
{
alpha = value;
//if we are in the actual state of the game, that means we found a new best move
if (depth == 1)
{
bestMove = action;
}
}
}
}
return(value);
}
/// <summary>
/// Function that will determine all possible moves for the piece
/// </summary>
/// <param name="gameBoard">The gameboard</param>
/// <param name="gameState">The current state of the game</param>
/// <param name="noShow">Whether or not to mark the board</param>
/// <returns>Type of move the piece has (NONE, MOVE, JUMP)</returns>
public TileStatus determineMoves(CheckersBoard gameBoard, CheckersGameState gameState, bool noShow = false)
{
TileStatus foundMove = TileStatus.NONE;
possibleMoves.Clear();
Vector2 tilePosition = new Vector2(position.X, position.Y);
List <GameMove> jumps = getJumps(tilePosition, gameBoard, gameState);
//Look for any jumps by the piece
if (jumps.Count != 0)
{
foundMove = TileStatus.JUMP;
possibleMoves = jumps;
gameState.jumpExists = true;
//Reset that the piece was just jumped over
//Necessary for multi-jumps
if (color == PieceColor.Black)
{
foreach (CheckersPiece piece in gameState.whiteGamePieces)
{
piece.justJumpedOver = false;
}
}
else if (color == PieceColor.White)
{
foreach (CheckersPiece piece in gameState.blackGamePieces)
{
piece.justJumpedOver = false;
}
}
}
//If no jump was found in the context of the turn find possible regular moves for the piece
else if (gameState.jumpExists == false)
{
List <GameMove> regularMoves = getRegularMoves(tilePosition, gameBoard, gameState);
if (regularMoves.Count != 0)
{
foundMove = TileStatus.MOVE;
possibleMoves = regularMoves;
}
}
if (noShow == false)
{
gameBoard.clearMarkings();
if (foundMove != TileStatus.NONE)
{
foreach (GameMove move in possibleMoves)
{
gameBoard.getTileAt(move.destinationPosition).setStatus(foundMove);
}
}
}
return(foundMove);
}
/// <summary>
/// Main alpha-beta search algorithm
/// </summary>
/// <param name="state">The current state of the game</param>
/// <returns>The value for the best next move</returns>
public int AlphaBetaSearch(CheckersGameState state)
{
//Initialize all the variables to be used in the algorithm
int alpha = MIN_INT;
int beta = MAX_INT;
nodes = 0;
maxDepth = 0;
maxPruned = 0;
minPruned = 0;
startTime = DateTime.Now;
int value = MaxValue(state, alpha, beta, 0);
endTime = DateTime.Now;
return(value);
}
/// <summary>
/// Function handles the updating of checkers piece.
/// This function is called whenever a successful move is done.
/// This function will update the piece's position on the board, and change who's turn it is.
/// </summary>
/// <param name="gameState">The gamestate to update</param>
public void Update(CheckersGameState gameState)
{
if (destination != Vector2.Zero)
{
position = destination;
destination = Vector2.Zero;
if (gameState.turnColor == PieceColor.Black)
{
gameState.changePlayerTurn(PieceColor.White);
}
else
{
gameState.changePlayerTurn(PieceColor.Black);
}
}
}
/// <summary>
/// Copy constructor to make a new copy of this current state
/// This constructor is used to create temporary states in the ai.
/// </summary>
/// <param name="gameState">The state to be copied</param>
public CheckersGameState(CheckersGameState gameState)
{
whiteGamePieces = new List <CheckersPiece>();
blackGamePieces = new List <CheckersPiece>();
moveablePieces = new List <CheckersPiece>();
gameBoard = new CheckersBoard(gameState.gameBoard);
foreach (CheckersPiece piece in gameState.blackGamePieces)
{
CheckersPiece newPiece = new CheckersPiece(piece);
//find the active game piece
if (gameState.activeGamePiece != null && newPiece.position == gameState.activeGamePiece.position)
{
activeGamePiece = newPiece;
}
blackGamePieces.Add(newPiece);
}
foreach (CheckersPiece piece in gameState.whiteGamePieces)
{
CheckersPiece newPiece = new CheckersPiece(piece);
//find the active game piece
if (gameState.activeGamePiece != null && newPiece.position == gameState.activeGamePiece.position)
{
activeGamePiece = newPiece;
}
whiteGamePieces.Add(newPiece);
}
foreach (CheckersPiece piece in gameState.moveablePieces)
{
CheckersPiece newPiece = new CheckersPiece(piece);
moveablePieces.Add(newPiece);
}
playerColor = gameState.playerColor;
aiColor = gameState.aiColor;
turnColor = gameState.turnColor;
jumpExists = gameState.jumpExists;
winner = gameState.winner;
numTurnsPassed = gameState.numTurnsPassed;
}
/// <summary>
/// Function that will find all regular moves for this piece
/// A regular move is a non-jump move
/// </summary>
/// <param name="tilePosition">The position of the tile to check jumps from</param>
/// <param name="gameBoard">The gameboard</param>
/// <param name="gameState">The current gamestate</param>
/// <returns>A list of possible regular moves</returns>
public List <GameMove> getRegularMoves(Vector2 tilePosition, CheckersBoard gameBoard, CheckersGameState gameState)
{
List <GameMove> regularMoves = new List <GameMove>();
//Below is the logic for if the checkers piece is black
if (color == PieceColor.Black)
{
//Get the two possible tiles a black piece could move to
BoardTile topLeftTile = gameBoard.getTileAt((int)tilePosition.X - 1, (int)tilePosition.Y - 1);
BoardTile topRightTile = gameBoard.getTileAt((int)tilePosition.X + 1, (int)tilePosition.Y - 1);
//If the tile exists on the board, add that tile as a possible move
if (topLeftTile != null && topLeftTile.getOccupiedStatus() == PieceColor.None)
{
regularMoves.Add(new GameMove(this, topLeftTile.position));
}
if (topRightTile != null && topRightTile.getOccupiedStatus() == PieceColor.None)
{
regularMoves.Add(new GameMove(this, topRightTile.position));
}
}
//Below is the logic for if the checkers piece is white
if (color == PieceColor.White)
{
//Get the two possible tiles a black piece could move to
BoardTile bottomLeftTile = gameBoard.getTileAt((int)tilePosition.X - 1, (int)tilePosition.Y + 1);
BoardTile bottomRightTile = gameBoard.getTileAt((int)tilePosition.X + 1, (int)tilePosition.Y + 1);
//If the tile exists on the board, add that tile as a possible move
if (bottomLeftTile != null && bottomLeftTile.getOccupiedStatus() == PieceColor.None)
{
regularMoves.Add(new GameMove(this, bottomLeftTile.position));
}
if (bottomRightTile != null && bottomRightTile.getOccupiedStatus() == PieceColor.None)
{
regularMoves.Add(new GameMove(this, bottomRightTile.position));
}
}
return(regularMoves);
}
/// <summary>
/// Function that will recursively find all the jump sequences possible by this piece
/// </summary>
/// <param name="tilePosition">The position of the tile to check jumps from</param>
/// <param name="gameBoard">The gameboard</param>
/// <param name="gameState">The current gamestate</param>
/// <returns>A list of possible jumps</returns>
public List <GameMove> getJumps(Vector2 tilePosition, CheckersBoard gameBoard, CheckersGameState gameState)
{
List <GameMove> jumps = new List <GameMove>();
//Get all the possible tiles that could result with a jump
BoardTile topLeftTile = gameBoard.getTileAt((int)tilePosition.X - 1, (int)tilePosition.Y - 1);
BoardTile topRightTile = gameBoard.getTileAt((int)tilePosition.X + 1, (int)tilePosition.Y - 1);
BoardTile bottomLeftTile = gameBoard.getTileAt((int)tilePosition.X - 1, (int)tilePosition.Y + 1);
BoardTile bottomRightTile = gameBoard.getTileAt((int)tilePosition.X + 1, (int)tilePosition.Y + 1);
BoardTile topLeftJumpTile = gameBoard.getTileAt((int)tilePosition.X - 2, (int)tilePosition.Y - 2);
BoardTile topRightJumpTile = gameBoard.getTileAt((int)tilePosition.X + 2, (int)tilePosition.Y - 2);
BoardTile bottomLeftJumpTile = gameBoard.getTileAt((int)tilePosition.X - 2, (int)tilePosition.Y + 2);
BoardTile bottomRightJumpTile = gameBoard.getTileAt((int)tilePosition.X + 2, (int)tilePosition.Y + 2);
//Set the enemy color
PieceColor enemyColor;
if (this.color == PieceColor.Black)
{
enemyColor = PieceColor.White;
}
else
{
enemyColor = PieceColor.Black;
}
//The below four if-elses will basically determine if there was a piece of the enemy color was jumped over
//by moving to a tile 2 diagonal tiles away. If there was a jump, it will mark the piece that it just jumped over
//and then recursively look for any other following jumps from that tile.
if (topLeftTile != null && topLeftTile.getOccupiedStatus() == enemyColor)
{
//Get the piece that was jumped over
CheckersPiece adjacentPiece = gameState.getPiece(enemyColor, topLeftTile.position);
if (topLeftJumpTile != null && topLeftJumpTile.getOccupiedStatus() == PieceColor.None && adjacentPiece.justJumpedOver == false)
{
//mark the piece as jumped over
adjacentPiece.justJumpedOver = true;
//Find any jumps from the new tile position
List <GameMove> sequenceJumps = getJumps(topLeftJumpTile.position, gameBoard, gameState);
//If there was no following jump then add the jump to the list of jump
if (sequenceJumps.Count == 0)
{
GameMove newJump = (new GameMove(this, topLeftJumpTile.position));
newJump.capturedPieces.Add(adjacentPiece);
jumps.Add(newJump);
}
//Else for each following jump, add the piece the first jump captured to the list of captured pieces
else
{
foreach (GameMove jump in sequenceJumps)
{
//GameMove newJump = (new GameMove(this, jump.destinationPosition));
//jump.capturedPieces = jump.capturedPieces;
jump.capturedPieces.Add(adjacentPiece);
jumps.Add(jump);
}
}
}
}
if (topRightTile != null && topRightTile.getOccupiedStatus() == enemyColor)
{
CheckersPiece adjacentPiece = gameState.getPiece(enemyColor, topRightTile.position);
if (topRightJumpTile != null && topRightJumpTile.getOccupiedStatus() == PieceColor.None && adjacentPiece.justJumpedOver == false)
{
//get any jumps from that tile
adjacentPiece.justJumpedOver = true;
List <GameMove> sequenceJumps = getJumps(topRightJumpTile.position, gameBoard, gameState);
if (sequenceJumps.Count == 0)
{
GameMove newJump = (new GameMove(this, topRightJumpTile.position));
newJump.capturedPieces.Add(adjacentPiece);
jumps.Add(newJump);
}
else
{
foreach (GameMove jump in sequenceJumps)
{
GameMove newJump = (new GameMove(this, jump.destinationPosition));
newJump.capturedPieces = jump.capturedPieces;
newJump.capturedPieces.Add(adjacentPiece);
jumps.Add(newJump);
}
}
}
}
if (bottomLeftTile != null && bottomLeftTile.getOccupiedStatus() == enemyColor)
{
CheckersPiece adjacentPiece = gameState.getPiece(enemyColor, bottomLeftTile.position);
if (bottomLeftJumpTile != null && bottomLeftJumpTile.getOccupiedStatus() == PieceColor.None && adjacentPiece.justJumpedOver == false)
{
//get any jumps from that tile
adjacentPiece.justJumpedOver = true;
List <GameMove> sequenceJumps = getJumps(bottomLeftJumpTile.position, gameBoard, gameState);
if (sequenceJumps.Count == 0)
{
GameMove newJump = (new GameMove(this, bottomLeftJumpTile.position));
newJump.capturedPieces.Add(adjacentPiece);
jumps.Add(newJump);
}
else
{
foreach (GameMove jump in sequenceJumps)
{
GameMove newJump = (new GameMove(this, jump.destinationPosition));
newJump.capturedPieces = jump.capturedPieces;
newJump.capturedPieces.Add(adjacentPiece);
jumps.Add(newJump);
}
}
}
}
if (bottomRightTile != null && bottomRightTile.getOccupiedStatus() == enemyColor)
{
CheckersPiece adjacentPiece = gameState.getPiece(enemyColor, bottomRightTile.position);
if (bottomRightJumpTile != null && bottomRightJumpTile.getOccupiedStatus() == PieceColor.None && adjacentPiece.justJumpedOver == false)
{
//get any jumps from that tile
adjacentPiece.justJumpedOver = true;
List <GameMove> sequenceJumps = getJumps(bottomRightJumpTile.position, gameBoard, gameState);
if (sequenceJumps.Count == 0)
{
GameMove newJump = (new GameMove(this, bottomRightJumpTile.position));
newJump.capturedPieces.Add(adjacentPiece);
jumps.Add(newJump);
}
else
{
foreach (GameMove jump in sequenceJumps)
{
GameMove newJump = (new GameMove(this, jump.destinationPosition));
newJump.capturedPieces = jump.capturedPieces;
newJump.capturedPieces.Add(adjacentPiece);
jumps.Add(newJump);
}
}
}
}
return(jumps);
}