''' Chess program '' Written by KC Goldberg and Sons, November, 2004 '' Written in SmallBASIC for Windows, 0.9.5.2 '' This program was written as a teaching example for me and my sons '' We used SmallBASIC mostly because it is cool and free. For this particular '' application, the array structure (including nested arrays) and the ability '' of functions to return an array make this almost LISP-like, which is perfect '' for turn-based games and the MiniMax algorithm '' In addition to the rich array strucure, there is a simple mechanism to '' capture both console input and mouse clicks, and a very accessible '' graphics primitives package. '' Finally, although I have not done this, the ability to port this to my '' PalmPilot is just too cool! '' The program here will either ask the user to make a move using a '' "click on the board" interface, or generate one itself using the '' MiniMax algorithm. '' Due to performance problems, this game is just too slow to '' use for good computer AI. On my fast system, a level 2 ply depth is '' barely playable '' Also, in many places the code is far from elegant. I would like to blame '' a lot of that on the complications of the rules of chess, making it quite '' difficult to generate generalized rules and routines, and some of it on '' my not spending the time to tighten it up. '' As near as I can tell, the code is correct. However, this has not '' been ''professionally'' tested. In about 20 games, I have only seen '' legal moves allowed. You mileage may vary! '' ===================================================================== '' Data types: '' Board: Array Squares x Squares of pieces '' B(1,1) = lower left '' B(Squares,Squares) = upper right '' BoardSet: Array of 4 arrays '' 1st is a Board '' 2nd is a 6-value array of true-false values: '' Black Rook/King/Rook, White Rook/King/Rook '' This value is True if they have not been '' moved, and False once the appropriate piece has been moved '' This is used to see if castling is still possible '' 3rd is the last Move made in the board (to check for en passant) '' 4th is a KingPosition array; although we could just search the BOARD for '' the King, since the King position is used repeatedly to detect the '' CHECK status, it saves time to keep track of the Kings separately '' KingPosition: Array{Black .. White] of (x,y) : Lists current King positions '' Side: [Black, White] ; -1 for Dark, 1 for light '' Piece: Integer; see constants below for piece each value represents '' (Side * Piece) denotes color of piece '' Move: Array of 4x1 listing coordinates (from, to) e.g. [x1,y1,x2,y2] '' Castling is denoted by the KING move (the king ONLY moves 2 squares '' during castling, although rooks may move two/three moves with or without '' a castle '' MoveArray: An array of Moves, e.g.[[1,1,2,2],[1,2,1,4],[8,2,8,3]] '' MiniMaxResult: [Score, Move] where score is a numeric board evaluation Score '' =========================================================================== '' Procedures: '' DisplayBoard (BoardSet) : Display a board '' Main : Main procedure loop '' Functions: '' MakeMove (BoardSet, MoveList, ShowMoves) = BoardSet : Apply a MoveList to a Board '' If ShowMoves = TRUE then display the moves as we make them '' This procedure will also promote pawns to queesn if appropriate, manage castling, '' and keep the components of the BoardSet updated '' If does NOT do error checking - be sure the move passed is correct/legal! '' GenerateMoveList (BoardSet, Side) = MoveArray : Generate list of all valid moves for Side '' GetUserMove (BoardSet, Side) = Move : Ask user to move for Side '' InitBoard = BoardSet : Return a new board with pieces in initial position '' Func MiniMax(BoardSet, Side, Depth, DepthMax, Evaluator) = MiniMaxResult '' : Perform MiniMax algorithm search to find best move for Side (see declaration '' for description of all parameters) '' EvaluateBoard (BoardSet, Side, Evaluator) = Score : Return a numeric score with positive '' numbers favoring Side using the evaluation function specified by Evaluator '' This should only be called from within MiniMax; technically I should probably make '' it a private function of Minimax, but as it too has private functions, that seemed '' like a lot of overhead for Minimax, which will be called recursively '' DetermineMove (BoardSet, Side) = Move : Use the method stored in PlayerStrategy(Side) '' to determine the next move for Side to make '' IsCheck(Boardm KingPosition, Side) = Boolean : Returns True if side SIDE is in check, else false '' '' =================================================================== '' =================================================================== '' Constants '' Size of the board (default = 8 for standard board - don''t change this!) Const Squares = 8 '' These constants denote what occupies a piece on any board square Const Pawn = 1 Const Bishop = 2 Const Knight = 3 Const Rook = 4 Const Queen = 5 Const King = 6 Const Blank = 0 '' This defines the sides Const Black = -1 Const White = 1 '' Figure out how big the boxes should be for graphical display, in pixels '' (board will be square) Const BoxSize = (Min(xmax, ymax - 3 * TextHeight ("TO MOVE")) / Squares) '' Colors for display '' Color of board squares (background) Const ColorDarkSquare = 8 '' Dark gray Const ColorLightSquare =7 '' Light gray Const ColorSelect = 1 '' Deep Blue Const ColorSelectFinal = 9 '' Bright blue Const ColorCheck = 12 '' Bright red '' Color of pieces on squares Const ColorBlack = 0 '' Black Const ColorWhite = 15 '' White '' ========================================================================= '' ========================================================================= '' ------------------------------------------------------------------------- '' ------------------------------------------------------------------------- '' This will Generate a BoardSet to the game starting values Func InitBoard '' Variables we will be using Local x, y, Board, CanCastle, KingPosition Dim Board (1 to Squares, 1 to Squares) '' Initially, rooks and kings for both sides have not been moved '' BR BK BR WR WK WR CanCastle = [True, True, True, True, True, True] '' List the initial position of the Black and White Kings Dim KingPosition(Black to White,1) KingPosition(Black,0) = 5 KingPosition(Black,1) = 8 KingPosition(White,0) = 5 KingPosition(White,1) = 1 For x = 1 to Squares '' Second, second-to-last rows are Pawns Board (x, 2) = Pawn * White Board (x, 7) = Pawn * Black '' Middle squares are Blank For y = 3 to 6 Board (x, y) = Blank Next y Next x '' Now, hand-code in first and last row Board (1,1) = Rook * White : Board (1,8) = Rook * Black Board (2,1) = Knight * White : Board (2,8) = Knight * Black Board (3,1) = Bishop * White : Board (3,8) = Bishop * Black Board (4,1) = Queen * White : Board (4,8) = Queen * Black Board (5,1) = King * White : Board (5,8) = King * Black Board (6,1) = Bishop * White : Board (6,8) = Bishop * Black Board (7,1) = Knight * White : Board (7,8) = Knight * Black Board (8,1) = Rook * White : Board (8,8) = Rook * Black '' Return type BoardSet InitBoard = [Board, CanCastle, [0,0,0,0], KingPosition] End '' ------------------------------------------------------------------------- '' ------------------------------------------------------------------------- '' This routine will display a graphic square with the checkers pieces '' kept in board B Sub DisplayBoard (BoardSet) '' Variables we will be using '' x and y for board coordinates Local x, y, Board, PieceColor '' ---------------------------------------------------------------- '' Subroutines to draw specific pieces at coordinates (x,y) for '' Side Sub DrawPawn (x, y, FillColor) '' This is a triangle on top of a circle Local bx, by, PolyArray bx = BoxSize * (x - 1) by = BoxSize * (Squares + 1 - y) '' The triangle base will be 1/3 square width '' the triangle height will be 1/2 square height PolyArray = [[bx + BoxSize / 3, by], & [bx + BoxSize / 2, by - BoxSize / 2], & [bx + 2 * BoxSize / 3, by]] DrawPoly PolyArray Color FillColor Filled '' Draw Circle on top of triangle, with radius = 1/8 window height Circle (bx + BoxSize / 2), (by - BoxSize / 2), BoxSize / 8, & 1, FillColor Filled End '' Sub DrawPawn Sub DrawRook (x, y, FillColor) Local bx, by, dx, dy, PolyArray bx = BoxSize * (x - 1) by = BoxSize * (Squares + 1 - y) dx = BoxSize / 7 dy = BoxSize / 6 PolyArray = [ [bx + 2 * dx, by - 0 * dy], & [bx + 2 * dx, by - 3 * dy], & [bx + 1 * dx, by - 3 * dy], & [bx + 1 * dx, by - 5 * dy], & [bx + 2 * dx, by - 5 * dy], & [bx + 2 * dx, by - 4 * dy], & [bx + 3 * dx, by - 4 * dy], & [bx + 3 * dx, by - 5 * dy], & [bx + 4 * dx, by - 5 * dy], & [bx + 4 * dx, by - 4 * dy], & [bx + 5 * dx, by - 4 * dy], & [bx + 5 * dx, by - 5 * dy], & [bx + 6 * dx, by - 5 * dy], & [bx + 6 * dx, by - 3 * dy], & [bx + 5 * dx, by - 3 * dy], & [bx + 5 * dx, by - 0 * dy] ] DrawPoly PolyArray Color FillColor Filled End '' Sub DrawRook Sub DrawBishop (x, y, FillColor) '' This is a triangle on top of a circle, but bigger than a pawn '' and with a visor slit in the circle Local bx, by, PolyArray bx = BoxSize * (x - 1) by = BoxSize * (Squares + 1 - y) '' The triangle base will be 1/3 square width '' the triangle height will be 2/3 square height PolyArray = [[bx + BoxSize / 3, by], & [bx + BoxSize / 2, by - 2 * BoxSize / 3], & [bx + 2 * BoxSize / 3, by]] DrawPoly PolyArray Color FillColor Filled '' Draw Circle on top of triangle, with radius = 1/6 window height Circle (bx + BoxSize / 2), (by - 2 * BoxSize / 3), BoxSize / 6, & 1, FillColor Filled '' Use a polygon to make the slit '' Now, add a slit for the visor PolyArray = [[bx, by - BoxSize + BoxSize * 1/8], & [bx + BoxSize / 2, by - 2 * BoxSize /3], & [bx + BoxSize * 1/8, by - BoxSize]] '' Check Background color of square If (x+y) Mod 2 = 1 Then FillColor = ColorLightSquare Else FillColor = ColorDarkSquare EndIf DrawPoly PolyArray Color FillColor Filled End '' Sub DrawBishop Sub DrawKnight (x, y, FillColor) Local bx, by, PolyArray bx = BoxSize * (x - 1) by = BoxSize * (Squares + 1 - y) '' Draw triangle as the base of the knight PolyArray = [ [bx + 1 * BoxSize / 3, by], & [bx + 3 *BoxSize / 4, by], & [bx + 3 * BoxSize / 4, by - 5 * BoxSize / 6] ] DrawPoly PolyArray Color FillColor Filled '' Draw Rectangle for the snout PolyArray = & [[bx + 1*BoxSize/3, by - 2*BoxSize/3 - 2*BoxSize/20], & [bx + 3*BoxSize/4, by - 2*BoxSize/3 - 2*BoxSize/20], & [bx + 3*BoxSize/4, by - 2*BoxSize/3 + 3*BoxSize/20], & [bx + 1*BoxSize/3, by - 2*BoxSize/3 + 3*BoxSize/20]] DrawPoly PolyArray Color FillColor Filled '' Place an eye in the center (circle) If (x+y) Mod 2 = 0 Then FillColor = ColorDarkSquare Else FillColor = ColorLightSquare EndIf Circle (bx + 3*BoxSize/4 - 2* BoxSize / 20),(by - 2*BoxSize/3), BoxSize / 20, & 1, FillColor Filled End '' Sub DrawKnight Sub DrawKing (x, y, FillColor) '' This basically draws a cross on top of a triangular base '' Triangle is same dimensions as queen Local bx, by, PolyArray bx = BoxSize * (x - 1) by = BoxSize * (Squares + 1 - y) '' The triangle base will be 1/2 square width '' the triangle height will be 2/3 square height PolyArray = [[bx + BoxSize / 4, by], & [bx + BoxSize / 2, by - BoxSize + BoxSize / 3], & [bx + 3 * BoxSize / 4, by]] DrawPoly PolyArray Color FillColor Filled '' Now, draw two rectangles crossing the center Rect (bx + BoxSize / 4), (by - BoxSize + BoxSize / 3 - BoxSize / 15), & (bx + 3 * BoxSize / 4), (by - BoxSize + BoxSize / 3 + BoxSize / 15), & Color FillColor Filled Rect (bx + BoxSize / 2 - BoxSize / 15), (by - BoxSize + BoxSize / 15), & (bx + BoxSize / 2 + BoxSize / 15), (by - BoxSize + 5 * BoxSize / 8), & Color FillColor Filled End '' Sub DrawKing Sub DrawQueen (x, y, FillColor) '' Triangle with a circle on top, but bigger than pawn or '' bishop Local bx, by, PolyArray bx = BoxSize * (x - 1) by = BoxSize * (Squares + 1 - y) '' The triangle base will be 1/2 square width '' the triangle height will be 2/3 square height PolyArray = [[bx + BoxSize / 4, by], & [bx + BoxSize / 2, by - BoxSize + BoxSize / 3], & [bx + 3 * BoxSize / 4, by]] DrawPoly PolyArray Color FillColor Filled '' Draw Circle on top of triangle, with radius = 1/8 window height Circle (bx + BoxSize / 2), (by - BoxSize + BoxSize / 4), BoxSize / 5, & 1, FillColor Filled End '' Sub DrawQueen '' ---------------------------------------------------------------- '' Function begins here '' Clear screen Cls '' Extract the board Board = BoardSet(0) '' Draw the background squares For x = 1 to Squares For y = 1 to Squares Rect (x-1)*BoxSize, (Squares-y)*BoxSize, & x*BoxSize, ((Squares + 1)-y)*BoxSize, & Color IF((x+y) Mod 2 = 0, ColorDarkSquare, ColorLightSquare) & Filled Next y Next x For x = 1 to Squares For y = 1 to Squares If Sgn(Board(x,y)) = Black Then PieceColor = ColorBlack Else PieceColor = ColorWhite EndIf If Abs(Board(x,y)) = Pawn then DrawPawn x, y, PieceColor ElseIf Abs(Board(x,y)) = Rook then DrawRook x, y, PieceColor ElseIf Abs(Board(x,y)) = Knight then DrawKnight x, y, PieceColor ElseIf Abs(Board(x,y)) = Bishop then DrawBishop x, y, PieceColor ElseIf Abs(Board(x,y)) = King then DrawKing x, y, PieceColor ElseIf Abs(Board(x,y)) = Queen then DrawQueen x, y, PieceColor EndIf Next y Next x End '' Sub DisplayBoard '' ------------------------------------------------------------------------- '' ------------------------------------------------------------------------- '' This function is passed a BoardSet and a Move and returns the '' BoardSet after that move is made '' If ShowMoves = True, then display intermediate moves and play '' appropriate tunes, allowing the user to follow along Func MakeMove(BoardSet, Move, ShowMoves) '' Piece is the type of piece we are making Local Piece, Board, CanCastle, KingPosition Board = BoardSet(0) '' Used to see if castling is still allowed after this move CanCastle = BoardSet(1) '' Keep track of King Positions KingPosition = BoardSet(3) '' Record initial piece Piece = Board(Move(0), Move(1)) '' Check for en passant - have to capture the pawn left behind If Abs(Piece) = Pawn Then '' Show that we are moving diagnonally - only happens with a capture If Abs(Move(2) - Move(0)) = 1 Then If Board(Move(2), Move(3)) = Blank Then '' There SHOULD be a pawn to delete one square toward center - '' pawns should not be capturing a blank square except during '' en passant Board(Move(2), Move(3) - Sgn(Piece)) = Blank EndIf EndIf EndIf '' Move that piece to the target Board (Move(2), Move(3)) = Piece '' Blank out original score Board (Move(0), Move(1)) = Blank '' Check for promotion - here, we will only allow promotion to '' a Queen - consider revision in the future If Abs(Piece) = Pawn And (Move(3)=1 Or Move(3)=Squares) Then Board(Move(2), Move(3)) = Queen * Sgn (Piece) EndIf '' If we are moving a Rook, then we cannot castle on that side '' in the future If Abs(Piece) = Rook Then If Sgn(Piece) = White Then If Move(0)=1 And Move(1)=1 Then '' Queen rook CanCastle(3) = False ElseIf Move(0)=8 And Move(1)=1 Then '' King rook CanCastle(5) = False EndIf ElseIf Sgn(Piece) = Black Then If Move(0)=1 And Move(1)=8 Then '' Queen rook CanCastle(0) = False ElseIf Move(0)=8 And Move(1)=8 Then '' King Rook CanCastle(2) = False EndIf EndIf EndIf '' Check for castle - we''ll have to assume here the move is legal '' And, if we castle, then we cannot castle again ... '' Actually, if we just move the King (castling or not), we cannot '' castle again If Abs(Piece) = King Then If Sgn(Piece)=White Then '' White king CanCastle(4) = False '' Update KingPosition for White KingPosition(White,0)=Move(2) KingPosition(White,1)=Move(3) '' Check to see if moving from initial square, (5,1) If Move(0)=5 And Move(1)=1 Then '' Check if castling toward queenside If Move(2)=7 And Move(3)=1 Then '' Kingside Castle - Move Rook as well Board(6,1) = Board(8,1) Board(8,1) = Blank CanCastle(5) = False '' Check to see if castling toward kingside ElseIf Move(2)=3 And Move(3) = 1 Then '' Queenside Castle - Move Rook as well Board(4,1) = Board(1,1) Board(1,1) = Blank CanCastle(3) = False EndIf EndIf ElseIf Sgn(Piece)=Black Then '' Black king CanCastle(1) = False '' Update KingPosition for Black KingPosition(Black,0)=Move(2) KingPosition(Black,1)=Move(3) '' See if moving from initial square (5,8) If Move(0)=5 And Move(1)=8 Then '' Check if castling toward queenside If Move(2)=7 And Move(3)=8 Then '' Kingside Castle - Move Rook as well Board(6,8) = Board(8,8) Board(8,8) = Blank CanCastle(2) = False '' Check to see if castling toward kingside ElseIf Move(2)=3 And Move(3) = 8 Then '' Queenside Castle - Move Rook as well Board(4,8) = Board(1,8) Board(1,8) = Blank CanCastle(0) = False EndIf EndIf EndIf EndIf If ShowMoves Then '' Highlight original square '' Paint a rectangle inside the box to bound the fill Rect (Move(0)-1)*BoxSize+1, (Squares-Move(1))*BoxSize+1, & Move(0)*BoxSize-1, ((Squares + 1)-Move(1))*BoxSize-1, & Color ColorSelectFinal Paint (Move(0)-1)*BoxSize + 2, (Squares-Move(1))*BoxSize + 2, & ColorSelectFinal Play "V025O3C" '' Highlight the square that is being moved to, pause '' Paint a rectangle inside the box to bound the fill Rect (Move(2)-1)*BoxSize+1, (Squares-Move(3))*BoxSize+1, & Move(2)*BoxSize-1, ((Squares + 1)-Move(3))*BoxSize-1, & Color ColorSelectFinal Paint (Move(2)-1)*BoxSize + 2, (Squares-Move(3))*BoxSize + 2, & ColorSelectFinal Play "V025O3C" '' Update board, play terminal sound DisplayBoard BoardSet Play "O3G" EndIf '' Return the new BoardSet MakeMove = [Board, CanCastle, Move, KingPosition] End '' Func MakeMove '' ------------------------------------------------------------------------- '' ------------------------------------------------------------------------- '' This will return TRUE if, in the given board, side SIDE '' is in check. Otherwise it will return false Func IsCheck(Board, KingPosition, Side) '' This function will move off down the vector defined by (dx, dy) '' for a maximum of Limit squares. If it encounters an enemy piece '' of a type in the array PieceArray, then we return True Func WalkLine (dx, dy, PieceArray, Limit) Local Counter, NewX, NewY WalkLine = False For Counter = 1 to Limit NewX = KingPosition(Side,0) + Counter * dx NewY = KingPosition(Side,1) + Counter * dy If (NewX >=1) And (NewX <= Squares) And & (NewY >= 1) And (NewY <= Squares) Then If Board(NewX, NewY) <> Blank Then If Abs(Board(NewX, NewY)) in PieceArray Then If Sgn(Board(NewX,Newy)) = -Side Then WalkLine = True EndIf EndIf '' If we get here, we''re done one way or another- '' exit function Exit Func EndIf Else '' If we are off the board, stop looking Exit Func EndIf Next Counter End '' Func WalkLine '' ---------------------------------------------------------------- '' Main function starts here IsCheck = False '' Check on diagonals for bishop, queen '' (pawns only going forward) If WalkLine (-1, -1, [Queen, Bishop], Squares) Then IsCheck = True Exit Func EndIf If WalkLine (-1, 1, [Queen, Bishop], Squares) Then IsCheck = True Exit Func EndIf If WalkLine (1, -1, [Queen, Bishop], Squares) Then IsCheck = True Exit Func EndIf If WalkLine (1, 1, [Queen, Bishop], Squares) Then IsCheck = True Exit Func EndIf '' Check pawns If WalkLine (-1, Side, [Pawn], 1) Then IsCheck = True Exit Func EndIf If WalkLine (1, Side, [Pawn], 1) Then IsCheck = True Exit Func EndIf '' Check on orthagonals for rook, queen If WalkLine (-1, 0, [Queen, Rook], Squares) Then IsCheck = True Exit Func EndIf If WalkLine (1, 0, [Queen, Rook], Squares) Then IsCheck = True Exit Func EndIf If WalkLine (0, -1, [Queen, Rook], Squares) Then IsCheck = True Exit Func EndIf If WalkLine (0, 1, [Queen, Rook], Squares) Then IsCheck = True Exit Func EndIf '' Check for knights If WalkLine (-2, 1, [Knight], 1) Then IsCheck = True Exit Func EndIf If WalkLine (-2, -1, [Knight], 1) Then IsCheck = True Exit Func EndIf If WalkLine (2, 1, [Knight], 1) Then IsCheck = True Exit Func EndIf If WalkLine (2, -1, [Knight], 1) Then IsCheck = True Exit Func EndIf If WalkLine (-1, 2, [Knight], 1) Then IsCheck = True Exit Func EndIf If WalkLine (-1, -2, [Knight], 1) Then IsCheck = True Exit Func EndIf If WalkLine (1, 2, [Knight], 1) Then IsCheck = True Exit Func EndIf If WalkLine (1, -2, [Knight], 1) Then IsCheck = True Exit Func EndIf '' Check for Kings If WalkLine (-1, -1, [King], 1) Then IsCheck = True Exit Func EndIf If WalkLine (-1, 0, [King], 1) Then IsCheck = True Exit Func EndIf If WalkLine (-1, 1, [King], 1) Then IsCheck = True Exit Func EndIf If WalkLine (0, -1, [King], 1) Then IsCheck = True Exit Func EndIf If WalkLine (0, 1, [King], 1) Then IsCheck = True Exit Func EndIf If WalkLine (1, -1, [King], 1) Then IsCheck = True Exit Func EndIf If WalkLine (1, 0, [King], 1) Then IsCheck = True Exit Func EndIf If WalkLine (1, 1, [King], 1) Then IsCheck = True Exit Func EndIf End '' Func IsCheck '' ------------------------------------------------------------------- '' This function is passed a board and a color and returns a MoveArray listing '' all valid moves that color Side can make Func GenerateMoveList (BoardSet, Side) '' MoveArray is an array of MoveLists Local MoveArray '' Coordinates to move through the board Local x, y, Board '' -------------------------------------------------------------------- '' This routine will take the piece starting at (x,y) in Board '' and walk off in vector (dx, dy) until it jumps off the board, '' captures another piece in that vector, runs into one of its '' own pieces in that vector, or exceeds the number of squares in '' limit (1 for King, infinity for rook, queen, bishop). '' For each change to board, if making this move does NOT result '' in a check situation for Side (the color of the piece at x, y) '' then the postulated move will be added into MoveArray Sub WalkLine(x, y, dx, dy, Limit) Local Counter, NewBoard, Piece, NewX, NewY, MustCheck, KingPosition '' Grab current position of the Kings - needed for IsCheck KingPosition = BoardSet(3) '' This is TRUE if we must check to see if this '' movement results in a check before adding it to the list '' We must check if: '' It is the first move (if we are in check) '' The piece is a king (any move can result in check) '' If, after the first move, the piece is not a king, and '' we don''t start out in check, then we don''t need to check again '' It''s worth trying to avoid the check "check" to save time MustCheck = ((Abs(Board(x,y)) = King) Or IsCheck(Board, KingPosition, Side)) For Counter = 1 to Limit NewX = x + Counter * dx NewY = y + Counter * dy '' Make sure the proposed move is still on the board If (NewX<1) or (NewY<1) or (NewX>Squares) or (NewY>Squares) Then Exit For Else '' See if piece is either empty or occupied by piece from '' the other side '' If so, this is a valid move If Sgn(Board(NewX, NewY)) <> Side Then '' Make the move on a "virtual" board NewBoard = Board Piece = NewBoard(x,y) NewBoard(x,y) = Blank NewBoard(NewX, NewY) = Piece '' If that move does not result in check, then '' add it to possible move list '' If the piece is a King, then update KingPosition If Abs(Piece) = King Then KingPosition(Side,0) = NewX KingPosition(Side,1) = NewY EndIf If MustCheck Or (Counter <= 2) Then If Not IsCheck(NewBoard, KingPosition, Side) Then MoveArray << [x, y, NewX, NewY] EndIf Else MoveArray << [x, y, NewX, NewY] EndIf '' If this was a capture, then end the loop as we '' can''t advance any further in this direction If Sgn(Board(NewX, NewY)) = -Side Then Exit For EndIf ElseIf Sgn(Board(NewX, NewY)) = Side Then '' We''re done - can''t move over our own piece; exit '' the loop Exit For EndIf EndIf Next Counter End '' WalkLine '' ------------------------------------------------------------------------- '' Specific piece checks start here Sub CheckPawn(x, y) Local NewBoard, Piece, Counter, LastMove, KingPosition '' Grab current positions of Kings, for IsCheck KingPosition = BoardSet(3) '' Check for single move If Board(x, y + Side) = Blank Then NewBoard = Board Piece = NewBoard (x,y) NewBoard (x,y) = Blank NewBoard(x, y + Side) = Piece If Not IsCheck(NewBoard, KingPosition, Side) Then MoveArray << [x, y, x, y + side] EndIf EndIf '' Check for double move, if starting in 2/7 row If ((Side = White) And (y=2)) or ((Side=Black) And (y=7)) Then If (Board(x,y+Side)=Blank) And (Board(x,y+2*Side)=Blank) Then NewBoard = Board Piece = NewBoard (x,y) NewBoard (x,y) = Blank NewBoard(x, y + 2*Side) = Piece If Not IsCheck(NewBoard, KingPosition, Side) Then MoveArray << [x, y, x, y + 2*Side] EndIf EndIf EndIf '' Check for capture on diagonals For Counter in [-1, 1] If ((x+Counter) >= 1) And ((x+Counter)<= Squares) And & ((y+Side)>=1) And ((y+Side)<=Squares) Then If Sgn(Board(x+Counter,y+Side)) = -Side Then NewBoard = Board Piece = NewBoard (x,y) NewBoard (x,y) = Blank NewBoard(x + Counter, y + Side) = Piece If Not IsCheck(NewBoard, KingPosition, Side) Then MoveArray << [x, y, x + Counter, y + Side] EndIf EndIf EndIf Next Counter '' Check for en-passant (look at previous move - BoardSet(2) and BoardSet(3)) '' Grab this for convenience LastMove = BoardSet(2) If LastMove <> [0,0,0,0] Then If Board(LastMove(2), LastMove(3)) = -Side * Pawn Then '' Check to see if last move was one column away from current pawn '' and the last move was a double advance; In theory, '' Abs(LastMove(2)-LastMove(0)) = 0, so we won''t check to save time If Abs(LastMove(0) - x) = 1 And (Abs(LastMove(3)-LastMove(1))=2) Then '' See if we are in the correct Row If ((Side=White) and (y=5)) Or ((Side=Black) And (y=4)) Then '' If we get here, en passant is possible! NewBoard = Board Piece = NewBoard (x,y) NewBoard (x,y) = Blank NewBoard(LastMove(0), y + Side) = Piece If Not IsCheck(NewBoard, KingPosition, Side) Then MoveArray << [x, y, LastMove(0), y + Side] EndIf EndIf EndIf EndIf EndIf End '' Func CheckPawn Sub CheckRook (x,y) '' Rooks move orthogonally WalkLine x, y, 1, 0, Squares WalkLine x, y, 0, 1, Squares WalkLine x, y, -1, 0, Squares WalkLine x, y, 0, -1, Squares End '' Func CheckRook Sub CheckKnight (x,y) '' Check all the squares a Knight could go to WalkLine x, y, -1, 2, 1 WalkLine x, y, 1, 2, 1 WalkLine x, y, -1, -2, 1 WalkLine x, y, 1, -2, 1 WalkLine x, y, -2, 1, 1 WalkLine x, y, -2, -1, 1 WalkLine x, y, 2, 1, 1 WalkLine x, y, 2, -1 , 1 End '' Func CheckKnight Sub CheckBishop (x,y) '' Bishops can move diagonally only - check all four diagonals WalkLine x, y, 1, 1, Squares WalkLine x, y, 1, -1, Squares WalkLine x, y, -1, 1, Squares WalkLine x, y, -1, -1, Squares End '' Func CheckBishop Sub CheckQueen (x,y) '' Queens can move either diagonally or orthagonally '' Check all 8 directions, up to Squares moves WalkLine x, y, 1, 0, Squares WalkLine x, y, 0, 1, Squares WalkLine x, y, -1, 0, Squares WalkLine x, y, 0, -1, Squares WalkLine x, y, 1, 1, Squares WalkLine x, y, 1, -1, Squares WalkLine x, y, -1, 1, Squares WalkLine x, y, -1, -1, Squares End '' Func CheckQueen Sub CheckKing (x,y) Local CanCastle, NewBoard, KingPosition '' Kings can move either diagonally or orthagonally for 1 square '' Check all 8 directions, 1 move only WalkLine x, y, 1, 0, 1 WalkLine x, y, 0, 1, 1 WalkLine x, y, -1, 0, 1 WalkLine x, y, 0, -1, 1 WalkLine x, y, 1, 1, 1 WalkLine x, y, 1, -1, 1 WalkLine x, y, -1, 1, 1 WalkLine x, y, -1, -1, 1 '' Use this to keep track of the king for IsCheck KingPosition = BoardSet(3) '' Also, check for potential to castle either '' a-ward or g-ward CanCastle = BoardSet(1) '' See if King has been moved If ((Side=Black) And CanCastle(1)) Or ((Side=White) And CanCastle(4)) Then '' If here, then check and see if queen-rook has been moved If ((Side=Black) And CanCastle(0)) Or ((Side=White) And CanCastle(3)) Then '' See if intermediate squares are clear If (Board(4,y)=Blank) and (Board(3,y)=Blank) And (Board(2, y)= Blank) Then '' See if intermediate moves cause check NewBoard = Board '' Can''t castle out of check! If Not IsCheck(NewBoard, KingPosition, Side) Then '' Check to see if one square to left causes check NewBoard(x,y) = Blank NewBoard(x-1,y) = King * Side KingPosition(Side,0) = x-1 KingPosition(Side,1) = y If Not IsCheck(NewBoard, KingPosition, Side) Then '' Check to see if two squares to left causes check NewBoard(x-1,y) = Blank NewBoard(x-2,y) = King * Side KingPosition(Side,0) = x-2 KingPosition(Side,1) = y If Not IsCheck(NewBoard, KingPosition, Side) Then '' If we get here, king-side castle is allowed! MoveArray << [x, y, x-2, y] EndIf EndIf EndIf EndIf EndIf '' See if king-rook has been moved If ((Side=Black) And CanCastle(2)) Or ((Side=White) And CanCastle(5)) Then '' See if intermediate squares are clear If (Board(6, y)=Blank) and (Board(7, y)=Blank) Then '' See if intermediate moves cause check NewBoard = Board '' Can''t castle out of check! If Not IsCheck(NewBoard, KingPosition, Side) Then '' Check to see if one square to right causes check NewBoard(x,y) = Blank NewBoard(x+1,y) = King * Side KingPosition(Side,0) = x+1 KingPosition(Side,1) = y If Not IsCheck(NewBoard, KingPosition, Side) Then '' Check to see if two squares to right causes check NewBoard(x+1,y) = Blank NewBoard(x+2,y) = King * Side KingPosition(Side,0)=x+2 KingPosition(Side,1)=y If Not IsCheck(NewBoard, KingPosition, Side) Then '' If we get here, king-side castle is allowed! MoveArray << [x, y, x+2, y] EndIf EndIf EndIf EndIf EndIf EndIf '' Whew! End '' Func CheckKing '' ------------------------------------------------------------------- '' Function actually begins here '' Board = BoardSet(0) For x = 1 to Squares For y = 1 to Squares If Board(x,y) = Side * Pawn Then CheckPawn x, y ElseIf Board(x,y) = Side * Rook Then CheckRook x, y ElseIf Board(x,y) = Side * Knight Then CheckKnight x, y ElseIf Board(x,y) = Side * Bishop Then CheckBishop x, y ElseIf Board(x,y) = Side * Queen Then CheckQueen x, y ElseIf Board(x,y) = Side * King Then CheckKing x, y EndIf Next y Next x GenerateMoveList = MoveArray End '' Func GenerateMoveList '' ------------------------------------------------------------------------- '' ------------------------------------------------------------------------- '' This function will allow the user to enter a move for a side '' It outputs a Move Func GetUserMove (BoardSet, Side) '' Where the user is actually moving Local ValidMoveArray, Move, ClickMove, Board, OldClickMove, Local ValidMove, IsValid, IsInCheck, KingPosition '' -------------------------------------------------------- '' Waits for the user to click on a square and returns '' the x,y board components as (x, y, 0, 0) '' (DataType = Move) '' Also, we will only accept clicks on Dark squares (X+Y) Mod 2 = 0 Func GetSquare '' Enable tracking of mouse Pen on '' Loop until the left mouse button is pressed Repeat Until Pen(0) '' Convert mouse coordinates into Board coordinates '' Pen(1) = X of mouse position "Last mouse button down X" '' Pen(2) = Y of mouse position "Last mouse button down Y" GetSquare = [1 + Int(Pen(1)/BoxSize),Squares - Int(Pen(2)/BoxSize),0,0] '' Stop Mouse mechanism Pen Off End '' --------------------------------------------------------------- '' This will change the background of a square to color SquareColor Sub HighlightSquare (x, y, SquareColor) '' Only highlight a valid square If (x >= 1) and (x <= Squares) And (y >= 1) And (y <= Squares) Then '' Paint a rectangle inside the box to bound the fill Rect (x-1)*BoxSize+1, (Squares-y)*BoxSize+1, & x*BoxSize-1, ((Squares + 1)-y)*BoxSize-1, & Color SquareColor Paint (x-1)*BoxSize + 2, (Squares-y)*BoxSize + 2, SquareColor EndIf End '' Sub HighLightSquare (x,y, SquareColor) '' ------------------------------------------------------------------ '' Function actually starts here OldClickMove = [0,0,0,0] Board = BoardSet(0) KingPosition = BoardSet(3) IsInCheck = IsCheck(Board, KingPosition, Side) '' Initialize variables ValidMoveArray = GenerateMoveList (BoardSet, Side) Move = [0,0,0,0] Done = False Repeat '' Put up a fresh board DisplayBoard BoardSet '' If we are in check, highlight this Side''s King square If IsInCheck Then HighlightSquare KingPosition(Side,0), KingPosition(Side,1), ColorCheck EndIf '' Inform use of which side is to move At 0, BoxSize * Squares '' + TextHeight (PlayerName(Side))/2 If Side = Black Then Color ColorBlack, ColorDarkSquare Else Color ColorWhite, ColorDarkSquare EndIf Print PlayerName(Side) + " to move"; '' Get First Move Repeat ClickMove = GetSquare Until ClickMove <> OldClickMove OldClickMove = ClickMove ''See if it is valid IsValid = False For ValidMove in ValidMoveArray IsValid = (ClickMove(0) = ValidMove(0)) And & (ClickMove(1) = ValidMove(1)) If IsValid Then Exit For EndIf Next ValidMove If IsValid Then HighLightSquare ClickMove(0), ClickMove(1), ColorSelect Move = ClickMove '' Get Second Move Repeat ClickMove = GetSquare Until ClickMove <> OldClickMove OldClickMove = ClickMove HighLightSquare ClickMove(0), ClickMove(1), ColorSelect Move(2) = ClickMove(0) Move(3) = ClickMove(1) Else '' Give error beep Play "O3A" EndIf '' Check to see if the move is valid Until Move in ValidMoveArray '' Return the move list GetUserMove = Move End '' Func GetUserMove '' ------------------------------------------------------------------------- '' ------------------------------------------------------------------------- '' This function processes the Artificial Intelligence aspects for '' computer move generation, using the standard Minimax game algorithm '' recursively '' Because of the nature of MiniMax, it has to return two values: '' a MoveList and a Score. We will define a data structure of '' [Score, MoveList] to hold these '' Board is a board to process; Side is the side whose turn it is to move, '' Depth is CURRENT search depth (initally set to zero), '' DepthMax = Deepest level to explore, Evaluator is used to determine '' which board evaluation function to use (see EvaluateBoard) '' We keep all moves with same score in BestMoveList and choose randomly '' among them to try and avoid loops of repetitive moves Func MiniMax(BoardSet, Side, Depth, DepthMax, Evaluator) Local MoveList, Move, Score, BestScore, NextMini, BestMoveList, Board Board = BoardSet(0) If Depth > DepthMax Then '' If we have exceeded the specified search depth, '' return the value of our board at this point and '' a null movelist MiniMax = [(EvaluateBoard (Board, Side, Evaluator)), 0] Else '' Find all possible moves for Side with the current Board MoveList = GenerateMoveList (BoardSet, Side) '' If there are no moves, then return the score '' of the current board and a null MoveList If Empty (MoveList) Then MiniMax = [EvaluateBoard (Board, Side, Evaluator), 0] Else '' Find the move that yields the best MiniMax score '' Set initial BestScore to lowest conceivable results, to '' guarantee it will be replaced with an actual result later BestScore = -999999 Erase BestMoveList '' Step through each possible move For Move in MoveList '' Recurse down the search tree for the board that '' would result from making that move NextMini = MiniMax(MakeMove(BoardSet, Move, False), & -Side, Depth+1, DepthMax, Evaluator) '' If that move results in a better MiniMax score, then '' save that result Score = -NextMini(0) If Score >= BestScore Then '' If this ties the current best score, add to the list If Score = BestScore Then BestMoveList << Move Else '' If this is a new best score, set the list to this '' move only and update best score BestScore = Score BestMoveList = [Move] EndIf EndIf Next Move '' Return our best move '' Select randomly from the list of moves with an equal / best score MiniMax = [BestScore, BestMoveList(Int(Rnd * UBound(BestMoveList)))] EndIf EndIf End '' Func Minimax '' ------------------------------------------------------------------------- '' ------------------------------------------------------------------------- '' This function applies a custom evaluator to be used by MiniMax '' There should be a private function for each different approach '' to scoring the boards, and the main function code will chose among '' them based on Evaluator '' Right now we are just using "SimpeScore", which adds up points for '' pieces. You could add something that gives bonus points for control of '' the center, bonus points for knights in a closed games or bishops in '' an open game, etc. Func EvaluateBoard (Board, Side, Evaluator) '' ------------------------------------------------------------------ '' This function just adds up the pieces in Board (1=piece,2=King) '' and returns the net sum '' It was the simplest one I could think of Func ScoreSimple(Board, Side) Local x, y, Score Score = 0 For x = 1 to Squares For y = 1 to Squares If Abs(Board(x,y)) = Pawn Then Score = Score + 1 * Sgn(Board(x,y)) ElseIf Abs(Board(x,y)) = Rook Then Score = Score + 5 * Sgn(Board(x,y)) ElseIf Abs(Board(x,y)) = Knight Then Score = Score + 3 * Sgn(Board(x,y)) ElseIf Abs(Board(x,y)) = Bishop Then Score = Score + 3.25 * Sgn(Board(x,y)) ElseIf Abs(Board(x,y)) = Queen Then Score = Score + 9 * Sgn(Board(x,y)) ElseIf Abs(Board(x,y)) = KingThen Score = Score + 100 * Sgn(Board(x,y)) EndIf Next y Next x ScoreSimple = Score * Side End '' Func ScoreSimple '' ------------------------------------------------------------------------ '' Function begins here '' The idea is that we have multiple Evaluator functions as a test '' of different strategies If Evaluator = 2 Then EvaluateBoard = ScoreSimple (Board, Side) EndIf End '' Func EvaluateBoard '' ------------------------------------------------------------------------- '' ------------------------------------------------------------------------- '' This function will determine the next move for Side based on the '' strategy in PlayerStrategy(Side) and return a MoveList Func DetermineMove (BoardSet, Side) Local Temp '' This will display text to the right (by 1/4 square) of the board '' listing who is currently moving '' The color of the text will match the color of the pieces '' Set text color to match If Side = Black Then Color ColorBlack Else Color ColorWhite EndIf At 0, BoxSize * Squares '' + TextHeight (PlayerName(Side))/2 Print PlayerName(Side) + " to move"; If PlayerStrategy(Side) = 1 Then DetermineMove = GetUserMove (BoardSet, Side) ElseIf PlayerStrategy(Side) = 2 Then Temp = MiniMax(BoardSet, Side, 0, 1, 2) DetermineMove = Temp(1) ElseIf PlayerStrategy(Side) = 3 Then Temp = MiniMax(BoardSet, Side, 0, 2, 2) DetermineMove = Temp(1) ElseIf PlayerStrategy(Side) = 4 Then Temp = MiniMax(BoardSet, Side, 0, 3, 2) DetermineMove = Temp(1) EndIf End '' Func DetermineMove '' ------------------------------------------------------------------------- '' ------------------------------------------------------------------------- '' This is the main control function for the checkers program Sub Main Local BoardSet, MoveList, Winner, Counter '' Get User information: '' For each color, get a unique name for the player and '' a strategy for determining the move to make For Counter in [White, Black] '' Get the name of the players Print "Please enter the name for the "; If Counter = White Then Print "white"; Else Print "black"; EndIf Print " player :"; Input PlayerName (Counter) Print Repeat '' Get the strategy for each player to use Print "1. Ask the user" Print "2. Use SimpleScore Level 1" Print "3. Use SimpleScore Level 2" Print "4. Use SimpleScore Level 3" Print "Enter the strategy to use for "; PlayerName(Counter); Input PlayerStrategy(Counter) Until PlayerStrategy(Counter) in [1,2,3,4] Print Print Next Counter '' Initialize the board BoardSet = InitBoard '' Display the board DisplayBoard BoardSet '' Loop until game is over - it is over when one side cannot '' make any more moves While True '' Allow white to move is there is a move for White to make If Empty(GenerateMoveList (BoardSet, White)) Then Winner = Black Exit Loop Else '' Get White Move MoveList = DetermineMove (BoardSet, White) '' Apply White Move BoardSet = MakeMove (BoardSet, MoveList, True) '' Show the new board DisplayBoard BoardSet EndIf '' Allow Black to move if there is a move for Black to make If Empty(GenerateMoveList (BoardSet, Black)) Then Winner = White Exit Loop Else '' Get Black Move MoveList = DetermineMove (BoardSet, Black) '' Apply Black Move BoardSet = MakeMove (BoardSet, MoveList, True) '' Show the new board DisplayBoard BoardSet EndIf Wend '' Now, display the winner At 0, BoxSize * Squares ''+ TextHeight ("Wins!") / 2 If IsCheck (BoardSet(0), BoardSet(3), -Winner) Then If Winner = Black Then Color ColorBlack Else Color ColorWhite EndIf Print "CheckMate! " ; PlayerName(Winner) ; " wins!"; Else Print "Stalemate!" EndIf '' Play a little fanfare and pause for 1 second Play "O2CEGO3CP1" End '' Sub Main '' ------------------------------------------------------------------------- '' ------------------------------------------------------------------------- '' Call the Main procedure, then exit the program '' Declare array of player names Dim PlayerName (Black to White) '' Declare array of strategy choices Dim PlayerStrategy (Black to White) Main End'