Chess: Implement "5-times same position" rule
This rule draws the game if the same position appeared 5 times (FIDE Laws of Chess Jan 2023, article 9.6.1)
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Wuzzy
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313
src/chess.lua
313
src/chess.lua
@ -14,7 +14,7 @@ screwdriver = screwdriver or {}
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local ENABLE_CHESS_GAMES = true
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-- If true, will show some hidden state for debugging purposes
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local CHESS_DEBUG = true
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local CHESS_DEBUG = false
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local function index_to_xy(idx)
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if not idx then
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@ -61,6 +61,7 @@ function get_square_index_color(idx)
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end
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local chat_prefix = minetest.colorize("#FFFF00", "["..S("Chess").."] ")
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local chat_prefix_debug = minetest.colorize("#FFFF00", "["..S("Chess Debug").."] ")
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local letters = {'a','b','c','d','e','f','g','h'}
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local function index_to_notation(idx)
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@ -177,6 +178,59 @@ local function get_current_fullmove(meta)
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return math.floor(#mrsplit / 2)
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end
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-- Returns a FEN-style string to represent castling rights
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-- Will return a sequence of K, Q, k and q, with each letter
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-- representing castling rights:
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-- * K: white kingside
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-- * Q: white queenside
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-- * k: black kingside
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-- * q: black queenside
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-- If all castling rights are gone, will return "-" instead.
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-- The 4 arguments are booleans for each possible castling,
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-- true means the castling is possible.
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local function castling_to_string(white_kingside, white_queenside, black_kingside, black_queenside)
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local s_castling = ""
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if white_kingside then
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s_castling = s_castling .. "K"
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end
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if white_queenside then
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s_castling = s_castling .. "Q"
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end
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if black_kingside then
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s_castling = s_castling .. "k"
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end
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if black_queenside then
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s_castling = s_castling .. "q"
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end
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if s_castling == "" then
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s_castling = "-"
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end
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return s_castling
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end
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-- Returns a FEN-style string to represent the state of a theoretically
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-- possible en passant capture on the board (even if no pawn can actually
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-- capture). If an en passant capture is possible, returns the square
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-- coordinates in algebraic notation of the square the vulnerable pawn
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-- has just crossed. If no en passant capture is possible, returns "-".
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-- double_step is the board index of the square the vulnerable
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-- pawn has just double-stepped to or 0 if there is no such pawn.
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local function en_passant_to_string(double_step)
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local s_en_passant = "-"
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if double_step ~= 0 and double_step ~= nil then
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-- write the square crossed by the pawn who made
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-- the double step
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local dsx, dsy = index_to_xy(double_step)
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if dsy == 3 then
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dsy = dsy - 1
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else
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dsy = dsy + 1
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end
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s_en_passant = index_to_notation(xy_to_index(dsx, dsy))
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end
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return s_en_passant
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end
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local function can_castle(meta, board, from_list, from_idx, to_idx)
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local from_x, from_y = index_to_xy(from_idx)
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local to_x, to_y = index_to_xy(to_idx)
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@ -1009,6 +1063,189 @@ local function add_special_to_moves_list(meta, special)
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add_move_to_moves_list(meta, "", "", "", "", special)
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end
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-- Returns a list of all positions so far, for the purposes
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-- of determining position equality under the "same position
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-- repeated X times" draw rule.
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-- Each possible position is uniquely identified by a string
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-- so equal positions have the same string and unequal positons
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-- have a different string.
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-- A position string containts the following data:
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-- * position of pieces on the board
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-- * current player
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-- * castling rights
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-- * target coords of the square crossed by the pawn who
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-- made a double step in the prvious turn (if any)
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--
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-- Patemeter: meta is the node metadata of the chessboard
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--
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-- NOTE: The FIDE Laws of Chess (Jan 2023, article 9.2.3.1)
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-- are somewhat unclear about en passant here ... Is it important
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-- the pawn was only theoretically vulnerable to being
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-- captured en passant without being actually threatened
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-- that way, or does it only count if the pawn was actually
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-- threatened by another pawn to be captured that way?
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-- This mod currently interprets the rule in the former way,
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-- i.e. a double step by a pawn
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local function get_positions_history(meta)
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-- Turns a board table to a string.
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-- The syntax is inspired by FEN but not identical.
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-- It iterates through the table from start
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-- to finish and turns every square to a character,
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-- representing a piece or an empty square.
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local function board_to_string(board)
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local str = ""
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for b=1, #board do
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local piece = board[b]
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local append
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if piece == "" then
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str = str .. "."
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elseif piece:find("white") then
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if piece:find("pawn") then
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str = str .. "P"
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elseif piece:find("bishop") then
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str = str .. "B"
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elseif piece:find("knight") then
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str = str .. "N"
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elseif piece:find("rook") then
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str = str .. "R"
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elseif piece:find("queen") then
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str = str .. "Q"
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elseif piece:find("king") then
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str = str .. "K"
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end
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elseif piece:find("black") then
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if piece:find("pawn") then
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str = str .. "p"
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elseif piece:find("bishop") then
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str = str .. "b"
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elseif piece:find("knight") then
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str = str .. "n"
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elseif piece:find("rook") then
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str = str .. "r"
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elseif piece:find("queen") then
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str = str .. "q"
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elseif piece:find("king") then
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str = str .. "k"
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end
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end
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end
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return str
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end
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local moves_raw = meta:get_string("moves_raw")
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local moves_split = string.split(moves_raw, ";")
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local positions_list = ""
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local board = table.copy(starting_grid)
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local castling_state = { true, true, true, true }
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local castling_str = castling_to_string(unpack(castling_state))
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positions_list = {}
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local current_player = "w"
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local position_string = board_to_string(board) .. " " ..
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current_player .. " " ..
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castling_str .. " " ..
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en_passant_to_string(nil)
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table.insert(positions_list, position_string)
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for m=1, #moves_split do
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local move_split = string.split(moves_split[m], ",", true)
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local pieceFrom = move_split[1]
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local pieceTo = move_split[2]
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local from_idx = tonumber(move_split[3])
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local to_idx = tonumber(move_split[4])
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local special = move_split[5]
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if special == "" or special:sub(1,7) == "promo__" then
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if current_player == "w" then
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current_player = "b"
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else
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current_player = "w"
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end
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-- Piece movement
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board[to_idx] = board[from_idx]
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board[from_idx] = ""
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-- Pawn promotion
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if special:sub(1, 7) == "promo__" then
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local promoSym = special:sub(8)
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board[to_idx] = promoSym
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end
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local from_x, from_y = index_to_xy(from_idx)
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local to_x, to_y = index_to_xy(to_idx)
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if pieceFrom:sub(11,14) == "king" then
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-- Castling (move rook)
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if (from_y == 7 and to_y == 7) then
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if (from_x == 4 and to_x == 2) then
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board[60] = board[57]
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board[57] = ""
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elseif (from_x == 4 and to_x == 6) then
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board[62] = board[64]
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board[64] = ""
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end
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elseif (from_y == 0 and to_y == 0) then
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if (from_x == 4 and to_x == 2) then
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board[4] = board[1]
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board[1] = ""
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elseif (from_x == 4 and to_x == 6) then
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board[6] = board[8]
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board[8] = ""
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end
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end
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-- Lose castling rights on any king move
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if pieceFrom:find("white") then
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castling_state[1] = false
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castling_state[2] = false
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else
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castling_state[3] = false
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castling_state[4] = false
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end
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-- Lose castling rights on lone rook move
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elseif pieceFrom:sub(11,14) == "rook" then
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if from_idx == 57 then
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-- white queenside
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castling_state[2] = false
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elseif from_idx == 64 then
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-- white kingside
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castling_state[1] = false
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elseif from_idx == 1 then
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-- black queenside
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castling_state[4] = false
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elseif from_idx == 8 then
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-- black kingside
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castling_state[3] = false
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end
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end
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local pawn_double_step_index
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if pieceTo == "" and pieceFrom:sub(11,14) == "pawn" then
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-- En passant (remove captured pawn)
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if from_x ~= to_x then
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local epp_y
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if pieceFrom:find("white") then
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epp_y = to_y + 1
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else
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epp_y = to_y - 1
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end
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board[xy_to_index(to_x, epp_y)] = ""
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-- Double pawn step (record positoin)
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elseif math.abs(from_y-to_y) == 2 then
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pawn_double_step_index = to_idx
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end
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end
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castling_str = castling_to_string(unpack(castling_state))
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local position_string = board_to_string(board) .. " " ..
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current_player .. " " ..
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castling_str .. " " ..
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en_passant_to_string(pawn_double_step_index)
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table.insert(positions_list, position_string)
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end
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end
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local p=#positions_list
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return positions_list
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end
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-- Create the full formspec string for the sequence of moves.
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-- Uses Figurine Algebraic Notation.
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local function get_moves_formstring(meta)
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@ -1281,36 +1518,15 @@ local function update_formspec(meta)
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d_turn = "w"
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end
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-- castling rights
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local d_castling = ""
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if meta:get_int("castlingWhiteR") == 1 then
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d_castling = d_castling .. "K"
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end
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if meta:get_int("castlingWhiteL") == 1 then
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d_castling = d_castling .. "Q"
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end
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if meta:get_int("castlingBlackR") == 1 then
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d_castling = d_castling .. "k"
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end
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if meta:get_int("castlingBlackL") == 1 then
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d_castling = d_castling .. "q"
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end
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if d_castling == "" then
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d_castling = "-"
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end
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local d_castling = castling_to_string(
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meta:get_int("castlingWhiteR") == 1,
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meta:get_int("castlingWhiteL") == 1,
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meta:get_int("castlingBlackR") == 1,
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meta:get_int("castlingBlackL") == 1)
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-- en passant possible?
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local double_step = meta:get_int("prevDoublePawnStepTo")
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local d_en_passant = "-"
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if double_step ~= 0 then
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-- write the square crossed by the pawn who made
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-- the double step
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local dsx, dsy = index_to_xy(double_step)
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if dsy == 3 then
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dsy = dsy - 1
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else
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dsy = dsy + 1
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end
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d_en_passant = index_to_notation(xy_to_index(dsx, dsy))
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end
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local d_en_passant = en_passant_to_string(double_step)
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-- The halfmove clock counts for how many consecutive halfmoves
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-- have been made with no pawn advancing and no piece being captured
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local d_halfmove_clock = meta:get_int("halfmoveClock")
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@ -1469,6 +1685,45 @@ local function update_game_result(meta)
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minetest.log("action", "[xdecor] Chess: A game between "..playerWhite.." and "..playerBlack.." ended in a draw via the 75-move rule")
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end
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local repetitionDraw = false
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local positions = get_positions_history(meta)
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local positions_counter = {}
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for p = 1, #positions do
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local position = positions[p]
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if positions_counter[position] == nil then
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positions_counter[position] = 1
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else
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positions_counter[position] = positions_counter[position] + 1
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end
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if CHESS_DEBUG and p == #positions then
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local msg = chat_prefix_debug .. "Current position: \"" .. position .. "\""
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if positions_counter[position] > 1 then
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msg = msg .. " (occurred "..positions_counter[position].." times)"
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end
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minetest.chat_send_player(playerWhite, msg)
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if playerWhite ~= playerBlack then
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minetest.chat_send_player(playerBlack, msg)
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end
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end
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if positions_counter[position] == 5 then
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repetitionDraw = true
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break
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end
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end
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if repetitionDraw then
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meta:set_string("gameResult", "draw")
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meta:set_string("gameResultReason", "same_position_5")
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add_special_to_moves_list(meta, "draw")
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local msg = S("The exact same position has occured 5 times. It's a draw!")
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minetest.chat_send_player(playerWhite, chat_prefix .. msg)
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if playerWhite ~= playerBlack then
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minetest.chat_send_player(playerBlack, chat_prefix .. msg)
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end
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minetest.log("action", "[xdecor] Chess: A game between "..playerWhite.." and "..playerBlack.." ended in a draw because the same position has appeared 5 times")
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end
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end
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