Chess: Restrict 'same position' rule a bit
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Wuzzy
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@ -1245,12 +1245,28 @@ local function get_positions_history(meta)
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return str
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end
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-- Record the position no. of the position from which
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-- all positions before that can be ignored
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-- when counting same positions.
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-- This number is updated each time an irreversible
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-- move is made:
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-- * pawn move
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-- * capturing move
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-- * loss of castling rights
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-- * loss of (theoretical) en passant availability
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-- This works cuz when an irreversible move is made,
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-- it is impossible for this and all positions before
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-- that to occur again so the "repetition counter"
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-- for each of these position never increases again.
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local no_repetitions_before = 1
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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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local pawn_double_step_index
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positions_list = {}
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local current_player = "w"
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@ -1273,6 +1289,11 @@ local function get_positions_history(meta)
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else
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current_player = "w"
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end
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-- Reset repetition counter on piece capture
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if pieceTo ~= "" then
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no_repetitions_before = m
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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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@ -1291,24 +1312,34 @@ local function get_positions_history(meta)
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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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no_repetitions_before = m
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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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no_repetitions_before = m
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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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no_repetitions_before = m
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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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no_repetitions_before = m
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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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if castling_state[1] or castling_state[2] then
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no_repetitions_before = m
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end
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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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if castling_state[3] or castling_state[4] then
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no_repetitions_before = m
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end
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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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@ -1317,20 +1348,43 @@ local function get_positions_history(meta)
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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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if castling_state[2] then
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castling_state[2] = false
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no_repetitions_before = m
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end
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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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if castling_state[1] then
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castling_state[1] = false
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no_repetitions_before = m
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end
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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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if castling_state[4] then
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castling_state[4] = false
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no_repetitions_before = m
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end
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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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if castling_state[3] then
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castling_state[3] = false
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no_repetitions_before = m
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end
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end
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end
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local pawn_double_step_index
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-- Pawn movement resets repetition counter
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if pieceFrom:sub(11,14) == "pawn" then
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no_repetitions_before = m
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end
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-- Loss of (theoretical) en passant capture availability
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-- resets repetition counter
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if pawn_double_step_index then
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no_repetitions_before = m
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pawn_double_step_index = nil
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end
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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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@ -1341,7 +1395,7 @@ local function get_positions_history(meta)
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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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-- Double pawn step (record pos)
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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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@ -1356,7 +1410,7 @@ local function get_positions_history(meta)
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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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return positions_list, no_repetitions_before
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end
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-- Returns the highest number of positions that are repeated
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@ -1364,11 +1418,13 @@ end
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-- Arguments:
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-- * positions: positions history list returned by get_position_history()
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-- * stop_counting_at: stop counting when this many repetitons have been found (optional)
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local function count_repeated_positions(positions, stop_counting_at)
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-- * first_position: index of first position to check (default: 1)
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local function count_repeated_positions(positions, stop_counting_at, first_position)
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-- Count how often each position occurred
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local positions_counter = {}
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local maxRepeatedPositions = 0
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for p = 1, #positions do
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first_position = first_position or 1
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for p = first_position, #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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@ -1733,8 +1789,8 @@ local function update_formspec(meta)
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-- "same position has occured 3 times" rule
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-- Count how often each position occurred
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local positions = get_positions_history(meta)
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local maxRepeatedPositions = count_repeated_positions(positions, 3)
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local positions, first_p = get_positions_history(meta)
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local maxRepeatedPositions = count_repeated_positions(positions, 3, first_p)
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if maxRepeatedPositions == 2 then
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-- If the same position is about to occur 3 times.
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-- Will trigger "draw claim" mode in which player must do the final move that triggers the draw.
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@ -1969,9 +2025,9 @@ local function update_game_result(meta)
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-- First, generate the position history
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local forceRepetitionDraw = false
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local chosenRepetitionDraw = false
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local positions = get_positions_history(meta)
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local positions, first_p = get_positions_history(meta)
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-- Then count the repeated positions
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local maxRepeatedPositions = count_repeated_positions(positions, 5)
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local maxRepeatedPositions = count_repeated_positions(positions, 5, first_p)
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if maxRepeatedPositions >= 3 then
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chosenRepetitionDraw = true
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end
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@ -2878,8 +2934,8 @@ function realchess.fields(pos, _, fields, sender)
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return
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end
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local positions = get_positions_history(meta)
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local maxRepeatedPositions = count_repeated_positions(positions, 3)
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local positions, first_p = get_positions_history(meta)
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local maxRepeatedPositions = count_repeated_positions(positions, 3, first_p)
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if maxRepeatedPositions == 2 then
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meta:set_string("drawClaim", "same_position_3")
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update_formspec(meta)
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