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LibChess: Forbid King moving into check by a pawn on the home rank

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A player can no longer move the King piece into any position on
their home rank if the move would place the King in check.

A player can also no longer ignore a check position when in check
by a pawn on their home rank. The player must now resolve the check
during their move.
This commit is contained in:
Brendan Coles 2020-10-30 06:39:44 +00:00 • committed by Andreas Kling
parent 6365b44773
commit d4c34d50c9
2 changed files with 60 additions and 25 deletions
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84
Libraries/LibChess/Chess.cpp
View file

@ -176,6 +176,35 @@ Piece Board::set_piece(const Square& square, const Piece& piece)
return m_board[square.rank][square.file] = piece;
}
bool Board::is_legal_promotion(const Move& move, Colour colour) const
{
auto piece = get_piece(move.from);
if (move.promote_to == Type::Pawn || move.promote_to == Type::King) {
// attempted promotion to invalid piece
return false;
}
if (piece.type != Type::Pawn && move.promote_to != Type::None) {
// attempted promotion from invalid piece
return false;
}
unsigned promotion_rank = (colour == Colour::White) ? 7 : 0;
if (move.to.rank != promotion_rank && move.promote_to != Type::None) {
// attempted promotion from invalid rank
return false;
}
if (piece.type == Type::Pawn && move.to.rank == promotion_rank && move.promote_to == Type::None) {
// attempted move to promotion rank without promoting
return false;
}
return true;
}
bool Board::is_legal(const Move& move, Colour colour) const
{
if (colour == Colour::None)
@ -184,6 +213,9 @@ bool Board::is_legal(const Move& move, Colour colour) const
if (!is_legal_no_check(move, colour))
return false;
if (!is_legal_promotion(move, colour))
return false;
Board clone = *this;
clone.apply_illegal_move(move, colour);
if (clone.in_check(colour))
@ -218,49 +250,47 @@ bool Board::is_legal(const Move& move, Colour colour) const
bool Board::is_legal_no_check(const Move& move, Colour colour) const
{
auto piece = get_piece(move.from);
if (piece.colour != colour)
// attempted move of opponent's piece
return false;
if (move.to.rank > 7 || move.to.file > 7)
return false;
if (piece.type != Type::Pawn && move.promote_to != Type::None)
return false;
if (move.promote_to == Type::Pawn || move.promote_to == Type::King)
// attempted move outside of board
return false;
if (piece.type == Type::Pawn) {
int dir = (colour == Colour::White) ? +1 : -1;
unsigned start_rank = (colour == Colour::White) ? 1 : 6;
unsigned other_start_rank = (colour == Colour::White) ? 6 : 1;
unsigned en_passant_rank = (colour == Colour::White) ? 4 : 3;
unsigned promotion_rank = (colour == Colour::White) ? 7 : 0;
if (move.to.rank == promotion_rank) {
if (move.promote_to == Type::Pawn || move.promote_to == Type::King || move.promote_to == Type::None)
return false;
} else if (move.promote_to != Type::None) {
return false;
if (move.from.rank == start_rank && move.to.rank == move.from.rank + (2 * dir) && move.to.file == move.from.file
&& get_piece(move.to).type == Type::None && get_piece({ move.from.rank + dir, move.from.file }).type == Type::None) {
// 2 square pawn move from initial position.
return true;
}
if (move.to.rank == move.from.rank + dir && move.to.file == move.from.file && get_piece(move.to).type == Type::None) {
if (move.to.rank != move.from.rank + dir)
// attempted backwards or sideways move
return false;
if (move.to.file == move.from.file && get_piece(move.to).type == Type::None) {
// Regular pawn move.
return true;
} else if (move.to.rank == move.from.rank + dir && (move.to.file == move.from.file + 1 || move.to.file == move.from.file - 1)) {
}
if (move.to.file == move.from.file + 1 || move.to.file == move.from.file - 1) {
unsigned other_start_rank = (colour == Colour::White) ? 6 : 1;
unsigned en_passant_rank = (colour == Colour::White) ? 4 : 3;
Move en_passant_last_move = { { other_start_rank, move.to.file }, { en_passant_rank, move.to.file } };
if (get_piece(move.to).colour == opposing_colour(colour)) {
// Pawn capture.
return true;
} else if (m_last_move.has_value() && move.from.rank == en_passant_rank && m_last_move.value() == en_passant_last_move
}
if (m_last_move.has_value() && move.from.rank == en_passant_rank && m_last_move.value() == en_passant_last_move
&& get_piece(en_passant_last_move.to) == Piece(opposing_colour(colour), Type::Pawn)) {
// En passant.
return true;
}
} else if (move.from.rank == start_rank && move.to.rank == move.from.rank + (2 * dir) && move.to.file == move.from.file
&& get_piece(move.to).type == Type::None && get_piece({ move.from.rank + dir, move.from.file }).type == Type::None) {
// 2 square pawn move from initial position.
return true;
}
return false;
@ -614,15 +644,19 @@ bool Board::is_promotion_move(const Move& move, Colour colour) const
if (colour == Colour::None)
colour = turn();
unsigned promotion_rank = (colour == Colour::White) ? 7 : 0;
if (move.to.rank != promotion_rank)
return false;
if (get_piece(move.from).type != Type::Pawn)
return false;
Move queen_move = move;
queen_move.promote_to = Type::Queen;
if (!is_legal(queen_move, colour))
return false;
if (get_piece(move.from).type == Type::Pawn && ((colour == Colour::Black && move.to.rank == 0) || (colour == Colour::White && move.to.rank == 7)))
return true;
return false;
return true;
}
bool Board::operator==(const Board& other) const