🕸📝Fergus Duniho wrote on Thu, Jun 22, 2017 08:37 PM UTC:
Castling moves are now displayed among the legal moves. I added a castlepos subroutine to indicate whether castling was possible, and I gave the game its own stalemated subroutine. There was no need to change the checkmated subroutine, since castling is never legal when the King is checked, and that subroutine is used only when the King is in check.
Castling works by having the King or Rook move to the space it would move to during castling, so long as this would otherwise be an illegal move. When the King and Rook are each occupying the position that the other piece would go to during castling, castling may be done by moving either one to the other's space, but in displaying legal moves, only the King moving to the Rook's space gets displayed. The castling move is displayed as a Rook move when it involves the Rook leaping over the King, because the King already started in the spot it would go to during castling, or the King is in the spot the Rook will move to, which is only one space away from the King, and the Rook is not in the space the King will move to.
It would never happen that castling was impossible because both the King and Rook started out in the spaces they would move to while castling. In the position shown below, for example, the King started out in the g file, and one of the Rooks started in the f file. Although this is a position that the King and Rook would take for King-side castling, it is the Queen-side Rook that is in the f file. The King can castle with that Rook by moving to the c file, and if the f Rook moves out, the King-side Rook can castle with the King by leaping from the h file to the f file.
Castling moves are now displayed among the legal moves. I added a castlepos subroutine to indicate whether castling was possible, and I gave the game its own stalemated subroutine. There was no need to change the checkmated subroutine, since castling is never legal when the King is checked, and that subroutine is used only when the King is in check.
Castling works by having the King or Rook move to the space it would move to during castling, so long as this would otherwise be an illegal move. When the King and Rook are each occupying the position that the other piece would go to during castling, castling may be done by moving either one to the other's space, but in displaying legal moves, only the King moving to the Rook's space gets displayed. The castling move is displayed as a Rook move when it involves the Rook leaping over the King, because the King already started in the spot it would go to during castling, or the King is in the spot the Rook will move to, which is only one space away from the King, and the Rook is not in the space the King will move to.
It would never happen that castling was impossible because both the King and Rook started out in the spaces they would move to while castling. In the position shown below, for example, the King started out in the g file, and one of the Rooks started in the f file. Although this is a position that the King and Rook would take for King-side castling, it is the Queen-side Rook that is in the f file. The King can castle with that Rook by moving to the c file, and if the f Rook moves out, the King-side Rook can castle with the King by leaping from the h file to the f file.