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Grotesque Chess. A variant of Capablanca's Chess with no unprotected Pawns. (10x8, Cells: 80) [All Comments] [Add Comment or Rating]

H. G. Muller wrote on Thu, Jun 19, 2008 10:52 AM UTC:

I am still contemplating how to generalize the castling in Joker80. There are two issues there: how to commnicate the move from and to the GUI, and how to indicate the existence of the rights. Currently WinBoard protocol has two mechanisms to set up a position: by loading the engine with a FEN, or (obsolete) through an edit command to enter a list of pieces+squares combinations. The latter mode does not support transmission of castling rights at all, and is only a legacy for backward compatibility with old engines. So for loading position, we only have to provide a mechanism for indicating castling rights in a FEN.

The FRC-type notation only indicates the position of the Rook. The King does not need to be indicated in games where there is only one King, and the positioning of Rook w.r.t. King implies where both will end up. This means we would have to devise some other notation for cases where the King ends elsewhere. I am not sure if it would make sense to generalize so much as to allow castlings where the Rook does not end up next to, and on the other side of the King. There is of course no limit to the craziness of moves that could be called a castling, but one would have to put a limit somewhere, to not fall victim to the 'maximum-flexibility, minimum-usefulness' principle.

I would probably implement it like this: in the castling-rights field of the FEN, the letter indicating the file of the Rook that can castle (which does not necessarily have to be an orthodox Rook, as the FEN makes it obvious what piece is standing there) can be followed by a digit, indicating the number of squares the King ends up away from the corner. The final position of the Rook would be implied by this.

Example: normal King-side castling rights could be indicated by H1. The 1 would be the default (on an 8x8 board), and could be omitted for upward compatibility with Shredder-FEN. In Capablanca Chess the opening would have castling rights A2J1a2j1, equivalent to AJaj (or KQkq). Symmetric castling rights like in Janus Chess would be indicated as A1J1a1j1, or A1Ja1j when deleting the redundant defaults. Multiple castling rights to the same side could exist next to each other: A2A1J2J1a2a1j2j1 would allow short as well as long castling in both directions.

For transmitting the castling moves, one could use King captures own Rook. In games where the same Rook could be used for castlings with multiple King destinations, one could give the King step to its final destination in stead. If this could also be a normal King move, one could append an r as 5th character to identify it as a castling, using the syntax that would otherwise be used for promotions. In PGN one could use similar strategies to indicate non-orthodox castlings, and use suffix =R on a King move to specify castling.

I think this covers most cases encountered in practice. Problems only occur only if there would be multiple castlings with the same Rook, and at the same time castlings with a Rook on the left would have the same King destination as those with a Rook on the right. Because the move notation cannot indicate at the same time which Rook to use and specify where the King should go. But this seems to outlandish to worry about.

To cover cases where K and R do not end up next to each other, we could put a second digit in the FEN castling-rights specifier for the final position of the Rook wrt the corner. (I.e. normal king-side castling = h12.) This obviously could lead to problems on very wide boards, that require multiple digits to specify distance to the corner. So perhaps it is better to separate King and Rook destination by a period (h1.2). Indicating the move would be a problem, as two destinations might have to be specified to unambiguously identify the move (e.g. if all castlings are allowed weher the King steps any number of squares >=2 towards a Rook, and then the Rook can go to any square the King passed over.) One could just specify King and Rook final squares (i.e. O-O = g1f1), but in FRC there is no guarantee that this cannot be a normal move. In which case the 'r' could again be used as 5th character, to indicate castling. In PGN we could reserve a character used in stead of the piece indicator for castlings, say 'O'.

Conclusion: it is difficult to design a notation that would be general and universal; different games seem to need different ways to specify the moves and rights.