#94 Misleading game shown if a Chess960 PGN is opened

[Bruno Rizzuti]

When i opened with ChessX the database of the FiNet Chess960 Rapid World Championship in Mainz, i noticed that ChessX tries to read the games even if it is not able to support them (probably because of the symbols in the castling field of the FEN). ChessX shows the classical starting position instead, and then it also allows to play all the moves in the game up to the first "illegal" move.

Needless to say, ChessX should refuse to show a Chess960 game (more generally, refuse to start the game from an unsupported FEN) rather then show a senseless game (unless Chess960 is supported, of course).

An example of game:

[Event "FiNet Chess960 Rapid World Championship"]
[Site "Chess Classic Mainz"]
[Date "2007.??.??"]
[Round "1.1"]
[White "Aronian, Levon"]
[Black "Bacrot, Etienne"]
[Result "1-0"]
[SetUp "1"]
[FEN "qnbbnrkr/pppppppp/8/8/8/8/PPPPPPPP/QNBBNRKR w HFhf - 0 1"]
[PlyCount "49"]
[EventDate "2007.??.??"]

1. c4 c5 2. Nf3 Nc6 3. b3 e6 4. d4 cxd4 5. Nxd4 Bf6 6. Bb2 b6 7. Nf3 Bxb2 8.
Qxb2 Nf6 9. Nc3 d5 10. cxd5 exd5 11. e3 Rd8 12. Nb5 Bg4 13. Nbd4 Nxd4 14. Nxd4
Bxd1 15. Rxd1 O-O 16. O-O Qb7 17. Rd3 Rc8 18. Rfd1 Rc5 19. Nf5 Kh8 20. b4 Rc7
21. Rxd5 Qc8 22. h3 Rc2 23. Qa1 Rg8 24. Nh6 Qe6 25. Rd6 1-0

[Michal Rudolf]

But how to recognize such games? Using FEN special fields?

[Bruno Rizzuti]

1. One can recognize for sure a chess960 game when there are unconventional letters (other than K,Q,k,q) in the castling field of the FEN. In this case, ChessX should say something like "we don't support chess960".

Please note that the chess960 game provided in the original bug report makes ChessX go crazy. In fact, the position shown on board is the one of a classical game (rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR), in spite of the fact that the first field is different (qnbbnrkr/pppppppp/8/8/8/8/PPPPPPPP/QNBBNRKR). The very same FEN without unconventional letters in the castling field (qnbbnrkr/pppppppp/8/8/8/8/PPPPPPPP/QNBBNRKR w - - 0 1) is handled correctly.

2. One can recognize for sure a chess960 game because the pieces in the starting positions in the first and last ranks are not in the classical position, whereas all the pawns are still on the second and second-to-last rank. Again, in this case ChessX should say something like "we don't support chess960".

3. One can suspect that we are in the presence of a chess960 game if in any moment the PGN indicates a castling that is impossible to perform. In this case ChessX should say something like "castling is impossible - perhaps a chess960 game? - we don't support chess960".

[Michal Rudolf]

ChessX should detect unusual castling rights. If there is no castling, game will be handled correctly, so no reason to ignore it.

[Jens Nissen]

As there is no way to tell a Chess960 Game from a standard game except by detecting illegal castlings, we will have to live with that. Note that the HFhf FEN-tag came out of use and today this would be written with KQkq, so the FEN looks like standard chess!
There is a change request for integrating castiling rules for chess960, which I leave open (will be implemented for the next release or the one after that)