A PGN interface that shows en passant?

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Norm Pollock
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A PGN interface that shows en passant?

Post by Norm Pollock » Thu Dec 05, 2013 8:59 pm

I once saw a pgn interface or diagram where a circle was put into an active "en passant" square. Such notation would only make sense if the "en passant" square was actively being attacked by a pawn of the side with the move.

I don't recall where I saw it. But it would be nice if all the PGN GUIs and interfaces - Winboard, Arena, Scid, etc had some sort of notation for the en passant square.

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Re: A PGN interface that shows en passant?

Post by hgm » Thu Dec 05, 2013 9:18 pm

Not sure what you mean by 'notation'. You mean some marker in the display of the Chess board?

WinBoard does not normally mark squares you can move to. Why should en-passant be different? It only puts markers (fat dots) in squares you can move to when you lift a piece to move. If you would lift a Pawn that can e.p. capture it would certainly mark the e.p. square (with a red dot, because it is a capture).

Why would it be 'nice' to have that? To me, it just seems distracting. You put something on the board that does not belong there. If the argument is that you want the board to indicate game state, the same argument could be applied to castling rights. Why do one, and not the other?

Sorry for being such a skeptic...

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Re: A PGN interface that shows en passant?

Post by hgm » Thu Dec 05, 2013 10:06 pm

On second thought, what you propose does not really seem different from "Highlight last move". The e.p. square could be marked by drawing a big fat arrow through it, between the squares of the Pawn double-push. The only new thing is that you would want only double-pushes to have such highlighting, and then only if there is an enemy Pawn beside them.

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Re: A PGN interface that shows en passant?

Post by Norm Pollock » Fri Dec 06, 2013 12:16 am

hgm wrote:On second thought, what you propose does not really seem different from "Highlight last move". The e.p. square could be marked by drawing a big fat arrow through it, between the squares of the Pawn double-push. The only new thing is that you would want only double-pushes to have such highlighting, and then only if there is an enemy Pawn beside them.
You have the idea. I was thinking of just having a circle or some other simple non-chess character occupy the target square, and only if there is an enemy pawn that can attack that square. As a user I want to know what all the possible moves are in a position, and right now, possible ep moves are not shown in the visual diagram.

I hope to see this implemented in WinBoard. Good Luck with it! ;)

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Re: A PGN interface that shows en passant?

Post by hgm » Fri Dec 06, 2013 6:14 am

But castlings can also not be seen on a regular board. So what about those?

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Re: A PGN interface that shows en passant?

Post by Norm Pollock » Fri Dec 06, 2013 7:01 am

hgm wrote:But castlings can also not be seen on a regular board. So what about those?
If you can put in a special character in the empty target square to show "ep" opportunity, then it should be similar to put in another special character in the empty travel squares for "castling" opportunity. And opportunity may exist for both castlings at the same time. However only put in the special character if the travel squares are empty and the active side has castling rights without a king attack along the way.

However "castling" opportunity can be inferred 99% of the time by visual inspection. And the extra characters (2, 3 or 5) on the board for castling, for a great number of moves, will make the board confusing and messy. So I do not recommend doing this for "castling".

"ep" opportunity is different. "ep" opportunity is fleeting, it is gone after the next move, whereas castling opportunity can stay around, or come and go and return.

And it is not obvious if "ep" opportunity exists. For example, a White pawn could move to d5, with Black pawns already at c5 and e5, and empty squares at c6 and e6, and then Black could make a move like h7-h6. So someone looking at White's position will wonder if he has "ep" rights at c6 or e6 or no rights.

[d]rnbqkbnr/pp1p1pp1/7p/2pPp3/8/2N5/PPP1PPPP/R1BQKBNR w KQkq -

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Re: A PGN interface that shows en passant?

Post by Norm Pollock » Fri Dec 06, 2013 7:38 am

Here is a constructed position, with 4 possible "ep" target squares, 3 of which would have double "ep" attacks. Without an indicator of an active "ep" target square, a person looking at this diagram would not know all the possible moves.

[d]rnbqk2b/1p1pnp1r/7p/pPpPpPpP/8/2N5/P1P1P1P1/R1BQKBNR w KQq -

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Re: A PGN interface that shows en passant?

Post by hgm » Fri Dec 06, 2013 8:10 am

Well, personally I think even indicating the e.p. square is messy. But I don't understand why you would mark 2, 3 or 5 squares for castling. You would not mark the squares the King skips over. Just where it goes. So you would mark g1/g8 (if f1/f8 is empty, and O-O is legal) or c1/c8. That is at most two.

Using the arrow that indicates the previous double push would be necessary, however. The e.p. square alone does not provide enough information to see which e.p. capture is possible. In Berolina Chess, for the position you give, you would not know whether the previous move was a7-c5 or c7-a5 (and hence whether b5xb6 would capture Pc5 or Pa5) if you just marked b6. The arrows would never be ambiguous, and intuitively obvious to decode.

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Re: A PGN interface that shows en passant?

Post by smrf » Fri Dec 06, 2013 10:14 am

SMIRF does it that way:

Image

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Re: A PGN interface that shows en passant?

Post by Norm Pollock » Fri Dec 06, 2013 1:09 pm

Thanks Reinhard. That is EXACTLY what I'm trying to express with regard to "ep" move availability. I have never seen that symbol before. It took a few seconds then I realized it was "ep" in a circular font.

As H.G. pointed out, we could use another symbol, perhaps "cs", at g8 or c8, to show castling availability.

Let the diagram of a chess position show ALL available and non-available "ep" and "castling" moves. This can be done in a way that is NOT messy.

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