Backgammon Programming

Programming

Methods of encoding positions

From:   Gary Wong
Address:   gtw@research.att.com
Date:   23 January 2001
Subject:   Re: Entering board positions
Forum:   rec.games.backgammon
Google:   dh6u26qb55f.fsf@pc-gtw.research.att.com

> In these days of human-mediated machine-to-machine communication, > would it not be possible for your programmes to export and read a > compact board notation? Something a bit like the Forsythe notation > for a chess position. A simple example of what might be possible: > <m/x4/o2222//o4/o4/o4/19/x/x5> > Meaning: > Money game. > X owns a 4 cube. > O has all of a double two to move. > No men on the bar. > O has four men each on his 1, 2 and 3 points. > X has one man on his 2 point and five on his 1 point. There are a few schemes for recording positions that (I think) come close to what you want. Jellyfish ".pos" files are perhaps the most widely used; programs that handle it include Jellyfish (surprise!), the BBGT FIBS client, BGBlitz, and GNU Backgammon. The format is documented at: http://jelly.effect.no/fspec.htm FIBS "boardstyle 3" output is nice and compact, and implicitly understood by pretty much every FIBS client out there, although it's not currently used as an external representation. The description is: http://www.fibs.com/fibscmds.html#rawboard GNU Backgammon uses a very short text string to describe a board position; for instance, when running on a text terminal, it shows the position you describe as: GNU Backgammon Position ID: XwAAgPceAAAAAA +12-11-10--9--8--7-------6--5--4--3--2--1-+ O: gnubg | | | O O O | O Rolled 22 | | | O O O | O | | | O O O | O | | | O O O | | | | | ^| |BAR| | | | | X | X | | | X | XX | | | X | XX | | | X | XX | | | X X | XX +13-14-15-16-17-18------19-20-21-22-23-24-+ X: gary (Cube: 4) The "XwAAgPceAAAAAA" describes the chequer positions; the gnubg command "set board XwAAgPceAAAAAA" will restore the above position. The position ID format is documented at: http://www.cs.arizona.edu/~gary/backgammon/positionid.html Position IDs do not include the cube value, match score, player names, etc., however; an extensible format for recording auxiliary information like that is SGF (Smart Game Format): http://www.red-bean.com/sgf/ and SGF for backgammon in particular: http://www.red-bean.com/sgf/backgammon.html Cheers, Gary.

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