1. Short introduction
Jeiqi (in Chinese: 揭棋, in Vietnamese: Cờ Úp, probably other names in English: uncovering / dark / unveiling chess / xiangqi) is a Xiangqi (Chinese chess) variant rising star when the number of players grows rapidly, especially in China and Vietnam.
Basically the game plays with typical Xiangqi board and pieces. The main differences are:
- At start point except the King, all 15 pieces of each side will be covered (usually by small plastic covers or simply put them face down to hide their symbols) and randomly put on original positions. Those covered pieces are called dark or covered or mystery ones
- A dark piece should do the first move as the original piece in which it is located. After the first move it will be revealed / uncovered to show its real material. From now on that (unveiled) piece will move as its real chess type. The revealing is similar to chess promotion but in this case players cannot control which new types the pieces can become. We call it “revelation” to distinguish from promotion
- Revealed Advisors and Elephants can move freely without any limited by area as they were in Xiangqi. It means they can appear out of palaces and can cross the river to attack opposite Kings
- Kings are still limited in palaces, Pawns could be revealed anywhere but can go ahead only when they are still in their home land and could go sidedly after crossing the river
- Captures: dark pieces could be captured as usual. However after being captured they may still remain in covered status. It means no one knows which real pieces are captured
2. Names / terms
We should follow notation in Wiki / Chess programming wiki for names of pieces as well as some terms:
Typical names from Xiangqi:
King / k
Advisor / a
Elephant / e
Rook / r
Cannon / c
Horse / h
Pawn / p
White / w
Black / b
Additional names for Jeiqi
Dark / d (dark/unseen/covered piece)
Standard FEN has 6 fields as below, only field 3 should changed meaning:
1) Piece placement: similar to ches. Use d/D for dark pieces
2) Active color: similar to chess. w for white, b for black
3) Captured pieces (the original one is Castling availability): Both Xiangqi and Jeiqi don’t have castling moves. Instead we use this field for recording captures because it is very important to guess to which piece a dark piece could be revealed. We write down all revealed captured pieces and their numbers but ignore ones with no capture. We don’t need (not compulsory) to write down dark captures as well since we can calculate them from the board and revealed captures. That can make the FEN string a bit shorter, avoid redundancy and inconsistent data, avoid ugly using 2 digit numbers (dark pieces could be 15 - two digit number). However we may not be so strict in this issue (have or have not dark captures).
Example of a capturing record:
H2P3C1r1p3: white loses 2 horses, 3 Pawns 1 Cannon, black loses 1 Rook, 3 Pawns
4) En passant: ignore. Use ‘-’ instead.
5) Halfmove clock: similar to chess. This is the number of halfmoves since the last capture or pawn advance.
6) Fullmove number: similar to chess. The number of the full moves. It starts at 1, and is incremented after Black's move.
ddddkdddd/9/1d5d1/d1d1d1d1d/9/9/D1D1D1D1D/1D5D1/9/DDDDKDDDD w - - 0 1
d1d1kdddd/4c4/1dp6/2d1d1d2/p7r/2R1P1R2/D7D/4H2D1/4C4/DDD1KDDH1 b D1e1 - 0 6
From above figure:
2e6/4k4/9/2Ha1P2p/2a2P3/9/3p5/4E4/e8/2D1K4 w R1C1P1D7r1h1p1d6 - 3 55
3. Move notations
Basically it is similar to chess/Xiangqi move notations. Columns are named from a to i, rows from 0 to 9. For a move of a dark piece we notate it as its original piece and use promotion notation for the revelation. Bellow is a revelation move when a dark piece in original Pawn position i3 pushed to i4 and revealed into an Horse, Rook on i5 moves to d5, dark Horse in b0 moves to c2 and revealed to a Pawn:
1 i3i4=h i5d5 2) b0c2=p
1) i4=h rc7 2) Hc2=p
The traditional move notation uses column number by side as image. We can use them as Xiangqi with some notes:
- revealing move uses promotional symbol: P1+1=h
- Don’t count dark pieces with revealed pieces of same types for solving ambitious cases. The dark and revealed pieces can be easily distinguished by revealing symbol
For example, in above board even there are two black Rooks in column 9, their moves can not be ambiguous since r9.1 is definitely by revealed Rook and r9.1=c is definitely by dark one.
Use Jeiqi as the variant name:
Inform the engine can play Jeiqi variant:
UCI_Variant var jeiqi
bestmove: as typical and it could not have revelational piece even the moving piece is a dark one. Reason: the engine cannot decides that piece:
GUI should adds revelational pieces to dark moves:
position startpos moves e3e4e b9c7c h2h7r i9h9p e4g2