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[vchess.git] / views / rules / Chess960.pug

p.boxed
	| Orthodox rules (with shuffled starting position).

h3 Basics

p.
	Chess is played between two players, one moving the white pieces and the other
	the black pieces. A "move" consists of a piece's movement on the board.
	White and black moves alternate until a specific situation occurs (checkmate,
	stalemate, or draw criteria met; this is detailed later).
	White pieces always make the first move.

p.
	Each piece has a particular way to move, but almost always captures by moving to an
	occupied square (with only one exception, detailed later).

figure.diagram-container
	.diagram
		| fen:rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR:
	figcaption Standard initial position.

p.
	Board coordinates: squares are always identified by a couple (letter, number).
	The letter starts from 'a' and indicates the column, while the number starts
	at '1' and indicates the row.
	Since the chessboard is 64 squares, 8x8, this results in a coordinates system
	from a1 to h8. 'a1' is the bottom left corner square from the white pieces
	player perspective, while 'h8' is in the upper right corner.

h3 Regular moves

h4 Pawns

p.
	They are the weakest pieces on board, but the most complex to move.
	From their initial rank they can either jump two squares forward (vertically),
	or advance only one square in this same direction. After that first move they
	only advance one square at a time, vertically, moving up.

p.
	Pawns capture by moving forward (upper on the board) one square diagonally,
	when an enemy piece sits on that square.

p.
	When reaching the last rank, pawns must promote into any (friendly)
	other non-royal piece: queen, rook, knight or bishop.

p.
	Moves notations: "pawn" is implicit, so for a simple move we only write the
	destination square (because only one pawn at most can move forward to a specific
	square). Thus, 1.e4 means "pawn from e2 to e4". However, in case of captures
	the situation could be ambiguous (two pawns on the same rank), so the column
	is specified too: "fxe6" (for example).
	As you can see capture is marked by a cross symbol: "x".

figure.diagram-container
	.diagram
		| fen:k7/8/8/1prp4/1P1P4/8/6P1/7K:
	figcaption Possible pawn moves: g3, g4, dxc5, bxc5

p
	| For a piece movement, we just prepend the upper-case piece initial before the
	| previously described notation. A rook taking something on f3 square writes:
	| Rxf3. There are rules for ambiguous situation, but discussing them now would
	| be too far off-topic. Please visit for example the 
	a(href="https://en.wikipedia.org/wiki/Algebraic_notation_(chess)")
		| Wikipedia page 
	| for full information on this subject.

h4 Rooks

p.
	They move either horizontally or vertically, as far as they want while the path
	is free of pieces. If this path ends with an enemy piece, it can a priori be captured
	(a priori because if the move ends up with the king in check, then it's illegal).

h4 Knights

p.
	They are the only units able to jump over other pieces (without capturing them).
	They do "L" moves: two squares in one direction (horizontally or vertically),
	and then one square in an orthogonal direction.

figure.diagram-container
	.diagram
		| fen:k7/2p5/5q2/2b5/4N3/2R3r1/3P4/7K f6,d6,c5,f2,g3,g5:
	figcaption Possible knight moves from e4.

h4 Bishops

p.
	They move diagonally, as far as they want while the path is free of pieces.
	If this path ends with an enemy piece, it can a priori be captured.

h4 Queen

p This piece combines the movement of a rook and a bishop, with the same conditions.

h4 King

p.
	This piece moves like a queen, but only by one square at a time. The final square
	must be either vacant or occupied by an enemy piece (therefore captured).

p.
	The king cannot be captured, but a move may ends up attacking enemy's king.
	It is said to be "under check" (or "in check") and the opponent must either:
ul
	li move the king to a safe square, or
	li capture the attacker, or
	li intercept the attacking line.
p Depending on the situation one or more of these counter-measures could be impossible.

p Leaving our king in check after a move is forbidden.

TODO: diagram let king in check capturing queen, bishop pinned
figure.diagram-container
	.diagram
		| fen:r6k/4q3/8/8/8/B7/8/K7:
	figcaption Bxe7 is illegal (it allows Rxa1).

h3 Special moves

p Apart from pawn promotion which has already been introduced, two special moves exist:
ul
	li.
		castle: if both the king and the right-most (from white player perspective) rook
		haven't moved yet, and if nothing stand in the path from king to rook, and if the
		squares f1 and g1 are either free or occupied by the king or rook implied, then
		the king can go to g1 while the rook moves to f1. Note that since positions are
		shuffled one of these two pieces may apparently not move.
		The same can be done on the other side (left-most rook), and end squares are c1
		for king and d1 for rook. The former is small castle, and the latter large castle.
		Notation: small castle writes "0-0" while large castle is "0-0-0".
	li.
		en-passant: after a pawn has jumped two squares, if an enemy pawn stands just next
		to it then it can capture the jumping pawn "en passant", exactly as if it had
		advanced only one square. The move is noted as usual, but with "e.p." in the end
		to indicate the special move.
		The capture is possible only right after the pawn jump: not later in the game.

figure.diagram-container
	.diagram.diag12
		| fen:nr1kb1r1/ppp3pp/8/2Pp4/8/7P/PP3PP1/1R3KBR:
	.diagram.diag22
		| fen:nr1kb1r1/ppp3pp/3P4/8/8/7P/PP3PP1/2KR2BR:
	figcaption.
		Left: black just played d5 (jump from d7).
		Right: after cxd6 e.p. and 0-0-0.

h3 End of the game

p.
	The best-known way to end a game is by "checkmating" the enemy king.
	This means that you end a move in a situation where the king can be captured,
	and your opponent has no way to avoid the capture.
	The checkmating player has one point and the other zero, so the score writes 1-0
	or 0-1 depending if white pieces or black pieces mated.

figure.diagram-container
	.diagram
		| fen:rnbqkbnr/ppp2Qpp/2np4/4p3/2B1P3/8/PPPP1PPP/RNB1K1NR:
	figcaption Famous mating pattern: 1-0

p All other ways to end the game lead to a draw (1/2-1/2): nobody wins:
ul
	li when a player has no legal move but is not under check,
	li.
		when a position is repeated three times with the same castling right and
		same player in turn,
	li when 50 moves are played without pawn movement or capture.
p.
	Note: this last way to end a game is not implemented, because it quite seldom occurs,
	does not generalize so well to variants (it depends), and more important because
	games played on this website are not official tournament games. If you feel like
	manoeuvring for 200 moves and your opponent isn't bored, then why would I stop you?
	☺