The Rules of Onyx
This is the initial layout for a standard game of Onyx. Each player starts with two pieces along each of the two sides of the board belonging to the opponent.
A B C D E F G H I J K L
12 - - - - - H - H - - - - - 12
| / | | / | | / | | / | | / | | / |
11 - - - - - - - - - - - 11
| | \ | | \ | | \ | | \ | | \ | |
10 - - - - - - - - - - - 10
| / | | / | | / | | / | | / | | / |
9 - - - - - - - - - - - 9
| | \ | | \ | | \ | | \ | | \ | |
8 - - - - - - - - - - - 8
| / | | / | | / | | / | | / | | / |
7 V - - - - - - - - - - - V 7
| | \ | | \ | | \ | | \ | | \ | |
6 V - - - - - - - - - - - V 6
| / | | / | | / | | / | | / | | / |
5 - - - - - - - - - - - 5
| | \ | | \ | | \ | | \ | | \ | |
4 - - - - - - - - - - - 4
| / | | / | | / | | / | | / | | / |
3 - - - - - - - - - - - 3
| | \ | | \ | | \ | | \ | | \ | |
2 - - - - - - - - - - - 2
| / | | / | | / | | / | | / | | / |
1 - - - - - H - H - - - - - 1
A B C D E F G H I J K L
Onyx is a connection game with a unique capturing rule. It is played by two players; 'V' Player (Vertical Player or Player playing Black) and 'H' Player (Horizontal Player or Player playing White).
The Onyx board is comprised of interlocking squares and equilateral triangles. Each square is further divided into four non-equilateral triangles by lines that join opposite corner points of the square. These lines form a midpoint at the center of each square. A move consists of placing a piece of one's color on the midpoint of a square or on the corner point of a square or equilateral triangle. One restriction on placement is that a piece can only be placed on the midpoint of a square if the four corner points of that square are unoccupied. Two pieces joined by a single straight line are considered to be connected. With the ascii representation of the board the equilateral triangles are comprised of adjacent diagonal, horizontal and vertical lines that are joined to each other. (Therefore, these triangles lose their equilateral shape due to the limitation of the ascii representation. Also, two triangles that share a diagonal line appear to form a square. However, the real squares are the ones that do not show a diagonal line in them.)
Squares are shown without any diagonal lines joining the opposite corners. Nonetheless, a piece can be placed in the center (midpoint) of a square and that piece is considered to be connected to any piece that occupies a corner point of that same square.
Capturing: If the midpoint of a square is unoccupied and a player places a piece on the corner point of the square with the result that both player's have two pieces occupying opposite corner points of the square then the two opponent's pieces on that square are captured and removed from the board. It is possible to capture two pairs of pieces on two different squares with one move. In that case all four captured pieces are removed from the board.
The object of the game is to construct an unbroken chain of your connected pieces linking one side of the board to the opposite side. The Vertical Player must complete a chain from top to bottom, while the Horizontal Player must complete a chain from left to right. Pieces may be placed either at an intersection of a letter and number (i.e. D10 - the corner point of a square) or inside an empty square that does not have a line through it (ie. the midpoint of a square). The corners of the board (A1, L1, A12, and L12) belong to the sides of either player and may be part of an unbroken chain for either player in the connection of two opposite sides of the board.
Example 1: Midpoint moves
2 - - - - In this example, 'V' Player placed one of his
| / | V | / | H | pieces at BC12 (the midpoint of the square bounded
1 - - - - by columns B and C and rows 1 and 2) while
A B C D E 'H' Player placed one of his pieces at DE12
In example 1, the inside of a square is noted with the two letters and
two numbers of the two columns and two rows that surround the desired
location. Notice that CD12 is not a valid place to make a move (it has a
'/' through it).
Example 2: Restriction on midpoint moves
10 - - V - - Neither player may play at BC910 nor at DE910.
| / | ? | / | ? |
9 - - - - H
A B C D E
In example 2, neither player may place a piece at the locations
marked with a question mark ('?') since one or more of the corners of
the square is occupied with a player's piece; there is a piece at C10.
Remember that a player may place a piece inside of a square only if all
four corners of that square are empty. Likewise, neither player may
play at DE910 because of the piece at E9.
Example 3: Linking pieces
10 - V - - H -
| / | | / | H |
9 V - - V - - H
G H I J K
In example 3, the pieces at H10 and G9 are connected by the '/' line
that links them. Also, the pieces at J10 and K9 are both connected
to the piece at JK910 and are therefore part of the same connected chain.
A piece located in the center of a square is linked to any pieces of the
same color located at any of the corners of that square. Notice that
the 'V' pieces at H10 and I9 are not connected. A 'V' piece placed at
either H9 or I10 would connect to both the 'V' piece at I9 and the
'V' piece at H10 making them all part of one connected chain.
Example 4: Captures
4 - - V - V - H 4 - H - - V - H
| / | | / | ? | ---> | / | | / | ? |
3 - V - H - - V 3 - - H - - V
C D E F G C D E F G
In example 4, the 'H' Player may make a single capture by playing
D4 (or D4*); he then captures the two 'V' pieces at E4 and D3 and they
are removed from the board as shown on the right. A capture may only
occur when the opponent's pieces are at diagonally opposite corners of
a square. The 'H' Player may also capture at F3 only if the location
marked with the question mark were empty. A capture may only occur if
the center of the square is empty; if the location marked with the
question mark had a piece in it, then a capture would not be possible
at that square.
Example 5: Double captures
4 V - H - V - - 4 V - - V - -
| / | | / | | | / | | / | |
3 H - - H - - ---> 3 - V - - -
| | \ | | \ | | | \ | | \ |
2 V - H - - H - H 2 V - - - H - H
C D E F G C D E F G
Example 5 shows a double capture. Player 'V' makes the move, D3,
(or D3**) and captures the opponent at two squares and removes all the
opponent's pieces at D2, C3, E3, and D4 as shown on the right. (BTW:
just to make clear, the 'V' pieces at D3 and C4 are not connected
because the slash/line is in the wrong direction. The slash/line at
CD34 connects any pieces that would occupy D4 and C3; while the
slash/line at DE23 would connect pieces located at D3 and E2. A
piece located in the center of a square is connected to any pieces
of the same color located at any of the corners of that square.
The two 'H' pieces located at F2 and G2 are connected by the
horizontal line between them.)
Example 6: Alternate ascii representation
4 - - V - 4 -- --V--
| | / | | -> |\/| /|\/|
3 - - - V -> |/\|/ |/\|
D E F G 3 -- -- --V
D E F G
Example 6 shows an alternate ascii representation of the Onyx board.
The squares that appear empty on the left are actually filled by four
lines going to the center as shown on the right. The pieces
at F4 and G3 are not yet part of the same connected chain.
If a 'V' piece were located at F3 or G4 or FG34 then the two
'V' pieces on the board would be part of the same connected chain.