The 'diagram of the week' is for Gross Chess, a large-board variant that complements the FIDE army with some fairy pieces known from several other popular variants: the Archbishop and Chancellor from Capablanca Chess, the Champion and Wizard from Omega Chess, and the Cannon from Xiangqi plus its diagonal cousin, the Vao.
The moves of most pieces are not very special,
and have very basic descriptions in Betza notation,
all supported by the Interactive Diagram script.
The main challenge was in the promotion rules.
The diagram allows you to specify a list of legal promotion choices,
and even allow you to specify that these pieces come from holdings
that accumulate captured pieces,
as well as some pieces that start there.
But has no standard mechanism for making this choice rank-dependent.
For this a small extra script routine had to be added,
which corrects any invalid choice to a non-promotion.
The flexible castling is achieved in the diagram by specifying all possible different castlings as separate moves on the King: isO2, isO3 and isO4. This is needed because unlike with other Betza atoms, a range specifier on the O atom in the XBetza extension used in the diagram indicates an exact range, rather than a maximum. That the castling partner is not at the board edge poses no special problem, because the diagram always allows castling with a virgin piece that moves as a Rook. (Which actually is in violation of the XBetza specs, which would need an extra j modifier to specify the castling partner is one square away from the board edge. But which is almost always what you want.)
Gross Chess
The 'diagram of the week' is for Gross Chess, a large-board variant that complements the FIDE army with some fairy pieces known from several other popular variants: the Archbishop and Chancellor from Capablanca Chess, the Champion and Wizard from Omega Chess, and the Cannon from Xiangqi plus its diagonal cousin, the Vao.
The moves of most pieces are not very special, and have very basic descriptions in Betza notation, all supported by the Interactive Diagram script. The main challenge was in the promotion rules. The diagram allows you to specify a list of legal promotion choices, and even allow you to specify that these pieces come from holdings that accumulate captured pieces, as well as some pieces that start there. But has no standard mechanism for making this choice rank-dependent. For this a small extra script routine had to be added, which corrects any invalid choice to a non-promotion.
The flexible castling is achieved in the diagram by specifying all possible different castlings as separate moves on the King: isO2, isO3 and isO4. This is needed because unlike with other Betza atoms, a range specifier on the O atom in the XBetza extension used in the diagram indicates an exact range, rather than a maximum. That the castling partner is not at the board edge poses no special problem, because the diagram always allows castling with a virgin piece that moves as a Rook. (Which actually is in violation of the XBetza specs, which would need an extra j modifier to specify the castling partner is one square away from the board edge. But which is almost always what you want.)