Yes, I originally would have thought when an Advancer made a move that threatened a King, an enforcing preset would automatically announce check.
However, maybe the Advancer, being an Ultima-like piece, does not actually make a check in an Ultima-like game (which Butterfly Chess is not)?
So I now ask, is that the usual assumption that Applet generated preset code makes for every CV put through the generating process?
I don't know how a generated preset works, but the checked subroutine I use in the fairychess include file normally checks for captures by displacement by checking if each enemy piece on the board can move to the King's position. This would not normally work with Ultima pieces, which do not normally capture by displacement, but I have managed to use this subroutine with Ultima without modifying it. First, let's look at the subroutine:
sub checked king:
my from piece;
local movetype;
set movetype CHECK;
if isupper cond empty var king $moved space var king:
def enemies onlylower;
else:
def enemies onlyupper;
endif;
for (from piece) fn enemies:
if fn const alias #piece #from var king:
return #from;
endif;
next;
return false;
endsub;
The key to working with Ultima is that it sets movetype to CHECK. With this in mind, I have written functions for Ultima pieces like this:
def Black_Withdrawer fn join "Black_Withdrawer_" var movetype #0 #1;
Depending upon the value of movetype, it will call either Black_Withdrawer_MOVE or Black_Withdrawer_CHECK, which I have defined separately and differently. Thanks to setting movetype to CHECK, the checked subroutine will use the *_CHECK functions for Ultima pieces. Instead of going through a normal move, one of these functions will check whether the piece at the first coordinate can capture the piece at the second. For example:
def Black_Withdrawer_CHECK
empty where #frm - file #frm file #to - rank #frm rank #to
and == distance #frm #to 1
and not near #frm I 1
=frm =to;
This first makes sure that the piece is not next to a White Immobilizer (designated as I). It then verifies that the two spaces are adjacent. Calculating the direction away from the piece at #to, it checks whether there is an adjacent empty space in that direction. If there is, it returns true.
I don't know how a generated preset works, but the
checkedsubroutine I use in the fairychess include file normally checks for captures by displacement by checking if each enemy piece on the board can move to the King's position. This would not normally work with Ultima pieces, which do not normally capture by displacement, but I have managed to use this subroutine with Ultima without modifying it. First, let's look at the subroutine:The key to working with Ultima is that it sets movetype to CHECK. With this in mind, I have written functions for Ultima pieces like this:
Depending upon the value of movetype, it will call either Black_Withdrawer_MOVE or Black_Withdrawer_CHECK, which I have defined separately and differently. Thanks to setting movetype to CHECK, the checked subroutine will use the *_CHECK functions for Ultima pieces. Instead of going through a normal move, one of these functions will check whether the piece at the first coordinate can capture the piece at the second. For example:
This first makes sure that the piece is not next to a White Immobilizer (designated as I). It then verifies that the two spaces are adjacent. Calculating the direction away from the piece at #to, it checks whether there is an adjacent empty space in that direction. If there is, it returns true.