Games-Go-SimpleBoard/SimpleBoard.pm

package Games::Go::SimpleBoard;

=head1 NAME

Games::Go::SimpleBoard - represent a simple go board

=head1 SYNOPSIS

   use Games::Go::SimpleBoard;

=head1 DESCRIPTION

Please supply a description )

=head2 EXPORTED CONSTANTS

Marker types for each board position (ORed together):

   MARK_TRIANGLE # triangle mark
   MARK_SQUARE   # square mark
   MARK_CIRCLE   # circle mark
   MARK_CROSS    # cross mark
   MARK_SMALL_B  # small stone, used for scoring or marking
   MARK_SMALL_W  # small stone, used for scoring or marking
   MARK_B        # normal black stone
   MARK_W        # normal whit stone
   MARK_GRAYED   # in conjunction with MARK_[BW], grays the stone
   MARK_LABEL    # a text label
   MARK_HOSHI    # this is a hoshi point (not used much)
   MARK_MOVE     # this is a regular move
   MARK_KO       # this is a ko position
   MARK_REDRAW   # ignored, can be used for your own purposes

   COLOUR_WHITE  # guarenteed to be 0
   COLOUR_BLACK  # guarenteed to be 1

   MOVE_HANDICAP # used as "x-coordinate" for handicap moves
   MOVE_PASS     # can be used as "x-coordinate" for pass moves

=head2 METHODS

=over 4

=cut

no warnings;
use strict;

use Carp ();

use base Exporter::;

our $VERSION = '1.0';

our @EXPORT = qw(
   MARK_TRIANGLE MARK_SQUARE MARK_CIRCLE MARK_SMALL_B MARK_SMALL_W MARK_B
   MARK_W MARK_GRAYED MARK_MOVE MARK_LABEL MARK_HOSHI MARK_KO MARK_CROSS
   MARK_REDRAW
   COLOUR_BLACK COLOUR_WHITE
   MOVE_HANDICAP MOVE_PASS
);

# marker types for each board position (ORed together)

sub MARK_TRIANGLE (){ 0x0001 }
sub MARK_SQUARE   (){ 0x0002 }
sub MARK_CIRCLE   (){ 0x0004 }
sub MARK_SMALL_B  (){ 0x0008 } # small stone, used for scoring or marking
sub MARK_SMALL_W  (){ 0x0010 } # small stone, used for scoring or marking
sub MARK_B        (){ 0x0020 } # normal black stone
sub MARK_W        (){ 0x0040 } # normal whit stone
sub MARK_GRAYED   (){ 0x0080 } # in conjunction with MARK_[BW], grays the stone
sub MARK_LABEL    (){ 0x0100 }
sub MARK_HOSHI    (){ 0x0200 } # this is a hoshi point (not used much)
sub MARK_MOVE     (){ 0x0400 } # this is a regular move
sub MARK_KO       (){ 0x0800 } # this is a ko position
sub MARK_CROSS    (){ 0x1000 }
sub MARK_REDRAW   (){ 0x8000 }

sub COLOUR_WHITE  (){ 0 }
sub COLOUR_BLACK  (){ 1 }

sub MOVE_PASS     (){ undef }
sub MOVE_HANDICAP (){ -2 }

=item my $board = new $size

Creates a new empty board of the given size.

C<< $board->{size} >> stores the board size.

C<< $board->{max} >> stores the maximum board coordinate (size-1).

C<< $board->{captures}[COLOUR_xxx] >> stores the number of captured stones for
the given colour.

C<< $board->{board} >> stores a two-dimensional array with board contents.

=cut

sub new {
   my $class = shift;
   my $size = shift;

   bless {
      max       => $size - 1,
      size      => $size,
      board     => [map [(0) x $size], 1 .. $size],
      captures  => [0, 0], # captures
     #timer     => [],
     #score     => [],
      @_,
      unmark    => [],
   }, $class
}

# inefficient and primitive, I hear you say?
# well... you are right :)
# use an extremely dumb floodfill algorithm to get rid of captured stones
sub capture {
   my ($self, $mark, $x, $y) = @_;

   my %seen;
   my @found;
   my @nodes = ([$x,$y]);
   my $board = $self->{board};

   my $max = $self->{max};

   while (@nodes) {
      my ($x, $y) = @{pop @nodes};
      unless ($seen{$x,$y}++) {
         if ($board->[$x][$y] & $mark) {
            push @found, [$x, $y];

            push @nodes, [$x-1, $y] unless $seen{$x-1, $y} || $x <= 0;
            push @nodes, [$x+1, $y] unless $seen{$x+1, $y} || $x >= $max;
            push @nodes, [$x, $y-1] unless $seen{$x, $y-1} || $y <= 0;
            push @nodes, [$x, $y+1] unless $seen{$x, $y+1} || $y >= $max;
         } elsif (!($board->[$x][$y] & (MARK_B | MARK_W))) {
            return;
         }
      }
   }

   @found
}

=item $hint = $board->update ([update-structures...])

Each update-structure itself is also an array-ref:

   [$x, $y, $clr, $set, $label, $hint] # update or move
   [MOVE_HANDICAP, $handicap]          # black move, setup handicap
   [MOVE_PASS]                         # pass
   []                                  # also pass (deprecated!)

It changes the board or executes a move, by first clearing the bits
specified in C<$clr>, then setting bits specified in C<$set>.

If C<$set> includes C<MARK_LABEL>, the label text must be given in
C<$label>.

If C<$set> contains C<MARK_MOVE> then surrounded stones will be removed
from the board and (simple) Kos are detected and marked with square
symbols and C<MARK_KO>, after removing other marking symbols. The
markings are also removed with the next next update structure that uses
C<MARK_MOVE>, so this flag is suited well for marking, well, moves. Note
that you can make invalid "moves" (such as suicide) and C<update> will
try to cope with it. You can use C<is_valid_move> to avoid making illegal
moves.

For handicap "moves", currently only board sizes 9, 13 and 19 are
supported and only handicap values from 2 to 9. The placement follows the
IGS rules, if you want other placements, you have to set it up yourself.

This function modifies the C<$hint> member of the specified structure
to speed up repeated board generation and updates with the same update
structures.

If the hint member is a reference the scalar pointed to by the reference
is updated instead.

If all this hint member thing is confusing, just ignore it and specify
it as C<undef> or leave it out of the array entirely. Do make sure that
you keep your update structures around as long as previous updates don't
change, however, as regenerating a full board position from hinted
update structures is I<much> faster then recreating it from fresh update
structures.

Example, make two silly moves:

  $board->update ([[0, 18, -1, MARK_B | MARK_MOVE],
                   [0, 17, -1, MARK_W | MARK_MOVE]]);

=cut

our %HANDICAP_COORD =  (
    9 => [2, 4,  6],
   13 => [3, 6,  9],
   19 => [3, 9, 15],
);
our %HANDICAP_XY = (
   2 => [qw(0,2 2,0                            )],
   3 => [qw(0,2 2,0 0,0                        )],
   4 => [qw(0,2 2,0 0,0 2,2                    )],
   5 => [qw(0,2 2,0 0,0 2,2                 1,1)],
   6 => [qw(0,2 2,0 0,0 2,2 0,1 2,1            )],
   7 => [qw(0,2 2,0 0,0 2,2 0,1 2,1         1,1)],
   8 => [qw(0,2 2,0 0,0 2,2 0,1 2,1 1,0 1,2    )],
   9 => [qw(0,2 2,0 0,0 2,2 0,1 2,1 1,0 1,2 1,1)],
);

our $mark_symbols = MARK_CIRCLE | MARK_SQUARE | MARK_TRIANGLE | MARK_CROSS | MARK_KO;

sub update {
   my ($self, $path) = @_;

   my $board = $self->{board};

   for (@$path) {
      my ($x, $y, $clr, $set, $label) = @$_;

      if (!defined $x) {
         # pass

      } elsif ($x == MOVE_HANDICAP) {
         # $y = #handicap stones
         my $c = $HANDICAP_COORD{$self->{size}}
            or Carp::croak "$self->{size}: illegal board size for handicap";
         my $h = $HANDICAP_XY{$y}
            or Carp::croak "$y: illegal number of handicap stones";

         for (@$h) {
            my ($x, $y) = map $c->[$_], split /,/;
            $board->[$x][$y] = MARK_B | MARK_MOVE;
         }

      } else {
         my $space = \$board->[$x][$y];

         $$space = $$space & ~$clr | $set;

         $self->{label}[$x][$y] = $label if $set & MARK_LABEL;

         if ($set & MARK_MOVE) {
            $$_ &= ~$mark_symbols for @{ $self->{unmark} };
            @{ $self->{unmark} } = $space;

            unless (${ $_->[5] ||= \my $hint }) {
               my ($own, $opp) =
                  $set & MARK_B
                     ? (MARK_B, MARK_W)
                     : (MARK_W, MARK_B);

               my (@capture, $suicide);

               push @capture, $self->capture ($opp, $x-1, $y) if $x > 0            && $board->[$x-1][$y] & $opp;
               push @capture, $self->capture ($opp, $x+1, $y) if $x < $self->{max} && $board->[$x+1][$y] & $opp;
               push @capture, $self->capture ($opp, $x, $y-1) if $y > 0            && $board->[$x][$y-1] & $opp;
               push @capture, $self->capture ($opp, $x, $y+1) if $y < $self->{max} && $board->[$x][$y+1] & $opp;

               # keep only unique coordinates
               @capture = do { my %seen; grep !$seen{"$_->[0],$_->[1]"}++, @capture };

               # remove captured stones
               $self->{captures}[$own == MARK_B ? COLOUR_BLACK : COLOUR_WHITE] += @capture;
               $self->{board}[$_->[0]][$_->[1]] = 0
                  for @capture;

               $suicide += $self->capture ($own, $x, $y);

               ${ $_->[5] } ||= !(@capture || $suicide);

               if (!$suicide && @capture == 1) {
                  # possible ko. now check liberties on placed stone

                  my $libs;

                  $libs++ if $x > 0            && !($board->[$x-1][$y] & $opp);
                  $libs++ if $x < $self->{max} && !($board->[$x+1][$y] & $opp);
                  $libs++ if $y > 0            && !($board->[$x][$y-1] & $opp);
                  $libs++ if $y < $self->{max} && !($board->[$x][$y+1] & $opp);
                  
                  if ($libs == 1) {
                     $$space = $$space & ~$mark_symbols | MARK_KO;

                     ($x, $y) = @{$capture[0]};
                     $board->[$x][$y] |= MARK_KO;

                     push @{ $self->{unmark} }, \$board->[$x][$y];
                  }
               }
            }
         }
      }
   }
}

=item $board->is_valid_move ($colour, $x, $y[, $may_suicide])

Returns true if the move of the given colour on the given coordinates is
valid or not. Kos are taken into account as long as they are marked with
C<MARK_KO>. Suicides are invalid unless C<$may_suicide> is true (e.g. for
new zealand rules)

=cut

sub is_valid_move {
   my ($self, $colour, $x, $y, $may_suicide) = @_;

   my $board = $self->{board};

   return if $board->[$x][$y] & (MARK_B | MARK_W | MARK_KO);

   if ($may_suicide) {
      return 1;
   } else {
      my ($own, $opp) = $colour == COLOUR_BLACK
                           ? (MARK_B, MARK_W)
                           : (MARK_W, MARK_B);

      # try the move
      local $board->[$x][$y] = $board->[$x][$y] | $own;

      return 1 if $x > 0            && $board->[$x-1][$y] & $opp && $self->capture ($opp, $x-1, $y, 1);
      return 1 if $x < $self->{max} && $board->[$x+1][$y] & $opp && $self->capture ($opp, $x+1, $y, 1);
      return 1 if $y > 0            && $board->[$x][$y-1] & $opp && $self->capture ($opp, $x, $y-1, 1);
      return 1 if $y < $self->{max} && $board->[$x][$y+1] & $opp && $self->capture ($opp, $x, $y+1, 1);

      return !$self->capture ($own, $x, $y, 1);
   }
}

1;

=back

=head2 AUTHOR

Marc Lehmann <schmorp@schmorp.de>

=head2 SEE ALSO

L<Gtk2::GoBoard>.

=cut

Revision:	1.9
Committed:	Wed Jun 25 20:11:33 2008 UTC (15 years, 10 months ago) by root
Branch:	MAIN
Changes since 1.8:	+38 -42 lines
Log Message:	completely rewrote mvoe logic
#	User	Rev	Content
1	root	1.1	package Games::Go::SimpleBoard;
2
3			=head1 NAME
4
5			Games::Go::SimpleBoard - represent a simple go board
6
7			=head1 SYNOPSIS
8
9			use Games::Go::SimpleBoard;
10
11			=head1 DESCRIPTION
12
13			Please supply a description )
14
15			=head2 EXPORTED CONSTANTS
16
17			Marker types for each board position (ORed together):
18
19			MARK_TRIANGLE # triangle mark
20			MARK_SQUARE # square mark
21			MARK_CIRCLE # circle mark
22	root	1.6	MARK_CROSS # cross mark
23	root	1.1	MARK_SMALL_B # small stone, used for scoring or marking
24			MARK_SMALL_W # small stone, used for scoring or marking
25			MARK_B # normal black stone
26			MARK_W # normal whit stone
27			MARK_GRAYED # in conjunction with MARK_[BW], grays the stone
28			MARK_LABEL # a text label
29			MARK_HOSHI # this is a hoshi point (not used much)
30			MARK_MOVE # this is a regular move
31			MARK_KO # this is a ko position
32			MARK_REDRAW # ignored, can be used for your own purposes
33
34	root	1.9	COLOUR_WHITE # guarenteed to be 0
35			COLOUR_BLACK # guarenteed to be 1
36	root	1.1
37	root	1.3	MOVE_HANDICAP # used as "x-coordinate" for handicap moves
38	root	1.9	MOVE_PASS # can be used as "x-coordinate" for pass moves
39	root	1.3
40	root	1.1	=head2 METHODS
41
42			=over 4
43
44			=cut
45
46	root	1.3	no warnings;
47			use strict;
48
49			use Carp ();
50
51			use base Exporter::;
52	root	1.1
53			our $VERSION = '1.0';
54
55	root	1.3	our @EXPORT = qw(
56	root	1.1	MARK_TRIANGLE MARK_SQUARE MARK_CIRCLE MARK_SMALL_B MARK_SMALL_W MARK_B
57	root	1.7	MARK_W MARK_GRAYED MARK_MOVE MARK_LABEL MARK_HOSHI MARK_KO MARK_CROSS
58	root	1.1	MARK_REDRAW
59			COLOUR_BLACK COLOUR_WHITE
60	root	1.3	MOVE_HANDICAP MOVE_PASS
61	root	1.1	);
62
63			# marker types for each board position (ORed together)
64
65			sub MARK_TRIANGLE (){ 0x0001 }
66			sub MARK_SQUARE (){ 0x0002 }
67			sub MARK_CIRCLE (){ 0x0004 }
68			sub MARK_SMALL_B (){ 0x0008 } # small stone, used for scoring or marking
69			sub MARK_SMALL_W (){ 0x0010 } # small stone, used for scoring or marking
70			sub MARK_B (){ 0x0020 } # normal black stone
71			sub MARK_W (){ 0x0040 } # normal whit stone
72			sub MARK_GRAYED (){ 0x0080 } # in conjunction with MARK_[BW], grays the stone
73			sub MARK_LABEL (){ 0x0100 }
74			sub MARK_HOSHI (){ 0x0200 } # this is a hoshi point (not used much)
75			sub MARK_MOVE (){ 0x0400 } # this is a regular move
76			sub MARK_KO (){ 0x0800 } # this is a ko position
77	root	1.8	sub MARK_CROSS (){ 0x1000 }
78	root	1.1	sub MARK_REDRAW (){ 0x8000 }
79
80	root	1.9	sub COLOUR_WHITE (){ 0 }
81			sub COLOUR_BLACK (){ 1 }
82	root	1.1
83	root	1.3	sub MOVE_PASS (){ undef }
84			sub MOVE_HANDICAP (){ -2 }
85
86	root	1.1	=item my $board = new $size
87
88			Creates a new empty board of the given size.
89
90	root	1.3	C<< $board->{size} >> stores the board size.
91
92	root	1.1	C<< $board->{max} >> stores the maximum board coordinate (size-1).
93
94	root	1.9	C<< $board->{captures}[COLOUR_xxx] >> stores the number of captured stones for
95	root	1.1	the given colour.
96
97			C<< $board->{board} >> stores a two-dimensional array with board contents.
98
99			=cut
100
101			sub new {
102			my $class = shift;
103			my $size = shift;
104	root	1.9
105	root	1.1	bless {
106	root	1.9	max => $size - 1,
107			size => $size,
108			board => [map [(0) x $size], 1 .. $size],
109			captures => [0, 0], # captures
110			#timer => [],
111			#score => [],
112			@_,
113			unmark => [],
114			}, $class
115	root	1.1	}
116
117			# inefficient and primitive, I hear you say?
118			# well... you are right :)
119			# use an extremely dumb floodfill algorithm to get rid of captured stones
120			sub capture {
121			my ($self, $mark, $x, $y) = @_;
122
123			my %seen;
124			my @found;
125			my @nodes = ([$x,$y]);
126			my $board = $self->{board};
127
128			my $max = $self->{max};
129
130			while (@nodes) {
131			my ($x, $y) = @{pop @nodes};
132			unless ($seen{$x,$y}++) {
133			if ($board->[$x][$y] & $mark) {
134			push @found, [$x, $y];
135
136			push @nodes, [$x-1, $y] unless $seen{$x-1, $y} \|\| $x <= 0;
137			push @nodes, [$x+1, $y] unless $seen{$x+1, $y} \|\| $x >= $max;
138			push @nodes, [$x, $y-1] unless $seen{$x, $y-1} \|\| $y <= 0;
139			push @nodes, [$x, $y+1] unless $seen{$x, $y+1} \|\| $y >= $max;
140			} elsif (!($board->[$x][$y] & (MARK_B \| MARK_W))) {
141			return;
142			}
143			}
144			}
145
146			@found
147			}
148
149	root	1.2	=item $hint = $board->update ([update-structures...])
150	root	1.1
151	root	1.2	Each update-structure itself is also an array-ref:
152	root	1.1
153			[$x, $y, $clr, $set, $label, $hint] # update or move
154	root	1.4	[MOVE_HANDICAP, $handicap] # black move, setup handicap
155	root	1.3	[MOVE_PASS] # pass
156	root	1.4	[] # also pass (deprecated!)
157	root	1.1
158	root	1.2	It changes the board or executes a move, by first clearing the bits
159	root	1.1	specified in C<$clr>, then setting bits specified in C<$set>.
160
161			If C<$set> includes C<MARK_LABEL>, the label text must be given in
162			C<$label>.
163
164	root	1.9	If C<$set> contains C<MARK_MOVE> then surrounded stones will be removed
165			from the board and (simple) Kos are detected and marked with square
166			symbols and C<MARK_KO>, after removing other marking symbols. The
167			markings are also removed with the next next update structure that uses
168			C<MARK_MOVE>, so this flag is suited well for marking, well, moves. Note
169			that you can make invalid "moves" (such as suicide) and C<update> will
170			try to cope with it. You can use C<is_valid_move> to avoid making illegal
171			moves.
172	root	1.3
173			For handicap "moves", currently only board sizes 9, 13 and 19 are
174			supported and only handicap values from 2 to 9. The placement follows the
175			IGS rules, if you want other placements, you have to set it up yourself.
176
177	root	1.4	This function modifies the C<$hint> member of the specified structure
178			to speed up repeated board generation and updates with the same update
179			structures.
180	root	1.1
181			If the hint member is a reference the scalar pointed to by the reference
182			is updated instead.
183
184	root	1.4	If all this hint member thing is confusing, just ignore it and specify
185			it as C<undef> or leave it out of the array entirely. Do make sure that
186			you keep your update structures around as long as previous updates don't
187			change, however, as regenerating a full board position from hinted
188			update structures is I<much> faster then recreating it from fresh update
189			structures.
190	root	1.2
191	root	1.1	Example, make two silly moves:
192
193	root	1.4	$board->update ([[0, 18, -1, MARK_B \| MARK_MOVE],
194			[0, 17, -1, MARK_W \| MARK_MOVE]]);
195	root	1.1
196			=cut
197
198	root	1.3	our %HANDICAP_COORD = (
199			9 => [2, 4, 6],
200			13 => [3, 6, 9],
201			19 => [3, 9, 15],
202			);
203			our %HANDICAP_XY = (
204			2 => [qw(0,2 2,0 )],
205	root	1.5	3 => [qw(0,2 2,0 0,0 )],
206			4 => [qw(0,2 2,0 0,0 2,2 )],
207			5 => [qw(0,2 2,0 0,0 2,2 1,1)],
208			6 => [qw(0,2 2,0 0,0 2,2 0,1 2,1 )],
209			7 => [qw(0,2 2,0 0,0 2,2 0,1 2,1 1,1)],
210			8 => [qw(0,2 2,0 0,0 2,2 0,1 2,1 1,0 1,2 )],
211			9 => [qw(0,2 2,0 0,0 2,2 0,1 2,1 1,0 1,2 1,1)],
212	root	1.3	);
213
214	root	1.9	our $mark_symbols = MARK_CIRCLE \| MARK_SQUARE \| MARK_TRIANGLE \| MARK_CROSS \| MARK_KO;
215
216	root	1.1	sub update {
217			my ($self, $path) = @_;
218
219			my $board = $self->{board};
220
221			for (@$path) {
222			my ($x, $y, $clr, $set, $label) = @$_;
223
224	root	1.3	if (!defined $x) {
225			# pass
226
227			} elsif ($x == MOVE_HANDICAP) {
228			# $y = #handicap stones
229			my $c = $HANDICAP_COORD{$self->{size}}
230			or Carp::croak "$self->{size}: illegal board size for handicap";
231			my $h = $HANDICAP_XY{$y}
232			or Carp::croak "$y: illegal number of handicap stones";
233
234			for (@$h) {
235			my ($x, $y) = map $c->[$_], split /,/;
236			$board->[$x][$y] = MARK_B \| MARK_MOVE;
237			}
238
239			} else {
240	root	1.9	my $space = \$board->[$x][$y];
241
242			$$space = $$space & ~$clr \| $set;
243	root	1.1
244			$self->{label}[$x][$y] = $label if $set & MARK_LABEL;
245
246			if ($set & MARK_MOVE) {
247	root	1.9	$$_ &= ~$mark_symbols for @{ $self->{unmark} };
248			@{ $self->{unmark} } = $space;
249	root	1.1
250			unless (${ $_->[5] \|\|= \my $hint }) {
251			my ($own, $opp) =
252			$set & MARK_B
253			? (MARK_B, MARK_W)
254			: (MARK_W, MARK_B);
255
256			my (@capture, $suicide);
257
258			push @capture, $self->capture ($opp, $x-1, $y) if $x > 0 && $board->[$x-1][$y] & $opp;
259			push @capture, $self->capture ($opp, $x+1, $y) if $x < $self->{max} && $board->[$x+1][$y] & $opp;
260			push @capture, $self->capture ($opp, $x, $y-1) if $y > 0 && $board->[$x][$y-1] & $opp;
261			push @capture, $self->capture ($opp, $x, $y+1) if $y < $self->{max} && $board->[$x][$y+1] & $opp;
262
263			# keep only unique coordinates
264			@capture = do { my %seen; grep !$seen{"$_->[0],$_->[1]"}++, @capture };
265
266			# remove captured stones
267	root	1.9	$self->{captures}[$own == MARK_B ? COLOUR_BLACK : COLOUR_WHITE] += @capture;
268			$self->{board}[$_->[0]][$_->[1]] = 0
269	root	1.1	for @capture;
270
271			$suicide += $self->capture ($own, $x, $y);
272
273			${ $_->[5] } \|\|= !(@capture \|\| $suicide);
274
275			if (!$suicide && @capture == 1) {
276			# possible ko. now check liberties on placed stone
277
278			my $libs;
279
280			$libs++ if $x > 0 && !($board->[$x-1][$y] & $opp);
281			$libs++ if $x < $self->{max} && !($board->[$x+1][$y] & $opp);
282			$libs++ if $y > 0 && !($board->[$x][$y-1] & $opp);
283			$libs++ if $y < $self->{max} && !($board->[$x][$y+1] & $opp);
284
285			if ($libs == 1) {
286	root	1.9	$$space = $$space & ~$mark_symbols \| MARK_KO;
287
288	root	1.1	($x, $y) = @{$capture[0]};
289	root	1.9	$board->[$x][$y] \|= MARK_KO;
290
291			push @{ $self->{unmark} }, \$board->[$x][$y];
292	root	1.1	}
293			}
294			}
295			}
296			}
297			}
298			}
299
300			=item $board->is_valid_move ($colour, $x, $y[, $may_suicide])
301
302			Returns true if the move of the given colour on the given coordinates is
303	root	1.4	valid or not. Kos are taken into account as long as they are marked with
304			C<MARK_KO>. Suicides are invalid unless C<$may_suicide> is true (e.g. for
305			new zealand rules)
306	root	1.1
307			=cut
308
309			sub is_valid_move {
310			my ($self, $colour, $x, $y, $may_suicide) = @_;
311
312			my $board = $self->{board};
313
314			return if $board->[$x][$y] & (MARK_B \| MARK_W \| MARK_KO);
315
316			if ($may_suicide) {
317			return 1;
318			} else {
319			my ($own, $opp) = $colour == COLOUR_BLACK
320			? (MARK_B, MARK_W)
321			: (MARK_W, MARK_B);
322
323			# try the move
324			local $board->[$x][$y] = $board->[$x][$y] \| $own;
325
326			return 1 if $x > 0 && $board->[$x-1][$y] & $opp && $self->capture ($opp, $x-1, $y, 1);
327			return 1 if $x < $self->{max} && $board->[$x+1][$y] & $opp && $self->capture ($opp, $x+1, $y, 1);
328			return 1 if $y > 0 && $board->[$x][$y-1] & $opp && $self->capture ($opp, $x, $y-1, 1);
329			return 1 if $y < $self->{max} && $board->[$x][$y+1] & $opp && $self->capture ($opp, $x, $y+1, 1);
330
331			return !$self->capture ($own, $x, $y, 1);
332			}
333			}
334
335			1;
336
337			=back
338
339			=head2 AUTHOR
340
341			Marc Lehmann <schmorp@schmorp.de>
342
343			=head2 SEE ALSO
344
345	root	1.3	L<Gtk2::GoBoard>.
346	root	1.1
347			=cut
348