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_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_BLACK  # used for $board->{last}
   COLOUR_WHITE  # to mark the colour of the last move

   MOVE_HANDICAP # used as "x-coordinate" for handicap moves
   MOVE_PASS     # can be used as "x-coordinate" for handicap 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_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_REDRAW   (){ 0x8000 }

sub COLOUR_BLACK  (){ 0 }
sub COLOUR_WHITE  (){ 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] >> stores the number of captured stones for
the given colour.

C<< $board->{last} >> stores the colour of the last move that was played.

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    => [],
        #last     => COLOUR_...,
         @_
      },
      $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 a circle symbol will be placed
at this coordinate. Also, surrounded stones will be removed from the
board and (simple) Kos are detected and marked with square symbols and
C<MARK_KO>. The circle and square markings are removed with the next
update 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)],
);

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

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

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

      my $nodemask =
            $_ == $path->[-1]
               ? ~0
               : ~(MARK_SQUARE | MARK_TRIANGLE | MARK_CIRCLE | MARK_LABEL | MARK_KO);

      if (!defined $x) {
         # pass
         $self->{last} = $set & MARK_B ? COLOUR_BLACK : COLOUR_WHITE;

      } 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 {
         $board->[$x][$y] =
            $board->[$x][$y]
            & ~$clr
            | $set
            & $nodemask;

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

         if ($set & MARK_MOVE) {
            $self->{last} = $set & MARK_B ? COLOUR_BLACK : COLOUR_WHITE;

            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
               $self->{captures}[$self->{last}] += @capture;
               $self->{board}[$_->[0]][$_->[1]] &= ~(MARK_B | MARK_W | MARK_MOVE)
                  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) {
                     $board->[$x][$y] = $board->[$x][$y] & ~MARK_CIRCLE | (MARK_KO & $nodemask);
                     ($x, $y) = @{$capture[0]};
                     $board->[$x][$y] |= MARK_KO & $nodemask;
                  }
               }
            }
         }
      }
   }
}

=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:	1.5
Committed:	Tue Jun 24 19:22:08 2008 UTC (15 years, 10 months ago) by root
Branch:	MAIN
Changes since 1.4:	+7 -7 lines
Log Message:	* empty log message *
#	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			MARK_SMALL_B # small stone, used for scoring or marking
23			MARK_SMALL_W # small stone, used for scoring or marking
24			MARK_B # normal black stone
25			MARK_W # normal whit stone
26			MARK_GRAYED # in conjunction with MARK_[BW], grays the stone
27			MARK_LABEL # a text label
28			MARK_HOSHI # this is a hoshi point (not used much)
29			MARK_MOVE # this is a regular move
30			MARK_KO # this is a ko position
31			MARK_REDRAW # ignored, can be used for your own purposes
32
33			COLOUR_BLACK # used for $board->{last}
34			COLOUR_WHITE # to mark the colour of the last move
35
36	root	1.3	MOVE_HANDICAP # used as "x-coordinate" for handicap moves
37			MOVE_PASS # can be used as "x-coordinate" for handicap moves
38
39	root	1.1	=head2 METHODS
40
41			=over 4
42
43			=cut
44
45	root	1.3	no warnings;
46			use strict;
47
48			use Carp ();
49
50			use base Exporter::;
51	root	1.1
52			our $VERSION = '1.0';
53
54	root	1.3	our @EXPORT = qw(
55	root	1.1	MARK_TRIANGLE MARK_SQUARE MARK_CIRCLE MARK_SMALL_B MARK_SMALL_W MARK_B
56			MARK_W MARK_GRAYED MARK_MOVE MARK_LABEL MARK_HOSHI MARK_KO
57			MARK_REDRAW
58			COLOUR_BLACK COLOUR_WHITE
59	root	1.3	MOVE_HANDICAP MOVE_PASS
60	root	1.1	);
61
62			# marker types for each board position (ORed together)
63
64			sub MARK_TRIANGLE (){ 0x0001 }
65			sub MARK_SQUARE (){ 0x0002 }
66			sub MARK_CIRCLE (){ 0x0004 }
67			sub MARK_SMALL_B (){ 0x0008 } # small stone, used for scoring or marking
68			sub MARK_SMALL_W (){ 0x0010 } # small stone, used for scoring or marking
69			sub MARK_B (){ 0x0020 } # normal black stone
70			sub MARK_W (){ 0x0040 } # normal whit stone
71			sub MARK_GRAYED (){ 0x0080 } # in conjunction with MARK_[BW], grays the stone
72			sub MARK_LABEL (){ 0x0100 }
73			sub MARK_HOSHI (){ 0x0200 } # this is a hoshi point (not used much)
74			sub MARK_MOVE (){ 0x0400 } # this is a regular move
75			sub MARK_KO (){ 0x0800 } # this is a ko position
76			sub MARK_REDRAW (){ 0x8000 }
77
78			sub COLOUR_BLACK (){ 0 }
79			sub COLOUR_WHITE (){ 1 }
80
81	root	1.3	sub MOVE_PASS (){ undef }
82			sub MOVE_HANDICAP (){ -2 }
83
84	root	1.1	=item my $board = new $size
85
86			Creates a new empty board of the given size.
87
88	root	1.3	C<< $board->{size} >> stores the board size.
89
90	root	1.1	C<< $board->{max} >> stores the maximum board coordinate (size-1).
91
92			C<< $board->{captures}[COLOUR] >> stores the number of captured stones for
93			the given colour.
94
95			C<< $board->{last} >> stores the colour of the last move that was played.
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			bless {
105			max => $size - 1,
106	root	1.3	size => $size,
107	root	1.1	board => [map [(0) x $size], 1 .. $size],
108			captures => [0, 0], # captures
109			#timer => [],
110			#score => [],
111			#last => COLOUR_...,
112			@_
113			},
114			$class;
115			}
116
117			# inefficient and primitive, I hear you say?
118			# well... you are right :)
119			# use an extremely dumb floodfill algorithm to get rid of captured stones
120			sub capture {
121			my ($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<$label>.
163
164	root	1.4	If C<$set> contains C<MARK_MOVE>, then a circle symbol will be placed
165			at this coordinate. Also, surrounded stones will be removed from the
166			board and (simple) Kos are detected and marked with square symbols and
167			C<MARK_KO>. The circle and square markings are removed with the next
168			update that uses C<MARK_MOVE>, so this flag is suited well for marking,
169			well, moves. Note that you can make invalid "moves" (such as suicide) and
170			C<update> will try to cope with it. You can use C<is_valid_move> to avoid
171			making illegal 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	$board->update ([[0, 18, -1, MARK_B \| MARK_MOVE],
194			[0, 17, -1, MARK_W \| MARK_MOVE]]);
195	root	1.1
196			=cut
197
198	root	1.3	our %HANDICAP_COORD = (
199			9 => [2, 4, 6],
200			13 => [3, 6, 9],
201			19 => [3, 9, 15],
202			);
203			our %HANDICAP_XY = (
204			2 => [qw(0,2 2,0 )],
205	root	1.5	3 => [qw(0,2 2,0 0,0 )],
206			4 => [qw(0,2 2,0 0,0 2,2 )],
207			5 => [qw(0,2 2,0 0,0 2,2 1,1)],
208			6 => [qw(0,2 2,0 0,0 2,2 0,1 2,1 )],
209			7 => [qw(0,2 2,0 0,0 2,2 0,1 2,1 1,1)],
210			8 => [qw(0,2 2,0 0,0 2,2 0,1 2,1 1,0 1,2 )],
211			9 => [qw(0,2 2,0 0,0 2,2 0,1 2,1 1,0 1,2 1,1)],
212	root	1.3	);
213
214	root	1.1	sub update {
215			my ($self, $path) = @_;
216
217			my $board = $self->{board};
218
219			for (@$path) {
220			my ($x, $y, $clr, $set, $label) = @$_;
221
222			my $nodemask =
223			$_ == $path->[-1]
224			? ~0
225			: ~(MARK_SQUARE \| MARK_TRIANGLE \| MARK_CIRCLE \| MARK_LABEL \| MARK_KO);
226
227	root	1.3	if (!defined $x) {
228			# pass
229			$self->{last} = $set & MARK_B ? COLOUR_BLACK : COLOUR_WHITE;
230
231			} elsif ($x == MOVE_HANDICAP) {
232			# $y = #handicap stones
233			my $c = $HANDICAP_COORD{$self->{size}}
234			or Carp::croak "$self->{size}: illegal board size for handicap";
235			my $h = $HANDICAP_XY{$y}
236			or Carp::croak "$y: illegal number of handicap stones";
237
238			for (@$h) {
239			my ($x, $y) = map $c->[$_], split /,/;
240			$board->[$x][$y] = MARK_B \| MARK_MOVE;
241			}
242
243			} else {
244	root	1.1	$board->[$x][$y] =
245			$board->[$x][$y]
246			& ~$clr
247			\| $set
248			& $nodemask;
249
250			$self->{label}[$x][$y] = $label if $set & MARK_LABEL;
251
252			if ($set & MARK_MOVE) {
253			$self->{last} = $set & MARK_B ? COLOUR_BLACK : COLOUR_WHITE;
254
255			unless (${ $_->[5] \|\|= \my $hint }) {
256			my ($own, $opp) =
257			$set & MARK_B
258			? (MARK_B, MARK_W)
259			: (MARK_W, MARK_B);
260
261			my (@capture, $suicide);
262
263			push @capture, $self->capture ($opp, $x-1, $y) if $x > 0 && $board->[$x-1][$y] & $opp;
264			push @capture, $self->capture ($opp, $x+1, $y) if $x < $self->{max} && $board->[$x+1][$y] & $opp;
265			push @capture, $self->capture ($opp, $x, $y-1) if $y > 0 && $board->[$x][$y-1] & $opp;
266			push @capture, $self->capture ($opp, $x, $y+1) if $y < $self->{max} && $board->[$x][$y+1] & $opp;
267
268			# keep only unique coordinates
269			@capture = do { my %seen; grep !$seen{"$_->[0],$_->[1]"}++, @capture };
270
271			# remove captured stones
272			$self->{captures}[$self->{last}] += @capture;
273			$self->{board}[$_->[0]][$_->[1]] &= ~(MARK_B \| MARK_W \| MARK_MOVE)
274			for @capture;
275
276			$suicide += $self->capture ($own, $x, $y);
277
278			${ $_->[5] } \|\|= !(@capture \|\| $suicide);
279
280			if (!$suicide && @capture == 1) {
281			# possible ko. now check liberties on placed stone
282
283			my $libs;
284
285			$libs++ if $x > 0 && !($board->[$x-1][$y] & $opp);
286			$libs++ if $x < $self->{max} && !($board->[$x+1][$y] & $opp);
287			$libs++ if $y > 0 && !($board->[$x][$y-1] & $opp);
288			$libs++ if $y < $self->{max} && !($board->[$x][$y+1] & $opp);
289
290			if ($libs == 1) {
291			$board->[$x][$y] = $board->[$x][$y] & ~MARK_CIRCLE \| (MARK_KO & $nodemask);
292			($x, $y) = @{$capture[0]};
293			$board->[$x][$y] \|= MARK_KO & $nodemask;
294			}
295			}
296			}
297			}
298			}
299			}
300			}
301
302			=item $board->is_valid_move ($colour, $x, $y[, $may_suicide])
303
304			Returns true if the move of the given colour on the given coordinates is
305	root	1.4	valid or not. Kos are taken into account as long as they are marked with
306			C<MARK_KO>. Suicides are invalid unless C<$may_suicide> is true (e.g. for
307			new zealand rules)
308	root	1.1
309			=cut
310
311			sub is_valid_move {
312			my ($self, $colour, $x, $y, $may_suicide) = @_;
313
314			my $board = $self->{board};
315
316			return if $board->[$x][$y] & (MARK_B \| MARK_W \| MARK_KO);
317
318			if ($may_suicide) {
319			return 1;
320			} else {
321			my ($own, $opp) = $colour == COLOUR_BLACK
322			? (MARK_B, MARK_W)
323			: (MARK_W, MARK_B);
324
325			# try the move
326			local $board->[$x][$y] = $board->[$x][$y] \| $own;
327
328			return 1 if $x > 0 && $board->[$x-1][$y] & $opp && $self->capture ($opp, $x-1, $y, 1);
329			return 1 if $x < $self->{max} && $board->[$x+1][$y] & $opp && $self->capture ($opp, $x+1, $y, 1);
330			return 1 if $y > 0 && $board->[$x][$y-1] & $opp && $self->capture ($opp, $x, $y-1, 1);
331			return 1 if $y < $self->{max} && $board->[$x][$y+1] & $opp && $self->capture ($opp, $x, $y+1, 1);
332
333			return !$self->capture ($own, $x, $y, 1);
334			}
335			}
336
337			1;
338
339			=back
340
341			=head2 AUTHOR
342
343			Marc Lehmann <schmorp@schmorp.de>
344
345			=head2 SEE ALSO
346
347	root	1.3	L<Gtk2::GoBoard>.
348	root	1.1
349			=cut
350