bool
is_border_ladder(Board *b, Coord coord, Stone lcolor)
{
int x = X(coord), y = Y(coord);
/*
if (DEBUGL(5))
fprintf(stderr, "border ladder\n");
*/
/* Direction along border; xd is horiz. border, yd vertical. */
int xd = 0, yd = 0;
if (b->_infos[L(coord)].color == S_OFFBOARD || b->_infos[R(coord)].color == S_OFFBOARD)
yd = 1;
else
xd = 1;
/* Direction from the border; -1 is above/left, 1 is below/right. */
int dd = (board_atxy(b, x + yd, y + xd) == S_OFFBOARD) ? 1 : -1;
if (DEBUGL(6))
fprintf(stderr, "xd %d yd %d dd %d\n", xd, yd, dd);
/* | ? ?
* | . O #
* | c X #
* | . O #
* | ? ? */
/* This is normally caught, unless we have friends both above
* and below... */
if (board_atxy(b, x + xd * 2, y + yd * 2) == lcolor
&& board_atxy(b, x - xd * 2, y - yd * 2) == lcolor)
return false;
/* ...or can't block where we need because of shortage
* of liberties. */
group_t g1 = group_atxy(b, x + xd - yd * dd, y + yd - xd * dd);
int libs1 = b->_groups[g1].liberties;
group_t g2 = group_atxy(b, x - xd - yd * dd, y - yd - xd * dd);
int libs2 = b->_groups[g2].liberties;
/*
if (DEBUGL(6))
fprintf(stderr, "libs1 %d libs2 %d\n", libs1, libs2);
*/
/* Already in atari? */
if (libs1 < 2 || libs2 < 2)
return false;
Coord libs_g1[2], libs_g2[2];
get_nlibs_of_group(b, g1, 2, libs_g1);
get_nlibs_of_group(b, g2, 2, libs_g2);
/* Would be self-atari? */
if (libs1 < 3 && (board_atxy(b, x + xd * 2, y + yd * 2) != S_NONE || NEIGHBOR4(libs_g1[0], libs_g1[1])))
return false;
if (libs2 < 3 && (board_atxy(b, x - xd * 2, y - yd * 2) != S_NONE || NEIGHBOR4(libs_g2[0], libs_g2[1])))
return false;
return true;
}
bool
board_stone_radar(struct board *b, coord_t coord, int distance)
{
int bounds[4] = {
coord_x(coord, b) - distance,
coord_y(coord, b) - distance,
coord_x(coord, b) + distance,
coord_y(coord, b) + distance
};
for (int i = 0; i < 4; i++)
if (bounds[i] < 1)
bounds[i] = 1;
else if (bounds[i] > board_size(b) - 2)
bounds[i] = board_size(b) - 2;
for (int x = bounds[0]; x <= bounds[2]; x++)
for (int y = bounds[1]; y <= bounds[3]; y++)
if (board_atxy(b, x, y) != S_NONE) {
/* fprintf(stderr, "radar %d,%d,%d: %d,%d (%d)\n",
coord_x(coord, b), coord_y(coord, b),
distance, x, y, board_atxy(b, x, y)); */
return true;
}
return false;
}