tactics.h

   1 #ifndef ZZGO_TACTICS_H
   2 #define ZZGO_TACTICS_H
   3
   4 /* Advanced tactical checks non-essential to the board implementation. */
   5
   6 #include "board.h"
   7
   8 struct move_queue;
   9
  10 /* Check if this move is undesirable self-atari (resulting group would have
  11  * only single liberty and not capture anything; ko is allowed); we mostly
  12  * want to avoid these moves. The function actually does a rather elaborate
  13  * tactical check, allowing self-atari moves that are nakade, eye falsification
  14  * or throw-ins. */
  15 static bool is_bad_selfatari(struct board *b, enum stone color, coord_t to);
  16
  17 /* Check if escaping on this liberty by given group in atari would play out
  18  * a simple ladder. */
  19 /* Two ways of ladder reading can be enabled separately; simple first-line
  20  * ladders and trivial middle-board ladders. */
  21 static bool is_ladder(struct board *b, coord_t coord, group_t laddered,
  22                       bool border_ladders, bool middle_ladders);
  23
  24 /* Checks if there are any stones in n-vincinity of coord. */
  25 bool board_stone_radar(struct board *b, coord_t coord, int distance);
  26
  27 /* Measure various distances on the board: */
  28 /* Distance from the edge; on edge returns 0. */
  29 static int coord_edge_distance(coord_t c, struct board *b);
  30 /* Distance of two points in gridcular metric - this metric defines
  31  * circle-like structures on the square grid. */
  32 static int coord_gridcular_distance(coord_t c1, coord_t c2, struct board *b);
  33
  34 /* Construct a "common fate graph" from given coordinate; that is, a weighted
  35  * graph of intersections where edges between all neighbors have weight 1,
  36  * but edges between neighbors of same color have weight 0. Thus, this is
  37  * "stone chain" metric in a sense. */
  38 /* The output are distanes from start stored in given [board_size2()] array;
  39  * intersections further away than maxdist have all distance maxdist+1 set. */
  40 void cfg_distances(struct board *b, coord_t start, int *distances, int maxdist);
  41
  42 /* Compute an extra komi describing the "effective handicap" black receives
  43  * (returns 0 for even game with 7.5 komi). */
  44 /* This is just an approximation since in reality, handicap seems to be usually
  45  * non-linear. */
  46 float board_effective_handicap(struct board *b);
  47
  48 /* Decide if the given player wins counting on the board, considering
  49  * that given groups are dead. (To get the list of dead groups, use
  50  * e.g. groups_of_status().) */
  51 bool pass_is_safe(struct board *b, enum stone color, struct move_queue *mq);
  52
  53
  54 bool is_bad_selfatari_slow(struct board *b, enum stone color, coord_t to);
  55 static inline bool
  56 is_bad_selfatari(struct board *b, enum stone color, coord_t to)
  57 {
  58         /* More than one immediate liberty, thumbs up! */
  59         if (immediate_liberty_count(b, to) > 1)
  60                 return false;
  61
  62         return is_bad_selfatari_slow(b, color, to);
  63 }
  64
  65 bool is_border_ladder(struct board *b, coord_t coord, enum stone lcolor);
  66 bool is_middle_ladder(struct board *b, coord_t coord, enum stone lcolor);
  67 static inline bool
  68 is_ladder(struct board *b, coord_t coord, group_t laddered,
  69           bool border_ladders, bool middle_ladders)
  70 {
  71         enum stone lcolor = board_at(b, group_base(laddered));
  72
  73         if (DEBUGL(6))
  74                 fprintf(stderr, "ladder check - does %s play out %s's laddered group %s?\n",
  75                         coord2sstr(coord, b), stone2str(lcolor), coord2sstr(laddered, b));
  76
  77         /* First, special-case first-line "ladders". This is a huge chunk
  78          * of ladders we actually meet and want to play. */
  79         if (border_ladders
  80             && neighbor_count_at(b, coord, S_OFFBOARD) == 1
  81             && neighbor_count_at(b, coord, lcolor) == 1)
  82                 return is_border_ladder(b, coord, lcolor);
  83
  84         if (middle_ladders)
  85                 return is_middle_ladder(b, coord, lcolor);
  86
  87         return false;
  88 }
  89
  90
  91 static inline int
  92 coord_edge_distance(coord_t c, struct board *b)
  93 {
  94         int x = coord_x(c, b), y = coord_y(c, b);
  95         int dx = x > board_size(b) / 2 ? board_size(b) - 1 - x : x;
  96         int dy = y > board_size(b) / 2 ? board_size(b) - 1 - y : y;
  97         return (dx < dy ? dx : dy) - 1 /* S_OFFBOARD */;
  98 }
  99
 100 static inline int
 101 coord_gridcular_distance(coord_t c1, coord_t c2, struct board *b)
 102 {
 103         int dx = abs(coord_dx(c1, c2, b)), dy = abs(coord_dy(c1, c2, b));
 104         return dx + dy + (dx > dy ? dx : dy);
 105 }
 106
 107 #endif