src/attack.cpp

   1 /* Copyright (C) 2007-2011 Vincent Ollivier
   2  *
   3  * Purple Haze is free software: you can redistribute it and/or modify
   4  * it under the terms of the GNU General Public License as published by
   5  * the Free Software Foundation, either version 3 of the License, or
   6  * (at your option) any later version.
   7  *
   8  * Purple Haze is distributed in the hope that it will be useful,
   9  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  10  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  11  * GNU General Public License for more details.
  12  *
  13  * You should have received a copy of the GNU General Public License
  14  * along with this program. If not, see <http://www.gnu.org/licenses/>.
  15  */
  16
  17 #include <assert.h>
  18
  19 #include "game.h"
  20
  21 /*
  22  * Return true if the square s is attacked by one of the c color's pieces.
  23  */
  24 bool Board::is_attacked_by(Color c, Square s, const Pieces& pieces) const
  25 {
  26     for (const PieceType& t : NOT_PAWN_TYPES) {
  27         int n = pieces.count(c, t);
  28         for (int i = 0; i < n; ++i) {
  29             Square from = pieces.position(c, t, i);
  30             if (!can_attack(t, from, s)) continue;
  31             if (t == KNIGHT || t == KING) return true;
  32             Direction d = direction_to(from, s);
  33             Square to = Square(from + d);
  34             while (to != s && is_empty(to)) {
  35                 to = Square(to + d);
  36             }
  37             if (to == s) return true;
  38         }
  39     }
  40
  41     // Specific code for pawns
  42     for (int i = 0; i < 2; ++i) {
  43         Square from = Square(s + PAWN_CAPTURE_DIRS[!c][i]);
  44         if (board[from].type() == PAWN && board[from].color() == c) {
  45             return true;
  46         }
  47     }
  48
  49     return false;
  50 }
  51
  52 /*
  53  * Return true if a piece p can do a capture or a quiet move from square from
  54  * to square to on the board. This method does not say if the move is a legal
  55  * one.
  56  */
  57 bool Board::can_go(Piece p, Square from, Square to) const
  58 {
  59     PieceType t = p.type();
  60     Color c = p.color();
  61     Direction d = direction_to(from, to);
  62
  63     // A piece cannot capture another piece of the same color
  64     if (!is_empty(to) && board[to].color() == c) return false;
  65
  66     Direction push_dir;
  67     Square s;
  68     switch (t) {
  69         case PAWN:
  70             push_dir = (c == WHITE ? UP : DOWN);
  71             if (!is_empty(to)) { // Capture
  72                 if (to == Square(from + push_dir + LEFT)) return true;
  73                 if (to == Square(from + push_dir + RIGHT)) return true;
  74             } else { // Pawn push (and double push)
  75                 if (to == Square(from + push_dir)) return true;
  76                 if (to == Square(from + 2 * push_dir) &&
  77                     is_empty(Square(from + push_dir)) &&
  78                     is_pawn_begin(c, from)) return true;
  79             }
  80             break;
  81         default:
  82             if (!can_attack(t, from, to)) return false;
  83             if (t == KNIGHT || t == KING) return true;
  84             s = Square(from + d);
  85             while (s != to && is_empty(s)) { // Search for a blocker
  86                 s = Square(s + d);
  87                 assert(!is_out(s));
  88             }
  89             if (s == to) return true;
  90             break;
  91     }
  92     return false;
  93 }