made ai better at endgames (it's just a start)

src/main.cpp

@@ -13,24 +13,26 @@
 int main(int argc, char* argv[]) {
     // std::string pos =
     //     "r2qkb1r/2p1pppp/p1n1b3/1p6/B2P4/2P1P3/P4PPP/R1BQK1NR w KQkq - 0 9 ";
-    // std::string pos = "8/6K1/5P2/8/1k6/8/8/8 w - - 0 1";
+    std::string pos = "3r4/3r4/3k4/8/3K4/8/8/8 w - - 0 1";
 
     // pos for ai timing<
-    std::string pos =
-        "r3k2r/p1ppqpb1/Bn2pnp1/3PN3/1p2P3/2N2Q1p/PPPB1PPP/R3K2R b KQkq - 0 3";
+    // std::string pos =
+    //     "r3k2r/p1ppqpb1/Bn2pnp1/3PN3/1p2P3/2N2Q1p/PPPB1PPP/R3K2R b KQkq - 0
+    //     3";
 
     Board b = Board::setup_fen_position(pos);
 
     ai::v0_random p1(true, std::chrono::milliseconds(1000));
     // ai::v1_pure_minimax p2(false, std::chrono::milliseconds(20000));
     // ai::v2_alpha_beta p2(false, std::chrono::milliseconds(20000));
-    ai::v3_AB_ordering p2(false, std::chrono::milliseconds(20000));
+    // ai::v3_AB_ordering p2(false, std::chrono::milliseconds(20000));
     // ai::v4_search_captures p2(false, std::chrono::milliseconds(20000));
+    ai::v5_better_endgame p2(false, std::chrono::milliseconds(20000));
 
-    // GUI gui;
-    NoOpView gui;
-    AIvsAIController manual(b, gui, p1, p2);
-    // HumanVsAIController manual(b, gui, p2);
+    GUI gui;
+    // NoOpView gui;
+    // AIvsAIController manual(b, gui, p1, p2);
+    HumanVsAIController manual(b, gui, p2);
 
     Controller& controller = manual;
 

src/model/ais/ai.hpp

@@ -76,4 +76,15 @@ namespace ai {
         v4_search_captures(bool w, std::chrono::milliseconds tt)
             : v3_AB_ordering(w, tt) {}
     };
+
+    class v5_better_endgame : public v4_search_captures {
+        // same as v4, but with a better evaluation function, that forces the
+        // king towards the corner of the board for endgames
+
+      public:
+        v5_better_endgame(bool w, std::chrono::milliseconds tt)
+            : v4_search_captures(w, tt) {}
+
+        int eval(const Board&) override;
+    };
 } // namespace ai

src/model/ais/v5_better_endgames.cpp

@@ -0,0 +1,52 @@
+#include "../pieces/piece.hpp"
+#include "../utils/utils.hpp"
+#include "ai.hpp"
+
+#include <algorithm>
+
+static int force_king_to_corner(
+    int8_t attacking_king, int8_t defending_king, float endgame_weight
+) {
+    int eval = 0;
+    Coords def_xy = Coords::from_index(defending_king);
+
+    Coords def_dist_to_center{
+        std::max(3 - def_xy.x, def_xy.x - 4),
+        std::max(3 - def_xy.y, def_xy.y - 4)
+    };
+    eval += def_dist_to_center.x + def_dist_to_center.y;
+
+    // make attacking king go closer to defending king to cut off escape routes
+    Coords attack_xy = Coords::from_index(attacking_king);
+    Coords dist_between_kings{
+        std::abs(attack_xy.x - def_xy.x),
+        std::abs(attack_xy.y - def_xy.y)
+    };
+    int distance = dist_between_kings.x + dist_between_kings.y;
+    eval += 14 - distance;
+
+    return (int) (eval * 10 * endgame_weight);
+}
+
+static float endgame_phase_weight(int material_count_no_pawns) {
+    static int endgame_material_start =
+        RookValue * 2 + BishopValue + KnightValue;
+
+    float multiplier = 1.f / endgame_material_start;
+    return 1.f - std::min(1.f, material_count_no_pawns * multiplier);
+}
+
+int ai::v5_better_endgame::eval(const Board& b) {
+    int old_eval = v4_search_captures::eval(b);
+    Colour attacking_colour = b.white_to_play ? White : Black;
+    Colour defending_colour = b.white_to_play ? Black : White;
+    return old_eval
+         + force_king_to_corner(
+               b.get_king_of(attacking_colour),
+               b.get_king_of(defending_colour),
+               endgame_phase_weight(
+                   count_material(b, attacking_colour, false)
+                   + count_material(b, defending_colour, false)
+               )
+         );
+}

src/model/board/board.hpp

@@ -8,7 +8,6 @@
 
 struct Board {
   private:
-    int8_t get_king_of(int8_t) const;
     bool _no_legal_moves_for(Colour) const;
     bool _is_check_for(Colour) const;
     bool nlm = false, check = false;
@@ -25,6 +24,7 @@ struct Board {
 
     static Board setup_fen_position(std::string fen);
 
+    int8_t get_king_of(int8_t) const;
     Board skip_turn() const;
     Board make_move(Move, bool = true) const;
     std::string to_fen() const;

src/model/utils/utils.cpp

@@ -26,10 +26,13 @@ int piece_value(Piece p) {
     }
 }
 
-int count_material(const Board& b, int8_t colour) {
+int count_material(const Board& b, int8_t colour, bool count_pawns) {
     int ret = 0;
-    for (int i = 0; i < 64; i++)
+    for (int i = 0; i < 64; i++) {
+        if (b.piece_at(i) == Pawn && !count_pawns)
+            continue;
         if (b.colour_at(i) == colour)
             ret += piece_value(b.piece_at(i));
+    }
     return ret;
 }

src/model/utils/utils.hpp

@@ -7,7 +7,7 @@
 #include <vector>
 
 std::vector<int8_t> to_target_square(std::vector<Move>);
-int count_material(const Board&, int8_t);
+int count_material(const Board&, int8_t, bool = true);
 int piece_value(Piece);
 
 const int INFINITY = std::numeric_limits<int>::max();