ChessEngine: Add ChessEngine

This engine is pretty bad, but doesn't let itself get checkmated

Applications/CMakeLists.txt

@@ -2,6 +2,7 @@ add_subdirectory(About)
 add_subdirectory(Browser)
 add_subdirectory(Calculator)
 add_subdirectory(Calendar)
+add_subdirectory(ChessEngine)
 add_subdirectory(Debugger)
 add_subdirectory(DisplaySettings)
 add_subdirectory(FileManager)

Applications/ChessEngine/CMakeLists.txt

@@ -0,0 +1,8 @@
+set(SOURCES
+    ChessEngine.cpp
+    main.cpp
+    MCTSTree.cpp
+)
+
+serenity_bin(ChessEngine)
+target_link_libraries(ChessEngine LibChess LibCore)

Applications/ChessEngine/ChessEngine.cpp

@@ -0,0 +1,76 @@
+/*
+ * Copyright (c) 2020, the SerenityOS developers.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "ChessEngine.h"
+#include "MCTSTree.h"
+#include <LibCore/ElapsedTimer.h>
+
+using namespace Chess::UCI;
+
+void ChessEngine::handle_uci()
+{
+    send_command(IdCommand(IdCommand::Type::Name, "ChessEngine"));
+    send_command(IdCommand(IdCommand::Type::Author, "the SerenityOS developers"));
+    send_command(UCIOkCommand());
+}
+
+void ChessEngine::handle_position(const PositionCommand& command)
+{
+    // FIXME: Implement fen board position.
+    ASSERT(!command.fen().has_value());
+    m_board = Chess::Board();
+    for (auto& move : command.moves()) {
+        ASSERT(m_board.apply_move(move));
+    }
+}
+
+void ChessEngine::handle_go(const GoCommand& command)
+{
+    // FIXME: A better algorithm than naive mcts.
+    // FIXME: Add different ways to terminate search.
+    ASSERT(command.movetime.has_value());
+
+    srand(arc4random());
+
+    Core::ElapsedTimer elapsed_time;
+    elapsed_time.start();
+
+    MCTSTree mcts(m_board);
+
+    // FIXME: optimize simulations enough for use.
+    mcts.set_eval_method(MCTSTree::EvalMethod::Heuristic);
+
+    int rounds = 0;
+    while (elapsed_time.elapsed() <= command.movetime.value()) {
+        mcts.do_round();
+        ++rounds;
+    }
+    dbg() << "MCTS finished " << rounds << " rounds.";
+    dbg() << "MCTS evaluation " << mcts.expected_value();
+    auto best_move = mcts.best_move();
+    dbg() << "MCTS best move " << best_move.to_long_algebraic();
+    send_command(BestMoveCommand(best_move));
+}

Applications/ChessEngine/ChessEngine.h

@@ -0,0 +1,49 @@
+/*
+ * Copyright (c) 2020, the SerenityOS developers.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <LibChess/Chess.h>
+#include <LibChess/UCIEndpoint.h>
+
+class ChessEngine : public Chess::UCI::Endpoint {
+    C_OBJECT(ChessEngine)
+public:
+    virtual ~ChessEngine() override { }
+
+    ChessEngine() { }
+    ChessEngine(NonnullRefPtr<Core::IODevice> in, NonnullRefPtr<Core::IODevice> out)
+        : Endpoint(in, out)
+    {
+    }
+
+    virtual void handle_uci();
+    virtual void handle_position(const Chess::UCI::PositionCommand&);
+    virtual void handle_go(const Chess::UCI::GoCommand&);
+
+private:
+    Chess::Board m_board;
+};

Applications/ChessEngine/MCTSTree.cpp

@@ -0,0 +1,180 @@
+/*
+ * Copyright (c) 2020, the SerenityOS developers.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "MCTSTree.h"
+#include <AK/String.h>
+#include <stdlib.h>
+
+MCTSTree::MCTSTree(const Chess::Board& board, double exploration_parameter, MCTSTree* parent)
+    : m_parent(parent)
+    , m_exploration_parameter(exploration_parameter)
+    , m_board(board)
+{
+    if (m_parent)
+        m_eval_method = m_parent->eval_method();
+}
+
+MCTSTree& MCTSTree::select_leaf()
+{
+    if (!expanded() || m_children.size() == 0)
+        return *this;
+
+    MCTSTree* node = nullptr;
+    double max_uct = -double(INFINITY);
+    for (auto& child : m_children) {
+        double uct = child.uct(m_board.turn());
+        if (uct >= max_uct) {
+            max_uct = uct;
+            node = &child;
+        }
+    }
+    ASSERT(node);
+    return node->select_leaf();
+}
+
+MCTSTree& MCTSTree::expand()
+{
+    ASSERT(!expanded() || m_children.size() == 0);
+
+    if (!m_moves_generated) {
+        m_board.generate_moves([&](Chess::Move move) {
+            Chess::Board clone = m_board;
+            clone.apply_move(move);
+            m_children.append(make<MCTSTree>(clone, m_exploration_parameter, this));
+            return IterationDecision::Continue;
+        });
+        m_moves_generated = true;
+    }
+
+    if (m_children.size() == 0) {
+        return *this;
+    }
+
+    for (auto& child : m_children) {
+        if (child.m_simulations == 0) {
+            return child;
+        }
+    }
+    ASSERT_NOT_REACHED();
+}
+
+int MCTSTree::simulate_game() const
+{
+    ASSERT_NOT_REACHED();
+    Chess::Board clone = m_board;
+    while (!clone.game_finished()) {
+        clone.apply_move(clone.random_move());
+    }
+    return clone.game_score();
+}
+
+int MCTSTree::heuristic() const
+{
+    if (m_board.game_finished())
+        return m_board.game_score();
+
+    double winchance = max(min(double(m_board.material_imbalance()) / 6, 1.0), -1.0);
+
+    double random = double(rand()) / RAND_MAX;
+    if (winchance >= random)
+        return 1;
+    if (winchance <= -random)
+        return -1;
+
+    return 0;
+}
+
+void MCTSTree::apply_result(int game_score)
+{
+    m_simulations++;
+    m_white_points += game_score;
+
+    if (m_parent)
+        m_parent->apply_result(game_score);
+}
+
+void MCTSTree::do_round()
+{
+    auto& node = select_leaf().expand();
+
+    int result;
+    if (m_eval_method == EvalMethod::Simulation) {
+        result = node.simulate_game();
+    } else {
+        result = node.heuristic();
+    }
+    node.apply_result(result);
+}
+
+Chess::Move MCTSTree::best_move() const
+{
+    int score_multiplier = (m_board.turn() == Chess::Colour::White) ? 1 : -1;
+
+    Chess::Move best_move = { { 0, 0 }, { 0, 0 } };
+    double best_score = -double(INFINITY);
+    ASSERT(m_children.size());
+    for (auto& node : m_children) {
+        double node_score = node.expected_value() * score_multiplier;
+        if (node_score >= best_score) {
+            // The best move is the last move made in the child.
+            best_move = node.m_board.moves()[node.m_board.moves().size() - 1];
+            best_score = node_score;
+        }
+    }
+
+    return best_move;
+}
+
+double MCTSTree::expected_value() const
+{
+    if (m_simulations == 0)
+        return 0;
+
+    return double(m_white_points) / m_simulations;
+}
+
+double MCTSTree::uct(Chess::Colour colour) const
+{
+    // UCT: Upper Confidence Bound Applied to Trees.
+    //      Kocsis, Levente; Szepesvári, Csaba (2006). "Bandit based Monte-Carlo Planning"
+
+    // Fun fact: Szepesvári was my data structures professor.
+    double expected = expected_value() * ((colour == Chess::Colour::White) ? 1 : -1);
+    return expected + m_exploration_parameter * sqrt(log(m_parent->m_simulations) / m_simulations);
+}
+
+bool MCTSTree::expanded() const
+{
+    if (!m_moves_generated)
+        return false;
+
+    for (auto& child : m_children) {
+        if (child.m_simulations == 0)
+            return false;
+    }
+
+    return true;
+}

Applications/ChessEngine/MCTSTree.h

@@ -0,0 +1,67 @@
+/*
+ * Copyright (c) 2020, the SerenityOS developers.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <AK/Function.h>
+#include <AK/NonnullOwnPtrVector.h>
+#include <LibChess/Chess.h>
+#include <math.h>
+
+class MCTSTree {
+public:
+    enum EvalMethod {
+        Simulation,
+        Heuristic,
+    };
+
+    MCTSTree(const Chess::Board& board, double exploration_parameter = sqrt(2), MCTSTree* parent = nullptr);
+
+    MCTSTree& select_leaf();
+    MCTSTree& expand();
+    int simulate_game() const;
+    int heuristic() const;
+    void apply_result(int game_score);
+    void do_round();
+
+    Chess::Move best_move() const;
+    double expected_value() const;
+    double uct(Chess::Colour colour) const;
+    bool expanded() const;
+
+    EvalMethod eval_method() const { return m_eval_method; }
+    void set_eval_method(EvalMethod method) { m_eval_method = method; }
+
+private:
+    NonnullOwnPtrVector<MCTSTree> m_children;
+    MCTSTree* m_parent { nullptr };
+    int m_white_points { 0 };
+    int m_simulations { 0 };
+    bool m_moves_generated { false };
+    double m_exploration_parameter;
+    EvalMethod m_eval_method { EvalMethod::Simulation };
+    Chess::Board m_board;
+};

Applications/ChessEngine/main.cpp

@@ -0,0 +1,36 @@
+/*
+ * Copyright (c) 2020, the SerenityOS developers.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "ChessEngine.h"
+#include <LibCore/EventLoop.h>
+#include <LibCore/File.h>
+
+int main()
+{
+    Core::EventLoop loop;
+    auto engine = ChessEngine::construct(Core::File::stdin(), Core::File::stdout());
+    return loop.exec();
+}

Games/Chess/ChessWidget.cpp

@@ -272,7 +272,7 @@ void ChessWidget::maybe_input_engine_move()
     if (drag_was_enabled)
         set_drag_enabled(false);
 
-    m_engine->get_best_move(board(), 500, [this, drag_was_enabled](Chess::Move move) {
+    m_engine->get_best_move(board(), 4000, [this, drag_was_enabled](Chess::Move move) {
         set_drag_enabled(drag_was_enabled);
         ASSERT(board().apply_move(move));
         update();

Libraries/LibChess/Chess.cpp

@@ -425,8 +425,8 @@ bool Board::apply_illegal_move(const Move& move, Colour colour)
         if (move.to == Square("a8") || move.to == Square("c8")) {
             set_piece(Square("e8"), EmptyPiece);
             set_piece(Square("a8"), EmptyPiece);
-            set_piece(Square("c8"), { Colour::White, Type::King });
-            set_piece(Square("d8"), { Colour::White, Type::Rook });
+            set_piece(Square("c8"), { Colour::Black, Type::King });
+            set_piece(Square("d8"), { Colour::Black, Type::Rook });
             return true;
         } else if (move.to == Square("h8") || move.to == Square("g8")) {
             set_piece(Square("e8"), EmptyPiece);
@@ -463,6 +463,23 @@ bool Board::apply_illegal_move(const Move& move, Colour colour)
     return true;
 }
 
+Move Board::random_move(Colour colour) const
+{
+    if (colour == Colour::None)
+        colour = turn();
+
+    Move move = { { 50, 50 }, { 50, 50 } };
+    int probability = 1;
+    generate_moves([&](Move m) {
+        if (rand() % probability == 0)
+            move = m;
+        ++probability;
+        return IterationDecision::Continue;
+    });
+
+    return move;
+}
+
 Board::Result Board::game_result() const
 {
     bool sufficient_material = false;
@@ -533,6 +550,65 @@ Board::Result Board::game_result() const
     return Result::StaleMate;
 }
 
+Colour Board::game_winner() const
+{
+    if (game_result() == Result::CheckMate)
+        return opposing_colour(turn());
+
+    return Colour::None;
+}
+
+int Board::game_score() const
+{
+    switch (game_winner()) {
+    case Colour::White:
+        return +1;
+    case Colour::Black:
+        return -1;
+    case Colour::None:
+        return 0;
+    }
+    return 0;
+}
+
+bool Board::game_finished() const
+{
+    return game_result() != Result::NotFinished;
+}
+
+int Board::material_imbalance() const
+{
+    int imbalance = 0;
+    Square::for_each([&](Square square) {
+        int value = 0;
+        switch (get_piece(square).type) {
+        case Type::Pawn:
+            value = 1;
+            break;
+        case Type::Knight:
+        case Type::Bishop:
+            value = 3;
+            break;
+        case Type::Rook:
+            value = 5;
+            break;
+        case Type::Queen:
+            value = 9;
+            break;
+        default:
+            break;
+        }
+
+        if (get_piece(square).colour == Colour::White) {
+            imbalance += value;
+        } else {
+            imbalance -= value;
+        }
+        return IterationDecision::Continue;
+    });
+    return imbalance;
+}
+
 bool Board::is_promotion_move(const Move& move, Colour colour) const
 {
     if (colour == Colour::None)

Libraries/LibChess/Chess.h

@@ -135,7 +135,12 @@ public:
 
     template<typename Callback>
     void generate_moves(Callback callback, Colour colour = Colour::None) const;
+    Move random_move(Colour colour = Colour::None) const;
     Result game_result() const;
+    Colour game_winner() const;
+    int game_score() const;
+    bool game_finished() const;
+    int material_imbalance() const;
 
     Colour turn() const { return m_turn; }
     const Vector<Move>& moves() const { return m_moves; }