Geminina is a UCI (Universal Chess Interface) compatible chess engine written in C++. It's designed with a focus on clarity, correctness, and simplicity, providing a foundational example of a legal-move-generating chess engine. While not aiming for grandmaster strength in its current iteration, it implements core chess logic, search algorithms, and UCI communication, making it suitable for learning and as a base for further development.
This engine was developed iteratively, with each step adding a meaningful improvement to its playing strength or functionality.
- UCI Compatibility: Supports standard UCI commands for easy integration with chess GUIs (e.g., Arena, CuteChess, BanksiaGUI).
uciisreadyucinewgameposition [startpos | fen <fenstring>] moves <move1> <move2> ...go [wtime <ms> btime <ms> winc <ms> binc <ms> movestogo <n> | movetime <ms>]quit
- Legal Move Generation: Generates all fully legal moves for the current player, including:
- Standard piece movements
- Pawn promotions (auto-queens for simplicity in some internal contexts, but respects UCI promotion character)
- Castling (Kingside and Queenside)
- En passant
- Board Representation: Uses an 8x8 array (
char board[8][8]) for straightforward board representation. - Search Algorithm:
- Iterative Deepening: Searches to increasing depths.
- Alpha-Beta Pruning: Optimizes the search by cutting off unpromising branches.
- Quiescence Search: Extends the search for tactical sequences (captures) beyond the main search depth to mitigate the horizon effect.
- Evaluation Function:
- Material Count: Basic scoring based on piece values.
- Piece-Square Tables (PSTs): Positional bonuses for pieces based on their location, encouraging better development and control.
- Game End Detection: Explicitly checks for and recognizes:
- Checkmate
- Stalemate
- Draw by Threefold Repetition
- Draw by Fifty-Move Rule
- Time Management:
- Parses UCI time controls (
wtime,btime,winc,binc,movestogo,movetime). - Dynamically allocates time per move based on remaining time, increments, and moves to go.
- Responsive time checks within the search to adhere to time limits.
- Parses UCI time controls (
- Move Ordering: Implements simple move ordering (captures first) at the root of the search and within the main search to improve alpha-beta pruning efficiency.
- Single File Implementation: All code is contained within
main.cppfor simplicity. - Usage
- Geminina is a UCI engine, which means it's designed to be used with a UCI-compatible chess graphical user interface (GUI).
- Compile the engine as described above.
- Open your preferred chess GUI (e.g., Arena, CuteChess, Tarrasch GUI, BanksiaGUI).
- Add Geminina as a new UCI engine in the GUI. You will usually need to browse to the location of the compiled executable.
- Once configured, you can play against the engine or have it analyze positions through the GUI.
The engine is designed to be compiled with g++ (GCC).
g++ -o Geminina main.cpp -std=c++17 -O2
-std=c++17: Specifies the C++17 standard.
-O2: Enables optimizations (optional, but recommended for better performance). You can also use -O3.
An executable named Geminina (or Geminina.exe on Windows) will be created.