Introduction

This repo is for creating a chess engine specifically for chess.com's Spell Chess variant using the Minimax algorithm. The engine is written in C and the playable game is made with Unity.

Plan

State Representation

The state of the game will be stored in as few bytes as possible. One integer will store the position of all black pawns where a bit set to one means a pawn exists while a zero means it doesn't exist in that position. Bit 0 will be the square "a8" going across where bit 7 is the square "h8". One advantage of this trick is to allow a bitwise "and" to reduce the set of potential moves.

Comunication between Unity and C

The current plan is to have Unity call the compiled C program as a subprocess with the state of the game as an extended FEN code. The C program will then return the move it thinks is best in the format of "a2a4" for example. The Unity program will then make the move and repeat the process.

Compiling the Engine

With gcc installed, run the following command in the root directory of the repo:

make

Running the Engine

To run the engine, run the following command in the root directory of the repo:

main <FEN> [<frozen> <jumpable> <spells> <waiting_spells>]

Where:

• <FEN>: the FEN code of the current state of the game. See here for more information.
• <frozen>: The square with the current usage of freeze (there can only be one square at a time). If no square is frozen, the "-" char will be used. (ex. a2 means the square "a2" and the nearest squares to in all directions are frozen)
• <jumpable>: The square with the current usage of jump. As with the frozen square there can only be one at a time. If no square is jumpable, the "-" char is used. (ex. a2 means the square "a2" is jumpable)
• <spells>: Number of spells each player has: It has freeze followed by jump. White's spells are first. (ex. 5241 means white has 5 freezes and 2 jumps while black has 4 freezes and 1 jump)
• <waiting_spells>: How many half turns until each spell can be used. It goes freeze then jump, where white is first. (ex. 0000 means all spells are ready to be used while 1300 means white has to wait 1 half turn to use freeze and 3 half turns to use jump while black can use both spells now)