Chess-On-Chain | StarkNet ✨

A fully on-chain player-vs-AI chess game built on StarkNet with customizable game depth.

play the game

• go to website:
• View chess board contract:
• View AI player contract:

Game Rules

                Black
             ♜ ♝ ♛ ♚ ♝ ♜
             ♟ ♟ ♟ ♟ ♟ ♟


             ♙ ♙ ♙ ♙ ♙ ♙
             ♖ ♘ ♕ ♔ ♘ ♖
                White

• A 6x6 simplified chess board (each side has one knight, one bishop, and six pawns).
• All rules are the same as regular chess with the above simplification being the only exception.
• Player plays against an AI engine that can be adjusted to different game depths as defined by the player
  • The value depth can range from 3 to 20.
  • The larger the depth value is, the more intelligent the AI becomes.
  • Larger depth value also comes with higher gas fees, but is generally affordable on StarkNet.
• The game automatically terminates when checkmate is reached.

A Gas-optimized Game - more on the program itself.

Greatly enhanced computation efficiency via bitpacking and bitwise operations.

• The board is an 8x8 representation of a 6x6 chess board, with all information bitpacked into a single uint256
• board positions are accessed via bit shifts and bit masks rather than array[index].

chess piece representation

• Each chess piece is defined with 4 bits as follows: The first bit denotes the color: 0 means black; 1 means white). The last 3 bits denote the type:

        | Bits | # | Type   |
        | ---- | - | ------ |
        | 000  | 0 | Empty  |
        | 001  | 1 | Pawn   |
        | 010  | 2 | Bishop |
        | 011  | 3 | Rook   |
        | 100  | 4 | Knight |
        | 101  | 5 | Queen  |
        | 110  | 6 | King   |
  

• for example, a black Knight is represented by 0100, a white Bishop is represented by 1010, etc.

• the program automatically assigns white to player and black to AI.

chess board representation

• Since each piece is 4 bits, there are 64 indices to access, and a total numnber of 256 bits are used.
• For example, the piece at index 14 is accessed with (board >> (14 << 2)) & 'OxF'.
• The top/bottom rows and left/right columns are treated as sentinel rows/columns for efficient boundary validation. Namely, (07, ..., 00), (63, ..., 07), and (56, ..., 00) never contain pieces.

63	62	61	60	59	58	57	56
55	54	53	52	51	50	49	48
47	46	45	44	43	42	41	40
39	38	37	36	35	34	33	32
31	30	29	28	27	26	25	24
23	22	21	20	19	18	17	16
15	14	13	12	11	10	09	08
07	06	05	04	03	02	01	00

A quick example

                    Black
   0000 0000 0000 0000 0000 0000 0000 0000                      Black
   0000 0011 0010 0101 0110 0100 0011 0000                   ♜ ♝ ♛ ♚ ♝ ♜
   0000 0001 0001 0001 0001 0001 0001 0000                   ♟ ♟ ♟ ♟ ♟ ♟
   0000 0000 0000 0000 0000 0000 0000 0000      denotes
   0000 0000 0000 0000 0000 0000 0000 0000      the board
   0000 1001 1001 1001 1001 1001 1001 0000                   ♙ ♙ ♙ ♙ ♙ ♙
   0000 1011 1010 1101 1110 1100 1011 0000                   ♖ ♘ ♕ ♔ ♘ ♖ 
   0000 0000 0000 0000 0000 0000 0000 0001 ⬅️ white turn)        White         
                    White                                       

The last bit denotes whose turn it is to play (0 means black's turn; 1 means white's turn). e.g. a potential starting position.

Program Architecture

• The game rules are defined in chess_board.cairo.
• The AI decision-making machine is defined in ai_player.cairo

made with soul at StarkNet House Hackathon, 08.16.2022