Checkers Environment Documentation

Overview

Checkers (also known as Draughts) is a turn-based game played on an 8×8 board.
Each player controls a set of pieces placed on alternating dark squares.
Pieces move diagonally forward and can capture opponent pieces by jumping over them.
A piece that reaches the opposite side of the board becomes a "King," gaining the ability to move backward as well.
The game ends when one player’s pieces are all captured or when a player has no valid moves left.

In this environment:

• Players: 2 (Red and Black)
• Board Size: 8×8
• Pieces:
  • 'r': Red piece
  • 'b': Black piece
  • 'R': Red King
  • 'B': Black King
  • '.': Empty square
• Objective: Capture or block all opponent pieces.

Action Space

• Format: [r1 c1 r2 c2] indicating moving the piece at (r1, c1) to (r2, c2).
• Examples:
  • [2 1 3 2] moves the piece at row=2, col=1 to row=3, col=2.
• Notes:
  • Any extra text in the action string is acceptable as long as the bracketed substring matches the regex.
  • Invalid actions (e.g., out-of-bounds or illegal moves) trigger a penalty under the environment’s invalid_move logic.

Observation Space

Reset Observations

Upon resetting, each player receives:

You are Player 0 playing as Red.
Make your move in the format [rowFrom colFrom rowTo colTo], e.g. [2 1 3 2].
...
Here is the current board:
     0  1  2  3  4  5  6  7
   +-------------------------
 0 | .  b  .  b  .  b  .  b
 1 | b  .  b  .  b  .  b  .
 2 | .  b  .  b  .  b  .  b
 3 | .  .  .  .  .  .  .  .
 4 | .  .  .  .  .  .  .  .
 5 | r  .  r  .  r  .  r  .
 6 | .  r  .  r  .  r  .  r
 7 | r  .  r  .  r  .  r  .

Step Observations

After each step, all players see the relevant moves and updated board. For example:

[Player 1] [2 1 3 2]
[GAME] Player 1 moved (2,1) -> (3,2).
     0  1  2  3  4  5  6  7
   +-------------------------
 0 | .  b  .  b  .  b  .  b
 1 | b  .  b  .  b  .  b  .
 2 | .  .  .  b  .  b  .  b
 3 | .  .  b  .  .  .  .  .

Gameplay

1. Initial Setup:

   • Each player has 12 pieces on alternating dark squares in the first three rows for Black (rows 0..2) and last three rows for Red (rows 5..7).

2. Turns:

   • Red (player 0) goes first, then Black (player 1), alternating turns.

3. Movement:

   • Non-King pieces move diagonally forward by 1 step to an empty square ('.') or capture an opponent piece by jumping over it.
   • Kinged pieces (denoted 'R' or 'B') can move diagonally in any direction.

4. Capturing:

   • Pieces capture by jumping diagonally over an opponent’s piece into an empty space behind it.
   • Although not fully enforced here, standard Checkers typically requires multiple jumps if available.

5. Kinging:

   • A piece reaching the opposite end of the board becomes a King ('r' → 'R', 'b' → 'B').

6. Winning Conditions:

   • A player wins if the opponent has no pieces left or has no valid moves.
   • The environment may also declare a draw if the max_turns limit is reached.

Rewards

Parameters

• max_turns (int, default: 50):
  • Description: Maximum number of turns before the environment auto-ends in a draw.
  • Impact: Limits the game’s length; can be increased for more complex or complete play.

Variants

Contact

If you have questions or face issues with this Checkers environment, please reach out to
guertlerlo@cfar.a-star.edu.sg.