Video Chess

🕹

Registry name: videochess. Parity status in games_covered.md: 🥈.

Description

Atari 2600–style chess: move a cursor with the joystick, press FIRE to select a piece and again to move to a target square. By default you play white and black replies with a depth-2 (top-k pruned) minimax bot after each of your moves.

Actions

Observations

• board — (8, 8) piece codes

• cursor / selected — ObjectObservation pointers on the board grid (active when valid)

• to_move — side to move (0=white, 1=black)

Reward

Material change (in pawn units / 1000-style scaling via piece values) plus terminal outcomes from checkmate / king capture / stalemate.

Modifications

Registered via VideochessEnvMod:

Opponent / control

• play_both_sides — human controls both colours (disables the black bot)

• random_bot_black — black replies with a random legal move

• greedy_bot_black — black replies with a greedy capture heuristic

• minimax_bot_black — black replies with depth-2 minimax (unmodded default; useful to re-enable after another bot mod)

Input / display

• instant_movement — held direction inputs repeat every frame (FIRE stays edge-triggered)

• legal_moves_display — show legal-move indicator dots for the selected piece (off by default)

Board setups

• pawns_only / queens_only / rooks_only / knights_only / bishops_only

• checkmate_test — sparse mate-in-one style position

Recommended medal

🥈 Silver — playable chess rules with castling, en passant, promotions, check filtering, and a working black opponent, but not full ALE Video Chess parity (no cartridge AI levels / opening book / timing / audio), and the minimax bot is a Jaxtari addition rather than a faithful port of the 2600 engine.

Known issues

• Default bot cost — depth-2 minimax is expensive; after each white move the step can stall while black thinks. Use play_both_sides or random_bot_black for fast interaction / training loops.

• Legal-move dots are a mod — unmodded play does not highlight targets (ALE UX differed; enable legal_moves_display when useful).

• Edge-triggered cursor — by default held sticks do not auto-repeat; enable instant_movement for held-key cursor motion.

• AI ≠ cartridge — black is a simple pruned minimax / greedy / random helper, not the original Video Chess difficulty levels.

• No underpromotion — promotions always become queens.

• Draw rules incomplete — stalemate is detected; threefold repetition and fifty-move rule are not.

• Performance — even without the bot, FIRE-to-move still runs a full legal-move + check filter for the selected piece, and every board change runs a game-over / checkmate scan. Cursor-only steps and play_both_sides avoid compiling the minimax graph.

• Two-player ALE modes / select screen — not modeled; game starts mid-board.