Standard Portal Chess v1.1 - Rules and Gameplay

Welcome to Standard Portal Chess v1.1, a fascinating variant of traditional chess that introduces portals—special squares that allow pieces to teleport across the board. This game combines classic chess strategy with unique portal mechanics, offering a fresh and exciting challenge. Below are the complete rules and gameplay mechanics, derived straight from the game’s code.

Objective

The goal remains the same as in classic chess: to checkmate your opponent’s king—place it under an unavoidable threat of capture. However, portals add a twist, making strategic positioning and movement more dynamic.

Board Setup

• Size: The game is played on a standard 8x8 chessboard (64 squares).
• Initial Position: Pieces are set up as in traditional chess:
  • White: Pawns on row 7 (rank 2), Rooks on a1 and h1, Knights on b1 and g1, Bishops on c1 and f1, Queen on d1, King on e1.
  • Black: Pawns on row 2 (rank 7), Rooks on a8 and h8, Knights on b8 and g8, Bishops on c8 and f8, Queen on d8, King on e8.
• Portals: Eight portal squares are placed on the board, either in a predefined layout (e.g., from "dfp.txt") or customized by the player. These portals are empty at the start and must be on distinct squares.

Players and Turns

• Players: Two players—White (human) and Black (AI by default)—or self-play mode where one player controls both sides.
• Turn Order: White moves first, and turns alternate between White and Black.
• AI Mode: By default, Black is controlled by an AI using a minimax algorithm with a search depth of 3, evaluating moves based on piece value, center control, and mobility.

Piece Movement

All pieces move as in standard chess, with additional rules for portals:

• Pawn: Moves forward one square (or two from its starting rank), captures diagonally forward. Promotes to a Queen upon reaching the opponent’s back rank (row 1 for White, row 8 for Black) on a non-portal square.
• Knight: Moves in an L-shape (two squares in one direction, then one perpendicular).
• Bishop: Moves diagonally any number of squares.
• Rook: Moves horizontally or vertically any number of squares.
• Queen: Moves any number of squares diagonally, horizontally, or vertically.
• King: Moves one square in any direction (no castling in this version).

Portal Mechanics

Portals are the defining feature of this game, allowing pieces to teleport instantly across the board. Here’s how they work:

• Entering a Portal: A piece can move to a portal square if:
  • It’s empty, and at least one other portal is open (empty), or
  • It contains an enemy piece, making the portal unoccupied after capture.
• Exiting a Portal: After entering a portal, the piece must exit to another open portal square (not the entry portal) that doesn’t leave the player’s king in check.
• Portal Move Process:
  • Move to the entry portal (capturing if applicable).
  • Select a safe exit portal from available options.
  • The piece teleports to the exit, a new portal appears at the origin square, and one portal is removed from the entry square (maintaining exactly 8 portals).
• King and Check: A portal move is invalid if it leaves the king in check after exiting.

Game States

• Check: Occurs when a king is under threat of capture. The player must move the king, capture the threat, or block it (via portals if possible).
• Checkmate: If the king is in check and no legal move (standard or portal) can escape it, the game ends with the opponent winning.
• Stalemate: If a player has no legal moves and their king is not in check, the game ends in a draw.

Gameplay Features

• Interface: A graphical board with light and dark squares, portal tokens (blue circles), and piece images. Highlights show legal moves.
• Move History: Tracks all moves in algebraic notation (e.g., "White P: e2 to e4" or "Black Portal: e7 via d5 to f3").
• Portal Placement:
  • Standard Game: Loads a default layout (e.g., "dfp.txt").
  • Custom Game: Players place exactly 8 portals on empty squares before starting.
• Save/Load: Games and portal arrangements can be saved to and loaded from text files.
• Self-Play Mode: Toggle to control both sides manually.

AI Behavior

The AI (Black by default) uses a minimax algorithm with alpha-beta pruning to select moves, prioritizing:

• Capturing high-value pieces (Pawn: 1, Knight/Bishop: 3, Rook: 5, Queen: 9).
• Putting the opponent in check.
• Maintaining piece mobility and center control.

It evaluates all legal moves, including portal options, and chooses the best based on a calculated score.

Winning the Game

The game ends when:

• A player delivers checkmate, winning immediately.
• A stalemate occurs, resulting in a draw.
• The AI declares "no legal moves" (though this typically aligns with checkmate or stalemate).