Building a Tic Tac Toe Game on Aptos with Move Language - Part 1

Introduction

In this article, we embark on a journey to build a classic Tic Tac Toe game on the Aptos blockchain using the Move programming language. This project is not just about creating a simple game, it's about exploring the potential of blockchain technology for interactive applications and decentralized gaming experiences.

Why Aptos? Aptos is a Layer 1 blockchain designed for high throughput and low latency, making it ideal for building demanding applications like games. Move is Aptos's native programming language, known for its security features and expressiveness.

This article focuses on the core concepts and initial steps involved in building our Tic Tac Toe game, laying the foundation for a future, more advanced version.

Understanding the Fundamentals

Before we dive into the code, let's understand the essential components of our Tic Tac Toe game on Aptos:

Blockchain: Aptos provides the secure and transparent platform on which our game will run.
Move: The Move language allows us to define the game logic, manage player states, and ensure the integrity of the game's execution.
Smart Contract: The core of our game is represented by a smart contract, a program stored on the blockchain that defines the rules and enforces them.
Game State: The current state of the game, including the board configuration, current player, and game outcome, is stored securely on the blockchain.
User Interaction: Players interact with the game through their wallets and interact with the smart contract to make moves.
Setting up Your Environment
To get started, you'll need to have a few tools and set up your development environment:

Aptos CLI: The Aptos command-line interface provides tools for interacting with the network. Download and install it from https://aptoslabs.com/docs/getting-started/.
Move Language: The Move compiler and tools are necessary for writing and deploying your smart contracts. These are typically included in the Aptos CLI.
IDE: Choose your favorite IDE, such as VS Code or IntelliJ, for coding.
Creating the Tic Tac Toe Smart Contract
Let's start by defining the core of our game, the Tic Tac Toe smart contract:

module TicTacToe {
    use AptosFramework::Signer;
    use AptosFramework::BCS;

    // Define the game state structure
    struct GameState has key {
        board: vector
<u8>
 , // Represents the 3x3 board (0: empty, 1: X, 2: O)
        currentPlayer: u8, // 1 for X, 2 for O
        gameStatus: u8, // 0: ongoing, 1: X wins, 2: O wins, 3: Draw
    }

    // Public function to create a new game
    public fun create_game(account: &amp;signer) {
        let player = Signer::address_of(account);
        move_to(player, GameState {
            board: vec![0; 9], // Initialize an empty board
            currentPlayer: 1, // X starts the game
            gameStatus: 0, // Game is ongoing
        });
    }

    // Public function to make a move
    public fun make_move(account: &amp;signer, position: u8) {
        let player = Signer::address_of(account);
        let game_state = borrow_global_mut
 <gamestate>
  (player);

        // Validate move (check for valid position, turn, game status)
        assert!(position &lt; 9, 0); // Position must be within the board
        assert!(game_state.gameStatus == 0, 1); // Game must be ongoing
        assert!(game_state.currentPlayer == 1 &amp;&amp; game_state.board[position as usize] == 0, 2); // Only X can play in an empty cell

        // Update the board
        game_state.board[position as usize] = 1;
        // Switch to the next player
        game_state.currentPlayer = 2;
    }

    // Public function to check the game status
    public fun check_game_status(account: &amp;signer) {
        let player = Signer::address_of(account);
        let game_state = borrow_global
  <gamestate>
   (player);

        // Check for winning conditions (rows, columns, diagonals)
        // ...

        // Check for draw condition (board full)
        // ...

        // Update game status based on the result
        // ...
    }
}

This code snippet demonstrates the core components of our Tic Tac Toe game:

GameState Structure: This structure stores the game's current state (board, current player, game status).
create_game Function: This function is called to initialize a new game instance.
make_move Function: This function handles player moves, validates them, and updates the game state.
check_game_status Function: This function analyzes the board and determines the game's outcome (win, loss, draw).
Explanation of the Code
Let's break down the code and explain its purpose:

use Statements: The use statements bring in necessary modules from the Aptos framework for interacting with signers, encoding data (BCS), and managing global resources.
GameState Structure:
- board: This is a vector of u8 (unsigned 8-bit integers) representing the 3x3 board. Each cell's value indicates its state:
  - 0: Empty
  - 1: X
  - 2: O
- currentPlayer: This indicates whose turn it is (1 for X, 2 for O).
- gameStatus: This tracks the game's outcome:
  - 0: Game is ongoing.
  - 1: X wins.
  - 2: O wins.
  - 3: Draw.
create_game Function:
- This function is called by a player to initiate a new game.
- It obtains the player's address using Signer::address_of and stores the new GameState under this address as a global resource.
- The initial game state is set up with an empty board, X as the first player, and the game status as ongoing.
make_move Function:
- This function is called by a player to make a move.
- It retrieves the player's address and retrieves the GameState using borrow_global_mut, which allows modifying the state.
- It performs several validations:
  - position < 9: Ensures the move is within the board's bounds.
  - game_state.gameStatus == 0: Checks if the game is still ongoing.
  - game_state.currentPlayer == 1 && game_state.board[position as usize] == 0: Ensures it's the correct player's turn and the chosen cell is empty.
- If the move is valid, it updates the board at the chosen position with the current player's symbol and then switches the currentPlayer to the other player.
check_game_status Function:
- This function is called to determine the current game outcome.
- It retrieves the GameState using borrow_global.
- It will contain the logic to check for winning conditions (rows, columns, diagonals) and a draw condition (board full).
- Based on the result, it will update the gameStatus in the GameState.
  Next Steps
  This first part of our journey has laid the groundwork for our Tic Tac Toe game on Aptos. We've defined the game state, established the core functions for creating games, making moves, and checking the game status.

In the next part, we'll delve deeper into:

Implementing Winning Conditions: We will complete the check_game_status function to check for all winning combinations and draw conditions.
User Interface (UI): We will explore ways to interact with the game through a UI, potentially using tools like React or other front-end frameworks.
Testing and Deployment: We'll learn how to thoroughly test our smart contract and deploy it to the Aptos blockchain.
Conclusion
Building a game on Aptos with Move opens up new possibilities for decentralized gaming. This article has demonstrated how to define the core game logic and structure using a smart contract. We've learned how to use Move's features to manage the game state, validate player moves, and ensure the integrity of the game.

Stay tuned for the next installment where we'll dive deeper into the game's logic, user interface, and deployment process.