8.0 KiB

Raw Permalink Blame History Unescape Escape

Build a Space Game Part 6: End and Restart

Pre-Lecture Quiz

There are various ways to define an end condition in a game. As the creator, it's up to you to decide why the game ends. Here are some possible reasons, assuming we're talking about the space game you've been building:

N Enemy ships destroyed: It's common in games with levels to require the destruction of N enemy ships to complete a level.
Your ship is destroyed: Many games end when your ship is destroyed. Alternatively, some games use a "lives" system, where losing a ship deducts a life. If all lives are lost, the game ends.
Collect N points: Another common end condition is reaching a certain number of points. Points can be earned in various ways, such as destroying enemy ships or collecting items dropped by them.
Complete a level: This might involve multiple conditions, such as destroying X enemy ships, collecting Y points, or obtaining a specific item.

Restarting

If players enjoy your game, they'll likely want to replay it. When the game ends, for any reason, you should provide an option to restart.

✅ Take a moment to think about the conditions under which games you’ve played end, and how they prompt you to restart.

What to build

You’ll add the following rules to your game:

Winning the game: When all enemy ships are destroyed, the player wins. Display a victory message.
Restart: When all lives are lost or the game is won, provide a way to restart. Remember to reinitialize the game and clear the previous game state.

Recommended steps

Locate the files created for you in the your-work subfolder. It should contain the following:

-| assets
  -| enemyShip.png
  -| player.png
  -| laserRed.png
  -| life.png
-| index.html
-| app.js
-| package.json

Start your project in the your_work folder by typing:

cd your-work
npm start

This will start an HTTP server at http://localhost:5000. Open a browser and navigate to that address. Your game should be playable.

tip: To avoid warnings in Visual Studio Code, edit the window.onload function to call gameLoopId as is (without let), and declare gameLoopId at the top of the file separately: let gameLoopId;

Add code

Track end condition: Add code to track the number of enemies or whether the hero ship has been destroyed by adding these two functions:

function isHeroDead() {
  return hero.life <= 0;
}

function isEnemiesDead() {
  const enemies = gameObjects.filter((go) => go.type === "Enemy" && !go.dead);
  return enemies.length === 0;
}

Add logic to message handlers: Update the eventEmitter to handle these conditions:

eventEmitter.on(Messages.COLLISION_ENEMY_LASER, (_, { first, second }) => {
    first.dead = true;
    second.dead = true;
    hero.incrementPoints();

    if (isEnemiesDead()) {
      eventEmitter.emit(Messages.GAME_END_WIN);
    }
});

eventEmitter.on(Messages.COLLISION_ENEMY_HERO, (_, { enemy }) => {
    enemy.dead = true;
    hero.decrementLife();
    if (isHeroDead())  {
      eventEmitter.emit(Messages.GAME_END_LOSS);
      return; // loss before victory
    }
    if (isEnemiesDead()) {
      eventEmitter.emit(Messages.GAME_END_WIN);
    }
});

eventEmitter.on(Messages.GAME_END_WIN, () => {
    endGame(true);
});

eventEmitter.on(Messages.GAME_END_LOSS, () => {
  endGame(false);
});

Add new message types: Add these messages to the constants object:

GAME_END_LOSS: "GAME_END_LOSS",
GAME_END_WIN: "GAME_END_WIN",

Add restart code: Implement code to restart the game when a specific button is pressed.
1. Listen for the Enter key press: Update your window's eventListener to detect this key press:
```
 else if(evt.key === "Enter") {
    eventEmitter.emit(Messages.KEY_EVENT_ENTER);
  }
```
1. Add restart message: Add this message to your Messages constant:
```
KEY_EVENT_ENTER: "KEY_EVENT_ENTER",
```

Implement game rules: Add the following game rules:

Player win condition: When all enemy ships are destroyed, display a victory message.

First, create a displayMessage() function:

function displayMessage(message, color = "red") {
  ctx.font = "30px Arial";
  ctx.fillStyle = color;
  ctx.textAlign = "center";
  ctx.fillText(message, canvas.width / 2, canvas.height / 2);
}

Then, create an endGame() function:

function endGame(win) {
  clearInterval(gameLoopId);

  // set a delay so we are sure any paints have finished
  setTimeout(() => {
    ctx.clearRect(0, 0, canvas.width, canvas.height);
    ctx.fillStyle = "black";
    ctx.fillRect(0, 0, canvas.width, canvas.height);
    if (win) {
      displayMessage(
        "Victory!!! Pew Pew... - Press [Enter] to start a new game Captain Pew Pew",
        "green"
      );
    } else {
      displayMessage(
        "You died !!! Press [Enter] to start a new game Captain Pew Pew"
      );
    }
  }, 200)  
}

Restart logic: When all lives are lost or the player wins, display a message indicating the game can be restarted. Restart the game when the restart key is pressed (you can choose which key to use).

Create the resetGame() function:

function resetGame() {
  if (gameLoopId) {
    clearInterval(gameLoopId);
    eventEmitter.clear();
    initGame();
    gameLoopId = setInterval(() => {
      ctx.clearRect(0, 0, canvas.width, canvas.height);
      ctx.fillStyle = "black";
      ctx.fillRect(0, 0, canvas.width, canvas.height);
      drawPoints();
      drawLife();
      updateGameObjects();
      drawGameObjects(ctx);
    }, 100);
  }
}

Add a call to the eventEmitter to reset the game in initGame():

eventEmitter.on(Messages.KEY_EVENT_ENTER, () => {
  resetGame();
});

Add a clear() function to the EventEmitter:

clear() {
  this.listeners = {};
}

👽 💥 🚀 Congratulations, Captain! Your game is complete! Well done! 🚀 💥 👽

🚀 Challenge

Add sound effects! Can you enhance your gameplay by adding sounds, such as when a laser hits, the hero dies, or the player wins? Check out this sandbox to learn how to play sounds using JavaScript.

Post-Lecture Quiz

Post-lecture quiz

Review & Self Study

Your task is to create a new sample game. Explore some interesting games to get inspiration for the type of game you might want to build.

Assignment

Build a Sample Game

Disclaimer:
This document has been translated using the AI translation service Co-op Translator. While we aim for accuracy, please note that automated translations may include errors or inaccuracies. The original document in its native language should be regarded as the authoritative source. For critical information, professional human translation is advised. We are not responsible for any misunderstandings or misinterpretations resulting from the use of this translation.

8.0 KiB Raw Permalink Blame History Unescape Escape