Asteroids

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Game

Asteroids clone from p5.play examples. See Repl.it and repository.

Livestream

I recreated the asteroids game from p5.play examples in my 2021-02-06 livestream:

Code

Load the images with loadImage() in preload():

var shipImage;
var bulletImage;
var particleImage;
var asteroidImages = [];

function preload() {
  shipImage = loadImage('assets/asteroids_ship0001.png');
  bulletImage = loadImage('assets/asteroids_bullet.png');
  particleImage = loadImage('assets/asteroids_particle.png');

  for (var i = 0; i < 3; i++) {
    var asteroidImage = loadImage('assets/asteroid' + i + '.png');
    asteroidImages.push(asteroidImage);
  }
}

Use createCanvas() to create a canvas of 800px width by 600px height in setup():

function setup() {
  createCanvas(800, 600);
}

Create a ship sprite using createSprite():

function setup() {
  // ...
  ship = createSprite(width / 2, height / 2);
  ship.maxSpeed = 6;
  ship.friction = 0.01;
  ship.addImage('normal', shipImage);
  ship.addAnimation(
    'thrust',
    'assets/asteroids_ship0002.png',
    'assets/asteroids_ship0007.png'
  );
}

Replace the label identifiers for addImage() and addAnimation() with constants:

+var SHIP_NORMAL = 'normal';
+var SHIP_THRUST = 'thrust';

 function setup() {
   // ...
-  ship.addImage('normal', shipImage);
+  ship.addImage(SHIP_NORMAL, shipImage);
   ship.addAnimation(
-    'thrust',
+    SHIP_THRUST,
     'assets/asteroids_ship0002.png',
     'assets/asteroids_ship0007.png'
   );
 }

In draw(), set the background() to black and draw the ship with drawSprites():

function draw() {
  background(0);
  drawSprites();
}

Rotate the ship on keyDown() for the LEFT_ARROW and RIGHT_ARROW keys:

function draw() {
  // ...
  if (keyDown(LEFT_ARROW)) {
    ship.rotation -= 4;
  }
  if (keyDown(RIGHT_ARROW)) {
    ship.rotation += 4;
  }
  // ...
}

Move the ship forward and change the animation on keyDown() for the UP_ARROW key:

function draw() {
  // ...
  if (keyDown(UP_ARROW)) {
    ship.addSpeed(0.2, ship.rotation);
    ship.changeAnimation(SHIP_THRUST);
  } else {
    ship.changeAnimation(SHIP_NORMAL);
  }
  // ...
}

Fire a bullet when keyWentDown() for the x key is triggered:

function draw() {
  // ...
  if (keyWentDown('x')) {
    var bullet = createSprite(ship.position.x, ship.position.y);
    bullet.addImage(bulletImage);
    bullet.setSpeed(10 + ship.getSpeed(), ship.rotation);
    bullet.life = 30;
  }
  // ...
}

Prevent bullet firing when the player is dead:

 function draw() {
   // ...
-  if (keyWentDown('x')) {
+  if (!ship.removed && keyWentDown('x')) {
     // ...
   }
   // ...
 }

The difference between keyDown() and keyWentDown() is that the former can be held (ship moves continuously) while the latter can only be triggered once (bullet is fired during release and press).

The life property ensures that the bullet gets removed after a certain amount of time.

Create groups for bullets and asteroids:

var asteroids;
var bullets;

function setup() {
  // ...
  asteroids = new Group();
  bullets = new Group();
}

Add the bullet to the bullets group:

function draw() {
  // ...
  if (keyWentDown('x')) {
    // ...
    bullets.add(bullet);
  }
  // ...
}

Add a helper function that creates an asteroid:

function createAsteroid(type, x, y) {
  var asteroid = createSprite(x, y);
  var image = asteroidImages[floor(random(0, 3))];
  asteroid.addImage(image);
  asteroid.setSpeed(2.5 - type / 2, random(360));
  asteroid.rotationSpeed = 0.5;
  asteroid.type = type;

  if (type === 2) {
    asteroid.scale = 0.6;
  }
  if (type === 1) {
    asteroid.scale = 0.3;
  }

  asteroid.mass = 2 + asteroid.scale;
  asteroid.setCollider('circle', 0, 0, 50);
  asteroids.add(asteroid);
  return asteroid;
}

The image is randomized and the properties are set. The custom property type keeps track of the large (3), medium (2), and small (1) asteroid sizes. setCollider() sets the bounding box or circle for collision detection.

Create 8 asteroids in random positions outside of the canvas view:

function setup() {
  // ...
  for (var i = 0; i < 8; i++) {
    var angle = random(360);
    var x = width / 2 + 1000 * cos(radians(angle));
    var y = height / 2 + 1000 * sin(radians(angle));
    createAsteroid(3, x, y);
  }
}

To make the asteroids show up, reset the sprites positions when they’re out of bounds:

var MARGIN = 40;

function draw() {
  // ...
  for (var i = 0; i < allSprites.length; i++) {
    var sprite = allSprites[i];
    if (sprite.position.x < -MARGIN) {
      sprite.position.x = width + MARGIN;
    }
    if (sprite.position.x > width + MARGIN) {
      sprite.position.x = -MARGIN;
    }
    if (sprite.position.y < -MARGIN) {
      sprite.position.y = height + MARGIN;
    }
    if (sprite.position.y > height + MARGIN) {
      sprite.position.y = -MARGIN;
    }
  }
  // ...
}

This ensures that all sprites remains in the canvas view (e.g., if a ship goes out of bounds while moving up, the position gets reset to the bottom).

Handle overlap() between asteroids and ship/bullets:

function draw() {
  // ...
  asteroids.overlap(ship, asteroidHit);
  asteroids.overlap(bullets, asteroidHit);
  // ...
}

function asteroidHit(asteroid, sprite) {
  if (sprite.removed) {
    return;
  }

  var newType = asteroid.type - 1;

  if (newType > 0) {
    createAsteroid(newType, asteroid.position.x, asteroid.position.y);
    createAsteroid(newType, asteroid.position.x, asteroid.position.y);
  }

  sprite.remove();
  asteroid.remove();
}

Create particles when an asteroid gets hit by a ship or bullet:

function asteroidHit(asteroid, sprite) {
  // ...
  for (var i = 0; i < 10; i++) {
    var particle = createSprite(sprite.position.x, sprite.position.y);
    particle.addImage(particleImage);
    particle.setSpeed(random(3, 5), random(360));
    particle.friction = 0.01;
    particle.life = 15;
  }
  // ...
}

Display the text instructions for player controls:

function draw() {
  // ...
  drawSprites();

  fill(255);
  textAlign(CENTER);
  text('Controls: Arrow Keys + X', width / 2, 20);
}

Render the text instructions last so the layer is in front of the background and sprites.

To debug collisions between sprites, enable the sprite property debug:

ship.debug = true;

This goes over how to make the asteroids game from p5.play. You can make further improvements like adding a title and game over screen and improving the physics and mechanics.

Check out the Repl.it from the livestream for the full code.