day-062

Day 62: Project 17: Space Race, Part One

Follow along at https://www.hackingwithswift.com/100/62.

📒 Field Notes

This day covers the first part of Project 17: Space Race in Hacking with Swift.

I previously created projects alongside Hacking with Swift in a separate repository, and you can find Project 17 here. Even better, though, I copied it over to Day 62's folder so I could extend it for 100 Days of Swift.

With that in mind, Day 62 focuses on several specific topics:

• Setting up our UI
• Bring on the enemies: linearDamping, angularDamping
• Making contact: didBegin()

Setting up our UI

Wonderous as the universe itself, the power of SpriteKit allows us to create a "starfield" background with a small amount of clever configuration.

Given an emitter node that emits a horizontal stream of star-like particles, we can position the node in on the center-rightmost edge of the screen, set its zPosition to be behind everything else, and advance the node's simulation time so that it instantly renders as a full screen of stars ✨.

func makeStarfieldBackground() -> SKEmitterNode {
    guard let starfield = SKEmitterNode(fileNamed: "Starfield") else {
        preconditionFailure("Failed to starfield emitter effect")
    }

    starfield.position = CGPoint(x: frame.maxX, y: sceneCenterPoint.y)
    starfield.zPosition = -1

    // cause the particles to spread out over our background
    starfield.advanceSimulationTime(10)

    return starfield
}

Bring on the Enemies: linearDamping, angularDamping

Space junk is dangerous. So the nodes that we're flying our ship through need to look the part: massive, twirling, and with no end in sight.

Two properties of SpriteKit nodes that come in handy here are linearDamping and angularDamping. By default, these will have values, because gravity serves as a dampener on both angular and linear momentum. To simulate the zero-gravity atmosphere of outer space, though, we can set them to 0 to keep them floating and spinning along smoothly.

@objc func spawnEnemy() {
    let enemyType = EnemyType.allCases.randomElement()!
    let enemy = SKSpriteNode(imageNamed: enemyType.rawValue)
    let enemyWidth = CGFloat(enemy.size.width)
    let enemyHeight = CGFloat(enemy.size.height)

    let xPos = frame.maxX + enemyWidth
    let yPos = CGFloat.random(in: enemyHeight...(frame.maxY - enemyHeight))

    enemy.position = CGPoint(x: xPos, y: yPos)

    enemy.physicsBody = SKPhysicsBody(texture: enemy.texture!, size: enemy.size)
    enemy.physicsBody?.categoryBitMask = BitMask.enemy
    enemy.physicsBody?.velocity = CGVector(dx: -500, dy: 0)
    enemy.physicsBody?.angularDamping = 0
    enemy.physicsBody?.linearDamping = 0
    enemy.physicsBody?.angularVelocity = 5

    addChild(enemy)
}

Making Contact: didBegin()

Since emitter nodes are one-and-done, we can take advantage of this to place an explosion right at the position of the ship when we detect it colliding with an "enemy" — also utilizing SKNode.removeFromParent to vaporize our ship and the enemy at the same time:

func shipDestroyed(by enemy: SKNode) {
  guard let explosion = SKEmitterNode(fileNamed: "explosion") else {
      preconditionFailure("Failed to load explosion emitter effect")
  }

  explosion.position = playerShip.position

  remove(node: enemy)
  remove(node: playerShip)
  addChild(explosion)

  currentGameplayState = .over
}

🔗 Additional/Related Links

• Seriously... space junk is dangerous!