Swift / SpriteKit Collision producing varying results - swift

Question

I have a small test project (my first using Swift / XCode) which is designed to move me away from HTML5 and Canvas for game production.
The code compiles and runs fine. I use my iPhone as the test device rather than the built in simulator.
The symptoms of the problem are
that the lasers being repeatedly fired from the player's ship appear to occasionally bend around the aliens
the names being pulled out from the nodes are being shown as their default names not the names I assigned to them at creation
In some cases the collision works fine and the alien explosion is generated and the alien sprite node is removed from the scene.
I have named the alien nodes "alien" and the laser nodes "laser".
Both have their contactTestBitMask set to the same value.
Here is my GameScene.swift code:
import SpriteKit
class GameScene: SKScene, SKPhysicsContactDelegate {
var lastUpdateTime: TimeInterval = 0
var delta: TimeInterval = 0
var sp_player: SKSpriteNode!
var stars: SKSpriteNode!
var deeperstars: SKSpriteNode!
var laser: SKSpriteNode!
var alien: SKSpriteNode!
var explosionSplat1: SKSpriteNode!
var playerScore: UInt32!
struct PhysicsCategory {
static let base:UInt32 = 0x1 << 0
static let alien:UInt32 = 0x1 << 1
static let laser:UInt32 = 0x1 << 2
static let player:UInt32 = 0x1 << 3
}
override func didMove(to view: SKView) { // called when the scene is presented into view (happens only once)
playerScore = 0
physicsWorld.contactDelegate = self
physicsWorld.gravity = .zero
// BACKGROUND
backgroundColor = UIColor(red: 0/255, green: 0/255, blue: 48/255, alpha: 1.0)
print("Background color is set")
// WRAP THE STARFIELDS
// Front most layer of stars
let starsTexture = SKTexture(imageNamed: "stars.png")
let bgAnimation = SKAction.move(by: CGVector(dx: 0, dy: -starsTexture.size().height), duration: 5)
let bgReset = SKAction.move(by: CGVector(dx: 0, dy: starsTexture.size().height), duration: 0)
let bgConstantMotion = SKAction.repeatForever(SKAction.sequence([bgAnimation,bgReset]))
// Back layer of slower stars
let deeperStarsTexture = SKTexture(imageNamed: "stars-deeper.png")
let deeperStarsbgAnimation = SKAction.move(by: CGVector(dx: 0, dy: -deeperStarsTexture.size().height), duration: 8)
let deeperStarsbgReset = SKAction.move(by: CGVector(dx: 0, dy: deeperStarsTexture.size().height), duration: 0)
let deeperStarsbgConstantMotion = SKAction.repeatForever(SKAction.sequence([deeperStarsbgAnimation,deeperStarsbgReset]))
var i: CGFloat = 0
while i < 3
{
stars = SKSpriteNode(texture: starsTexture)
stars.position = CGPoint(x: frame.midX, y: starsTexture.size().height * i)
stars.size.height = frame.height
stars.run(bgConstantMotion)
stars.zPosition = -1
addChild(stars)
deeperstars = SKSpriteNode(texture: deeperStarsTexture)
deeperstars.position = CGPoint(x: frame.midX, y: deeperStarsTexture.size().height * i)
deeperstars.size.height = frame.height
deeperstars.run(deeperStarsbgConstantMotion)
deeperstars.zPosition = -1
addChild(deeperstars)
i += 1
}
// PLAYER
let playerTexture1 = SKTexture(imageNamed: "player-1.png")
let playerTexture2 = SKTexture(imageNamed: "player-2.png")
let playerAnimation = SKAction.animate(with: [playerTexture1, playerTexture2], timePerFrame: 0.2)
let constantAnimation = SKAction.repeatForever(playerAnimation)
sp_player = SKSpriteNode(texture: playerTexture1)
sp_player.position = CGPoint(x: frame.midX, y: (sp_player.size.height * 2))
sp_player.physicsBody = SKPhysicsBody(rectangleOf: sp_player.size)
sp_player.physicsBody!.isDynamic = false
sp_player.name = "player"
sp_player.run(constantAnimation)
addChild(sp_player)
// PLACE ALIENS
let alienTexture1 = SKTexture(imageNamed: "alien-1a.png")
let alienTexture2 = SKTexture(imageNamed: "alien-1b.png")
let alienAnimation = SKAction.animate(with: [alienTexture1, alienTexture2], timePerFrame: 0.4)
let constantAlienAnimation = SKAction.repeatForever(alienAnimation)
var x: CGFloat = 0, y: CGFloat = 0
while y < 6
{
while x < 6
{
alien = SKSpriteNode(texture: alienTexture1)
alien.position = CGPoint(x: 32 + (x * alien.size.width), y: (frame.size.height - (alien.size.height * 1.5) - (alien.size.height * y)))
print("Setting y to \(frame.size.height - (alien.size.height * y))")
alien.physicsBody = SKPhysicsBody(rectangleOf: CGSize(width: alien.size.width, height: alien.size.height))
alien.physicsBody!.isDynamic = false
alien.name = "alien"
alien.physicsBody!.contactTestBitMask = PhysicsCategory.laser
alien.run(constantAlienAnimation)
addChild(alien)
x += 1
}
y += 1
x = 0
}
print("Sprites added to scene")
spawnLasers()
}
func spawnLasers()
{
let delay1 = SKAction.wait(forDuration: 0.5)
let spawn = SKAction.run {
let laserTexture = SKTexture(imageNamed: "laser-1.png")
self.laser = SKSpriteNode(texture: laserTexture)
self.laser.position = CGPoint(x: self.sp_player.position.x, y: self.sp_player.position.y + self.sp_player.size.height)
self.laser.physicsBody = SKPhysicsBody(rectangleOf: CGSize(width: self.laser.size.width, height: self.laser.size.height))
self.laser.physicsBody!.isDynamic = true
self.laser.physicsBody!.linearDamping = 0
self.laser.physicsBody!.allowsRotation = false
self.laser.physicsBody!.contactTestBitMask = PhysicsCategory.laser
self.laser.name = "laser"
self.addChild(self.laser)
let shoot = SKAction.moveTo(y: self.frame.size.height, duration: 1)
let killLaser = SKAction.removeFromParent()
let handleLaser = SKAction.sequence([shoot,killLaser])
self.laser.run(handleLaser)
}
let action = SKAction.sequence([delay1,spawn])
let constantLasers = SKAction.repeatForever(action)
self.run(constantLasers)
}
func didBegin(_ contact: SKPhysicsContact) {
var check: UInt32 = 0
if contact.bodyA.node != nil
{
check += 1
}
if contact.bodyB.node != nil
{
check += 1
}
if check == 2
{
if contact.bodyA.node!.name == "alien" && contact.bodyB.node!.name == "laser"
{
// EXPLOSION
let explosionSplatTexture1 = SKTexture(imageNamed: "explosion-1a.png")
let explosionSplatTexture2 = SKTexture(imageNamed: "explosion-1b.png")
let explosionSplatTexture3 = SKTexture(imageNamed: "explosion-1c.png")
let explosionSplatTexture4 = SKTexture(imageNamed: "explosion-1d.png")
let explosionSplatAnimation = SKAction.animate(with: [explosionSplatTexture1, explosionSplatTexture2, explosionSplatTexture3, explosionSplatTexture4], timePerFrame: 0.1)
let killExplosion = SKAction.removeFromParent()
let explosionSequence = SKAction.sequence([explosionSplatAnimation,killExplosion])
explosionSplat1 = SKSpriteNode(texture: explosionSplatTexture1)
explosionSplat1.name = "explosion"
explosionSplat1.position = CGPoint(x: contact.bodyA.node!.position.x, y: contact.bodyA.node!.position.y)
addChild(explosionSplat1)
explosionSplat1.run(explosionSequence)
self.playerScore += 1
print("Score: \(self.playerScore!)")
contact.bodyA.node?.removeFromParent()
print("Alien named \(contact.bodyA.node?.name ?? "defaultAlienName") from scene")
contact.bodyB.node?.removeFromParent()
print("Laser named \(contact.bodyB.node?.name ?? "defaultLaserName") from scene")
}
}
}
func didEnd(_ contact: SKPhysicsContact) {
//print("Contact ended between \(contact.bodyA) and \(contact.bodyB)")
}
override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?)
{
// if let touch = touches.first {
// let position = touch.location(in: view)
// storedTouch = position
// }
}
override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent?)
{
if let touch = touches.first {
let position = touch.location(in: view)
var playerpos: CGPoint!
playerpos = sp_player.position
let pl_move = SKAction.move(to: CGPoint(x: position.x, y: playerpos.y), duration: 0.1)
sp_player.run(pl_move)
}
}
override func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent?)
{
/*
Need to figure out how to use storedTouch properly
to move player relative to the screen touch co-ordinates
*/
// if let touch = touches.first {
// let position = touch.location(in: view)
// }
}
override func update(_ currentTime: TimeInterval) {
// Called before each frame is rendered
if (lastUpdateTime > 0)
{
delta = currentTime - lastUpdateTime
} else {
delta = 0
}
lastUpdateTime = currentTime
}
}
When the game runs it produces this screen:
You can see the unexpected laser behavior here:
In my diags I get the following output from the collision function:
Score: 1
Alien named defaultAlienName removed from scene
Laser named laser removed from scene
Score: 2
Alien named defaultAlienName removed from scene
Laser named laser removed from scene
Score: 3
Alien named defaultAlienName removed from scene
Laser named laser removed from scene
Score: 4
Alien named defaultAlienName removed from scene
Laser named defaultLaserName removed from scene
Score: 5
Alien named defaultAlienName removed from scene
Laser named defaultLaserName removed from scene
Score: 6
Alien named defaultAlienName removed from scene
Laser named defaultLaserName removed from scene
This is most likely my complete lack of understanding for optionals and how collision actually works. I'd be super grateful for any insights.

Answer 1

In your alien loop, as well as spawnLasers(), you are not giving the sprite nodes an actual PhysicsBody category. For sprites to be able to detect contact between one another, they need a category name and a contact name.
So in your while loop (building the aliens), you need to have this:
alien.physicsBody!.categoryBitMask = PhysicsCategory.alien
alien.physicsBody!.contactTestBitMask = PhysicsCategory.laser
And in spawnLasers(), you want this added:
self.laser.physicsBody!.categoryBitMask = PhysicsCategory.laser
and change the contactTestBitMask to alien, not laser:
self.laser.physicsBody!.contactTestBitMask = PhysicsCategory.alien
Hopefully you can see that the alien category wants to know when lasers touch, and the laser category wants to know when the aliens touch.
To visually help you, turn on the show physics option, this way you can see the actual physics bodies you are dealing with.
To do this, in your GameViewController (or similar), find:
showsFPS = true
showsNodeCount = true
You want to add the following:
showsPhysics = true
This will help with seeing the actual physics bodies on screen.
In:
func didBegin(_ contact: SKPhysicsContact)
you are only testing for BodyA being alien and BodyB being laser.
This is the contact test:
if contact.bodyA.node!.name == "alien" && contact.bodyB.node!.name == "laser"
I believe BodyA could be laser and BodyB be alien. Basically the physics engine contact events could be "A hitting B", or "B hitting A".
Therefore, a quick and dirty solution is to create another if statement below the current one, but changing the body names, so:
if contact.bodyA.node!.name == "laser" && contact.bodyB.node!.name == "alien" {
and duplicate the code from your existing if statement, and changing the two print statements.
This isn't the ideal way to do it, but hopefully when you tidy it up you'll get an understanding of what the physics contact is doing.
I am hoping once you have implmented the above, you will be in a much better shape.