Swift/SpriteKit Collision Detection Between Many Objects - swift

Question

So I have two objects that should lose health points at an collision.
func addPlayer(xPos: CGFloat, yPos: CGFloat){
playerNode = SKSpriteNode(imageNamed: "player")
playerNode.physicsBody = SKPhysicsBody(circleOfRadius: width/2)
playerNode.physicsBody!.affectedByGravity = false
playerNode.physicsBody!.categoryBitMask = PhysicsCategory.Player
playerNode.physicsBody!.contactTestBitMask = PhysicsCategory.Wall | PhysicsCategory.Zombie
playerNode.physicsBody!.collisionBitMask = PhysicsCategory.Wall | PhysicsCategory.Zombie
playerNode.name = "Player"
player = Player(node: playerNode, healthPoints: 100, attack: 10)
playerNode.position.x = xPos
playerNode.position.y = yPos
playerNode.size = CGSize(width: width, height: width)
addChild(playerNode)
}
func addZombie(xPos: CGFloat, yPos: CGFloat){
zombieNode = SKSpriteNode(imageNamed: "zombie")
zombieNode.physicsBody = SKPhysicsBody(circleOfRadius: width/2)
zombieNode.physicsBody!.affectedByGravity = false
zombieNode.physicsBody!.categoryBitMask = PhysicsCategory.Zombie
zombieNode.physicsBody!.contactTestBitMask = PhysicsCategory.Zombie | PhysicsCategory.Player | PhysicsCategory.Wall
zombieNode.physicsBody!.collisionBitMask = PhysicsCategory.Zombie | PhysicsCategory.Player | PhysicsCategory.Wall
zombieNode.name = "Zombie"
zombie = Zombie(node: zombieNode, healthPoints: 50, attack: 5)
Zombies.append(zombie!)
zombieNode.position.x = xPos
zombieNode.position.y = yPos
zombieNode.size = CGSize(width: width, height: width)
addChild(zombieNode)
}
When a collision appears this function get activated:
func didBeginContact(contact: SKPhysicsContact) {
let firstBody = contact.bodyA.node as! SKSpriteNode
let secondBody = contact.bodyB.node as! SKSpriteNode
if(firstBody.name == "Player" && secondBody.name == "Zombie"){
changeHealthPointsForZombieWithNode(secondBody, points: player!.attack)
} else if(firstBody.name == "Zombie" && secondBody.name == "Player"){
changeHealthPointsForPlayer(secondBody, points: zombie!.attack)
print(player!.healthPoints)
}
}
func changeHealthPointsForZombieWithNode(node: SKSpriteNode, points: Int) {
for zombie in Zombies {
if zombie.node == node {
zombie.healthPoints -= points
print(zombie.healthPoints)
if(zombie.healthPoints <= 0){
zombieNode.removeFromParent()
}
return
}
}
}
func changeHealthPointsForPlayer(node: SKSpriteNode, points: Int) {
player!.healthPoints -= points
if(player!.healthPoints <= 0){
playerNode.removeFromParent()
gameOver = true
}
}
I want to subtract the health points of the zombie depending on the attack of the player and other way around. When the player hits the zombie the zombie should lose life points. When the zombie hits the player the player should lose life points. Every player/zombie got health points and an attack value. The Problem is that some zombies are killable and lose health and other (normally 1-3) are not able to lose health. These zombies who aren't able to lose health are the only one able to kill the player. Zombies that lose health can't deal damage(why?)? So there only able to do one thing(attack or lose health) although they should be able to do two things(attack and lose health).

Answer 1

Keep in mind that the two physics bodies described in the contact parameter are not passed in a guaranteed order. Inside the delegate function there is not such a thing as "A is the one colliding with B, not the other way around". There is only "A and B are colliding". That said, you have two options at least, depending on your game mechanics:
Make player AND zombie deal damage to each other every time they collide.
Make for player and zombie a subclass of SKSpriteNode with a property isAttacking, a boolean to determine when the entity should deal damage when detecting a contact with it. For the player this boolean might get "activated" every button/tap press. For the zombie, every once in a while, if close enough to the player.
Additionally, the way you implemented you will be getting doubled contact notifications. SpriteKit will detect that the player is in contact with the zombie, by the player contact mask and zombie category mask, and that the zombie is in contact with the player, by the zombie contact mask and the player category mask. You usually don't want this to happen. You should make only one of them detect it. I would suggest the player. This way there is no need to set the zombie contact mask. As long as you set zombie in the player's contact mask and the zombie's category mask, you will already have the detection (and once).