Detecting multiple collisions in SpriteKit - ios

Question

I'm still a beginner in Swift and I'm having some trouble with collision detections in SpriteKit. I used this question from StackOverFlow which was great in showing my how to construct things neatly. But I'm having problems with my didBegin function, which does not even get called to at all. I'm hoping I missed something simple out that you guys can take a look at for me.
Thanks in advance.
Here is my PhysicsCatagoies struct:
import Foundation
import SpriteKit
struct PhysicsCatagories: OptionSet {
let rawValue: UInt32
init(rawValue: UInt32) { self.rawValue = rawValue }
static let None = PhysicsCatagories(rawValue: 0b00000) // Binary for 0
static let Player = PhysicsCatagories(rawValue: 0b00001) // Binary for 1
static let EnemyBullet = PhysicsCatagories(rawValue: 0b00010) // Binary for 2
static let PlayerBullet = PhysicsCatagories(rawValue: 0b00100) // Binary for 4
static let Enemy = PhysicsCatagories(rawValue: 0b01000) // Binary for 8
static let Boss = PhysicsCatagories(rawValue: 0b10000) // Binary for 16
}
extension SKPhysicsBody {
var category: PhysicsCatagories {
get {
return PhysicsCatagories(rawValue: self.categoryBitMask)
}
set(newValue) {
self.categoryBitMask = newValue.rawValue
}
}
}
And here is how I assigned my nodes in GameScene:
player.physicsBody = SKPhysicsBody(rectangleOf: player.size)
player.physicsBody!.affectedByGravity = false
player.physicsBody!.categoryBitMask = PhysicsCatagories.Player.rawValue
player.physicsBody!.collisionBitMask = PhysicsCatagories.None.rawValue
player.physicsBody!.category = [.Enemy, .EnemyBullet, .Boss]
bullet.physicsBody = SKPhysicsBody(rectangleOf: bullet.size)
bullet.physicsBody!.affectedByGravity = false
bullet.physicsBody!.categoryBitMask = PhysicsCatagories.PlayerBullet.rawValue
bullet.physicsBody!.collisionBitMask = PhysicsCatagories.None.rawValue
bullet.physicsBody!.category = [.Enemy, .Boss]
enemy.physicsBody = SKPhysicsBody(rectangleOf: enemy.size)
enemy.physicsBody!.affectedByGravity = false
enemy.physicsBody!.categoryBitMask = PhysicsCatagories.Enemy.rawValue
enemy.physicsBody!.collisionBitMask = PhysicsCatagories.None.rawValue
enemy.physicsBody!.category = [.Player, .PlayerBullet]
enemyBullet.physicsBody = SKPhysicsBody(rectangleOf: enemyBullet.size)
enemyBullet.physicsBody!.affectedByGravity = false
enemyBullet.physicsBody!.categoryBitMask = PhysicsCatagories.EnemyBullet.rawValue
enemyBullet.physicsBody!.collisionBitMask = PhysicsCatagories.None.rawValue
enemyBullet.physicsBody!.category = [.Player]
boss.physicsBody = SKPhysicsBody(rectangleOf: boss.size)
boss.physicsBody!.affectedByGravity = false
boss.physicsBody!.categoryBitMask = PhysicsCatagories.Boss.rawValue
boss.physicsBody!.collisionBitMask = PhysicsCatagories.None.rawValue
boss.physicsBody!.category = [.Player, .PlayerBullet]
bulletSpecial.physicsBody = SKPhysicsBody(rectangleOf: bulletSpecial.size)
bulletSpecial.physicsBody!.affectedByGravity = false
bulletSpecial.physicsBody!.categoryBitMask = PhysicsCatagories.PlayerBullet.rawValue
bulletSpecial.physicsBody!.collisionBitMask = PhysicsCatagories.None.rawValue
bulletSpecial.physicsBody!.category = [.Enemy, .Boss]
Finally, this is my didBegin function, which does not seem to work at all:
func didBegin(_ contact: SKPhysicsContact) {
let contactCategory: PhysicsCatagories = [contact.bodyA.category, contact.bodyB.category]
switch contactCategory {
case [.Player, .Enemy]:
print("player has hit enemy")
case [.PlayerBullet, .Enemy]:
print("player bullet has hit enemy")
case [.PlayerBullet, .Boss]:
print("player bullet has hit boss")
case [.Player, .Boss]:
print("player has hit boss")
case [.Player, .EnemyBullet]:
print("player has hit enemy bullet")
default:
preconditionFailure("Unexpected collision type: \(contactCategory)")
}
}

Answer 1

I've not used the OptionSet technique for cagegoryBitMasks, so here's how I'd do it:
Define unique categories, ensure your class is a SKPhysicsContactDelegate and make yourself the physics contact delegate:
//Physics categories
let PlayerCategory: UInt32 = 1 << 0 // b'00001'
let EnemyBulletCategory: UInt32 = 1 << 1 // b'00010'
let PlayerBulletCategory: UInt32 = 1 << 2 // b'00100'
let EnemyCategory: UInt32 = 1 << 3 // b'01000'
let BossCategory: UInt32 = 1 << 4 // b'10000'
class GameScene: SKScene, SKPhysicsContactDelegate {
physicsWorld.contactDelegate = self
Assign the categories (usually in didMove(to view:) :
player.physicsBody.catgeoryBitMask = PlayerCategory
bullet.physicsBody.catgeoryBitMask = BulletCategory
enemy.physicsBody.catgeoryBitMask = EnemyCategory
enemyBullet.physicsBody.catgeoryBitMask = EnemyBulletCategory
boss.physicsBody.catgeoryBitMask = BossCategory
(not sure about bulletSpecial - looks the same as bullet)
Set up contact detection:
player.physicsBody?.contactTestBitMask = EnemyCategory | EnemyBulletCategory | BossCategory
bullet.physicsBody?.contactTestBitMask = EnemyCategory | BossCategory
enemy.physicsBody?.contactTestBitMask = PlayerCategory | PlayerBulletCategory
enemyBullet.physicsBody?.contactTestBitMask = PlayerCategory
boss.physicsBody?.contactTestBitMask = PlayerCategory | PlayerBulletCategory
Turn off collisions: (on by default)
player.physicsBody?.collisionBitMask = 0
bullet.physicsBody?.collisionBitMask = 0
enemy.physicsBody?.collisionBitMask = 0
enemyBullet.physicsBody?.collisionBitMask = 0
boss.physicsBody?.collisionBitMask = 0
Implement didBegin:
func didBegin(_ contact: SKPhysicsContact) {
print("didBeginContact entered for \(String(describing: contact.bodyA.node!.name)) and \(String(describing: contact.bodyB.node!.name))")
let contactMask = contact.bodyA.categoryBitMask | contact.bodyB.categoryBitMask
switch contactMask {
case PlayerCategory | EnemyCategory:
print("player has hit enemy")
case PlayerBulletCategory | EnemyCategory:
print("player bullet has hit enemy")
case PlayerBulletCategory | BossCategory:
print("player bullet has hit boss")
case PlayerCategory | BossCategory:
print("player has hit boss")
case PlayerCategory | EnemyBulletCategory:
print("player has hit enemy bullet")
default:
print("Undetected collision occurred")
}
}
It's a bit late here, so hopefully I haven't made any stupid mistakes.
=======================
You could also include this function and then call it via checkPhysics() once you have set up all your physics bodies and collisions and contact bit masks. It will go through every node and print out what collides with what and what contacts what (it doesn't check the isDynamic property, so watch out for that):
//MARK: - Analyse the collision/contact set up.
func checkPhysics() {
// Create an array of all the nodes with physicsBodies
var physicsNodes = [SKNode]()
//Get all physics bodies
enumerateChildNodes(withName: "//.") { node, _ in
if let _ = node.physicsBody {
physicsNodes.append(node)
} else {
print("\(String(describing: node.name)) does not have a physics body so cannot collide or be involved in contacts.")
}
}
//For each node, check it's category against every other node's collion and contctTest bit mask
for node in physicsNodes {
let category = node.physicsBody!.categoryBitMask
// Identify the node by its category if the name is blank
let name = node.name != nil ? node.name : "Category \(category)"
if category == UInt32.max {print("Category for \(String(describing: name)) does not appear to be set correctly as \(category)")}
let collisionMask = node.physicsBody!.collisionBitMask
let contactMask = node.physicsBody!.contactTestBitMask
// If all bits of the collisonmask set, just say it collides with everything.
if collisionMask == UInt32.max {
print("\(name) collides with everything")
}
for otherNode in physicsNodes {
if (node != otherNode) && (node.physicsBody?.isDynamic == true) {
let otherCategory = otherNode.physicsBody!.categoryBitMask
// Identify the node by its category if the name is blank
let otherName = otherNode.name != nil ? otherNode.name : "Category \(otherCategory)"
// If the collisonmask and category match, they will collide
if ((collisionMask & otherCategory) != 0) && (collisionMask != UInt32.max) {
print("\(name) collides with \(String(describing: otherName))")
}
// If the contactMAsk and category match, they will contact
if (contactMask & otherCategory) != 0 {print("\(name) notifies when contacting \(String(describing: otherName))")}
}
}
}
}
It will produce output like:
Optional("shape_blueSquare") collides with Optional("Screen_edge")
Optional("shape_redCircle") collides with Optional("Screen_edge")
Optional("shape_redCircle") collides with Optional("shape_blueSquare")
Optional("shape_redCircle") notifies when contacting Optional("shape_purpleSquare")
Optional("shape_redCircle") collides with Optional("shape_greenRect")
Optional("shape_redCircle") notifies when contacting Optional("shape_greenRect")
Optional("shape_purpleSquare") collides with Optional("Screen_edge")
Optional("shape_purpleSquare") collides with Optional("shape_greenRect")
Category for Optional("shape_greenRect") does not appear to be set correctly as 4294967295
Optional("shape_greenRect") collides with Optional("Screen_edge")
Optional("shape_yellowTriangle") notifies when contacting Optional("shape_redCircle")
Optional("shape_yellowTriangle") collides with Optional("shape_greenRect")
Optional("shape_yellowTriangle") notifies when contacting Optional("shape_greenRect")
etc.