Why is spritekit/swift collision detection failing to fire in the "Head" to "Body" case?

Question

I have 3 collision types right now. "Head", "Body", and "Food".

The head collides with the food fine. The "Head" and "Body" are a SKNode and instances of the "SnakeBodyUnit" class. The "Head", however, does not fire when trying to collide with a "Body" object. Again, the "Head" collides fine with the "Food" SKSpriteNode. The "Food" class is separate.

Here are the 2 classes: SnakeBodyUnit:

class SnakeBodyUnit : SKNode {

var bodyDir: Direction?
var id = -1
var partX = -1
var partY = -1
var bodyT = -1

var unitHolder: SKSpriteNode?

init(size: CGSize, gap: CGFloat, bodyType: Int) {
    super.init()

    bodyT = bodyType

    let xPos = (size.width - (size.width * gap)) / 2
    let yPos = (size.height - (size.height * gap)) / 2
    let reducedSize = size.width*gap

    unitHolder = SKSpriteNode()
    unitHolder!.position = CGPoint(x:xPos, y:yPos);
    unitHolder!.size = CGSize(width: (size.width * gap), height: (size.height * gap))

    if (bodyT == 0) {
        //head
        unitHolder!.color = UIColor(
            red: 184/255,
            green: 252/255,
            blue: 101/255,
            alpha: 1.0)


        self.physicsBody = SKPhysicsBody(rectangleOfSize: CGSizeMake(reducedSize/2, reducedSize/2), center: CGPointMake(reducedSize/2, reducedSize/2))
        self.physicsBody?.affectedByGravity = false
        self.physicsBody?.categoryBitMask = ColliderType.Head
        self.physicsBody?.dynamic = false
        self.physicsBody?.contactTestBitMask = ColliderType.Food | ColliderType.Body

    } else if (bodyT == 1) {
        //body part
        unitHolder!.color = UIColor(
            red: 52/255,
            green: 229/255,
            blue: 253/255,
            alpha: 1.0)

        self.physicsBody = SKPhysicsBody(rectangleOfSize: CGSizeMake(reducedSize/2, reducedSize/2), center: CGPointMake(reducedSize/2, reducedSize/2))
        self.physicsBody?.affectedByGravity = false
        self.physicsBody?.categoryBitMask = ColliderType.Body
        self.physicsBody?.dynamic = false


    } else if (bodyT == 2) {
        //static corner
        unitHolder!.color = UIColor(
            red: 52/255,
            green: 229/255,
            blue: 0/255,
            alpha: 1.0)
    }

    unitHolder!.anchorPoint = CGPoint(x: 0, y: 0)

    self.addChild(unitHolder!)


}

required init?(coder aDecoder: NSCoder) {
    fatalError("init coder not implemented")
}

}

Here is the food class where the collision works fine:

class Food : SKSpriteNode {

func createFood(bodyamount: CGFloat, gap: CGFloat) {

    self.size = CGSizeMake(bodyamount * gap, bodyamount * gap)

    self.color = UIColor(
    red: 184/255,
    green: 252/255,
    blue: 101/255,
    alpha: 1.0)

    let reducedSize = bodyamount * gap
    self.position = CGPoint(x: bodyamount, y: reducedSize/2)
    self.zRotation = 45.0 * CGFloat(M_PI) / 180


    self.physicsBody = SKPhysicsBody(rectangleOfSize: self.size, center: CGPointMake(reducedSize/2, reducedSize/2))
    self.physicsBody?.affectedByGravity = false
    self.physicsBody?.categoryBitMask = ColliderType.Food


    self.anchorPoint = CGPoint(x: 0, y: 0)
}

} //these are in a struct called ColliderType

static let Head:          UInt32 = 0
static let Food:          UInt32 = 0b1
static let Body:          UInt32 = 0b10

Are you checking the right categories? Collision and contact are 2 different things in sprite kit — Knight0fDragon
i don't need them to physically collide. i just want to update the main scene in the didBeginContact function. the categoryBitMask ids are right. i get didBeginContact to fire in the "Head" to "Food" case which is what is confusing currently. "Head" to "Body" should work too. — josh k
Please reffer to this SO question and make sure your bitmasks are set correctly, there is an example as well ! stackoverflow.com/questions/19473598/… — ColdSteel

RoberRM RoberRM · Accepted Answer · 2015-10-07T01:13:30

You must tell to every node with what other nodes it collides. So, you must tell the head with which nodes it collides (as you already do):

self.physicsBody?.contactTestBitMask = ColliderType.Food | ColliderType.Body

But you also have to add a similar line to the body (updating the selected Collider):

self.physicsBody?.contactTestBitMask = ColliderType.Food | ColliderType.Head

and to the food:

self.physicsBody?.contactTestBitMask = ColliderType.Head | ColliderType.Body

This should fix your problem.

Why is spritekit/swift collision detection failing to fire in the "Head" to "Body" case?

2 Answers