Swift: Contact detection between 2 nodes? - swift

Question

Alright, so I've been following various other SO links and trying to figure this out- I need to have contact detection between 2 nodes. Not collision detection, which I learned results in the nodes bouncing each other around. I don't want them to knock each other around, I just want to know when they touch.
Right now I have physics bodies for the 2 nodes, savior and chicken1 as well as the ground (ground) upon which savior sits. These are all set up here:
savior.physicsBody?.dynamic = true
savior.physicsBody?.allowsRotation = false
savior.physicsBody = SKPhysicsBody(rectangleOfSize: CGSizeMake(savior.size.width, savior.size.height))
chicken1.physicsBody?.dynamic = true
chicken1.physicsBody?.allowsRotation = false
chicken1.physicsBody = SKPhysicsBody(rectangleOfSize: CGSizeMake(chicken1.size.width, chicken1.size.height))
ground.physicsBody = SKPhysicsBody(rectangleOfSize: CGSizeMake(self.frame.size.width, groundTexture.size().height*2))
ground.physicsBody?.dynamic = false
I need to set up contact detection between savior and chicken1. There seem to be various ways to do this, but this is what I put together:
//Contact detection
self.physicsWorld.contactDelegate = self
savior.physicsBody?.categoryBitMask = saviorCategory
savior.physicsBody?.contactTestBitMask = animalCategory
savior.physicsBody?.collisionBitMask = 0
chicken1.physicsBody?.categoryBitMask = animalCategory
chicken1.physicsBody?.contactTestBitMask = saviorCategory
chicken1.physicsBody?.collisionBitMask = 0
func didBeginContact(contact: SKPhysicsContact) {
var firstBody : SKPhysicsBody
var secondBody : SKPhysicsBody
if contact.bodyA.categoryBitMask < contact.bodyB.categoryBitMask
{
firstBody = contact.bodyA
secondBody = contact.bodyB
}
else {
firstBody = contact.bodyB
secondBody = contact.bodyA
}
if firstBody.categoryBitMask == 0 && secondBody.categoryBitMask == 1 {
println("they made contact")
}
}
This code results in savior falling right through ground and going right through chicken1, with no contact detection because even when savior and chicken1 touch, nothing happens.
I need savior and ground to continue to collide, but I don't want savior and chicken1 to collide, just touch.
The program needs to execute something when they touch.
It's a mess but how can I fix this?
EDIT:
Here is what I have, animalCategory has been changed to chickenCategory for clarity and no contact is detected. Also savior still falls through ground.
self.physicsWorld.contactDelegate = self
var screenTouches = Bool()
let saviorCategory: UInt32 = 0x1 << 0
let chickenCategory: UInt32 = 0x1 << 1
savior.physicsBody?.categoryBitMask = saviorCategory
savior.physicsBody?.contactTestBitMask = chickenCategory
savior.physicsBody?.collisionBitMask = chickenCategory
chicken1.physicsBody?.categoryBitMask = chickenCategory
chicken1.physicsBody?.contactTestBitMask = saviorCategory
chicken1.physicsBody?.collisionBitMask = saviorCategory
func didBeginContact(contact: SKPhysicsContact) {
var firstBody : SKPhysicsBody
var secondBody : SKPhysicsBody
if contact.bodyA.categoryBitMask == chickenCategory && contact.bodyB.categoryBitMask == saviorCategory {
println("contact made")
savior.hidden = true
}
else if contact.bodyA.categoryBitMask == saviorCategory && contact.bodyB.categoryBitMask == chickenCategory {
println("contact made")
savior.hidden = true
}
}

Answer 1

Ok so it seems like all you want is for just detection that they touched, but you don't want them to push each other. I would in the didBeginContact where ever you put your collision detection between them , make their physicsbody = nil, so that when they collide it knows that they collide and when you put this it makes them go through each other. And if you want to put code to do something else just put that code before you make the physicsbody nil. Also if you want to put back their physicsbody, just put it back.

Answer 2

For anyone who is still stuck on this, if you want to detect that two sprites are touching each other without them actually having a physical effect on each other (i.e. causing movement), then the key is to set the collisionBitMask property of the physicsBody to 0:
node.physicsBody!.collisionBitMask = 0
This means that you will receive events in didBeginContact but the interacting objects will not cause an actual physical effect on each other.

Answer 3

This is how to do it:
Set up your category bit masks:
let saviorCategory: UInt32 = 0x1 << 0
let chickenCategory: UInt32 = 0x1 << 1
let groundCategory: UInt32 = 0x1 << 2
Set up the physics bodies:
func didMove(to: View) {
savior.physicsBody?.categoryBitMask = saviorCategory
savior.physicsBody?.contactTestBitMask = chickenCategory
savior.physicsBody?.collisionBitMask = groundCategory
chicken1.physicsBody?.categoryBitMask = animalCategory
chicken1.physicsBody?.contactTestBitMask = saviorCategory
chicken1.physicsBody?.collisionBitMask = groundCategory
ground.physicsBody?.categoryBitMask = groundCategory
ground.physicsBody?.contactTestBitMask = 0 // No contact detection for ground
ground.physicsBody?.collisionBitMask = UInt32.Max // Everything collides with the ground
physicsWorld.contactDelegate = self
// Rest of didMoveToView
}
Note: It isn't actually necessary to define chicken as contacting saviour and saviour as contacting chicken; you only need to define that one contacts the other, but it can make the code more readable to say that each contacts the other.
Implement didBegin:
func didBeginContact(contact: SKPhysicsContact) {
let contactMask = contact.bodyA.categoryBitMask | contact.bodyB.categoryBitMask
switch contactMask {
case chickenCategory | saviourCategory:
print("Collision between chicken and saviour")
let saviour = contact.bodyA.categoryBitMask == saviourCategory ? contact.bodyA.node! : contact.bodyB.node!
saviour.hidden = true
default :
//Some other contact has occurred
print("Some other contact")
}
}
Don't forget to set your class as an SKPhysicsContactDelegate
Check out the examples here:
Attack button in SpriteKit