How to setup collisions correctly in SceneKit? - ios

Question

I'm facing a problem with collision detection.
Current setup
1) I extended ViewController class with SCNPhysicsContactDelegate:
class ViewController: UIViewController, SCNPhysicsContactDelegate
2) I setup an OptionSet to manage collision categories:
// Collisions
struct CollisionCategory: OptionSet {
let rawValue: Int
static let CoinsCategory = CollisionCategory(rawValue: 0) // Coin SCNNode
static let CarCategory = CollisionCategory(rawValue : 1) // Car SCNNode
static let FinishLineCategory = CollisionCategory(rawValue: 2) // FinishLine SCNNode
}
3) I setup categoryBitMask, contactTestBitMask and collisionBitMask of all of them:
// Setup car
carNode.physicsBody?.categoryBitMask = CollisionCategory.CarCategory.rawValue
carNode.physicsBody?.contactTestBitMask = CollisionCategory.CoinsCategory.rawValue | CollisionCategory.FinishLineCategory.rawValue
carNode.physicsBody?.collisionBitMask = CollisionCategory.CoinsCategory.rawValue | CollisionCategory.FinishLineCategory.rawValue
// Setup finishLine
planeNode.physicsBody?.categoryBitMask = CollisionCategory.FinishLineCategory.rawValue
planeNode.physicsBody?.contactTestBitMask = CollisionCategory.CarCategory.rawValue
planeNode.physicsBody?.collisionBitMask = CollisionCategory.CarCategory.rawValue
// Setup coin
coin.physicsBody?.categoryBitMask = CollisionCategory.CoinsCategory.rawValue
coin.physicsBody?.contactTestBitMask = CollisionCategory.CarCategory.rawValue
coin.physicsBody?.collisionBitMask = CollisionCategory.CarCategory.rawValue
4) I setup physicsWorld(_ world: SCNPhysicsWorld, didBegin contact: SCNPhysicsContact) to manage collision when they happen:
func physicsWorld(_ world: SCNPhysicsWorld, didBegin contact: SCNPhysicsContact) {
if(contact.penetrationDistance >= 0.08 && contact.nodeB.name!.contains("Coin")) {
// Remove coin from parent
contact.nodeB.removeFromParentNode()
// Increment counter
self.coinsCounter += 1
DispatchQueue.main.async {
// Increase coin counter
let view = self.arSceneView.viewWithTag(10) as! UILabel
view.text = String(self.coinsCounter)
}
}
// PROBLEMS HERE
if(contact.penetrationDistance >= 0.076 && contact.nodeB.name!.contains("FinishLine") && !self.startFinishLineCollision && !self.outOfTrack) {
self.startFinishLineCollision = true
// Increment lap
if(seconds > 10) {
self.laps += 1
DispatchQueue.main.async {
(self.arSceneView.viewWithTag(14) as! UILabel).text = String(self.laps)
}
if(self.laps == 4){
endGame()
}
}
}
}
Problem
I need to check when car touches finish line to mark a lap and increment the lap counter by 1. The problem is that I'm getting continuously contact messages from this function between nodeA and nodeB, even if there is no collision between car and finish line.
For example, in the following image there is a collision message, but there isn't an effective collision between car and finish line.
What is wrong with the current setup?
What I need
I need to check if there is a collision between car and finishline with precision.
Thank you
Update
I tried the following setup too, with no solution...
let CoinsCategory = 2
let CarCategory = 4
let FinishLineCategory = 6
carNode.physicsBody?.categoryBitMask = CarCategory
carNode.physicsBody?.collisionBitMask = CoinsCategory | FinishLineCategory
planeNode.physicsBody?.categoryBitMask = FinishLineCategory
planeNode.physicsBody?.collisionBitMask = CarCategory
coin.physicsBody?.categoryBitMask = CoinsCategory
coin.physicsBody?.collisionBitMask = CarCategory
func physicsWorld(_ world: SCNPhysicsWorld, didBegin contact: SCNPhysicsContact) {
switch contact.nodeB.physicsBody!.collisionBitMask {
case FinishLineCategory:
print("Finish Line Collision")
case CoinsCategory:
print("Coin Collision")
default:
print("Other collision")
}
}
No prints are called... It's like there is no collision between objects.
NOTE: finishline, car and coins are all children on the the same parent (the plane below them). Is it relevant?

Answer 1

Ok, I found a workaround to workaround my issue:
1) I used a coin (yellow cube) as collider.
2) I setup it with Color.clear (transparent color) in such a way as to make it invisible.
3) I placed it the center of the finish line.
4) Since contactTest is not working, I used penetrationDistance:
func physicsWorld(_ world: SCNPhysicsWorld, didBegin contact: SCNPhysicsContact) {
if(contact.penetrationDistance >= 0.08 && contact.nodeB.name! == "Coin") {
// Remove coin from parent
contact.nodeB.removeFromParentNode()
// Increment counter
self.coinsCounter += 1
DispatchQueue.main.async {
// Increase coin counter
let view = self.arSceneView.viewWithTag(10) as! UILabel
view.text = String(self.coinsCounter)
}
}
// >>>>> NEW CODE HERE! <<<<<
if(contact.penetrationDistance > 0.078 && contact.nodeB.name! == "CoinFinishLine" && !self.outOfTrack && !self.lapIncrement) {
self.lapIncrement = true
// Start lap increment timer (5 seconds)
self.startNSecondsTimer(howMuchTime: 1.0, target: 1)
// Increment lap
if(seconds > 10) {
self.laps += 1
DispatchQueue.main.async {
(self.arSceneView.viewWithTag(14) as! UILabel).text = String(self.laps)
}
if(self.laps == 3){
endGame()
}
}
}
}
Anyhow, if someone can explain me why I can't get contactTestBitMask to work and I can use only collisionBitMask with this solution is welcome. Thank you