SKPhysics not working properly? - swift

Question

struct PhysicsCategory {
static let None : UInt32 = 0
static let All : UInt32 = UInt32.max
static let planet : UInt32 = 0b1
static let rocket : UInt32 = 0b10 }
planet.physicsBody = SKPhysicsBody(circleOfRadius: planet.size.width / 2)
planet.physicsBody?.dynamic = true planet.physicsBody?.categoryBitMask = PhysicsCategory.planet
planet.physicsBody?.contactTestBitMask = PhysicsCategory.rocket
planet.physicsBody?.collisionBitMask = PhysicsCategory.None
func planetCollidedWithRocket(rocket: SKSpriteNode, planet: SKSpriteNode) {
println("collision planet") }
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 & PhysicsCategory.planet != 0) &&
(secondBody.categoryBitMask & PhysicsCategory.rocket != 0)) {
planetCollidedWithRocket(firstBody.node as! SKSpriteNode, planet: secondBody.node as! SKSpriteNode)}
I'm currently using this to add collision detection to my game (I've taken only taken out the bits of code I think are relevant). The first time I ran the game on the simulator it worked fine, and I added a game over scene to the planetCollidedWithRocket method. But I tested it again today and for some reason the game is detecting a collision between the rocket and the planet when they aren't colliding! Can anyone see what Ive done wrong??

Answer 1

Your contact isn't set up correctly. This is what you have, and what it translates to:
if((firstBody.categoryBitMask & PhysicsCategory.planet !=0)
// This is checking if the firstBody *has* a categoryBitMask, but it is not evaluating what it is.
// In addition to that, it is requiring that the PhysicsCategory.planet does not equal zero, which it doesn't.
// This would evaluate to true every time, no matter what.
// It is also requiring that...
&& (secondBody.categoryBitMask & PhysicsCategory.rocket != 0))
// This is checking if the secondBody *has* a categoryBitMask, but it is not evaluating what it is.
// In addition to that, it is requiring that the PhysicsCategory.planet does not equal zero, which it doesn't.
// This would evaluate to true every time, no matter what.
What you need to do is check that you categoryBitMask equals one of your PhysicsCategory variables, such that when a planet and a rocket contact, something evaluates to true. Try this:
if ((firstBody.categoryBitMask == PhysicsCategory.planet) &&
(secondBody.categoryBitMask == PhysicsCategory.rocket)){
// Code Here
}
Alternatively, since you know the hard-coded numbers in your PhysicsCategory struct, you can evaluate to hard numbers:
if ((firstBody.categoryBitMask == 1) &&
(secondBody.categoryBitMask == 2)){
// Code Here
}
What this will do is check to see if the physicsBody's categoryBitMask equals certain numbers when they contact. If they do, something happens, if not, nothing happens.