I was programming this simple space game in Swift until I encountered the problem of detecting collisions. After looking around forums, tutorials, etc, I tried to implement collisions by declaring bitmasks like so:
object 1
enemy?.physicsBody = SKPhysicsBody(circleOfRadius: ((enemy?.size.width)!/2))
enemy?.physicsBody?.categoryBitMask = enemyBitMask
enemy?.physicsBody?.contactTestBitMask = bulletBitMask
enemy?.physicsBody?.collisionBitMask = 0
object 2
bullet?.physicsBody? = SKPhysicsBody(rectangleOf: (bullet?.size)!)
bullet?.physicsBody?.categoryBitMask = bulletBitMask
bullet?.physicsBody?.contactTestBitMask = enemyBitMask
bullet?.physicsBody?.collisionBitMask = 0
bullet?.physicsBody?.usesPreciseCollisionDetection = true
I also put a print statement in the
func didBegin(_ contact: SKPhysicsContact) { print("Hello") }
here is how I configure my sprites:
func CreateNewEnemy() {
var enemy : SKSpriteNode?
let moveEnemyDown = SKAction.repeatForever(SKAction.moveBy(x: 0, y: -1, duration: 0.01))
let rotateEnemy = SKAction.repeatForever(SKAction.rotate(byAngle: 25, duration: 5))
let enemyXpos = randomNum(high: self.frame.size.width/2, low: -1 * self.frame.size.width/2)
let enemyYpos = randomNum(high: 2.5*self.frame.size.height, low: self.frame.size.height/2)
let enemyOrigin : CGPoint = CGPoint(x: enemyXpos, y: enemyYpos)
enemy = SKSpriteNode(imageNamed: possibleEnemyImage[Int(arc4random_uniform(4))])
print(enemy?.size.height)
enemy?.scale(to: CGSize(width: player.size.height, height: player.size.height))
print(enemy?.size.height)
enemy?.position = enemyOrigin
enemy?.run(moveEnemyDown)
enemy?.run(rotateEnemy)
let enemyRadius : CGFloat = (enemy?.size.width)!/2
print(enemyRadius)
enemy?.physicsBody? = SKPhysicsBody(circleOfRadius: enemyRadius)
enemy?.physicsBody?.categoryBitMask = enemyCategory
enemy?.physicsBody?.contactTestBitMask = bulletCategory
enemy?.physicsBody?.collisionBitMask = 0
enemy?.zPosition = 1
enemiesArray.append(enemy!)
self.addChild(enemy!)
}
to create enemy (Called in did move to view function)
func CreateAllEnemies(amountOfEnemies : UInt8) {
for _ in 0...amountOfEnemies {
CreateNewEnemy()
}
}
and the other sprite
func CreateNewBullet() {
let bulletOrigin : CGPoint = CGPoint(x: player.position.x, y: player.position.y+player.size.height/2)
let moveBulletUp = SKAction.repeatForever(SKAction.moveBy(x: 0, y: 3, duration: 0.01))
var bullet : SKSpriteNode?
bullet = SKSpriteNode(imageNamed: "bulletImage")
bullet?.position = bulletOrigin
bullet?.run(moveBulletUp)
bullet?.physicsBody? = SKPhysicsBody(rectangleOf: (bullet?.size)!)
bullet?.physicsBody?.categoryBitMask = bulletCategory
bullet?.physicsBody?.contactTestBitMask = enemyCategory
bullet?.physicsBody?.collisionBitMask = 0
bullet?.physicsBody?.isDynamic = true
bullet?.physicsBody?.usesPreciseCollisionDetection = true
bullet?.zPosition = 1
bulletsArray.append(bullet!)
self.addChild(bullet!)
}
this one is created with a timer
bulletTimer = Timer.scheduledTimer(timeInterval: 0.25, target: self, selector: #selector(CreateNewBullet) , userInfo: nil, repeats: true)
Unfortunately it does not print anything in the console after I see the two objects touching.
SKPhysicsContactDelegate
and make yourself the physics contact delegate://Physics categories
let enemyCategory: UInt32 = 1 << 1
let bulletCategory: UInt32 = 1 << 2
class GameScene: SKScene, SKPhysicsContactDelegate {
self.physicsWorld.contactDelegate = self
didMove(to view:)
) :enemy.physicsBody.categoryBitMask = enemyCategory
bullet.physicsBody.categoryBitMask = bulletCategory
(Make sure you've created physics bodies for each node)
enemy.physicsBody?.collisionBitMask = 0 // enemy collides with nothing
bullet.physicsBody?.collisionBitMask = 0 // bullet collides with nothing
or even:
for node in [enemy, bullet] {
node.physicsBody?.collisionBitMask = 0 // collides with nothing
}
Set up contacts
bullet.physicsBody?.collisionBitMask = enemyCategory // bullet contacts enemy
Make sure that at least one of the objects involved in each potential contact has the isDynamic
property on its physics body set to true
, or no contact will be generated. It is not necessary for both of the objects to be dynamic.
You should now get didBegin
called when the bullet and the enemy make contact. You could code didBegin
like this:
func didBegin(_ contact: SKPhysicsContact) {
print("didBegin 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 bulletCategory | enemyCategory:
print("bullet and enemy have contacted.")
let bulletNode = contact.bodyA.categoryBitMask == bulletCategory ? contact.bodyA.node : contact.bodyB.node
enemyHealth -= 10
bulletNode.removeFromParent
default:
print("Some other contact occurred")
}
}