Adding Physics and Collision Detection to Your Game - Beginning Swift Games Development for iOS - page 43

of the collision. Later in the game you will be adding a fuel element so that the orbs will
provide fuel for the player to ascend higher and higher.
To be able to detect when SKNode s come into contact with each other, you first imple-
ment the Sprite Kit protocol SKPhysicsContactDelegate in the GameScene class
and then implement the methods needed in your game. The SKPhysic-
sContactDelegate protocol defines two methods used to detect when SKNode s
touch each other: the didBeginContact and the didEndContact() methods. The
following snippet shows the protocol:
protocol SKPhysicsContactDelegate : NSObjectProtocol {
optional func didBeginContact(contact:
SKPhysicsContact!)
optional func didEndContact(contact: SKPhysicsContact!)
}
The method names make their function pretty straightforward. The didBe-
ginContact() method is invoked when the contact first begins, and the
didEndContact() method is invoked when contact ends. For this game, you are inter-
ested only in the first method, didBeginContact() , because you don't want the
playerNode to pass through the orb. You want the orb to be removed from the scene as
soon as the playerNode contacts the orb.
Go back to the GameScene.swift file and change the class definition to the following:
class GameScene: SKScene, SKPhysicsContactDelegate
After you change your class definition, add this implementation of the didBe-
ginContact() method to the end of the GameScene class:
func didBeginContact(contact: SKPhysicsContact!) {
println("There has been contact.")
}
Finally, you need to make the GameScene the delegate of the scene's physic-
sWorld.contactDelegate . This is done by adding the following line in the
GameScene.init(size: CGSize) method directly after the call to the su-
per.init(size: size) :
physicsWorld.contactDelegate = self