How do I make an object bounce off the edges in swift - ios

Question

I am trying to make my 'Enemy' bounce off all the boundaries. For example, when the Enemy collides with the left, right, top and bottom of the screen, it should change direction.
This is my current code:
import SpriteKit
import GameplayKit
struct Physics {
static let Enemy: UInt32 = 0x1 << 1
let BorderCategory : UInt32 = 0x1 << 2
let BottomCategory : UInt32 = 0x1 << 3
let BallCategory : UInt32 = 0x1 << 4
}
class GameScene: SKScene {
var Enemy = SKSpriteNode()
var gameStarted = Bool()
var gameState = "running"
var destX : CGFloat = 0.0
var destY : CGFloat = 0.0
var score = 0
override func didMove(to view: SKView) {
let borderBody = SKPhysicsBody(edgeLoopFrom: self.frame)
borderBody.friction = 0
self.physicsBody = borderBody
let screenSize: CGRect = UIScreen.main().bounds // get the screen size
let screenWidth = screenSize.width //get the width
let screenHeight = screenSize.height //get the height
Enemy = SKSpriteNode(imageNamed: "red2")
Enemy.size = CGSize(width: 60, height: 70)
Enemy.position = (CGPoint(x: self.frame.width / 6 - Enemy.frame.width, y: self.frame.height / 10))
Enemy.physicsBody = SKPhysicsBody(circleOfRadius: Enemy.frame.height / 2)
Enemy.physicsBody?.categoryBitMask = Physics.Enemy
//Enemy.physicsBody?.categoryBitMask = Physics.Ground | Physics.wall
//Enemy.physicsBody?.contactTestBitMask = Physics.Ground | Physics.wall
Enemy.physicsBody?.affectedByGravity = false
Enemy.physicsBody?.isDynamic = true
self.addChild(Enemy)
Enemy.physicsBody?.velocity = CGVector(dx: 50, dy: 50)
if (Enemy.position.x == screenWidth) {
Enemy.physicsBody?.velocity = CGVector(dx: -50, dy: 0) // change direction at edge DOESN'T WORK
}
if(Enemy.position.y == screenHeight){
Enemy.physicsBody?.velocity = CGVector(dx: 0, dy: -50) //change direction at edge DOESN'T WORK
}
}

Answer 1

OK, based on your code I've written a working bouncing sprite. It uses the physics-engine to achieve this, rather than manually changing the direction (which I guess is how you should go about doing this).
override func didMove(to view: SKView) {
let borderBody = SKPhysicsBody(edgeLoopFrom: frame)
borderBody.friction = 0
borderBody.categoryBitMask = Physics.wall
physicsBody = borderBody
let enemy = enemySprite(size: CGSize(width: 60, height: 70), position: CGPoint(x: frame.size.width/2, y: frame.size.height/2))
addChild(enemy)
let force = SKAction.applyForce(CGVector(dx: 300, dy: 300) , duration: 0.1)
enemy.run(force)
}
func enemySprite(size: CGSize, position: CGPoint) -> SKSpriteNode {
let enemy = SKSpriteNode(color: SKColor.red(), size: CGSize(width: 60, height: 80))
enemy.position = CGPoint(x: frame.width/2, y: frame.height/2)
enemy.physicsBody = SKPhysicsBody(circleOfRadius: enemy.frame.height / 2) // A bit silly with circle, but you seem to have an image for this use
enemy.physicsBody?.categoryBitMask = Physics.enemy
enemy.physicsBody?.restitution = 1
enemy.physicsBody?.friction = 0
enemy.physicsBody?.collisionBitMask = Physics.wall
enemy.physicsBody?.affectedByGravity = false
enemy.physicsBody?.angularDamping = 0
enemy.physicsBody?.linearDamping = 0
return enemy
}
A question to consider is also how you set up the scene? Is the scene-size the same as the view-size? Otherwise the scene's physicsBody will not make the ball bounce where you expect it to...

Answer 2

It won't (in most cases) because of your conditions - using equal to operators instead of greater/lower than.
import SpriteKit
class GameScene: SKScene {
override func didMoveToView(view: SKView) {
// Create enemy with physics body attached and add it to the scene
let enemy = SKSpriteNode(color: SKColor.greenColor(), size: CGSize(width: 20, height: 20))
enemy.name = "enemy"
enemy.position = CGPoint(x: size.width / 2, y: size.height / 2)
enemy.physicsBody = SKPhysicsBody(rectangleOfSize: enemy.size)
enemy.physicsBody!.affectedByGravity = false
enemy.physicsBody!.linearDamping = 0
enemy.physicsBody!.mass = 0.1
enemy.physicsBody!.velocity = CGVector(dx: 150, dy: 0)
addChild(enemy)
}
override func didSimulatePhysics() {
let enemy = childNodeWithName("enemy")!
if (enemy.position.x > size.width && enemy.physicsBody!.velocity.dx > 0)
|| (enemy.position.x < 0 && enemy.physicsBody!.velocity.dx < 0) {
enemy.physicsBody!.velocity.dx *= -1
}
}
}