How to make sprites follow a random pattern within a circle? - swift

Question

I am makeing a game in which I want that the enemies move following a random pattern within a circle. I already made that the enemies spawn randomly in all the sides of the screen, but the problem is that I dont know how to make the enemies move following a random pattern within a circle just like the image.
class GameScene: SKScene, SKPhysicsContactDelegate {
var circuloPrincipal = SKSpriteNode(imageNamed: "circulo")
var enemigoTimer = NSTimer()
}
override func didMoveToView(view: SKView) {
circuloPrincipal.size = CGSize(width: 225, height: 225)
circuloPrincipal.position = CGPoint(x: frame.width / 2, y: frame.height / 2)
circuloPrincipal.color = colorAzul
circuloPrincipal.colorBlendFactor = 1.0
circuloPrincipal.name = "circuloPrincipal"
circuloPrincipal.zPosition = 1.0
self.addChild(circuloPrincipal)
override func touchesBegan(touches: Set, withEvent event: UIEvent?) {
enemigoTimer = NSTimer.scheduledTimerWithTimeInterval(0.5, target: self, selector: Selector("enemigos"), userInfo: nil, repeats: true)
}
func enemigos() {
let enemigo = SKSpriteNode(imageNamed: "enemigo")
enemigo.size = CGSize(width: 25, height: 25)
enemigo.zPosition = 2.0
enemigo.name = "enemigo"
let posisionRandom = arc4random() % 4
switch posisionRandom {
case 0:
enemigo.position.x = 0
let posisionY = arc4random_uniform(UInt32(frame.size.height))
enemigo.position.y = CGFloat(posisionY)
self.addChild(enemigo)
break
case 1:
enemigo.position.y = 0
let posisionX = arc4random_uniform(UInt32(frame.size.width))
enemigo.position.x = CGFloat(posisionX)
self.addChild(enemigo)
break
case 2:
enemigo.position.y = frame.size.height
let posisionX = arc4random_uniform(UInt32(frame.size.width))
enemigo.position.x = CGFloat(posisionX)
self.addChild(enemigo)
break
case 3:
enemigo.position.x = frame.size.width
let posisionY = arc4random_uniform(UInt32(frame.size.height))
enemigo.position.y = CGFloat(posisionY)
self.addChild(enemigo)
break
default:
break
}
enemigo.runAction(SKAction.moveTo(circuloPrincipal.position, duration: 1.4))
}

Answer 1

Try to add this code:
let randomY = CGFloat(Int.random(-Int(circuloPrincipal.frame.height/2)...Int(circuloPrincipal.frame.height/2)))
let randomX = CGFloat(Int.random(-Int(circuloPrincipal.frame.width/2)...Int(circuloPrincipal.frame.width/2)))
let slopeToCirculoPrincipal = (enemigo.position.y - circuloPrincipal.position.y + randomY ) / (enemigo.position.x - circuloPrincipal.position.x + randomX)
let constant = enemigo.position.y - slopeToCirculoPrincipal * enemigo.position.x
let finalX : CGFloat = enemigo.position.x < circuloPrincipal.position.x ? 1500.0 : -1500.0 // Set it to somewhere outside screen size
let finalY = constant + slopeToCirculoPrincipal * finalX
let distance = (enemigo.position.y - finalY) * (enemigo.position.y - finalY) + (enemigo.position.x - finalX) * (enemigo.position.x - finalX)
let enemigoSpeed : CGFloat = 100.0
let timeToCoverDistance = sqrt(distance) / enemigoSpeed
let moveAction = SKAction.moveTo(CGPointMake(finalX, finalY), duration: NSTimeInterval(timeToCoverDistance))
let removeAction = SKAction.runBlock { () -> Void in
enemigo.removeFromParent()
}
enemigo.runAction(SKAction.sequence([moveAction,removeAction]))
Instead of:
enemigo.runAction(SKAction.moveTo(circuloPrincipal.position, duration: 1.4))
Also you need to put this extension somewhere in your project:
extension Int
{
static func random(range: Range<Int> ) -> Int
{
var offset = 0
if range.startIndex < 0 // allow negative ranges
{
offset = abs(range.startIndex)
}
let mini = UInt32(range.startIndex + offset)
let maxi = UInt32(range.endIndex + offset)
return Int(mini + arc4random_uniform(maxi - mini)) - offset
}
}