checking to see if location in scene is occupied by sprite - ios

Question

I am building my first iPhone game using Xcode, SpriteKit and Swift. I am new to these technologies but I am familiar with general programming concepts.
Here is what I am trying to do in English. I want circles to randomly appear on the screen and then begin to expand in size. However, I do not want a circle to appear in a location where a circle currently exists. I am having trouble determining each circle's position.
Inside GameScene.swift I have the following code inside the didMoveToView:
runAction(SKAction.repeatActionForever(
SKAction.sequence([
SKAction.runBlock(addCircle), SKAction.waitForDuration(3, withRange: 2)]
)))
The piece of code above calls my "addCircle" method:
func addCircle() {
// Create sprite.
let circle = SKSpriteNode(imageNamed: "grad640x640_circle")
circle.name = "circle"
circle.xScale = 0.1
circle.yScale = 0.1
// Determine where to position the circle.
let posX = random(min: 50, max: 270)
let posY = random(min: 50, max: 518)
// ***Check to see if position is currently occupied by another circle here.
circle.position = CGPoint(x: posX, y: posY)
// Add circle to the scene.
addChild(circle)
// Expand the circle.
let expand = SKAction.scaleBy(2, duration: 0.5)
circle.runAction(expand)
}
The random function above just chooses a random number within the given range. How can I check to see if my random functions are generating a location that is currently occupied by another circle?
I was thinking of using a do..while loop to randomly generate a set of x and y coordinates and then check to see if a circle is at that location but I cannot find how to check for that condition. Any help would be greatly appreciated.

Answer 1

There are a few methods which can help you in this regard:
(BOOL) intersectsNode: (SKNode*)node, available with SKNode, and
CGRectContainsPoint() as well as the CGRectContainsRect() methods.
For instance the loop to check for intersection can look as follows:
var point: CGPoint
var exit:Bool = false
while (!exit) {
let posX = random(min: 50, max: 270)
let posY = random(min: 50, max: 518)
point = CGPoint(x: posX, y: posY)
var pointFound: Bool = true
self.enumerateChildNodesWithName("circle", usingBlock: {
node, stop in
let sprite:SKSpriteNode = node as SKSpriteNode
if (CGRectContainsPoint(sprite.frame, point))
{
pointFound = false
stop.memory = true
}
})
if (pointFound)
{
exit = true
}
}
//point contains CGPoint where no other circle exists
//Declare new circle at point