Circular Transition, change initial circle size - ios

Question

I have a circular transition you can find in the code below. This transition creates an extending circle with the next view controller inside.
It works fine, but I've been trying to increase the circle size on start for a while now.
To be exact, currently on execution the circle will be drawn from zero, but I want it to have an initial size which appears immediately, from where it starts extending.
How can I change the initial size of the circle?
import UIKit
class CircularTransition: NSObject {
var circle = UIView()
var startingPoint = CGPoint.zero {
didSet {
circle.center = startingPoint
}
}
var circleColor = UIColor.white
var duration = 0.2
enum CircularTransitionMode:Int {
case present, dismiss, pop
}
var transitionMode:CircularTransitionMode = .present
}
extension CircularTransition:UIViewControllerAnimatedTransitioning {
func transitionDuration(using transitionContext: UIViewControllerContextTransitioning?) -> TimeInterval {
return duration
}
func animateTransition(using transitionContext: UIViewControllerContextTransitioning) {
let containerView = transitionContext.containerView
if transitionMode == .present {
if let presentedView = transitionContext.view(forKey: UITransitionContextViewKey.to) {
let viewCenter = presentedView.center
let viewSize = presentedView.frame.size
circle = UIView()
circle.frame = frameForCircle(withViewCenter: viewCenter, size: viewSize, startPoint: startingPoint)
circle.layer.cornerRadius = circle.frame.size.height / 2
circle.center = startingPoint
circle.backgroundColor = circleColor
circle.transform = CGAffineTransform(scaleX: 0.001, y: 0.001)
containerView.addSubview(circle)
presentedView.center = startingPoint
presentedView.transform = CGAffineTransform(scaleX: 0.001, y: 0.001)
presentedView.alpha = 0
containerView.addSubview(presentedView)
UIView.animate(withDuration: duration, animations: {
self.circle.transform = CGAffineTransform.identity
presentedView.transform = CGAffineTransform.identity
presentedView.alpha = 1
presentedView.center = viewCenter
}, completion: { (success:Bool) in
transitionContext.completeTransition(success)
})
}
}else{
let transitionModeKey = (transitionMode == .pop) ? UITransitionContextViewKey.to : UITransitionContextViewKey.from
if let returningView = transitionContext.view(forKey: transitionModeKey) {
let viewCenter = returningView.center
let viewSize = returningView.frame.size
circle.frame = frameForCircle(withViewCenter: viewCenter, size: viewSize, startPoint: startingPoint)
circle.layer.cornerRadius = circle.frame.size.height / 2
circle.center = startingPoint
UIView.animate(withDuration: duration, animations: {
self.circle.transform = CGAffineTransform(scaleX: 0.001, y: 0.001)
returningView.transform = CGAffineTransform(scaleX: 0.001, y: 0.001)
returningView.center = self.startingPoint
returningView.alpha = 0
if self.transitionMode == .pop {
containerView.insertSubview(returningView, belowSubview: returningView)
containerView.insertSubview(self.circle, belowSubview: returningView)
}
}, completion: { (success:Bool) in
returningView.center = viewCenter
returningView.removeFromSuperview()
self.circle.removeFromSuperview()
transitionContext.completeTransition(success)
})
}
}
}
func frameForCircle (withViewCenter viewCenter:CGPoint, size viewSize:CGSize, startPoint:CGPoint) -> CGRect {
let xLength = fmax(startPoint.x, viewSize.width - startPoint.x)
let yLength = fmax(startPoint.y, viewSize.height - startPoint.y)
let offestVector = sqrt(xLength * xLength + yLength * yLength) * 2
let size = CGSize(width: offestVector, height: offestVector)
return CGRect(origin: CGPoint.zero, size: size)
}
}