iOS: frame.size.width/2 doesn't produce a circle on every device

Question

I\'m aware that the formulae frame.size.width/2 should produce a circle border, however in XCode I am currently experiencing some discrepancies.

I have

Answer 1

Thanks to @leo Dabus for the original solution Following is just an update for swift 4.2

import UIKit
extension UIImage {
    var circleMask: UIImage {
        let square = size.width < size.height ? CGSize(width: size.width, height: size.width) : CGSize(width: size.height, height: size.height)
        let imageView = UIImageView(frame: CGRect(origin: CGPoint(x: 0, y: 0), size: square))
        imageView.contentMode = UIView.ContentMode.scaleAspectFill
        imageView.image = self
        imageView.layer.cornerRadius = square.width/2
        imageView.layer.borderColor = UIColor.white.cgColor
        imageView.layer.borderWidth = 5
        imageView.layer.masksToBounds = true
        UIGraphicsBeginImageContext(imageView.bounds.size)
        imageView.layer.render(in: UIGraphicsGetCurrentContext()!)
        let result = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()
        return result!
    }
}