Draw a simple circle uiimage

Question

I try to make a 20x20 UIImage with a simple blue circle. I try with this function, but the result is a blue circle in a black square. How do I remove the black square around

Answer 1

Swift 3 & 4:

extension UIImage {
    class func circle(diameter: CGFloat, color: UIColor) -> UIImage {
        UIGraphicsBeginImageContextWithOptions(CGSize(width: diameter, height: diameter), false, 0)
        let ctx = UIGraphicsGetCurrentContext()!
        ctx.saveGState()

        let rect = CGRect(x: 0, y: 0, width: diameter, height: diameter)
        ctx.setFillColor(color.cgColor)
        ctx.fillEllipse(in: rect)

        ctx.restoreGState()
        let img = UIGraphicsGetImageFromCurrentImageContext()!
        UIGraphicsEndImageContext()

        return img
    }
}

Swift autocorrect is godly. Thanks to Valentin.