SWIFT 3 示例

 override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
        let imageView = UIImageView(frame: CGRect(x: CGFloat(0), y: CGFloat(50), width: CGFloat(320), height: CGFloat(320)))
        view.addSubview(imageView)
        let image = UIImage(named: "Dubai-Photos-Images-Travel-Tourist-Images-Pictures-800x600.jpg")
        imageView.image = circularScaleAndCropImage(UIImage(named: "Dubai-Photos-Images-Travel-Tourist-Images-Pictures-800x600.jpg")!, frame: CGRect(x: CGFloat(0), y: CGFloat(0), width: CGFloat(100), height: CGFloat(100)))
    }

最后，执行繁重的 circularScaleAndCropImage 的功能如下所述

func circularScaleAndCropImage(_ image: UIImage, frame: CGRect) -> UIImage{
        // This function returns a newImage, based on image, that has been:
        // - scaled to fit in (CGRect) rect
        // - and cropped within a circle of radius: rectWidth/2
        //Create the bitmap graphics context
        UIGraphicsBeginImageContextWithOptions(CGSize(width: CGFloat(frame.size.width), height: CGFloat(frame.size.height)), false, 0.0)
        let context: CGContext? = UIGraphicsGetCurrentContext()
        //Get the width and heights
        let imageWidth: CGFloat = image.size.width
        let imageHeight: CGFloat = image.size.height
        let rectWidth: CGFloat = frame.size.width
        let rectHeight: CGFloat = frame.size.height
        //Calculate the scale factor
        let scaleFactorX: CGFloat = rectWidth / imageWidth
        let scaleFactorY: CGFloat = rectHeight / imageHeight
        //Calculate the centre of the circle
        let imageCentreX: CGFloat = rectWidth / 2
        let imageCentreY: CGFloat = rectHeight / 2
        // Create and CLIP to a CIRCULAR Path
        // (This could be replaced with any closed path if you want a different shaped clip)
        let radius: CGFloat = rectWidth / 2
        context?.beginPath()
        context?.addArc(center: CGPoint(x: imageCentreX, y: imageCentreY), radius: radius, startAngle: CGFloat(0), endAngle: CGFloat(2 * Float.pi), clockwise: false)
        context?.closePath()
        context?.clip()
        //Set the SCALE factor for the graphics context
        //All future draw calls will be scaled by this factor
        context?.scaleBy(x: scaleFactorX, y: scaleFactorY)
        // Draw the IMAGE
        let myRect = CGRect(x: CGFloat(0), y: CGFloat(0), width: imageWidth, height: imageHeight)
        image.draw(in: myRect)
        let newImage: UIImage? = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()
        return newImage!
    }