CAShapeLayer中的图像不适合Swift

Question

我通过UIBezierPath创建了一个Circle形状，然后将其设置为可以拖动的CAShapeLayer。另外，我在我的xcode项目中添加了PNG图像（30px，30px）。 我将PNG图像添加到CAShapeLayer中，但每次我移动它'切割'时都会看不到球的某些部分：

这是PNG图片：

到目前为止，这是我的代码：

class ViewController: UIViewController, UIGestureRecognizerDelegate {

var shapeLayer2 = CAShapeLayer()
var circlePath2 = UIBezierPath()

override func viewDidLoad() {
        super.viewDidLoad()

let angleEarth: Double = 0
        let angleEarthAfterCalculate: CGFloat = CGFloat(angleEarth*M_PI/180) - CGFloat(M_PI/2)
        let earthX = midViewX + cos(angleEarthAfterCalculate)*100
        let earthY = midViewY + sin(angleEarthAfterCalculate)*100
        circlePath2 = UIBezierPath(arcCenter: CGPoint(x: earthX,y: earthY), radius: CGFloat(10), startAngle: CGFloat(0), endAngle:CGFloat(M_PI * 2), clockwise: true)
        shapeLayer2.path = circlePath2.CGPath
        shapeLayer2.fillColor = UIColor.blueColor().CGColor
        shapeLayer2.strokeColor = UIColor.clearColor().CGColor
        shapeLayer2.lineWidth = 7
        view.layer.addSublayer(shapeLayer2)
let dragBall = UIPanGestureRecognizer(target: self, action:#selector(ViewController.dragBall(_:)))
        view.addGestureRecognizer(dragBall)

let image = UIImage(named: "rrr.png")
            if let realImage = image {
            let color = UIColor(patternImage: image!)
            shapeLayer2.fillColor = color.CGColor
            shapeLayer4.fillColor = color.CGColor
}

 @IBAction func dragBall(recognizer: UIPanGestureRecognizer) {
            let point = recognizer.locationInView(self.view)
            let earthX = Double(point.x)
            let earthY = Double(point.y)
            let midViewXDouble = Double(midViewX)
            let midViewYDouble = Double(midViewY)
            let angleX = (earthX - midViewXDouble)
            let angleY = (earthY - midViewYDouble)
            angle = atan2(angleY, angleX)
            let earthX2 = midViewXDouble + cos(angle)*100
            let earthY2 = midViewYDouble + sin(angle)*100
            circlePath2 = UIBezierPath(arcCenter: CGPoint(x: earthX2,y: earthY2), radius: CGFloat(10), startAngle: CGFloat(0), endAngle:CGFloat(M_PI * 2), clockwise: true)
            shapeLayer2.path = circlePath2.CGPath
}

快捷方式：如果没有在gif中获得结果，我无法将PNG图像放入CAShapeLayer。