문제 코드

CGContextDrawImage(context, CGRect(x: -self.size.width/2, y:-self.size.height/2, width:self.size.width, height:self.size.height), self.cgImage)

해결 코드

context.draw(context as! CGImage, in: CGRect(x: -self.size.width/2, y:-self.size.height/2, width:self.size.width, height:self.size.height), byTiling: (self.cgImage != nil))

참고