【Swift】切り抜かずにUIImageを回転させる ref: https://qiita.com/taji-taji/items/4f01273b303edec45d46

file0.swift

extension UIImage {

    func rotatedBy(degree: CGFloat) -> UIImage {
        let radian = -degree * CGFloat.pi / 180
        UIGraphicsBeginImageContext(self.size)
        let context = UIGraphicsGetCurrentContext()!
        context.translateBy(x: self.size.width / 2, y: self.size.height / 2)
        context.scaleBy(x: 1.0, y: -1.0)

        context.rotate(by: radian)
        context.draw(self.cgImage!, in: CGRect(x: -(self.size.width / 2), y: -(self.size.height / 2), width: self.size.width, height: self.size.height))

        let rotatedImage = UIGraphicsGetImageFromCurrentImageContext()!
        UIGraphicsEndImageContext()
        return rotatedImage
    }

}

file1.swift

extension UIImage {

    func rotatedBy(degree: CGFloat, isCropped: Bool = true) -> UIImage {
        let radian = -degree * CGFloat.pi / 180
        var rotatedRect = CGRect(origin: .zero, size: self.size)
        if !isCropped {
            rotatedRect = rotatedRect.applying(CGAffineTransform(rotationAngle: radian))
        }
        UIGraphicsBeginImageContext(rotatedRect.size)
        let context = UIGraphicsGetCurrentContext()!
        context.translateBy(x: rotatedRect.size.width / 2, y: rotatedRect.size.height / 2)
        context.scaleBy(x: 1.0, y: -1.0)

        context.rotate(by: radian)
        context.draw(self.cgImage!, in: CGRect(x: -(self.size.width / 2), y: -(self.size.height / 2), width: self.size.width, height: self.size.height))

        let rotatedImage = UIGraphicsGetImageFromCurrentImageContext()!
        UIGraphicsEndImageContext()
        return rotatedImage
    }

}

file2.swift

CGRect(origin: .zero, size: self.size).applying(CGAffineTransform(rotationAngle: radian))