How to flip UIImage horizontally with Swift?

Question

The solution to do UIImage flipping is with the Objective-C code:

[UIImage imageWithCGImage:img.CGImage scale:1.0 orientation: UIImageOrientationDownMirrored         


        

Answer 1

Swift 5

If your use case requires saving the UIImage after transforming, it will need to be drawn into a new CGContext.

extension UIImage {
  
  enum Axis {
    case horizontal, vertical
  }
  
  func flipped(_ axis: Axis) -> UIImage {
    let renderer = UIGraphicsImageRenderer(size: size)
    
    return renderer.image {
      let context = $0.cgContext
      context.translateBy(x: size.width / 2, y: size.height / 2)
      
      switch axis {
      case .horizontal:
        context.scaleBy(x: -1, y: 1)
      case .vertical:
        context.scaleBy(x: 1, y: -1)
      }
      
      context.translateBy(x: -size.width / 2, y: -size.height / 2)
      
      draw(at: .zero)
    }
  }
}

Answer 2

For me the simplest way was to use the .withHorizontallyFlippedOrientation() instance method of UIImage as follows:

let flippedImage = straightImage.withHorizontallyFlippedOrientation()

Simple one-liners always make me happy :)

Answer 3

Swift 4

YOURIMAGEVIEW.transform = CGAffineTransform(scaleX: -1, y: 1)