How to rotate image in Swift?

Question

I am unable to rotate the image by 90 degrees in swift. I have written below code but there is an error and doesn't compile

  func imageRotatedByDegrees(oldImage: UIImage, deg degrees: CGFloat) -> UIImage {

    //Calculate the size of the rotated view's containing box for our drawing space
    let rotatedViewBox: UIView = UIView(frame: CGRect(x: 0, y: 0, width: oldImage.size.width, height: oldImage.size.height))
    let t: CGAffineTransform = CGAffineTransform(rotationAngle: degrees * CGFloat(M_PI / 180))
    rotatedViewBox.transform = t
    let rotatedSize: CGSize = rotatedViewBox.frame.size

    //Create the bitmap context
    UIGraphicsBeginImageContext(rotatedSize)
    let bitmap: CGContext = UIGraphicsGetCurrentContext()!

    //Move the origin to the middle of the image so we will rotate and scale around the center.
    bitmap.translateBy(x: rotatedSize.width / 2, y: rotatedSize.height / 2)

    //Rotate the image context
    bitmap.rotate(by: (degrees * CGFloat(M_PI / 180)))

    //Now, draw the rotated/scaled image into the context
    bitmap.scaleBy(x: 1.0, y: -1.0)
    bitmap.draw(oldImage, in:  CGRect(origin: (x: -oldImage.size.width / 2,  y: -oldImage.size.height / 2, width:  oldImage.size.width, height: oldImage.size.height), size: oldImage.cgImage))

    let newImage: UIImage = UIGraphicsGetImageFromCurrentImageContext()!
    UIGraphicsEndImageContext()

    return newImage

  }

below is the code i am not sure about

bitmap.draw(oldImage, in:  CGRect(origin: (x: -oldImage.size.width / 2,  y: -oldImage.size.height / 2, width:  oldImage.size.width, height: oldImage.size.height), size: oldImage.cgImage))

Answer 1

This is an extension of UIImage that targets Swift 4.0 and can rotate just the image without the need for a UIImageView. Tested successfully that the image was rotated, and not just had its exif data changed.

import UIKit

extension UIImage {
    func rotate(radians: CGFloat) -> UIImage {
        let rotatedSize = CGRect(origin: .zero, size: size)
            .applying(CGAffineTransform(rotationAngle: CGFloat(radians)))
            .integral.size
        UIGraphicsBeginImageContext(rotatedSize)
        if let context = UIGraphicsGetCurrentContext() {
            let origin = CGPoint(x: rotatedSize.width / 2.0,
                                 y: rotatedSize.height / 2.0)
            context.translateBy(x: origin.x, y: origin.y)
            context.rotate(by: radians)
            draw(in: CGRect(x: -origin.y, y: -origin.x,
                            width: size.width, height: size.height))
            let rotatedImage = UIGraphicsGetImageFromCurrentImageContext()
            UIGraphicsEndImageContext()

            return rotatedImage ?? self
        }

        return self
    }
}

To perform a 180 degree rotation, you can call it like this:

let rotatedImage = image.rotate(radians: .pi)

If for whatever reason it fails to rotate, the original image will then be returned.

Answer 2

 let angle =  CGFloat(M_PI_2)
  let tr = CGAffineTransform.identity.rotated(by: angle)
  ImageView.transform = tr

Answer 3

In Swift 4.2 and Xcode 10.0

dropDownImageView.transform = dropDownImageView.transform.rotated(by: CGFloat(Double.pi / 2))

If you want to add animation...

UIView.animate(withDuration: 2.0, animations: {
   self.dropDownImageView.transform = self.dropDownImageView.transform.rotated(by: CGFloat(Double.pi / 2))
})

Answer 4

Your problem is that you use non-existing initializer for CGRect. If you want to use CGRect(origin:size:), then create origin properly, without width and height parameters. Or remove size parameter and use CGRect(x:y:width:height:).

Just replace this line

bitmap.draw(oldImage, in:  CGRect(origin: (x: -oldImage.size.width / 2,  y: -oldImage.size.height / 2, width:  oldImage.size.width, height: oldImage.size.height), size: oldImage.cgImage))

with this one:

let rect = CGRect(origin: CGPoint(x: -oldImage.size.width / 2,  y: -oldImage.size.height / 2), size: oldImage.size)
bitmap.draw(oldImage.cgImage!, in: rect)

Answer 5

Your code is not that far off from functional. You can apply the transform as you are doing directly to the bitmap, you don't need an intermediate view:

func imageRotatedByDegrees(oldImage: UIImage, deg degrees: CGFloat) -> UIImage {
    let size = oldImage.size

    UIGraphicsBeginImageContext(size)

    let bitmap: CGContext = UIGraphicsGetCurrentContext()!
    //Move the origin to the middle of the image so we will rotate and scale around the center.
    bitmap.translateBy(x: size.width / 2, y: size.height / 2)
    //Rotate the image context
    bitmap.rotate(by: (degrees * CGFloat(M_PI / 180)))
    //Now, draw the rotated/scaled image into the context
    bitmap.scaleBy(x: 1.0, y: -1.0)

    let origin = CGPoint(x: -size.width / 2, y: -size.width / 2)

    bitmap.draw(oldImage.cgImage!, in: CGRect(origin: origin, size: size))

    let newImage: UIImage = UIGraphicsGetImageFromCurrentImageContext()!
    UIGraphicsEndImageContext()
    return newImage
}

Also, if you're going to create a function that rotates an image, it is typically good form to include a clockwise: Bool parameter that will interpret the degrees argument as rotating clockwise or not. The implementation and appropriate conversion to radians I leave to you.

Also note that it's a bit hand-wavy on my part to assume that oldImage.size is non-zero. If it is, force-unwrapping UIGraphicsGetCurrentContext()! will probably crash. You should validate the oldImage's size and if it's invalid just return oldImage.

Answer 6

In one line:

rotatedViewBox.transform = CGAffineTransform(rotationAngle: CGFloat.pi/2)