How Can I Rotate A UIImage and Image Data By 90 Degrees

Question

I have a UIImageView that contains an image. At the minute the user can click to save the image within the UIImageView to disk.

I would like to make it so that the the user can click to rotate the UIImageView and also rotate the UImage within the view so that when the image is saved it keeps the new rotation.

At the minute I have

- (IBAction)rotateImage:(id)sender {

float degrees = 90; //the value in degrees
self.imagePreview.transform = CGAffineTransformMakeRotation(degrees * M_PI/180);

}

Can someone point me in the right direction regarding keeping the current rotation.

Thanks

Answer 1

I have such code in my old app. But this code can be simplified because you have no need to rotate it on non-90 degrees angle.

Objective-C

@implementation UIImage (Rotation)

- (UIImage *)imageRotatedOnDegrees:(CGFloat)degrees
{
  // Follow ing code can only rotate images on 90, 180, 270.. degrees.
  CGFloat roundedDegrees = (CGFloat)(round(degrees / 90.0) * 90.0);
  BOOL sameOrientationType = ((NSInteger)roundedDegrees) % 180 == 0;
  CGFloat radians = M_PI * roundedDegrees / 180.0;
  CGSize newSize = sameOrientationType ? self.size : CGSizeMake(self.size.height, self.size.width);

  UIGraphicsBeginImageContext(newSize);
  CGContextRef ctx = UIGraphicsGetCurrentContext();
  CGImageRef cgImage = self.CGImage;
  if (ctx == NULL || cgImage == NULL) {
    UIGraphicsEndImageContext();
    return self;
  }

  CGContextTranslateCTM(ctx, newSize.width / 2.0, newSize.height / 2.0);
  CGContextRotateCTM(ctx, radians);
  CGContextScaleCTM(ctx, 1, -1);
  CGPoint origin = CGPointMake(-(self.size.width / 2.0), -(self.size.height / 2.0));
  CGRect rect = CGRectZero;
  rect.origin = origin;
  rect.size = self.size;
  CGContextDrawImage(ctx, rect, cgImage);
  UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
  UIGraphicsEndImageContext();
  return image ?: self;
}

@end

Swift

extension UIImage {

  func imageRotated(on degrees: CGFloat) -> UIImage {
    // Following code can only rotate images on 90, 180, 270.. degrees.
    let degrees = round(degrees / 90) * 90
    let sameOrientationType = Int(degrees) % 180 == 0
    let radians = CGFloat.pi * degrees / CGFloat(180)
    let newSize = sameOrientationType ? size : CGSize(width: size.height, height: size.width)

    UIGraphicsBeginImageContext(newSize)
    defer {
      UIGraphicsEndImageContext()
    }

    guard let ctx = UIGraphicsGetCurrentContext(), let cgImage = cgImage else {
      return self
    }

    ctx.translateBy(x: newSize.width / 2, y: newSize.height / 2)
    ctx.rotate(by: radians)
    ctx.scaleBy(x: 1, y: -1)
    let origin = CGPoint(x: -(size.width / 2), y: -(size.height / 2))
    let rect = CGRect(origin: origin, size: size)
    ctx.draw(cgImage, in: rect)
    let image = UIGraphicsGetImageFromCurrentImageContext()
    return image ?? self
  }

}