How to flip UIImage horizontally?

Objective-C

UIImage* sourceImage = [UIImage imageNamed:@"whatever.png"];

UIImage* flippedImage = [UIImage imageWithCGImage:sourceImage.CGImage 
                                            scale:sourceImage.scale
                                      orientation:UIImageOrientationUpMirrored];

Swift

let flippedImage = myImage.withHorizontallyFlippedOrientation()

A very simple way you can achieve this is by creating a UIImageView instead of a UIImage and do the transform on UIImageView.

yourImageView.image =[UIImage imageNamed:@"whatever.png"];
yourImageView.transform = CGAffineTransform(scaleX: -1, y: 1); //Flipped

Hope this helps.

Vertical flip is often required to initialise OpenGL texture using glTexImage2d(...). The above proposed tricks do not actually modify image data and will not work in this case. Here is a code to do the actual data flip inspired by https://stackoverflow.com/a/17909372

- (UIImage *)flipImage:(UIImage *)image
{
    UIGraphicsBeginImageContext(image.size);
    CGContextDrawImage(UIGraphicsGetCurrentContext(),CGRectMake(0.,0., image.size.width, image.size.height),image.CGImage);
    UIImage *i = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return i;
}