flip UIImage

flipImage.m

// 直接翻转UIImageView
func flipImageView(imageView: UIView) {
  imageView.transform = CGAffineTransform(scaleX: -1, y: 1)
}

// 修改imageOrientation属性， 这个方法只适用于UIKit中显示的image
func flipImage(originImage: UIImage) -> UImage {
  let cgImage = originImage.cgImage!
  let flipedImage = UIImage(cgImage: originImage, 
                              scale: originImage.scale, 
                        orientation: UIImageOrientation.upMirrored)
  return flipedImage
}

// 如果需要处理图片数据，需要使用Quartz 2D重绘
- (UIImage *)horizontalFlip {
    CGRect newFrame = CGRectMake(0, 0, self.size.width, self.size.height);
    
    UIGraphicsBeginImageContextWithOptions(self.size, NO, self.scale);
    CGContextRef context =  UIGraphicsGetCurrentContext();
    
    CGContextClipToRect(context, newFrame);
    
    // 转换坐标系：quartz 2D的坐标系原点在屏幕左下角，方向向上
    // 转换成和UIKit坐标系一致需要 1.旋转180度; 2.向上平移height
    // 3.水平翻转需要将坐标系向左移动width
    CGContextRotateCTM(context, M_PI); // 反方向
    CGContextTranslateCTM(context, -newFrame.size.width, -newFrame.size.height); // 将 2、3步合并
    
    // 不做上述转换，重绘时默认是垂直翻转
    CGContextDrawImage(context, newFrame, self.CGImage);
    UIImage *resultImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    
    UIImage *flipedImage = [UIImage imageWithCGImage:resultImage.CGImage scale:self.scale orientation:self.imageOrientation];
    
    return flipedImage;
}