如何旋转rotate UIImage

+(UIImage *)rotateImage:(UIImage *)aImage

{

         CGImageRef imgRef = aImage.CGImage;

         CGFloat width = CGImageGetWidth(imgRef);

         CGFloat height = CGImageGetHeight(imgRef);

        

         CGAffineTransform transform = CGAffineTransformIdentity;

         CGRect bounds = CGRectMake(0, 0, width, height);

        

         CGFloat scaleRatio = 1;

        

         CGFloat boundHeight;

         UIImageOrientation orient = aImage.imageOrientation;

         switch(orient)

         {

              case UIImageOrientationUp: //EXIF = 1

                     transform = CGAffineTransformIdentity;

                     break;

                    

              case UIImageOrientationUpMirrored: //EXIF = 2

                     transform = CGAffineTransformMakeTranslation(width, 0.0);

                     transform = CGAffineTransformScale(transform, -1.0, 1.0);

                     break;

                    

              case UIImageOrientationDown: //EXIF = 3

                     transform = CGAffineTransformMakeTranslation(width, height);

                     transform = CGAffineTransformRotate(transform, M_PI);

                     break;

                    

              case UIImageOrientationDownMirrored: //EXIF = 4

                     transform = CGAffineTransformMakeTranslation(0.0, height);

                     transform = CGAffineTransformScale(transform, 1.0, -1.0);

                     break;

                    

              case UIImageOrientationLeftMirrored: //EXIF = 5

                     boundHeight = bounds.size.height;

                     bounds.size.height = bounds.size.width;

                     bounds.size.width = boundHeight;

                     transform = CGAffineTransformMakeTranslation(height, width);

                     transform = CGAffineTransformScale(transform, -1.0, 1.0);

                     transform = CGAffineTransformRotate(transform, 3.0 * M_PI / 2.0);

                     break;

                    

              case UIImageOrientationLeft: //EXIF = 6

                     boundHeight = bounds.size.height;

                     bounds.size.height = bounds.size.width;

                     bounds.size.width = boundHeight;

                     transform = CGAffineTransformMakeTranslation(0.0, width);

                     transform = CGAffineTransformRotate(transform, 3.0 * M_PI / 2.0);

                     break;

                    

              case UIImageOrientationRightMirrored: //EXIF = 7

                     boundHeight = bounds.size.height;

                     bounds.size.height = bounds.size.width;

                     bounds.size.width = boundHeight;

                     transform = CGAffineTransformMakeScale(-1.0, 1.0);

                     transform = CGAffineTransformRotate(transform, M_PI / 2.0);

                     break;

                    

              case UIImageOrientationRight: //EXIF = 8

                     boundHeight = bounds.size.height;

                     bounds.size.height = bounds.size.width;

                     bounds.size.width = boundHeight;

                     transform = CGAffineTransformMakeTranslation(height, 0.0);

                     transform = CGAffineTransformRotate(transform, M_PI / 2.0);

                     break;

                    

              default:

                     [NSException raise:NSInternalInconsistencyException format:@"Invalid image orientation"];

         }

        

         UIGraphicsBeginImageContext(bounds.size);

        

         CGContextRef context = UIGraphicsGetCurrentContext();

        

         if (orient == UIImageOrientationRight || orient == UIImageOrientationLeft) {

              CGContextScaleCTM(context, -scaleRatio, scaleRatio);

              CGContextTranslateCTM(context, -height, 0);

         }

         else {

              CGContextScaleCTM(context, scaleRatio, -scaleRatio);

              CGContextTranslateCTM(context, 0, -height);

         }

        

         CGContextConcatCTM(context, transform);

        

         CGContextDrawImage(UIGraphicsGetCurrentContext(), CGRectMake(0, 0, width, height), imgRef);

         UIImage *imageCopy = UIGraphicsGetImageFromCurrentImageContext();

         UIGraphicsEndImageContext();

        

         return imageCopy;

}