Does image rotation causes loss of pixels?(Core Graphics) - ios

Question

I'm trying to implement image rotation in my code and running a couple of tests. Since I don't know much about the math of how rotation is performed, I just followed some instructions that I'd found on the internet and implemented my code.
I found out that a whole row or column of 1-pixel around the edge is lost everytime I rotate the image. (more than M_PI degree at a time)
This is not obvious when I host the image as a UIImage object, but you can see it when you save the UIImage as a file.
Here's my test code link:
https://github.com/asldkfjwoierjlk/UIImageRotationTest/tree/master
I don't understand that this loss happens. Did I miss something? Or is it something mathematically inevitable?
Here's the rotation method that I implemented if you are interested.
- (UIImage*)rotateImg:(UIImage*)srcImg
{
UIView *rotatedViewBox = [[UIView alloc] initWithFrame:CGRectMake(0,0, srcImg.size.width, srcImg.size.height)];
CGFloat rotationInDegree = ROTATION_DEGREE;
CGAffineTransform t = CGAffineTransformMakeRotation(rotationInDegree);
rotatedViewBox.transform = t;
CGSize rotatedSize = rotatedViewBox.frame.size;
// set opaque option to NO to leave the alpha channel intact.
// Otherwise, there's no point of saving to either png or jpg.
UIGraphicsBeginImageContextWithOptions(rotatedSize, NO, 1.0);
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextTranslateCTM(context, rotatedSize.width / 2.0f, rotatedSize.height / 2.0f);
CGContextRotateCTM(context, rotationInDegree);
[srcImg drawInRect:CGRectMake(-srcImg.size.width / 2.0f, -srcImg.size.height / 2.0f, srcImg.size.width, srcImg.size.height)];
UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return newImage;
}

Answer 1

you can handle the UIImageView as a View. This code works perfectly for me!
CABasicAnimation *rotationAnimation = [CABasicAnimation animationWithKeyPath:#"transform.rotation.z"];
NSNumber *currentAngle = [rotatedViewBox.layer.presentationLayer valueForKeyPath:#"transform.rotation"];
rotationAnimation.fromValue = currentAngle;
rotationAnimation.toValue = #(50*M_PI);
rotationAnimation.duration = 50.0f; // this might be too fast
rotationAnimation.repeatCount = HUGE_VALF; // HUGE_VALF is defined in math.h so import it
[rotatedViewBox.layer addAnimation:rotationAnimation forKey:#"rotationAnimationleft"];
Happy coding!