Xamarin UIImage rotation - ios

Question

I try to rotate image and save it, when i save image as it, it works, but when i try to rotate the image, rotation works but image is blank.
public UIImage RotateImage (UIImage originalImage, int rotationAngle)
{
UIImage rotatedImage = originalImage;
if (rotationAngle > 0) {
CGSize rotatedSize;
float angle = Convert.ToSingle ((Math.PI / 180) * rotationAngle);
using (UIView rotatedViewBox = new UIView (new CGRect (0, 0, originalImage.Size.Width, originalImage.Size.Height))) {
CGAffineTransform t = CGAffineTransform.MakeRotation (angle);
rotatedViewBox.Transform = t;
rotatedSize = rotatedViewBox.Frame.Size;
UIGraphics.BeginImageContext (rotatedSize);
CGContext context = UIGraphics.GetCurrentContext ();
context.TranslateCTM (rotatedSize.Width / 2, rotatedSize.Height / 2);
context.RotateCTM (angle);
context.ScaleCTM ((nfloat)1.0, -(nfloat)1.0);
context.DrawImage (new CGRect (-originalImage.Size.Width / 2, -originalImage.Size.Height / 2, originalImage.Size.Width, originalImage.Size.Height), originalImage.CGImage);
rotatedImage = UIGraphics.GetImageFromCurrentImageContext ();
UIGraphics.EndImageContext ();
}
}
return rotatedImage;
}
Here is what i get :
Rotated image
And original image :
original image
update : little code change

Answer 1

rotate image using CGContextDrawImage
CGImage imgRef = originalImage.CGImage;
float width = imgRef.Width;
float height = imgRef.Height;
CGAffineTransform transform = CGAffineTransform.MakeIdentity();
RectangleF bounds = new RectangleF(0, 0, width, height);
float angle = Convert.ToSingle((rotationAngle / 180f) * Math.PI);
transform = CGAffineTransform.MakeRotation(angle);
UIGraphics.BeginImageContext(bounds.Size);
CGContext context = UIGraphics.GetCurrentContext();
context.TranslateCTM(width / 2, height / 2);
context.SaveState();
context.ConcatCTM(transform);
context.SaveState();
context.ConcatCTM(CGAffineTransform.MakeScale(1.0f, -1.0f));
context.DrawImage(new RectangleF(-width / 2, -height / 2, width, height), imgRef);
context.RestoreState();
UIImage imageCopy = UIGraphics.GetImageFromCurrentImageContext();
UIGraphics.EndImageContext();