CGContextClearRect with circle - iphone

Question

I am creating an app in which i am trying to clear the rect of UIImageView. I have achieved this with CGContextClearRect, but the problem is that it is clearing rect in square shape and i want to achieve this effect in round shape.
What i have tried so far:
UITouch *touch2 = [touches anyObject];
CGPoint point = [touch2 locationInView:img];
UIGraphicsBeginImageContextWithOptions(img.bounds.size, NO, 0.0f);
[img.image drawInRect:CGRectMake(0, 0, img.frame.size.width, img.frame.size.height) blendMode:kCGBlendModeNormal alpha:1.0];
CGContextRef context = UIGraphicsGetCurrentContext();
CGRect cirleRect = CGRectMake(point.x, point.y, 40, 40);
CGContextAddArc(context, 50, 50, 50, 0.0, 2*M_PI, 0);
CGContextClip(context);
CGContextClearRect(context,cirleRect);
//CGContextClearRect(context, CGRectMake(point.x, point.y, 30, 30));
img.image =UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();

Answer 1

I'm not sure exactly what you are doing, but your clipping arc isn't being created correctly. You are creating it at a fixed position which is why it doesn't really work - except it does, if you click in the top left corner.
If you want to see it working try this:
- (IBAction)clearCircle:(UITapGestureRecognizer *)sender {
UIImageView *imageView = self.imageView;
UIImage *currentImage = imageView.image;
CGSize imageViewSize = imageView.bounds.size;
CGFloat rectWidth = 40.0f;
CGFloat rectHeight = 40.0f;
CGPoint touchPoint = [sender locationInView:imageView];
UIGraphicsBeginImageContextWithOptions(imageViewSize, YES, 0.0f);
CGContextRef ctx = UIGraphicsGetCurrentContext();
[currentImage drawAtPoint:CGPointZero];
CGRect clippingEllipseRect = CGRectMake(touchPoint.x - rectWidth / 2, touchPoint.y - rectHeight / 2, rectWidth, rectHeight);
CGContextAddEllipseInRect(ctx, clippingEllipseRect);
CGContextClip(ctx);
CGContextClearRect(ctx, clippingEllipseRect);
imageView.image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
}
Which creates a clipping ellipse (in this case a circle) in the rect 40 x 40 centred at the touch point.
You can see this in an example project on Bitbucket which you can download for yourself to try