Rotation transformation with anchor point

gistfile1.m

- (void)rotateView:(UIView *)view
   byRadianDegrees:(CGFloat)radianDegrees
   withAnchorPoint:(CGPoint)relativeAnchorPoint
{
    const CGRect viewBounds = view.bounds;
    const CGPoint anchorPoint = CGPointMake(viewBounds.size.width * relativeAnchorPoint.x, viewBounds.size.height * relativeAnchorPoint.y);

    CGAffineTransform transform = CGAffineTransformIdentity;
    transform = CGAffineTransformTranslate(transform, anchorPoint.x, anchorPoint.y);
    transform = CGAffineTransformRotate(transform, radianDegrees);
    transform = CGAffineTransformTranslate(transform, -anchorPoint.x, -anchorPoint.y); // Translate back
    
    view.transform = transform;
}

- (void)example
{
    [self rotateView:self.view
     byRadianDegrees:(CGFloat)M_PI_2
     withAnchorPoint:CGPointMake(0.5f, 0.0f)];
}