Here is what I am try to do : 

Imagine my parentView as a book cover. This view has an UIImageView subView.
My problem is that when I flip the parentView for 180° (I open the book), I can still see the UIImageSubview in front of it. I would like the inside of my cover to be just white.

The only idea I came with was hide the UIImageView subview at half of the rotation but I don't think it is really smart.

If you guys can help me,

Thank's

EDIT : I'm actually using 

```
        [UIView animateWithDuration:someDuration animations:^{
             viewToTransform.layer.transform = CATransform3DRotate(transform,
                         (M_PI * 0.999 * -dir), 0.0, 1.0, 0.0);
       }];

```

I'm gonna try to hide when the rotation > PI/2

I'll keep you updated,

```
        [UIView animateWithDuration:someDuration animations:^{
             viewToTransform.layer.transform = CATransform3DRotate(transform,
                         (M_PI * 0.999 * -dir), 0.0, 1.0, 0.0);
             _coverImage.hidden = atan2f(viewToTransform.layer.transform.m12, viewToTransform.layer.transform.m11) > M_PI_2 ? YES : NO;
       }];

```

This doesn't work, cause it hides the subview at the begining of the animation :'(