How could I create two UIViews and have a swipe gesture to mask one over the other?

Question

So I am trying to mask a UIView over another one which will ideally appear once the swipe gesture has happened. There are a lot of libraries / example code out there I have come across that allow you to slide in a UIView which would appear on top, but it should really be masking over the first view, rather than simply overlaying it. There is most likely a simple elegant solution for this, but so far there is very little I have seen that supports this kind of animation. Image below helps describe the ideal solution:

Answer 1

Gist time: https://gist.github.com/mnmaraes/9529586

The magic happens at:

-(void)scrollViewDidScroll:(UIScrollView *)scrollView
{
    CGFloat xDelta = scrollView.contentOffset.x;

    self.topView.center = CGPointMake(self.topCenterInitialX + xDelta, self.topView.center.y);
}

So to explain better. You have a bottomView and a topView which are exactly the same, except the colors are switched. The topView is contained in a clipperView which is inside a UIScrollView (To handle panning and swiping). So when you scroll right/left the topView moves the opposite direction giving the impression that it is stationary, the excess is then clipped by clipperView . Anyways, it's all there. Let me know if you don't understand something.

Have fun!