Image Clipping Mask

Hi all!

I’m learning Axure at the mo and I can’t work out how to create a ‘clipping mask’ - Something very useful in other softwares. I’m trying to achieve the effect shown in the attached, whereby a click changes the size of the mask. I have shown the two moving shapes in the attached slightly differently so you can see easily what is happening.

https://u9tq8r.axshare.com

There is some delay in the prototype click action working. Please click on the image!
https://u9tq8r.axshare.com

Well, I can’t see a way to make a clipping mask from google, but I think I found a way to achieve the feature I wanted: