animated Image visibilty changer

I had an Idea For a UI Animation I dont know how to pull off…
the grey circle (red edge) has to make elements “visible” as it grows bigger.
everything on the side of the red edge should be visilbe, but everything on the right side, that is not covered with the circle Image should be invisible.
I hope someone can help me with this!

(p.s I have no clue what Title would describe this problem perfectly)