Well, the round button is not exactly what I'm looking for. What I'm looking is, if I have a star shape with borders, for pictures frame, so the user can upload a picture and it would be mask it to place on the star.
Like creating a sprite with this shader for masking any shape you want, and you can use any sprite with this shader for masking what ever you want, just need to use the same layer. But it could be a different way, this is the way I saw on PixelPlacement.