How to add gradient transparency mask in final cut pro x? I want to add a gradient transparency mask so that the front layer will slowly transform into the layer below. Can anybody suggest something?

I'm not talking about transition in time, but transition between layers. This is an example of video I want to get:


I think that in old final cut you could do this with black to white gradient and filters.
I don't know if you ever found a solution, but FCPX does have a Graduated Mask that works.