Check if visible in UI Mask

I want to check to see if a button is visible by the Mask. If i can see the button do something, else do something else.

Like i have a scrollbar with a mask attached and i want to do something to those objects within the scrollbar that are visible to the user. Is there any way i can do this with the new Unity UI?

Well, I have reached some good utility exist in Unity3d, I hope this helps:

RectTransformUtility.RectangleContainsScreenPoint

Hmm, I think you have to simply calculate that objects Y or X position (depends of your scrollbar) and compare that with object what have mask attached.
Example: you have mask on panel with height 100 (center pos X = 0, Y = 0) that mean top of that mask is Y = 50. Now you only have to check button position, if Y <= 50 && Y >= -50 you are inside mask.