How to swipe transparency? So I am making a video in blender, and it was originally an Adobe After Effects thing:

https://www.youtube.com/watch?v=kkTmU_hJbbw

So I'm using indirect lighting in the world tab, and the emit in the materials tab.
But I cant get the text/circles to disappear after it shows up.
At first I tried the mask option of the transparency option, but that showed up on the floor object.
Then I tried using the Boolean modifier, but when the circle hit the cube used to make it disappear, the cube would get the same material settings, which included the emit property.
So I really need help!
Any advice?
With the boolean on the circle set to 'Difference' I did not find that the circle lost it's material:



Note: Make sure that he circle has some volume so it isn't completely flat. Select all the faces of the circle and use 'Extrude' (E) to give the circle some volume.

The cube that is used as the masking object can then be set to not render by selecting it and pressing Ctrl+H. 

Resulting in: