Clickable infinite menu

most of us have probably seen this by now…

what i’d like to do is create that. but instead of a slider, with arrow buttons. So it would be static and then when an arrow is pressed (left or right) it shifts left or right one image.

So, the buttons and shifting is the easy part, but i’m having trouble making it loop.

How would i go about this?

and how would i go about this WITHOUT using actual pixels, but the width of the buttons as the _x reference(i.e. full screen)?