How to cut off stuff outside a prop perimeter

Hi,

I’ve got a prop with a grey box on it using cam.Start3D2D, but I want to make it scroll up when I look at it, I can do this but I want to cut off the stuff that will soon scroll up.

Where the red line is (the perimeter) I want everything OUTSIDE of that line to be invisible, and only render if it has the prop behind it

I’ve asked a few people and they say use stencils, but I’ve ready through the guides and they don’t cover what I wish to do.

Stencils. How do they not do what you want? You draw a square the size of the area you want to keep into the stencil, then when you draw the content anything outside is cut off.