Dragrigidbody help

Hi I’m very new to unity and need help with the dragrigidbody.js script that comes in the standard assets (my question might be hard to understand). I attached it to my First Person Controller with also comes with the standard assets and then created a box and made it a rigidbody. When playing my game, I have to hover the cursor over the box to drag it around. I would like to make it so that you have to look at the box with the crosshair (or the box has to be in the center of the screen/camera) in order to drag it around like in the games Amnesia: the Dark Descent, Penumbra, or Half life 2.

On lines 20 and 63 of DragRigidbody.js you will see an expression:-

mainCamera.ScreenPointToRay (Input.mousePosition)

If you change this to

mainCamera.ViewportPointToRay(new Vector3(0.5, 0.5, 0))

…then the centre of the screen will become the “hotspot” of the drag.