How do I drag viewport with touch/RMBDown?

I have sprite object "Camera" with behavior "Scroll to" and customized controls for keyboard, and i want to add "drag" function.

I need when RMB is pressed "grab" my Camera, but not by set position to mouse cursor.

Camera still must be centered in viewport no matter where i "grabbed" it.

So im thinking about every tick check difference between camera and cursor and move it together with cursor.

But maybe i can drag viewport?

This is commonly done by saving the previous coordinates of the mouse (store in variables at the end of the tick), comparing that against the current position of the mouse, and moving the camera object the same amount from its previous position.