For depletion type MOSFET that equation remains same. If you are using enhancement type NMOS then you need to use other equation which is kind of complex to solve. See some theory over internet you will be clear.
What I posted earlier is derived from ΔIds/ΔVgs where Ids= Idss(1-vgs/vgsoff)^2.
Ok a very simple solution for plotting. When you open the adda trace window on the right hand side you see matematical functions. you can select traces and make a function plot like Ids\vgs.
select ids->select operator \ -> select vgs