3D Lasso on volume

I’m looking for an algorithm or an example for a 3D Lasso on 3D Volume.
I was looking for VtkVolumePicker class, but in the example there is no volume that is input into that class, all I see is picker.Pick(x,y,0,ren).
Can you point to me an algorithm to achieve 3D Lasso rendering on a selected volume using mouse?
I have seen that paraview implement a lasso drawing tool, but I’m lost in the source code don’t know where is it