check if shading point is in group

[whodini]

I have primitive groups set up in SOP level, something simple like a box with a voronoi fracture applied with the inside and outside primitive groups. How can I access this primitive group in shop context? I am trying to compare whether or not a shading point belongs to a specified group so I can create a mask.

I can create a attribute at sop level to store the group information on the points and that works, but I want to do this in the shop context because the geometry will be heavily subdivided and displaced and I need the accuracy. Any thoughts? 

[dennis.albus]

You can also use primitive attributes and access them in a shader which should give you the accuracy / sharpness that you expect.

-dennis