I've also posted this on the V-Ray forums, but since this message board is more active I figured I'd try here, too–

I'm trying to get the toon material to work in Houdini and having no luck. Applying the material itself does nothing. There's also the atmospheric effect, but I can't figure out how to use it–it has no outputs to go into the material, and whether I create it in the mat or out context there's apparently something you have to do to make it work.

I'm new to V-Ray. I also speak Maya, so I tried looking up how to apply the toon material in Maya, thinking it would translate, but all I could find involved pressing a button on the V-Ray shelf that does exist in Maya, but doesn't in Houdini.

Thanks for any help!

In case someone runs across this, I quote “Puffball”'s response in the V-Ray forums, which did the trick for me:

you need to add/make a vray environment node in the OUT context - then add the toon atmospheric effect in there. Then add this node to the environment slot near the top of the vray render rollout. The lines then show up.
In regards to the toon material - it only seems to work correctly with omni lights at the moment.