I am trying to use a toon shader in Houdini to add a black outline for 3D objects for a book on illustrated knots. I want to preserve the texture on the objects but add the outline. In C4D this is easily done with the sketch and toon shader, and the outline will be there whether objects themselves have the equivalent of a principleshader or a tooncolor shader. (see attachment). In Houdini, the outline seems only to work if the object is given a tooncolor shader, and will not work with a principleshader assigned to the object. (see attachment). Obviously the setup in Houdini is more complicated than in C4D, and I created instances of the objects in Houdini and assigned these instances the outline shader. How do I create an outline yet keep the principle shader on the object? Houdini file attached.

This is how I would like the outline to occur in Houdini (render from C4D with sketch and toon, using substance material)

Playing with this some more in Houdini, it looks like the toon outline shader is pretty buggy, and sometimes it must get cached incorrectly and refuse to outline. One repeatable issue is that for this to work, using an instance for the outline frequently does not work, but if I create a copy of the object - then the outline works even with principle shader assigned to the original object.