I am a cg student currently learning Houdini and renderman by myself.
I just downloaded a gobo effects rman shader from the following link.

http://www.smartcg.com/tech/cg/books/RfB/download/contents/Ch08_Shading/slideshow.html [smartcg.com]

But it only works properly when I create script files (.rib) in Houdini and then manually type in “ prman xxxx.3.rib” in dos promt. It won't work if I render those sequence directly in Houdini. I mean the projected image would not be seen. Does anyone know why?

Also, can I make this projector shader in Vex builder? I tried it before but whenever I create “illumunate” node, the whole light shader turns black. Can anyone give me a hint?