Posting here just for continuity but otherwise I'm not here.

You are correct - no node will, by itself, give us the coordinate of the camera. However, a small, continuously running background python script does so with ease. I later wrote such a script. I use it to copy the camera coordinates into a User_Defined node in the shader.

Now -- given that you got this far, I'll tell you that 15 nodes is way more than necessary. Here's a hint: in FireFly, vector math and color math are the same damn thing.

The P (rendered point position) node gives a vector. The User_Defined node (for camera position) also gives a vector. How small can you get it using that tip?

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)