I'm sure it is ok to put the name of a known image in a shader - you're not copying the pixels in any way and the user has to already have a file with that name.  I used to do that, but lately I deliver shaders without any file names in them (use VSS to populate of course) so there's no question about it.

The issue of shader copyright itself is interesting. I have been careful to avoid even the hint of non-originality. For example, I have seen face_off post his favorite settings for Blinn parameters and a couple edge blends to go on it. I have never copied that, even though it looks good to me. I found other (perhaps inferior) ways to deal with skin specular, but they are different.

Now in most cases, I've given obvious and explicit permission for people to use various of my shaders in their products, but never given them permission to re-distribute my shaders as shaders per se. Can I even do that? There are some who argue I cannot.

This is a very interesting intellectual property issue. Can I copyright (Diffuse + Specular) ** gamma? How about can I copyright my conservation of energy trick Diffuse(Diffuse_Value = 1 - Specular) + Specular?

These little tricks they don't seem to be sensible as individual pieces of intellectual property.

But what about my Loom shader that is 140 nodes? Clearly that is in the realm of copyrightable, no?

There seems to be a belief that shaders are math formulas and math formulas cannot be copyrighted. Before anybody brings that up, let me dispel that notion. All computer software expresses math formulas (Boolean algebra and predicate calculus may be unfamiliar to some, but it is math). I have been involved in the development and use of techniques to create provably correct software via mathematical modeling. Just because some math underlies an implementation of something, does not make that implementation freely unprotected.

So - making a GC version of my Loom, by taking my 140 nodes and adding a couple Pow nodes, is that copyright theft or not? I think it is for sure, because it is so freaking big and so impossible to claim there is no intellectual property there.

But what about a RebelMommy skin shader, with say 9 nodes? Is that fair game for you to copy and tart up with GC? 

How about 3 nodes?

Where is the line?

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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)