Hint: (and my opinion)

When you have no control over the number or order of elements applied - you just decide parametric values used with those elements - is it copyrightable? No. Parameter settings for an application or machine (such as an oven's start and end time, and the tempurature) are not copyrightable.

When you have control over the number or order of things applied, and they are applied in great numbers with carefully chosen and exacting precision, is it copyrightable? Yes. Shaders are copyrightable. Whether written as code that calls built-in functions, or assembled from nodes that call those exact same functions doesn't change the nature of the task - to construct an assemblage that performs a specific task.

There is still an open question (IMO) regarding whether the underlying algorithm is protected. If it is, it would be by patent, not copyright. But that isn't the whole task of creativity and certainly I have proven often enough that while others can describe the algorithm they want to do in a shader, I or just a couple other people were the only ones who could show how to do it through a carefully chosen set of nodes and their connections. (Example - how to rotate a 2D image in a Poser shader. How to rotate bricks. Etc. The algorithm is no secret. The shader that implemented that algorithm was novel and was beyond the abilities of 99% of Poser users, even though the pieces are all there for all of us.)

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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)