I have a little more testing to do, but I think that about half of this shader is doing nothing noticeable. I'll demonstrate later. Which means we can eliminate a lot of it.

There are important things it is not doing, and to get those you have to add some specific things that are found in my VSS shader. At which point, you'd end up with my VSS shader, so I'm not sure there's any point in instructing you how to transform the IS shader to the next step if, in the end, it is exactly the same as my VSS shader. :)

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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)