Material Index:

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This socket just outputs index pass set by user, just like simple Value node.

At first I thought it can play a role with material override, to see passes of real materials. Unfortunately, it doesn't work that way, as it also overrides all passes.

So, what is usecase for it?


1 Answer 1


Maybe a slightly obscure one.. I've used the Material Index for discriminating between materials hit by a forward-cast ray in OSL.

Examples here and here... it's one of the few attributes actually returned by a shader-cast ray, at the moment..

  • 2
    $\begingroup$ Quite a voodoo magic you have here... $\endgroup$
    – Serge L
    Jan 16, 2020 at 19:14

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