Houdini BRDF Asset

I’m not sure why illuminance loops fascinate me so. It could be because I never had access to such a cool feature or maybe it leads me to re-visit classic bi-directional reflectance functions (I like the math). Whatever the reason, I decided to create a brdf VOP digital asset so you don’t need to type a lot to get the functions I describe in Part 3 of the Image Plane tutorial series. What’s interesting is that Peter Bowmar has created an asset for this already, but I wanted to learn how to make a digital asset. The interesting is that I didn’t look a Peter’s asset at all so I went about writing the code for it in my own way. It turns out we did it quite different.

One issue that arose though is that the help file and built-in Houdini icons don’t work as described in the Custom VOPs tutorial, so though the help file is written in the asset it doesn’t work right and there are no icons (at least the one I wanted to use).  Another issue is that Houdini (at least in 9.5) has the limitation that you can’t get illuminance loop derived image planes from area lights.

You can find the asset here (also linked to on the tutorial page).

  1. v1: Initial Release
  2. v2: Adding a parameter to rough now works.  The fix causes the rough not to be hidden when diffuse is used, but it doesn’t case any harm keeping it unhidden.
  3. v3: Added string input parameter so you could select the BRDF type after promoting the inputs.
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