I have been trying to figure out why I can't seem to get any data in certain AOVs. Those include SSS but also Coat and Diffuse. I assume I'm simply missing something like a wrong export name or I need to change something in the Shader since I haven't found any other posts mentioning this. In the images, I am using the principled shader and Karma CPU. But I have also tested this with CPU and the MaterialX shader. Also rendering to Disk or Mplay doesn't change it either.
Same result, no data in these AOVs.
Is there some trick to it that somebody could share?
Here I simply use a light behind tommy. All the red color is SSS.
That export is looking for a bsdf labeled 'sss', of which there probably isn't any. SSS is typically exported using as 'diffuse transmission' which can be gathered with an lpe such as 'C<TD>.*'
Why the karma hda is setup with an export that has never worked, and missing the correct one, I don't know.
Thank you that worked great! I don't think I ever would've thought to create a "custom" LPE for it as I never had to do that for Mantra. I guess I finally need to read through the LPE/OSL docs.
Weird that they added so many render vars to the Karma HDA that do nothing. I find myself unlocking and diving into the Karma HDA for pretty much every project anyway so I guess at this point I should simply make one myself with the render vars and settings I need.
Edit: Just saw the answer from a dev. Good to hear that this is being looked at. So it's probably just a bug and fixed in a future version.
Yes. Make sure to set both Data Type and Format to color3f:
You can also target only the contributions from a specific light like this:
C<TD>.*'MyLPETag'
BTW this is using the Mtlx Standard Surface. The SSS looks very similar to the Random Walk sss from the Principled Shader running on Karma. I wonder if it is the same. This also makes me wonder if we can expect to have different sss implementations in Mtlx Shaders. Like, does it support having several different kinds, or are we locked into a specific one because all hosts need to be able to implement it? I'm really curious how much flexibility this will allow in the future.
