I have been exploring rendering a human figure in H16 with Mantra using the Skin Shader Core and have run into a few things that I can't figure out.

When I add a GI light from the shelf to a scene it disables the SSS altogether on the shaders. I did not see anything about this behavior in the documentation or when searching the forums. Is GI light and SSS incompatible or is there some parameter or setting that needs to be set to enable them working together in the same scene?

About half of the frame I am rendering is occupied by a figure using the Skin Shader Core. I have noticed that the IPR is slow when it renders the SSS effect but when I render to Mplay it renders much faster than the IPR (7:04 IPR, 2:51 Mplay). Is there a way to make the IPR render in buckets instead of progressively? Also I noticed that when the IPR hits 100% it contains more noise than the Mplay render. Should I not use the IPR at all when working with SSS or are there some parameters or options I need to change?

Hi, if you can post the scene or a simple version that shows the problem, it would be easier to diagnose.

I had a quick look at the skin shader and GI light but didn't have the same issue. I'm not sure if this will help but I posted some info regarding photon maps/noise etc here… https://www.sidefx.com/forum/topic/48451/?page=1#post-218855 [www.sidefx.com]

Regarding buckets instead of progressively, this sounds like you have “preview” checked on the Render View tab…

From the docs page at http://www.sidefx.com/docs/houdini/ref/views/ipr [www.sidefx.com]
“When this option is on, the view will show progressively more detailed previews of the scene as it renders. This makes the final output take a little longer but lets you get a sense of what the image will look like much faster.”

Rob

I did try with Enable Absorption and Nested Dielectrics checked and All Paths selected and no change in the output. I attached a scene and two images, one with the GI Light Enabled checked and one without. When the GI light is enabled the SSS renders a charcoal black.

Thank you so much for pointing out the Preview button for buckets in IPR. That does exactly what I needed and really sped up my work.

Hi, I've found a couple of ways to fix the problem which point to possible causes…

1. I added a new GI light and it worked. (note: you also need to increase the light intensity above 0 to see the effect)
2. I added a new Mantra ROP and it worked. (your original GI light works with it too)

This could mean either..
a) You changed something on one of those two nodes which is causing an issue.
b) It's a bug fixed in a recent build. - I noticed an extra parameter on the new Mantra node I added which suggests we are using different builds. I'm using 16.0.705.

Rob