Hi;

I have some geometry 'beneath' a water surface; I would like to make the water murky, and would like the light to glow beneath the water surface.

I have an emissive shader on my geometry, and have marked it 'treat as light source' via a renderGeometrySettings node. Currently I am using materialX for the water surface; ignoring the 'murky' bit at the moment, simply setting transmission to 1, I can see my geom beneath the water, but the geo renders black. If I bypass the renderGeometrySettings node, it renders emissive. Is this expected? It's not clear to me what further I should adjust to produce a light source that can be refracted.

The 'murky' bit is ideally handled via transmission scattering; the shader says this isn't implemented yet, so I hope to use either a subsurface approach or a volumetric approach...but need to get the light actually illuminating things first.

Thanks!

dhemberg
I have an emissive shader on my geometry, and have marked it 'treat as light source' via a renderGeometrySettings node. Currently I am using materialX for the water surface; ignoring the 'murky' bit at the moment, simply setting transmission to 1, I can see my geom beneath the water, but the geo renders black. If I bypass the renderGeometrySettings node, it renders emissive. Is this expected? It's not clear to me what further I should adjust to produce a light source that can be refracted.

Yes, this is expected. There is an optimization to ignore direct refractions of light sources that have only passed through one refractive surface, since the assumption is that surfaces describe closed forms and light sources would always be outside of the closed surface. This assumption is wrong in your case. It's possible to disable the optimization, but this will make reflections on the surface very noisy. I would just leave 'treat as light source' disabled. The only thing it buys you is more efficient direct illumination of diffuse surfaces when the light source is small.