cloud under glass impossible?

[Dune]

I can't seem to get clouds to show up under a no shadow plane/sphere with just a glass shader (as seen from above), even with subdiv settings set to 1, and/or refraction set to 1, double sided or single side. Is it impossible, or am I doing something wrong?

[KlausK]

Hi Ulco,
something like this, perhaps?
I used a Displaceable Plane (don`t know if that makes a difference, just a habit).
Decay Distance is set to a really high value in the Glass shader.

CHeers, Klaus

[Dune]

I'll have a look, thanks Klaus!

[Dune]

No, it's not working as expected. What I forgot to mention is that I need just primary cloud. If you turn off secondary, it won't show up at all.

What I'm after is this. But this is tricked by a cloud and a duplicated upside-down heron

[WAS]

Definitely possible cause I put a whole forest, clouds, mountains, into a snow globe.

[Dune]

Well if you can come up with a solution, I'd be happy. The cloud method is very handy as stand-in for missing volumetrics in water, but it needs to be viewable through a reflective transparent plane/lake/sphere. And preferably as sharp as if the plane wasn't there.

[WAS]

I dig out the TGD and see if something is changed

[Tangled-Universe]

If you turn off secondary, it won't show up at all.

Doesn't that make sense, considering that underneath a refractive surface, the cloud only receives secondary rays?

[WAS]

Isn't secondary rays shadow rays? If glass/water isn't producing shadows, you'd think it'd have no interaction.

Or is THAT the actual problem. Glass/water culls shadows.

[WAS]

So it does work, you jut need high quality, and also high jitter (seems counterintuitive) so that the sampler can sample better slices on Y I guess. Though bubbles in ice are often undulating on Y IRL. May be more realistic mixing in a tighter solid high jitter one with a larger low jitter one for the columnar like effect.

[Tangled-Universe]

Secondary rays are all rays except primary. This may sound cheeky perhaps, don't mean to be cheeky, but as soon as a primary ray hits a volume/surface and bounces it undergoes a change and becomes a secondary ray.
At least, that's what I understood of the concept. Basically primary means visible to camera and secondary visible to other rays.
This was why I thought that disabling secondary in the cloud turns the clouds invisible, because it would make the cloud invisible to the refracted rays from the water plane/object.

[WAS]

I guess that would make sense, then. Cause you can turn off the primary, and secondary will produce a primary type effect. Interesting.

[Dune]

It may work that way in TG, but it shouldn't. If you have a sheet of glass in real world and someone is smoking a fat sigar outside your window, you'll see the smoke alright
Too bad if it works that way, so end of experiment.

[Tangled-Universe]

Yes and no Ulco... In your example and probably in general, the smoke you see at the other side of the window, is also secondary rays and beyond. Sun -> atmosphere -> smoke -> glass window -> eye.
I think it's a computational consideration made by Matt.

[Dune]

Well, if you look at it that way, even looking through the lens of your eye would mean everything outside the eye is secondary. It might indeed be a computational compromise.