Volume bug at opacity = 0?

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FarbigeWelt
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Volume bug at opacity = 0?

Post by FarbigeWelt » Tue Jul 09, 2019 9:29 am

Yesterday, I tried to set up a transparent Disney BRDF material but failed. I also tried to combine it with volumes and failed.
Are both possible and if yes how?

Note
With Lux materials opacity has a different effect than with BRDF materials. The latter disappears completely the first revels internal volume completely if opacity is set to 0.

(BRDF - Bidirectional reflectance distribution function)
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Re: Disney BRDF material

Post by B.Y.O.B. » Tue Jul 09, 2019 9:38 am

Works as expected here.
Can you upload a small scene showing the problem?
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2019-07-09_11-37-01.png
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Re: Disney BRDF material

Post by FarbigeWelt » Wed Jul 10, 2019 11:15 am

B.Y.O.B. wrote:
Tue Jul 09, 2019 9:38 am
Works as expected here.
Can you upload a small scene showing the problem?
Thank you for testing.

Yesterday, I had the same issue with Lux materials, the objects disappeared completely with opacity 0.0.
I wondered about it and looked for a solution. There is an easy one I do not understand. I removed the volume node from the camera. And there it was again, absorption and scattering of homogeneous volume. I am not sure if this is intended. I beg you an explanation.
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Re: Disney BRDF material

Post by B.Y.O.B. » Wed Jul 10, 2019 11:26 am

Your volume definitions are probably malformed. Hard to tell what exactly is wrong without the scene.
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Re: Disney BRDF material

Post by FarbigeWelt » Wed Jul 10, 2019 12:09 pm

B.Y.O.B. wrote:
Wed Jul 10, 2019 11:26 am
Your volume definitions are probably malformed. Hard to tell what exactly is wrong without the scene.
How? Volume definitions seem rather fool proof, aside of freaky values for scattering.
However, after I replaced the CPU fan, worn -out due to frequent high duty cycles, I post the relevant scenes.
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Re: Disney BRDF material

Post by B.Y.O.B. » Wed Jul 10, 2019 12:36 pm

FarbigeWelt wrote:
Wed Jul 10, 2019 12:09 pm
How? Volume definitions seem rather fool proof, aside of freaky values for scattering.
We get scenes with wrong setups all the time.
It's mostly about incoherent interior/exterior volume settings (e.g. ray starts in volume x but surfaces assumes volume y as exterior).
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Re: Disney BRDF material

Post by FarbigeWelt » Wed Jul 10, 2019 2:36 pm

B.Y.O.B. wrote:
Wed Jul 10, 2019 12:36 pm
We get scenes with wrong setups all the time.
It's mostly about incoherent interior/exterior volume settings (e.g. ray starts in volume x but surfaces assumes volume y as exterior).
Actually volumes are nicely described here Volumes and here Camera Panel - Camera Volume

Maybe there is one or are two things missing like volumes should overlap in case of a glass of water and priorities should increase from outest to most inner volume in this case.
A very important point is definitely missing (or I overlooked it by fast reading): Check the surface normals of your objects because internal and external volume depend on surface’s normal direction. (Most of time I get strange behavior/results the normals are the reason.

Depending on Blender operation surface normals get contra intuition directions.

I can only guess my observation is based again in wrongly oriented normals. All other stuff is logical and wrong scene setups have their roots in laziness or ignoring manual pages. RTFM, read the lovely manual. 😀
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Re: Disney BRDF material

Post by FarbigeWelt » Wed Jul 10, 2019 10:05 pm

B.Y.O.B. wrote:
Wed Jul 10, 2019 11:26 am
Your volume definitions are probably malformed. Hard to tell what exactly is wrong without the scene.
Please, have a look at both scenes. Enable view port rendering and spot the difference. Thank you. Because cannot see why object disappears completely when camera volume is set to air clear volume.
Disappearing with Opacity 0.0.zip
Disappearing with Opacity 0.0
(4.35 MiB) Downloaded 4 times
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Volume bug at opacity = 0?

Post by B.Y.O.B. » Thu Jul 11, 2019 8:19 am

I don't see anything wrong with the scene. It might be a bug or a limitation.
When using a null material, it works as expected.
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Re: Volume bug at opacity = 0?

Post by Dade » Thu Jul 11, 2019 6:27 pm

Transparency makes both the surface and the volume not visible: the object is not hit at all. If a ray doesn't hit the surface, it will never enter the interior volume (and then exit).

You should try to mix Disney wit Null, it should work :idea:
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