Bidirectional strange with glossy material

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wasd
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Re: Bidirectional strange with glossy material

Post by wasd » Thu Jul 05, 2018 1:04 am

Triple beam splitter
Beams which go toward object (mesh) are not visible. Those going toward nothing are visible.
"Floor" on the second image has Null material. Mirror 3 is absent, don't mind the number.
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6.png
7.png

Burk
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Re: Bidirectional strange with glossy material

Post by Burk » Thu Jul 05, 2018 6:16 am

@WASD: strangely funny effect! ... and a nice operater, too.

I have now decided to use pure glass for my analysis of the light path. For complex materials, I could get unforeseen effects. Pure glass is better for my purposes. In the example, there is a container with water in it (you can not see it, it's pure glass and water) and the laser comes from the left and is inclined at 42° downwards. You can perfectly see the light path:
LidR -42° nur Glas 500 Samples 32 Minuten.png

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Dade
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Re: Bidirectional strange with glossy material

Post by Dade » Thu Jul 05, 2018 7:26 am

B.Y.O.B. wrote:
Wed Jul 04, 2018 10:41 pm
Try setting the camera volume to the same you used as the world volume.
I'm a bit lost, as this fixed the problem (it should) ?
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wasd
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Re: Bidirectional strange with glossy material

Post by wasd » Thu Jul 05, 2018 7:33 pm

Burk wrote:
Thu Jul 05, 2018 6:16 am
I have now decided to use pure glass for my analysis of the light path. For complex materials, I could get unforeseen effects. Pure glass is better for my purposes. In the example, there is a container with water in it (you can not see it, it's pure glass and water) and the laser comes from the left and is inclined at 42° downwards. You can perfectly see the light path:
Can I have your scene? I can hardly get any effect with volumes and lasers.

wasd
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Re: Bidirectional strange with glossy material

Post by wasd » Thu Jul 05, 2018 8:17 pm

Dade wrote:
Thu Jul 05, 2018 7:26 am
B.Y.O.B. wrote:
Wed Jul 04, 2018 10:41 pm
Try setting the camera volume to the same you used as the world volume.
I'm a bit lost, as this fixed the problem (it should) ?
That did not fixed the problem, but I've found what it is.

Red beam emitter is inside the scattering volume and it behaves funny.
Green beam emitter is outside the volume and behaves well.
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8.png
laser-1.blend
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Burk
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Re: Bidirectional strange with glossy material

Post by Burk » Thu Jul 05, 2018 8:59 pm

wasd wrote:
Thu Jul 05, 2018 7:33 pm
Can I have your scene? I can hardly get any effect with volumes and lasers.
Sure, the scene has the settings of the file "Bidirectional strange with glossy material.blend" which I added to the initial post of this thread.
For the polystyrene material, it's better to set the mix factor of the material to 100 to use pure glass.

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B.Y.O.B.
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Re: Bidirectional strange with glossy material

Post by B.Y.O.B. » Thu Jul 05, 2018 9:47 pm

wasd wrote:
Thu Jul 05, 2018 8:17 pm
Red beam emitter is inside the scattering volume and it behaves funny.
Green beam emitter is outside the volume and behaves well.
Weird behaviour of light beams and volumes is almost always caused by incorrect settings.
We should probably make an in-depth tutorial and/or add warnings or tips to the UI.

You should always check if the interior/exterior volumes of the materials are correct and if the world and camera volume are set up correctly.
The camera volume auto-detection can only work with well-formed geometry and correctly specified interior/exterior volumes.
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wasd
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Re: Bidirectional strange with glossy material

Post by wasd » Thu Jul 05, 2018 11:19 pm

B.Y.O.B. wrote:
Thu Jul 05, 2018 9:47 pm
wasd wrote:
Thu Jul 05, 2018 8:17 pm
Red beam emitter is inside the scattering volume and it behaves funny.
Green beam emitter is outside the volume and behaves well.
Weird behaviour of light beams and volumes is almost always caused by incorrect settings.
We should probably make an in-depth tutorial and/or add warnings or tips to the UI.

You should always check if the interior/exterior volumes of the materials are correct and if the world and camera volume are set up correctly.
The camera volume auto-detection can only work with well-formed geometry and correctly specified interior/exterior volumes.
That doesn't explaing the picture. What is specifically wrong in my setup? The scene is attached to the message. I really can't see anything "wrong" with it. Wrong is - in my opinion - the behaviour of light source that's inside the volume. What is the reason for light to behave that way?

I've found a "fix" for that, though it doesn't look like "right" solution - it is boolean modificator, that is - I put another volume around light source, so it appears outside scattering volume while being within it boundaries.
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B.Y.O.B.
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Re: Bidirectional strange with glossy material

Post by B.Y.O.B. » Fri Jul 06, 2018 12:09 am

wasd wrote:
Thu Jul 05, 2018 11:19 pm
What is specifically wrong in my setup?
I guess you have layers 1 and 2 enabled?
Your mirror material does not have an exterior volume specified (should be set to dust_volume).

There's one thing I don't understand though:
Dade, why can't we specify exterior volumes for light sources?
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Dade
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Re: Bidirectional strange with glossy material

Post by Dade » Fri Jul 06, 2018 7:53 am

B.Y.O.B. wrote:
Fri Jul 06, 2018 12:09 am
Dade, why can't we specify exterior volumes for light sources?
I never tough to the implication, it is not required for Path tracing but it is for BiDir.
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