volume light difference

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DEBIHOOD
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volume light difference

Post by DEBIHOOD »

I have some minor problems with volumetric light in different rendering engines, as for me the result that gives the path more predictable and correct, but here it looks strange in the bidir, and I didn’t need it to look that way, tell me, it looks normal , or did I make some kind of mistake ?, I just think that it shouldn't look like that.I also want to ask why the auto detect camera volume function is needed, it's just not in cycles, and it has never been useful to me in cycles.
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path engine
path engine
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bidir engine
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B.Y.O.B.
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Re: volume light difference

Post by B.Y.O.B. »

Thanks for your report.
Please upload the scene so we can check the problem more easily.
DEBIHOOD wrote: Mon Jun 17, 2019 9:00 pm I also want to ask why the auto detect camera volume function is needed
The camera rays have to start in the correct volume.
The auto detect function shoots one ray into the middle of the image. This ray hits an object, and the camera uses the exterior volume of the material it hit as its exterior camera volume. For this to work, all materials need to have the correct interior/exterior volumes set.
DEBIHOOD
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Re: volume light difference

Post by DEBIHOOD »

B.Y.O.B. wrote: Mon Jun 17, 2019 9:09 pm Thanks for your report.
Please upload the scene so we can check the problem more easily.
okay :D
B.Y.O.B. wrote: Mon Jun 17, 2019 9:09 pm The camera rays have to start in the correct volume.
The auto detect function shoots one ray into the middle of the image. This ray hits an object, and the camera uses the exterior volume of the material it hit as its exterior camera volume. For this to work, all materials need to have the correct interior/exterior volumes set.
a little understood the essence of the function - for the correct display of the volume, thanks for the explanation, it just sounds too difficult for me :lol: :lol: :lol: :lol: )0))
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B.Y.O.B.
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Re: volume light difference

Post by B.Y.O.B. »

I think the problem is that the rays of the spot light have no volume set.
Volume settings for lights were not implemented yet unfortunately. This can be considered a missing feature in LuxCore.

In your scene, there are two ways to work around this:
- move the spot light outside of the "fog cube" - this way, the light is in an area without volume, which matches its missing exterior volume
- use your fog volume as world volume (in the world properties). This assigns the fog volume to everything where no volume is set, even to lights
DEBIHOOD
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Re: volume light difference

Post by DEBIHOOD »

B.Y.O.B. wrote: Mon Jun 17, 2019 9:31 pm I think the problem is that the rays of the spot light have no volume set.
Volume settings for lights were not implemented yet unfortunately. This can be considered a missing feature in LuxCore.
Oh, first the volume settings for the camera, now for the light sources, now I understood that I didn’t understand anything :lol: :lol: :lol:
I understand that this feature will be necessary only for bidir, because in the path everything works fine and without any problems *maybe I'm wrong*
B.Y.O.B. wrote: Mon Jun 17, 2019 9:31 pm In your scene, there are two ways to work around this:
- move the spot light outside of the "fog cube" - this way, the light is in an area without volume, which matches its missing exterior volume
- use your fog volume as world volume (in the world properties). This assigns the fog volume to everything where no volume is set, even to lights
Of course it works, but some people will probably need to place the light inside the fog box using bidir, and they just can't do it because there are some limitations with this :cry:
What do you think, when this feature may appear? I don’t need it right now, but maybe it will be necessary in the future for me and other users like me :)
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Re: volume light difference

Post by B.Y.O.B. »

I discovered that in this scene, it also works to assign the fog as exterior volume on the suzanne and ground plane objects (had to create a material for them first, of course).
Apparently, bidir is not as tolerant as path regarding malformed volume setups.
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sdfsdf.jpg
DEBIHOOD
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Re: volume light difference

Post by DEBIHOOD »

B.Y.O.B. wrote: Tue Jun 18, 2019 1:18 am I discovered that in this scene, it also works to assign the fog as exterior volume on the suzanne and ground plane objects (had to create a material for them first, of course).
Apparently, bidir is not as tolerant as path regarding malformed volume setups.
Well, now I’ve just made sure that I’m completely confused with the luxcore volume setting, too little information about setting them up, please, if you can, give a link on how to use volume in luxcore, what is the difference between interior volume and exterior volume, in the wiki, I did not find any understandable information about them, just a couple of words, and yet why luxcore does not have a single way out for a volume, such as in cycles or eevee ???? :?:
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Re: volume light difference

Post by B.Y.O.B. »

Yes, the documentation is lacking on this topic.

A material describes the properties of a surface, while a volume describes the properties of the "empty space" between surfaces. The exterior of a mesh is where its normal points to, the interior is the opposite side.

"No volume" means that a clean volume with no absorption and IOR = 1 is assumed. When a ray hits a material, it will check from which side it hit the material (interior or exterior, depending on the normal). Then it will either bounce off or pass through the material and use the interior/exterior volumes it found on the material for its evaluation.

Usually, you only have to set the interior volume of a material if it is transparent in some way - otherwise, rays can never pass through its interior volume. Setting the exterior volume is only important if the object is inside another volume, like in your fog scene.
DEBIHOOD wrote: Tue Jun 18, 2019 7:42 am why luxcore does not have a single way out for a volume, such as in cycles or eevee ????
You mean in the material output node?
It looks like in Cycles you can only set the interior volume of a material. I do not know how they determine the exterior volume and if that is always going to be correct.
In LuxCore, you can do any crazy intersection of multiple volumes and still have it working correctly because you can specify the interior and exterior volumes of each surface. But maybe we could automate this a bit more, not sure.

I made an illustration about the problem in your scene, hope it helps.
The rays are fired from the light, since the light tracing is the problematic part in your scene.
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incorrect volume setup (missing exterior volume on the suzanne material)
incorrect volume setup (missing exterior volume on the suzanne material)
correct volume setup
correct volume setup
DEBIHOOD
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Re: volume light difference

Post by DEBIHOOD »

B.Y.O.B. wrote: Tue Jun 18, 2019 9:12 am
DEBIHOOD wrote: Tue Jun 18, 2019 7:42 am why luxcore does not have a single way out for a volume, such as in cycles or eevee ????
You mean in the material output node?
Yep :)
B.Y.O.B. wrote: Tue Jun 18, 2019 9:12 am Yes, the documentation is lacking on this topic.

A material describes the properties of a surface, while a volume describes the properties of the "empty space" between surfaces. The exterior of a mesh is where its normal points to, the interior is the opposite side.

"No volume" means that a clean volume with no absorption and IOR = 1 is assumed. When a ray hits a material, it will check from which side it hit the material (interior or exterior, depending on the normal). Then it will either bounce off or pass through the material and use the interior/exterior volumes it found on the material for its evaluation.

Usually, you only have to set the interior volume of a material if it is transparent in some way - otherwise, rays can never pass through its interior volume. Setting the exterior volume is only important if the object is inside another volume, like in your fog scene.
Thanks for explaining this, now I understand about what I need to adjust the volume to display correctly, but now there is a need to add pointer to exterior for all objects, and what if there are thousands of objects in the scene, they all need to change the material? or can i just add world volume? :o
material for plane and suzanne
material for plane and suzanne
I did everything as you said and everything began to display correctly
after properly configured volumes
after properly configured volumes
there is also another question that caused me difficulties, how to put the smoke in the volume? when I try to make it becomes visible the edge of the domain
volume + smoke.png
B.Y.O.B. wrote: Tue Jun 18, 2019 9:12 am I made an illustration about the problem in your scene, hope it helps.
The rays are fired from the light, since the light tracing is the problematic part in your scene.
Thank you so much for the illustrations, they helped me understand the work of volumes in luxcore :D
igmar75
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Re: volume light difference

Post by igmar75 »

B.Y.O.B. wrote: Tue Jun 18, 2019 9:12 am Yes, the documentation is lacking on this topic.
...

I made an illustration about the problem in your scene, hope it helps.
The rays are fired from the light, since the light tracing is the problematic part in your scene.
Thank you for this explanation. For sure, we need a better documentation about volumes in luxrendercore
Ps. The attached images and files are no more available.. Is there a way to reach them?

Thanks!
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