Two well known luxcore problems.

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daros
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Two well known luxcore problems.

Post by daros » Fri Aug 20, 2021 11:25 am

Hi, I just wanted to say that we are really happy with Luxcore and how it performs. For us Luxcore is the best existing commercial and non-commercial rendering engine out there. Our ideal rendering engine doesn't need any technical rendering knowledge and should behave in a linear fashion. With a few small tricks we have managed to offer such an experience to our FELIX users when rendering with Luxcore.
However there are two issues that are problematic:
(a) the roughness limit on metals and glass (the darkening of the material after a certain value). For us this is the only really problematic handicap because we don't know of any workarounds.
b) Caustics almost never work on transparent surfaces.

Apart from these two problems, luxcore is almost perfect. Thanks!
I also think that if these two problems were solved Luxcore could become the preferred rendering engine for many industrial realities, which need accuracy both in the design and in the marketing phase. The rendering speed is relative... the important thing is that the man work is little and must not be too qualified, because man work and knowledge cost much more than machine work.

How complicated to fix are those two problems?

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Sharlybg
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Re: Two well known luxcore problems.

Post by Sharlybg » Fri Aug 20, 2021 11:45 am

b) Caustics almost never work on transparent surfaces.
You maybe need to show some actual image comaprison for understanding.
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daros
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Re: Two well known luxcore problems.

Post by daros » Fri Aug 20, 2021 12:39 pm

You are right.

Typical glass cage
View 01 800x800 shadows_1.jpg

Workaround, glass cage not casting shadows
View 01 800x800.png no shadows_1.jpg

This applies to whatever glass object which stands on a bright surface so that we expect to recognize some slight shadow+causitcs

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B.Y.O.B.
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Re: Two well known luxcore problems.

Post by B.Y.O.B. » Fri Aug 20, 2021 1:39 pm

Those are SDS caustics (specular-diffuse-specular).

LuxCore has three ways of dealing with this problem:
  • The archglass (architectural glass) material can be used, with the downside that it doesn't have refractions, only reflections. So it's only suited for thin glass sheets where refraction wouldn't make a difference anyway. In your scene, it might work.
  • So-called "hybrid glass": use a glass material and set the shadow color to white. It sounds like this is the workaround you currently use? The benefit over archglass is that refractions are visible.
  • PhotonGI with caustic cache enabled, and use regular glass with black shadow color as material. This will compute the correct caustic patterns of the light after getting refracted by the glass, but it's only really necessary when the glass surface is curved or bumpy. The downside is that building the caustics cache costs compute power and takes time to converge and it might take some trial-and-error until you get the settings like lookup radius right for a particular scene.
In general, SDS paths are a hard problem for renderers and there is not yet a simple, pain-free solution for them, as far as I know.

daros
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Re: Two well known luxcore problems.

Post by daros » Fri Aug 20, 2021 1:56 pm

Yes, i imagine those are difficult to solve issues.
But is there no solution of any kind to this very old problem?
I mean a solution with no workarounds and no sacrifices?

And regarding rough metals and glass?

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Dade
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Re: Two well known luxcore problems.

Post by Dade » Sun Aug 22, 2021 7:01 pm

daros wrote:
Fri Aug 20, 2021 1:56 pm
And regarding rough metals and glass?
You need to further elaborate the problem, may be, with the help of a rendering (but more than anything else of a test scene). I'm not sure of what problem are you talking about.
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Sharlybg
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Re: Two well known luxcore problems.

Post by Sharlybg » Mon Aug 23, 2021 9:08 am

(a) the roughness limit on metals and glass (the darkening of the material after a certain value). For us this is the only really problematic handicap because we don't know of any workarounds.


It is this issue : https://forums.luxcorerender.org/viewto ... ass#p27539


b) Caustics almost never work on transparent surfaces.

Normal Bidir used by Felix can't render SDS caustic and there is no way to go for caustics cache in felix as it is an extremelly user friendlly oriented software.
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Dade
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Re: Two well known luxcore problems.

Post by Dade » Mon Aug 23, 2021 9:44 am

Sharlybg wrote:
Mon Aug 23, 2021 9:08 am
It is this issue : https://forums.luxcorerender.org/viewto ... ass#p27539
There is no test scene in the linked post.
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Sharlybg
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Re: Two well known luxcore problems.

Post by Sharlybg » Mon Aug 23, 2021 10:19 am

Dade wrote:
Mon Aug 23, 2021 9:44 am
Sharlybg wrote:
Mon Aug 23, 2021 9:08 am
It is this issue : https://forums.luxcorerender.org/viewto ... ass#p27539
There is no test scene in the linked post.
here you go
RoughBall.blend
(895.41 KiB) Downloaded 13 times
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epilectrolytics
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Re: Two well known luxcore problems.

Post by epilectrolytics » Mon Aug 23, 2021 11:52 am

Sharlybg wrote:
Mon Aug 23, 2021 9:08 am
b) Caustics almost never work on transparent surfaces.
I'd assume that's how it is meant to be, the glass shader emulates an "ideal" material and that would indeed not receive caustics.
In reality glass is never perfect and clean, those imperfections could receive caustics.

Therefore you need to mix a receiving material in, like 90% glass + 10% white matte (slight imperceptible dust layer):
cautran.jpg
Attachments
cautran.blend.zip
(306.25 KiB) Downloaded 11 times

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