issue with glass

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daros
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issue with glass

Post by daros » Fri Oct 01, 2021 9:28 pm

Hi, i have again a problem with glass.
Unfortunately i cannot provide the luxcore scene. Hopefully someone knows already this kind of problem and can give me a explaination.

i have this scene with a display which has a glass cage on top. The glass cage is modelled with thickness and with no interesections between surfaces.
I told the glass to not cast shadows. I use this workaround in order to deal with bidir's caustics behind glass problem. Normally it works so i was expeccting to see it work even in this scene. The glass is a white glass with an attenuation at two meters.

This is what i get wen i render the display inside his oroginal space. All materials are simple diffuse white (0.7) exept some light emitting surfaces and the glass itself. As you see the glass keeps being extremely dark.

with glass_1.jpg

here the glass is turned off
noglass_1.jpg

By putting the display in a simplified space the result is correct
isolated_1.jpg

In maxwell by the way i get the correct result even in the original scene:
maxwell glass_1.jpg

So i started to turn off one by one all lights of the scene.

Te only light which makes the glass not cast shadows are the big area lights i have outside the main opening.
View 07 600x330 area_1.jpg

then i turned off everything and added just a few spots with IES data on top of the cage: still the correct result.
View 07 600x330 sopts ies_1.jpg

I don't know how to get any wiser with these tests. In Maxwell, which has the same issues as Luxcore regarding caustics behind the glass, excluding the glass from casting shadows was the solution that helped get relatively credible results because the glass really stopped casting shadows. In Luxcore it seems that under certain conditions the glass continues to cast shadows.
Is it possible that we are doing something wrong? Has anyone else experienced situations like this?
Thanks for any help.

daros
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Re: issue with glass

Post by daros » Sat Oct 02, 2021 8:38 am

here the final results of both maxwell and luxcore

Luxcore:
final lux_1.jpg

Maxwell
final max_1.jpg

At least this is what we are looking for.

Is there an other way to get that result under bidir?
Thanks again for any help.

daros
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Re: issue with glass

Post by daros » Tue Oct 05, 2021 2:24 am

Hi, here i share the geometry.
https://drive.google.com/file/d/1xf4b4k ... sp=sharing

Put whatever emitter to all layers starting with "emitter".
Put a clear glass to all layers starting with "vetro"
Put a white color in shadow output

in lux with bidir the best i get is this
lux glas_1.jpg
But i want to get a clear glass like this which comes from Maxwell
max glas_1.jpg
What i'm doing wrong?

daros
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Re: issue with glass

Post by daros » Tue Oct 05, 2021 3:21 pm

indeed the "white shadow" option seems to block more light as the architectural glass.

Architectural glass:
Bidir_ArchGlass.png

White shadow
Bidir_Glass_Shadow.png

Is there a workaround?

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Sharlybg
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Re: issue with glass

Post by Sharlybg » Tue Oct 05, 2021 3:30 pm

Here I have made the test between Archglass and Normal Glass+White_Shadow color.

Archglass
Bidir_ArchGlass.png
Glass+Shadow color
Bidir_Glass_Shadow.png
Edit Blendfile

https://drive.google.com/file/d/1YzhJdG ... sp=sharing
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daros
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Re: issue with glass

Post by daros » Fri Oct 08, 2021 7:56 am

Hi dade, i need your help!

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Dade
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Re: issue with glass

Post by Dade » Fri Oct 08, 2021 11:58 am

Sharlybg wrote:
Tue Oct 05, 2021 3:30 pm
Here I have made the test between Archglass and Normal Glass+White_Shadow color.

Archglass
Bidir_ArchGlass.png

Glass+Shadow color
Bidir_Glass_Shadow.png

Edit Blendfile

https://drive.google.com/file/d/1YzhJdG ... sp=sharing
You have to reproduce the problem with a cube and, may be, a couple of walls: I can not track a problem in a scene with hundreds of objects. Try to errase everything is not relevant for the problem.
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daros
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Re: issue with glass

Post by daros » Fri Oct 08, 2021 2:35 pm

I isolated the problem! I think It has to do with light bounces on glossy surfaces.
I cannot upload the blender file, only obj, but the scene is very simple to replicate.

materials on obj layers
emitter= light emitting material
glass=clear glass with shadow output set to white
floor = white matte
box = white matte


here the layer "space" has a glossy light gray assigned.
View 02 600x600.png

here the layer "space" has a white matte applied.
View 02 600x600b.png

It seems that the light bounced on the glossy surfaces is handled in a different way by the "shadow" output.
Attachments
black glass.zip
(4.22 KiB) Downloaded 11 times

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Dade
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Re: issue with glass

Post by Dade » Fri Oct 08, 2021 3:21 pm

.obj are useless, the problem is not in the geometry, at least post the LuxCore scene if you can not post the .blend: .cfg, .scn, etc.
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daros
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Re: issue with glass

Post by daros » Mon Oct 11, 2021 7:12 am

Hi dade, attached is the luxcore scene.
Attachments
glass.zip
(10.9 KiB) Downloaded 8 times

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