issue with glass

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Dade
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Re: issue with glass

Post by Dade » Mon Oct 11, 2021 9:38 am

daros wrote:
Mon Oct 11, 2021 7:12 am
Hi dade, attached is the luxcore scene.
The scene is just all black :?:

Have you tried it ?
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Re: issue with glass

Post by daros » Mon Oct 11, 2021 10:37 am

Slow on my 4 cores PC, but i get this...
glass progress.JPG
You don't get that?

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Dade
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Re: issue with glass

Post by Dade » Mon Oct 11, 2021 10:50 am

Are you using v2.5 ?!?
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Re: issue with glass

Post by daros » Mon Oct 11, 2021 1:00 pm

2.6 Alpha 0. Only on my machine i use the 2.5, sorry.
Anyway under 2.6 Alpha 0 we get this
View 02 600x600.png

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Re: issue with glass

Post by daros » Tue Oct 12, 2021 9:41 am

Hi dade, i upload you the scene again, who knows... We are using the Luxcore you uploaded yesterday.
Attachments
glass (1).zip
(10.89 KiB) Downloaded 8 times

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Dade
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Re: issue with glass

Post by Dade » Tue Oct 12, 2021 10:03 am

It render as black here, if I increase the exposure by 10 times, I start to see something.

Anyway, I loaded the .ply inside Blender to make some sense of it. I'm guessing your problem is: direct light goes trough "shadow transparency" while indirect light doesn't. And your test scene has no direct light at all.

To test this, you point a light source to the glass box (i.e. direct light). Than just flip the light source by 180 degree (i.e. it is pointed to a wall, so the glass box is lighted only by indirect light). Is that the problem ?
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Re: issue with glass

Post by daros » Tue Oct 12, 2021 1:07 pm

No, it's not a simple direct-indirect light problem.

I did some tests regarding this.

In this scene all materials are white matte.

Direct light
glass test direct.png

indirect light (min 8 bounces before reaching glass)
glass test indirect.png

As you see everything is correct.

The problem shows up as soon as the light is bounced by a slightly glossy material.
View 02 600x600.png
The only difference between this scene and the previous ones is that the wall material, which is reverberating the light to our cage, is slightly reflective/glossy.
The luxcore scene of the last picture is exactly the one i sent you today. If you replace the material assigned to the "space" layer with a white matte you get again the correct result.

Thanks a lot for your help dade.

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Re: issue with glass

Post by daros » Tue Oct 12, 2021 2:20 pm

I think it's a problem of caustics. Caustics are not let through a glass with white shadow output.

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Re: issue with glass

Post by daros » Wed Oct 13, 2021 7:56 pm

Hi dade, here are additional tests and comparisons with pure caustics lighting.

Luxcore white shadows
luxcore white shadow_1.jpg
interestingly luxcore is trying to build caustics behind glass

Maxwell white shadows (hidden from global illumination)
maxwell white shadow_1.jpg
interestingly maxwell il able to add a decent amount of light behind the glass.
But this light has not much to do with the original beam you notice if we hide the glass, see last picture.

Luxcore normal shadows
luxcore black shadow_1.jpg
interestingly this rendering is almost identical to the white shadows one, just a bit noisier.

Maxwell normal shadows
maxwell black shadow_1.jpg
It seems that the physically correct Maxwell do not even tries to let the caustics through

Luxcore and Maxwell no glass, same result.
luxcore no glass_1.jpg
The amount of light lost because bad caustichs calculations can be relevant.

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Re: issue with glass

Post by daros » Sat Oct 23, 2021 7:23 pm

Hi dade, can we help somehow to solves this problem? For the moment it would be a great help if, wen the shadow is set to white, the lighting behaves like with the architectural glass posted by sharlybg.

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