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Cloud Shader - Terragen VDB export wip.

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Cloud Shader - Terragen VDB export wip.

Unread postby paq » Wed Jun 20, 2018 5:21 pm

Hello,

So Matt from Planetside is working on a .vdb exporter feature for Terragen.
He has just released a first .vdb sample, the full thread is over here :
https://planetside.co.uk/forums/index.p ... #msg250577

I have convert the test scene for Clarisse, taking care of the camera/light position and the scene scaling.
You can download the file here : https://drive.google.com/open?id=1s5vag ... RUxB-MhG7V

It's the same content as on the Terragen thread, I have just added a scene in $PDIR/Public Share - Terragen VDB Tests/vdb_calib_01/scenes :
ClarisseSetup.project

The light calibration is done by eye ball.

ClarisseVsTerragen_Cloud.jpg


I would be really curious what trick can we use to simulate the light scattering the way Terragen do it.
I have tried to play 'just' with the volume shader settings, there is no way I could get anything convincing. For sure there is some physics phenomena that has to be simulate, it almost looks like the volume density need to be inverted, or modulated with Fresnel, or incidence ramp.
Maybe some of you guys have much more experience about volume rendering (for clouds) and could give a shot to it ?

(Hope Mr xilofoton is lurking around 8-) )
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Re: Cloud Shader - Terragen VDB export wip.

Unread postby dboude » Wed Jun 20, 2018 6:09 pm

Hi,

There is a property inside the VDB called Easy Cloud 01. Do you know what it is supposed to drive ?

I approach the render of terragen but not in a physical way, hahahah :mrgreen: Anyway, the terragen render looks very strange, this is brighter inside of the clouds than on the surface...

Terra_Test.jpg

ClarisseSetup_Daims.project
(9.42 KiB) Downloaded 19 times


More tests when I will have time.

Cheers ;)
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Re: Cloud Shader - Terragen VDB export wip.

Unread postby mdkai » Wed Jun 20, 2018 6:34 pm

It looks like the Volume adds brightness on areas inside the volume and also exits them less to the front and more to the side.. but that sure looks more like a trick to add more contrast.

If i remember correctly, Matt told me he was using some approximated GI inside the volume to increase the brightness inside.
You can try to use Ambient Occlusion inside the shader, and hook it in to the emission..
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Re: Cloud Shader - Terragen VDB export wip.

Unread postby paq » Wed Jun 20, 2018 6:54 pm

Hi Démian,

Cool, thanks a lot for giving a try, looks much better that what I have done so far !
Easy Cloud 01 is just the density field.

I think that the 'bright inside' effect is because clouds are supposed to be filled with water droplets, so the scatter is 'boosted' or modulated by some sort of refraction phenomena ? I guess the sun position need also to be considered at some point to fake the effect too.

Xilo post something about it here (: https://scivfx.wordpress.com/tutorials/
And I remember this idea was used long time ago by Dax Pandhi for a (dead) product called Helios, a Vue plugin.
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Re: Cloud Shader - Terragen VDB export wip.

Unread postby mdkai » Wed Jun 20, 2018 7:13 pm

I guess the question is then does the cloudshader in terragen act physically correct by conserving the energy law ?
If yes then you should be able to replicate it...

If not then the question is how does the shader then fake the extra lightboost..

The volume shader in clarisse can mimic these phenomena with the scatter value for forward or backward transmission. But that value is static through the entire medium unless a property is provided to multiply it with.
Something like a SDF value which gives a value how close a point is to the surface of the vdb ...
Something Matt sure can add..otherwise a run with Houdini would help as well.
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Re: Cloud Shader - Terragen VDB export wip.

Unread postby bazuka » Wed Jun 20, 2018 11:20 pm

Here is my solution ;)

attached the 2x bigger render, i can say im satisfied, if u ask me, but if this was a my project i would look the whole env and tweak the cloud to env

im off to bed now ;) i will share a proj file/shader in the morning if anyone is interested

cheers
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clouds_v02.jpg
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Re: Cloud Shader - Terragen VDB export wip.

Unread postby paq » Thu Jun 21, 2018 6:37 pm

Thanks for you input guys !

@mdkai, I'm forwarding your post to Matt :)
It would be indead great if we could have the same look without relying on self emission attribute.
That said it doesn't look that bad for a 5Mb VDB file :)

TerraToC.jpg
Terragen to Clarisse VDB
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Re: Cloud Shader - Terragen VDB export wip.

Unread postby bazuka » Sun Jun 24, 2018 1:56 pm

A small update from a different angle of view ;) and a bit tweaked shader
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cloudsAbove.jpg
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Re: Cloud Shader - Terragen VDB export wip.

Unread postby FilipO » Sun Jun 24, 2018 2:04 pm

5MB VDB :p have anyone tried exporting like 1 GB VDB ?
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Re: Cloud Shader - Terragen VDB export wip.

Unread postby xilofoton » Wed Jul 04, 2018 3:30 pm

Hi Paq,

Not lurking too much here. As you can see on that link, I moved to different directions in terms of software 8-)
So instead of writing an another forum post wrapped tutorial which I did many times here, these are some relevant and cloud optics related steps from my tutorials in 3D Artist mag #116 and #117:

3DArtist116_BasicsOfAtmos_step12-13.jpg


3DArtist_ScienceOfClouds_step08.jpg


Now with some GPU renderers it seems a working solution, but it's a different story and shouldn't be discussed here...

However the last renders in the previous posts seem a good direction.

Cheers ;)
VFX & Cinematic Scientific Visualization Artist, Clarisse Specialist
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