VRayMtl | Translucency

[JonasNöll]

Hi,

I'm enjoying update 1. I was very excited to see that there is a new way of how the translucency/transparency for VRayMtl is being handled. But I have some questions:

1. If Translucency is set to None then there is access to Fog Color and Depth. Do I understand correclty that there is no more option to control the fog bias? Before you could customize the transition gradient controlling the fog bias.
2. In both SSS and Volumetric its very easy to get really strange colors which always seem to be the oposite of whatever color you wanted to chose. So for example if choosing a reddish fog color / scatter radius you will get a lot of cyan colors. Is that something expected / physically accurate? Its a bit frustrating from an artist perspective
3. RefractionColor should be set to white and DiffuseColor to black for Volumetric/SSS mode or what is the intented settings to work phyiscally accurate?
4, In the VRayDocs for VRayMtl it states that Volumetric Mode takes RefractionColor/Glossiness into account while SSS does not. But RefractionColor/Glossiness also seem to influence the result in SSS Mode
5. The SSS amount set to 1 seems to create weird results/colors for most materials, while settings around 0.1 or so seem to give much more predictable results. Is there a reason why 1 is the default or is there any problem to use lower SSS amount values?
6. The Docs state that the GI bounces need to be set to at least 16 (!) in order to work. That means any scene using the new translucency has to set the BruteForceGI bounces to 16 at least? How about in IPR mode in the VFB?


Thanks for the clarification!

[vlado]

If Translucency is set to None then there is access to Fog Color and Depth. Do I understand correclty that there is no more option to control the fog bias? Before you could customize the transition gradient controlling the fog bias.

The option is hidden from the UI and only accessible from MaxScript. It is not physically accurate and is generally not available in any other renderer. You can still change it from MaxScript if you need it.

In both SSS and Volumetric its very easy to get really strange colors which always seem to be the oposite of whatever color you wanted to chose. So for example if choosing a reddish fog color / scatter radius you will get a lot of cyan colors. Is that something expected / physically accurate? Its a bit frustrating from an artist perspective.

This is also what you get in other physically based SSS materials like VRayFastSSS2, VRayALMtl, VRayScatterVolume and also other renderers. For the volumetric mode I generally leave the fog color to grey, and use only the scatter color; this corresponds to many materials that represent stuff diluted in water, like orange juice etc. For SSS mode, the SSS color generally represents the overall surface color.

RefractionColor should be set to white and DiffuseColor to black for Volumetric/SSS mode or what is the intented settings to work phyiscally accurate?

It depends on what you want to do, but generally black diffuse and white refraction work well for volumetric mode. For SSS mode, keep the refraction to black. In any case, you can still adjust any of those if needed; this is still physically accurate. For example, in volumetric mode, you can leave the fog/scatter color to some mid-gray value and instead control the effect from the refraction color only.

In the VRayDocs for VRayMtl it states that Volumetric Mode takes RefractionColor/Glossiness into account while SSS does not. But RefractionColor/Glossiness also seem to influence the result in SSS Mode

The refraction works differently in the two modes; in volumetric mode, you need refraction to see inside the material. In SSS mode, refraction will reduce the SSS effect and replace it with pure refraction.

The SSS amount set to 1 seems to create weird results/colors for most materials, while settings around 0.1 or so seem to give much more predictable results. Is there a reason why 1 is the default or is there any problem to use lower SSS amount values?

Can you show me? The default works fine for most of what I needed. I have some examples of different combinations here: https://docs.google.com/document/d/1...ort?format=pdf

The Docs state that the GI bounces need to be set to at least 16 (!) in order to work. That means any scene using the new translucency has to set the BruteForceGI bounces to 16 at least? How about in IPR mode in the VFB?

You can use the light cache just fine. The PDF above has an example of different GI settings. IPR should work fine.

Let me know if you have other questions. You will get the hang of it pretty quickly.

Best regards,
Vlado

[fixeighted]

Also, (as others have said they still want the old behaviour), the old settings are still there in shaders that use them, as I just discovered.
Just in case we don't want to go about converting absolutely everything that used old settings....which is handy.
Personally, I would link that pdf in the docs page, as it gives more information/examples

Extra question: What is the scale parameter relative to? In your example you set it to 15cm....

EDIT: Don't worry...got it

[JonasNöll]

Great, thanks for the replies for each point!
I will double check if the things you mentioned will elminate some of my issues and go through the PDF as well.
As for example I thought SSS mode also requires RefractionColor to anything else BUT black, and also the thing you mentioned with the FogColor as grey for Volumetric Mode.
If I still encounter issues I will update this thread here with some pictures!

Best regards!

[JonasNöll]

Ok, so I think I know where my confusion came from:

There is a problem with the IPR rendering that it doesn't seem to update the shader correctly when switching between the different modes.
For example I start with a standard grey material, start IPR and dial in translucency and put some settings. Somehow the result looks always very strange and behaves not really predictable.
But if I stop the rendering and start it again, then there is a huge change and it behaves more like one would expect.
You can see the pictures attached
1. Shader after dialing in translucency starting from a grey default shader
2. Exactly same shader after stopping and reintializing the IPR again.

Is that something that is only on my machine?

[fixeighted]

It seems to work as expected here, switching back and forth between sss/volumetric...changing stuff etc.
In fact I can't even get that dark red result with those settings at all....I have to tint it manually with scatter colour, which is odd.

[JonasNöll]

OK strange, did you start from newly created standard grey vray mtl? For me once i switch to translucency everything seems wrong and only when I reinitalize the renderer it seems correct.

[fixeighted]

Yeah, I can't find any way to get incorrect differences as you are getting....with just that same procedure.

Maybe save a scene at the point it occurs and looks wrong. Post that and I'll open it and see how it renders here...

[JonasNöll]

Update: For me the problem just happens with newly created vray materials. Once the material was switched one time already to the different translucency modes it seems fine.
But whenever I create a new V-Ray Mtl (In Classic Material Editor select one default swatch, click on "Standard (Legacy) to create a new material -> VRayMtl) I need to reinitialize the VFB for it to render correctly after switching to the new translucency modes.
It's not a huge deal but something to be aware of because you might dial in several settings and are ok with the result and then once you restart the rendering it looks completely different.

[fixeighted]

That is certainly a different step which I can't repeat, as I have things set so the mat editor is already populated with vray mats.

[JonasNöll]

I just checked, it also happens if I create a new VRayMtl on top of another VRayMtl. So the legacy materials are not a necessity.
So for me it happens with every newly create VRayMtl, and then once it was "initialized" with the translucency it works...

[fixeighted]

Weird indeed...just tried again and can't replicate that at all.
One thing I did notice is that the SSS amount does not work with volumetric type, only SSS.

[vlado]

I can easily reproduce the IPR issue and I'm looking into it; thanks for reporting it!

fixeighted - the SSS amount does work in volumetric mode, see the examples here: https://docs.google.com/document/d/1...ort?format=pdf

Best regards,
Vlado

[fixeighted]

lol...apologies....I think the side effects from my Covid jab were worse than I thought.
I recreated this over and over so many times the other day and couldn't get it to behave weirdly.
I just tried it again and of course it now does exactly that.
I think I may have been using gpu all the time or was switching to try multiple things....which is why also the other options were greyed out

[Ruairi Robinson]

The option is hidden from the UI and only accessible from MaxScript. It is not physically accurate and is generally not available in any other renderer. You can still change it from MaxScript if you need it.

Vlado

Is there any chance you could bring this back? it may not be physically accurate but it is a very useful cheat, I had to open an old copy of max (luckily still installed on my old machine) to edit the params and save individual objects out to use this.