Imposible to get real translucency on sinngle face models on the new Mtl

[adanmq]

Sure!. Tomorrow from the office I will send you photos of the setup and the sample scene so you can try it out. Thanks a lot!.


PD: The new SSS Thinwalled looks very good so far I need to do more tests on it. The problem I have now is when I try to set up different textures for the front and back of the leaves because it's a very important feature for some plants and also keeps the thin walled SSS. I will take more tests to explore it.


I'm sure the old hack it's not the best solution so I'm willing to see how this new SSS works.


Best!

[vlado]

Ok, thanks. How did you do the different front and back textures before?

Best regards,
Vlado

[adanmq]

Hi!.

Finally i have some time to try the thin walled SSS and works almost identical to the old method and renders much faster. The only problem now is how to set up different albedos for front and back. Using the old method i use 2Side where i can attach 2 Mtl but this can't be done with the SSS Thin Walled, i also try the old MAX top/Bottom but it doesn't work.

I try to make the same material on Corona using the map “Corona Front/Back” and works really well, you can get a very compact and effective material because you no longer need 2 material to get different albedos. I don't want to encourage any corona/vs Vray, I love Vray. It's my favorite render engine of all time, i´m using Corona Material just to show how effective this can be. Unfortunately in Vray I think we don't have something similar. Johan Sundberg, another Vray user recommended me to try to use this OSL (https://github.com/gkmotu/OSL-Shader.../FrontBack.osl) that does exactly that so now i can replicate the same material in Vray ( I attach some Screenshots). The only issue with this is that i don't like the idea of forcing my clients to use an OSL just to get something that i think the engine should be able to do by default so please if you can suggest me the right workflow i will really appreciate it.

I also attached some photos of the camera setup, it's just a very large led panel just behind the leaves and we calibrate exposure so the areas where there is no leaf have a value of 1. Needless to say we process all the textures in a linear way, avoiding any software that introduces variation. In Vray I just put a planar light using 1 as intensity just under the leaf (1mm) to replicate the real setup.

I know it's not perfect because it's almost impossible to capture albedo without part of translucency but this is another topic, i think it's accurate enough. I also attached a photo of one of the plants we have in the office right now that illustrate the effect we want to achieve and before this new Thin Walled SSS the only way we can do it was using the Translucency “trick”.

Thanks again for your time. I really appreciate it!

[vlado]

Ok, thank you so much for the tests! For the different front/back sides, there is the OSL shader for the moment (I thought it was you that posted in the stack group on Facebook ), but I can also think of some other options:
a) Implement a 2-sided map similar to Corona;
b) Make sure that the 2-sided material still works with thin mode as well (in that case the translucency in the 2-sided material should be zero, of course, since the individual materials have their own translucency).

Option a) could be more convenient if you just change one texture, but if you change also the reflection parameters, bump/normal map and other parameters, option b) might be more convenient than plugging a number of 2-sided maps.

Thoughts? We are due to release a hotfix in some days and I can try to slip these in.

Best regards,
Vlado

[adanmq]

Hi!.

Thanks for your reply.

I think the front/back map will be a great addition to have because you can put different glossy or reflect also on the front/back and the setup will look cleaner, but some people may need 2 different Materials so maybe both? xD.

Looking forward to seeing the result. Congratulations again on the new release and thanks for the time you put on the forums.

Best!

[Moriah]

I think having the 2 options would be great, b) for more basic setups a) for more advanced setups as adanmq showed, but it's also useful for other type of materials / tricks.

[kosso_olli]

I'd prefer option B.

[CityWrecker]

Both! a & b would be nice...a seems like an essential tool, b would be nice.

[vlado]

So some progress; in the stable builds the "thin-walled" option is now exposed in the UI of the VRayMtl and also the 2-sided material will work better when there are thin-walled sub-materials (in that case, the translucency value of the 2-sided material itself will be ignored). These will go officially into hotfix 2 for update one, but it will be great to get some feedback in the meantime. As usual, the stable builds are available here:
https://nightlies.chaosgroup.com/mai...ble/stable_5.1

Best regards,
Vlado

[kosso_olli]

Is the thin-walled option also a solution for single sided materials with fog color, ie. the red tinted covers of rear lights for cars?

[^Lele^]

Is the thin-walled option also a solution for single sided materials with fog color, ie. the red tinted covers of rear lights for cars?

Regardless of why you wouldn't be shelling the geo, why would you use fog if they are single-sided, instead of coloring the refraction color?
I mean it literally: what is the effect you're achieving with fog and you can't achieve with refraction color, on non-closed meshes?

[kosso_olli]

Regardless of why you wouldn't be shelling the geo, why would you use fog if they are single-sided, instead of coloring the refraction color?
I mean it literally: what is the effect you're achieving with fog and you can't achieve with refraction color, on non-closed meshes?

You simply can not shell CAD geometry. It will break normals, in all cases.
We are using the refraction color these days, just as you describe. But we would like to use the fog color, for the sake of realism. I thought maybe the thin walled option could act as a "rendertime thickness", so to speak. I remember Mental Ray had a feature similar to this. Hence my question.

[^Lele^]

Ah, i see.
The idea of fog is absorption, so if you don't have a back face for the ray to exit, you simply will get black.
Without the mesh having a back part, as well, fog wouldn't be able to provide for any sense of thickness.
The right way is to tint refraction itself, indeed.

Thin-walled would set IoR to 1.0, which will avoid the usual extreme-lensing of single-faced meshes, and perhaps provide for a visual result more similar to a thinly-shelled mesh.
I'm not sure it's what you were looking for, but i'd love to hear more about that mR feature.

[vlado]

Is the thin-walled option also a solution for single sided materials with fog color, ie. the red tinted covers of rear lights for cars?

The fog color is disabled in thin-walled mode. You can still use the refraction color though.

Best regards,
Vlado

[vlado]

Hmm, actually I can use the fog to emulate some thickness in thin mode... it's not a bad idea, will think about it.

Best regards,
Vlado