surfaceLuminance not supported

[ricorio]

Hey,

I wonder if there is any way to build up a shader with vray which shades a object dependent of it's brightness or even better with different colors in direct and indirect light. E.g. the objects is red when directly lit and green when only indirectly lit.

I want to archive something similar to this:
http://www.digitalartform.com/archiv...ticated_c.html

Thanks a lot

Rico

[vlado]

No, I don't think there is currently a way to do that, without some compositing based on the direct lighting and global illumination render elements.

The surface luminance node is not supported on purpose; it is not too hard to implement, but it will cause us a lot of headaches to support properly in all situations.

For your specific case, would it be enough to have a filter color for the GI (for example, in the V-Ray object settings node)?

Best regards,
Vlado

[Koshi]

I also would like to have that node, because there seems to be no alternative way to get that info (tried a couple of other utilities already)

it's very handy for a couple effects, like faking a peachfuzz-layer on skin which is basically a combination of a fresnel and the lightinfo. is there a way to provide this node to customers, even though it wont work properly
in all situations, so we could just give it a try if it work for us?

[vlado]

it's very handy for a couple effects, like faking a peachfuzz-layer on skin which is basically a combination of a fresnel and the lightinfo...

What kind of combination is it? Like I said, I'm reluctant to implement the surface luminance mode, but we may be able to get you a more physically plausible alternative.

Best regards,
Vlado

[Koshi]

in 3d max it would just be a just a multiply of a classic fresnel and a light/shadow falloff...this way you get kinda a rim light effect (or fresnel-border), that is masked by the amount of light...

and I use it to fake the little bit of glow,shine that actually appears on skin sometimes due to lots of very small hairs that scatter the light...especially when backlit, or when actually shading a peach.

I see the problem of implementing it, because there is nothing physical correct about it. it's a workaround to simulate something that would otherwise take forever to render(millions of of small hairs that scatter light...)

or is it something technical due to the render engine of vray? like measuring the amount of light, and then something in the shader-network actually changes the properties(brighter diffuse, or more reflections, or getting transparent)
so that there is more bouncelight or less light afterwards and whatever comes out leads to a loop or to a wrong result? probably it should only take direct light into consideration?

still it could be useful for other effects, especially shader based VFX..., just think of a material that changes any properties according to light intensity. It's just a utility node, not a physical effect.

don't think of it as something in the real world, whether metals nor dielectric materials actually really change their properties when the are light stronger, BUT the material itself might change.

just thinking of a very thin layer of ice or water that is melting or evaporating when I get close with a candle or something like that...I could get this effect with a blend material and surface-luminance as mask,

instead of actually animating a texture. especially for VFX or when creating material for sci-fi this node could be very useful to actual create surfaces that don't look like they are from this world...

[tinuz]

+1, I'd like this supported too,
even if it's simplified and ignored in GI for example and only works with direct lighting.

[vlado]

in 3d max it would just be a just a multiply of a classic fresnel and a light/shadow falloff...this way you get kinda a rim light effect (or fresnel-border), that is masked by the amount of light...

Hm, so how is this different from a diffuse material with a Fresnel texture in the diffuse color slot (probably with the roughness modified a bit)?

Best regards,
Vlado

[vlado]

Here are two images, one is done with a VRayMtl material with a Fresnel falloff map in the diffuse slot; the other is a VRayLightMtl material with a Shadow/light falloff multiplied by a Fresnel falloff. As you see, the results are identical.

Best regards,
Vlado

[Koshi]

yes, the funny thing is I already did the same test and thought I got it.

the problem is it's not possible to use the output of a shader inside a shading network (at least in vray for maya, it's possible in mental ray for maye and so on...).

so I can't use it as mask...I could only layer this shader completely in a VRay Blend Material. and that's not what I wanna use it for. It limits the amount of control I get. I can tweak the fresnel with utility nodes, but I can't tweak or use the diffuse/light output of a VRay material inside maya...

[vlado]

...but I can't tweak or use the diffuse/light output of a VRay material inside maya...

This is true, yes, and there are no immediate plans to support this, even if it is technically possible with the V-Ray SDK. You'd have to write your own BRDF to reflect light as you need it.

The reason the surface luminance is not supported is that it defines the material in a recursive way. F.e. if you plug it into the diffuse slot of a material, when V-Ray attempts to evaluate the material, it first needs to know its diffuse color before any lighting can be computed. However, since you plug a surface luminance node, V-Ray needs to first calculate the lighting in order to compute the color. So you get this weird hen-before-the-egg case. There is a way around it for direct lighting, but when GI jumps in, things become very messy. For this reason, I'm holding it off for as long as possible...

One work-around is to bake the lighting into textures, then you can do with it whatever you need.

Best regards,
Vlado

[Koshi]

I can totally understand this, you're trying to stick to physical limitations/logic as much as possible. Like I said it would be fine if it only works for direct lighting, but there is no immediate need for that. Just would be nice to have, mostly for VFX. not necessary for photoreal renderings.

[Yannick]

Hi Sorry to restart this thread, but is there any alternative to the surface luminance node?
I am looking in a way to have a 2 tones car paint shader.

Thanks,

Yannick

[Hos]

I am also very interested in a way to get the surface luminance of the direct lighting so you can for example remap it with a ramp.
This would be great for the more non realistic rendering.

[ivaylo.ivanov]

surfaceLuminance is supported in the last nightly builds. It works only with direct light by default, and have optional attributes to enable GI. This GI however is decoupled from the normal GI engine and can be used without it.

[matteley]

Hi, has anyone had any GI issues with the latest build in that it takes a long time to build and often crashes specifically when using the V-Ray attributes? Can anyone recommend V-Ray attribute settings to use with this node when rendering with GI?

Thanks