Author Topic: PBR tuning of the reflectivity ability  (Read 21670 times)

2014-09-09, 22:07:31
Reply #15

romullus

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I don't get it. It doesn't add any bit of funcionality nor eases workflow, just clutters CoronaMtl UI. I like very much Disney's PBR model, that Juraj Talcik talking about, but your concept isn't anything about it. Is it really needed?
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2014-09-09, 22:10:45
Reply #16

Juraj

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Well, now we're going somewhere, cheers :- ).

But I don't find that solution to be most fortunate, I know this thread requested single value (just inverting control choice), but that was largely taken out of context and out of misunderstanding imho.
Mixing something like that, even in crude form shows something that is very confusing and not set right. It just swaps grazing angle for facing angle, which is small subset of the whole philosophy only and not even the main idea.
The crucial core is in metalness/roughness combination, something that can work even with IOR input, grazing reflectivity intact. The other things are just matter of preference/choice.

I would follow quite strictly the Disney model, because it's laid out quite excellently and is very cohesive.

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2014-09-09, 22:58:47
Reply #17

Adanmq

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Hi.

But if you don´t fully change the material mode in order to be more like the alternative Juraj is talking about, i think adding extra parameters to the actual one can confuse some people.

Lets say you have a material using 1.5 IOR (0.04 - 4%refl) and you want 0.08 - 8%, you can use 1.79 IOR to get it. So actually you can easily control reflectivity this way. Now you can control max refl using the level mult and map and minimum using IOR or custom curve.

I reproduce this experiment in 3DStudio MAX: http://therenderblog.com/custom-fresnel-curves-in-maya/ Not the part of copy the curve, because i just use the refractiveindex.info data as a reference or starting point.

IOR 1.5


IOR 1.79



I don´t if this is what you mean or i´m missing something.
« Last Edit: 2014-09-09, 23:04:06 by Adanmq »

2014-09-09, 23:20:11
Reply #18

Stanislav_But

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Of course we can and we do it so now! But why will not to do it more correctly? People look for IOR of reflection in web and they cannot find - because it is not   anywhere and never been. But there is very much information about reflectivity of materials

The Disney model of BRDF is very interesting. I not read yet in details about it.
Here is the explaining with the samples: http://www.disneyanimation.com/technology/brdf.html

2014-09-09, 23:25:07
Reply #19

Juraj

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Yeah, one can uses curves, although it does sort of make sense only to do so if you want very precise metals that exhibit curve that differ strongly from one you can get with simple IOR.
Some have retro-grazing reflections,etc.. but, in everyday job, does not make big difference.

The issue with this is that it's overall measured reflectivity for given material, but it should be affected by 'roughness' in slightly different way than glossiness does, it should both spread but also loose its influence on the surface, moving towards lambertian shader on fully rough end of spectrum (100perc. rough= 0. glossy)
I am not actually sure what really happens in that relationship or how to describe it. It just behaves better, more natural.

In roughness model, you have reflectivity always, for every material in scene and in correct amount, simply by eye-balling its rough/glossy properties, something very easy for every artist to do. That's the key point I think, at least from my limited understanding.
I think my stance is often misrepresented here is pursue of utmost photorealness or arbitrary physical corectness for sake of it (and some really go after that). Not really, it's not what I strife for. I just wish to achieve photorealistic results in easiest, and most artist-friendly manner possible. I don't like the "just eye-ball everything in uncontrolled environment".
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2014-09-10, 00:09:00
Reply #20

Ludvik Koutny

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So...

Custom curve is easily doable using falloff node

The same node also allows non-physical artistic control of fresnel

Fresnel IOR in CoronaMTL allows for same PBR control, just in opposite direction

PBR mode would allow the same thing in the direction of control you request

Reflection level allows another layer of non physical fine tuning

So currently, there is all flexibility needed, and it's just about reducing it to guide people to create more physically based materials.


One of the ideas on the table is to create layering system, like in Blender Cycles, Octane, or what nVidia does with MILA. Of course, Corona implementation would be on par with Corona usability standard, so idea is to take best of all there is currently on the market, and wrap it into nice polished simple to use solution.

It would have following benefits:

CoronaMTL would stay uncluttered, and friendly for those who need to create quick simple materials. Even for those who create complex materials, it would serve as a material for objects out of area of interest. I doubt many would want to spent time creating layered shaders for distant background objects.

Since there would be basic components like diffuse, specular, scatter, refraction... every node could contain a bit more, and there could be nodes for specific worfklow. There could be for example legacy specular node with same system CoronaMTL has now, and PRB specular with roughness instead of glossiness, inverse Fresnel control, and BRDF picker to pick between ashikhmin and GGX.

GGX is probably necessary for the inverse control Fresnel model, because inverse control implies that max. reflectivity value is always 1. If you think about for example dusty old worn asphalt road, you can hardly imagine such material having maximal reflectivity at grazing angles. This is what GGX solves, because it's a microfacet model that takes self shadowing (and therefore light attenuation on the surface) into account so reflection would correctly dim with roughness.

It would of course give corona so much demanded layering system. There will of course be legacy style multilayer blend material too.

It would bring Corona closer on the same page with new PBR standards.

It would make it probably easier to implement experimental shading models, as when material is separated to basic shading elements, UI of individual nodes is a lot simpler, and therefore we can fit more things in without making it appear overwhelming.

BTW if anyone could get a screenshot of how Disney material UI looks like (the one their artists use day to day), it would help a lot.

Non the less, it's not gonna happen too soon, as there are other a lot more pressing things on the priority list.

2014-09-10, 00:16:31
Reply #21

Adanmq

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2014-09-10, 00:21:39
Reply #22

Juraj

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...

I finally agree with everything you said ;- ) All points.



Non the less, it's not gonna happen too soon, as there are other a lot more pressing things on the priority list.

Probably no issue for anyone. But lot to look for !



If anyone could get a screenshot of how Disney material UI looks like (the one their artists use day to day), it would help a lot.



Would love to see this too actually. Unreal engine 4 has a simplified version of it regarding attributes (but quite complex regarding input, 1/2/3/4 vectors in every parameter which is..interesting)
« Last Edit: 2014-09-10, 00:25:53 by Juraj_Talcik »
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2014-09-10, 00:40:57
Reply #23

romullus

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So...

[...]

Non the less, it's not gonna happen too soon, as there are other a lot more pressing things on the priority list.

If it's actuall plan for Corona's future developement and not just a dream of just another user, then i couldn't be hapier with it.
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2014-09-10, 00:47:05
Reply #24

Ludvik Koutny

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So...

[...]

Non the less, it's not gonna happen too soon, as there are other a lot more pressing things on the priority list.

If it's actuall plan for Corona's future developement and not just a dream of just another user, then i couldn't be hapier with it.

Consider it just a dream for now :)

2014-09-10, 01:37:50
Reply #25

Stanislav_But

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Even if it will happen not too soon in any case I'm happy we all have understood one another

I will be waiting for the best PBR Corons Renderer with eagerly (;
I will try too to find screenshot of how Disney material UI looks like if it was posted in web

here is something interesting: http://www.alexandre-pestana.com/physically-based-shading-metallic-specular-workflows/
and continue in: http://www.alexandre-pestana.com/disney-principled-brdf-implementation/

2014-09-10, 09:38:36
Reply #26

Ondra

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PBR will not happen before the commercial release (end of the year). But in long term, we would be happy to move users towards more physically based shading, so we are open to it.
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2014-09-10, 14:20:34
Reply #27

Juraj

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 http://www.alexandre-pestana.com/physically-based-shading-metallic-specular-workflows/
and continue in: http://www.alexandre-pestana.com/disney-principled-brdf-implementation/

These are really good ! And describe the benefits well.

"Using only these inputs you can’t change the specular value of your dielectric materials, but you can add another one, in the range 0.017 – 0.063, remapped to 0 – 1 to control this value."

It gives you a lot of 0-1 parameters, but at any given combination, result is always correct from real-world stand point reference.
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2014-09-13, 22:12:22
Reply #29

Juraj

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Seen the marmoset guide quite time ago, love their example :- ) Wish I had such texturing skillz...

http://www.rorydriscoll.com/2013/11/22/physically-based-shading/

Interesting picture comparison, shows how Disney's implementation (not controls now, but, algorithms) matches quite closely scanned MERL data, to much greater extent than Blinn/Phong.



Even better is the large comment from Exil, which goes into difference between 'physically-correct' and 'physically-based' and implementations into practice.
« Last Edit: 2014-09-13, 22:19:41 by Juraj_Talcik »
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