new features of 3.08

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Re: new features of 3.08

Postby wallace » Sun Nov 26, 2017 11:30 pm

wallace Sun Nov 26, 2017 11:30 pm
Hi,

So, a summary of the microfacet BRDFs and why they are implemented.

The microfacet BRDFs were originally implemented as part of the OSL materials to support the default microfacet BRDF closures in OSL. They are also useful to have for importing materials from other applications because microfacet models (especially GGX) is quite widely adopted across different applications, so we can get a much similar look in importing materials than our existing BRDF.

The main difference is that these microfacet models try to mimic the roughness of a surface, reconstructing the bumpiness of a surface at the microgeometry level. That is done by doing the BRDF sampling based on the microfacet normal rather than the light direction in the original Octane BRDF, thus enabling us to achieve material properties like "glossy fresnel", which reduces fresnel effect at grazing angle for high roughness surfaces. These models also allow for anisotropic roughness, so we can also simulate anisotropic surface reflectance with these. Both of these things are something we previously did not have.

OK, now the difference between the three microfacet models. The most obvious difference between the microfacet models are the specular highlight lobe, defined by the microfacet NDF (normal distribution function), the roughness controls the lobe size using this NDF, similar to how Octane's existing BRDF works (albeit without NDF). Generally speaking, the Ward BRDF behaves similar to the Beckmann BRDF model, but is considered to be cheaper to evaluate. While GGX is different visually compared to the two and is known for a longer specular tail. Here are some comparison images:

0_2_comparisons.png


At roughness = 0.2, you can see the difference between Ward and Beckmann aren't that big, while GGX's lobe is quite different. GGX's lobe tends to have a longer tail near the end of the specular highlight compared to both Ward and Beckmann BRDF.

0_5_comparisons.png


At roughness = 0.5, the difference between Ward and Beckmann are still very similar, while GGX's lobe remains to be very different from the two. Just as the above case, GGX's specular highlight spreads out more due to the longer tail, thus appears to be brighter in areas around the reflection of the direct light.

To see why this is the case, I have generated a logarithmic graph of GGX's NDF and Beckmann's NDF given their roughness (0.2) with varying angle of surface normal and microfacet normal. You can see that the teal curve (GGX) has a higher NDF value once the angle between surface normal and microfacet normal is greater than 37.5 degrees and never really gets down to 0, unlike the Beckmann's NDF, which goes to 0 before reaching 45 degrees.

0_2_log.png


For the sake of comparison at a different roughness level, here's the same graph but with roughness = 0.5. The main difference here is that both BRDFs now have a less bright but a wider specular highlight lobe, but this does not change the fact that the GGX's specular tail is longer than the Beckmann, as its NDF never goes to 0 in the hemisphere, while Beckmann's specular tail quickly goes to 0 after 45 degrees.

0_5_log.png


So that was a simple explanation of the difference in the microfacet BRDF models, hopefully I have explained it clear enough. I would point those who are interested in a more detailed explanation to the original paper of GGX by Walter et al: https://www.cs.cornell.edu/~srm/publications/EGSR07-btdf.pdf.

Thanks,
Wallace
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Re: new features of 3.08

Postby funk » Mon Nov 27, 2017 3:53 pm

funk Mon Nov 27, 2017 3:53 pm
Thanks for the great explanation Wallace

EDIT: I'm glad none of this went to waste, even though we didn't get OSL materials (with these closures).
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Re: new features of 3.08

Postby rmara » Thu Nov 30, 2017 2:58 am

rmara Thu Nov 30, 2017 2:58 am
Not being an expert i'll wait for the stable release ! but I'm looking forward some of the new possibilities here ! Thanks for the hard work !
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Re: new features of 3.08

Postby fabrizio_s » Fri Dec 01, 2017 12:17 am

fabrizio_s Fri Dec 01, 2017 12:17 am
Fantastic work!
For a long time, I was waiting for the ability to insert a custom LUT.
Will you in the future also insert the contrast?

bye
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Re: new features of 3.08

Postby fatrobotsneedlove » Sat Jan 06, 2018 2:09 am

fatrobotsneedlove Sat Jan 06, 2018 2:09 am
wallace wrote:
grimm wrote:Yay OSL!! This is an awesome update. :D

One question though, on the metallic material, the specular map is the same as a metal map? It's what I usually use to separate out the dialectic parts of the texture from the non-dielectric parts. Both 3D-Coat and Substance call this texture a metal map if it is what I'm thinking it is. :)

Jason


That is correct, specular map is exactly the same as metalness map.


how do we drive the IOR of the diffuse part? If I plug in a roughness texture it only affects the metallic areas.

I tried introducing non-black values to the specular map for the diffuse and got kinda close (attached), but I'm not sure what values to input (or if that even makes any sense).

testmetal.jpg

1.jpg

2.jpg


I just want a simple, accurate workflow I can use with substance painter. One material with 5 or 6 textures.

edit: the all grey ball is a simple glossy material with an ior of 1.5. the checker ball is a metallic material with the iron parts set to full white on the specular map, and the diffuse parts set to .512 grey on the specular map (as 1.5 is 51.2% of 2.93 which is the n value of iron). the results are close-ish. Diffuse color and roughness are identical across both balls. I know that it doesn't make sense logically because n values are all over the place with other metals but it gives me hope that some sort of greyscale ior map can be implemented very soon?? every other render engine can do this. I've been begging for years now, using one workaround after another, always getting subpar results. Every time I asked the answer was "we can solve this once we implement OSL." Well it's here. Can we please get this solved finally? Redshift supported substance painter when it was in Alpha. I'm not asking for the moon here.
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Re: new features of 3.08

Postby fatrobotsneedlove » Tue Jan 09, 2018 4:02 am

fatrobotsneedlove Tue Jan 09, 2018 4:02 am
Can I just get a reply one way or another please?

I have client work starting the 15th and it involves incorporating assets from other freelancers out of substance. Turnaround is too short for me to waste time tweaking their textures. I'll have to use redshift if this is still going to be an issue. I think redshift looks fake as crap. This sucks. What sucks more is I'll have to spend another $500 on another redshift license for my render slave.

I honestly can't believe this is still something I have to beg for. Multiple otoy people, including Goldorak, kept telling me on this very forum that this would get solved with OSL. Well, can we get it solved!?

If I ever need to render super duper, no holds barred, physically accurate copper where the glossy material can't cut it, then I'm set with the new metallic material. I can't imagine any possible scenario that I'll ever have to do that, but whatever. That was a priority for some reason and got it's own material. If I need to work with Substance Painter/Mari/Quixel Ddo/3Dcoat or any other of the super popular PBR painting apps I'm screwed though. What the hell. Give us a PBR material.

Anyway, please let me know if I have to use Redshift to collaborate with the other substance freelancers my clients hired. It will be a little embarrassing as I've been singing Octane's praises with these people, but I won't really have any other option a week from now if I'm gonna deliver on deadline.
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Re: new features of 3.08

Postby Goldorak » Tue Jan 09, 2018 4:33 am

Goldorak Tue Jan 09, 2018 4:33 am
fatrobotsneedlove wrote:Can I just get a reply one way or another please?

I have client work starting the 15th and it involves incorporating assets from other freelancers out of substance. Turnaround is too short for me to waste time tweaking their textures. I'll have to use redshift if this is still going to be an issue. I think redshift looks fake as crap. This sucks. What sucks more is I'll have to spend another $500 on another redshift license for my render slave.

I honestly can't believe this is still something I have to beg for. Multiple otoy people, including Goldorak, kept telling me on this very forum that this would get solved with OSL. Well, can we get it solved!?

If I ever need to render super duper, no holds barred, physically accurate copper where the glossy material can't cut it, then I'm set with the new metallic material. I can't imagine any possible scenario that I'll ever have to do that, but whatever. That was a priority for some reason and got it's own material. If I need to work with Substance Painter/Mari/Quixel Ddo/3Dcoat or any other of the super popular PBR painting apps I'm screwed though. What the hell. Give us a PBR material.

Anyway, please let me know if I have to use Redshift to collaborate with the other substance freelancers my clients hired. It will be a little embarrassing as I've been singing Octane's praises with these people, but I won't really have any other option a week from now if I'm gonna deliver on deadline.


I will escalate. We have one last update to 3.08 before this version (the one you are testing for this) is locked in, and I will see if we have to do anything in that update, or if we can share an template material that does it in the current version.
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Re: new features of 3.08

Postby fatrobotsneedlove » Tue Jan 09, 2018 7:48 pm

fatrobotsneedlove Tue Jan 09, 2018 7:48 pm
Goldorak wrote:
I will escalate. We have one last update to 3.08 before this version (the one you are testing for this) is locked in, and I will see if we have to do anything in that update, or if we can share an template material that does it in the current version.


Excellent! Thank you
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Re: new features of 3.08

Postby Goldorak » Thu Jan 11, 2018 10:20 pm

Goldorak Thu Jan 11, 2018 10:20 pm
fatrobotsneedlove wrote:
Goldorak wrote:
I will escalate. We have one last update to 3.08 before this version (the one you are testing for this) is locked in, and I will see if we have to do anything in that update, or if we can share an template material that does it in the current version.


Excellent! Thank you


We're on this and will look into addressing it before the final update of 3.08 goes out.
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Re: new features of 3.08

Postby fatrobotsneedlove » Thu Jan 11, 2018 10:33 pm

fatrobotsneedlove Thu Jan 11, 2018 10:33 pm
Goldorak wrote:
fatrobotsneedlove wrote:
Goldorak wrote:
I will escalate. We have one last update to 3.08 before this version (the one you are testing for this) is locked in, and I will see if we have to do anything in that update, or if we can share an template material that does it in the current version.


Excellent! Thank you


We're on this and will look into addressing it before the final update of 3.08 goes out.


Fantastic. I really appreciate the quick support.
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