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GGX BRDF - Metals or More?
show user profile  9krausec
Hey guys,

I've started playing around with the GGX BRDF type in my materials for recent projects. Starting to wrap my head around the added control it offers.

My question for all ya'll is for what applications do use use the GGX for? Although there is no "rule", would one be good with just using the GGX across the board for all materials? Most examples I see it being used on relates to metallic surfaces.

Just wondering what works best for some of you so I can shamelessly do the same as opposed to wasting time doing things the "wrong" way.

WARD = Broad speculars
PHONGE = Plastic-y surfaces
BLINNE = Metallic-y
GGX = Metallic-y and ?

Thanks guys for your input. I've been running tutorials and haven't found a solid for GGX outside of Viscorbel who suggests to use it on everything (he also states that 90% of the time a IOR of 1.5 should be used for all non-metal materials). Just wanted to confirm.

Thanks in advance.

- Portfolio-

read 858 times
10/14/2015 9:25:08 PM (last edit: 10/14/2015 9:25:08 PM)
show user profile  digs
metallicy and non metallicy

I spent about 8 hours messing with this a few days ago testing a substance painter to vray workflow

basically my conclusion at the end of the day was: for metallic things using ggx in vray and max, have fresnel reflections enabled and set to around 12-16.. non metallic thangs set @ around 1.1-1.6

you can generate an ior map and clamp it between 1 and 16 or w/e, driving a single material to have different surface properties (not sure how to clamp a bitmap value in max, the docs I were reading were on maya)

I'm still researching too tho, just what i came up with after a few hours of parameter changing and render comparing..

renders were looking good, got nearly identically looking objects in vray vs substance's renderer, but for w/e reason I felt I was getting a better result when using phong instead of ggx for non-metals
read 853 times
10/14/2015 10:04:11 PM (last edit: 10/14/2015 10:10:17 PM)
show user profile  9krausec
@Digs - thanks for the information.

Do you generally ignore the "K" value in the IOR of the metal objects then? (The dip in shown below towards the end of the Fresnel curve)?

Would you mind sharing what resources you found for the Substance painter to Vray workflow? I was planning on getting into substance painter and researching about it more.

I will start using GGX for all material types and see how it fits.

- Portfolio-

read 834 times
10/14/2015 11:06:51 PM (last edit: 10/14/2015 11:06:51 PM)
show user profile  Error404
GGX is definitely a fun shader to try with metallic surfaces. I've not had time or opportunity to play with it much, but I will definitely be putting it through some paces when I get some free time :-) -

read 803 times
10/15/2015 7:06:14 AM (last edit: 10/15/2015 7:06:14 AM)
show user profile  digs
9k - im not sure how you are using or determining a k value for specific metals, but will research if it's beneficial and you can share docs or info

generally we only care about how the final render looks, not if the metal is 100% accurate - when I get to work tomorrow I'll try to dig up some of the better information that I came across
read 776 times
10/16/2015 7:51:50 AM (last edit: 10/16/2015 8:00:15 AM)
show user profile  Nanne
The K value is not available as a parameter in the materials, so you can't use it, except for the Maxwell renderer, I think. This is why all those list of IOR values on the internet isn't very useful for metals, because the value given is not taking the K value into account.

Setting the IOR value to something like 12-50 or above is just a 'hack' that yields a result similar to that curve you showed above, but it isn't really physically accurate. I think this is due to the Schlick's approximation algoritm that is being used to speed up rendering by approximating the reflections.

Kristoffer Helander
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read 740 times
10/16/2015 11:29:03 PM (last edit: 10/16/2015 11:29:03 PM)
show user profile  9krausec
Using the built in Vray Fresnel the K value is not taken into account. Turning it off and drawing your own fresnel curve makes the K value possible. I honestly don't know if it's worth the time though...

 photo 2015-10-16 16_50_10-Hypershade_zpskqxanbg3.jpg

- Portfolio-

read 734 times
10/16/2015 11:52:45 PM (last edit: 10/16/2015 11:52:45 PM)
show user profile  herfst1
I'm inclined to say, "What you thinking, man?" that's way OTT... but if you do get it set up you can save out the material for all future projects, so that's kinda cool.

Be curious to see the results of high freznel vs your material.
read 707 times
10/17/2015 1:22:39 PM (last edit: 10/17/2015 1:22:39 PM)
show user profile  Nanne
Hmm... that seams very time consuming if done on a daily basis. But I suppose you can save some basic materials to disc for reuse later.

On the other hand, if you're working with Maya. Here is a script for creating custom Fresnel curves that allow you to add the K value.

And if you are working in Max, you can try this

Kristoffer Helander
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read 695 times
10/18/2015 12:48:41 AM (last edit: 10/18/2015 12:58:23 AM)
show user profile  herfst1
Can someone explain why metal has the spoon dip before reaching the limit? Other materials don't have it. Is it some break in the matrix? i.e. is there no spoon?
read 653 times
10/20/2015 7:55:26 PM (last edit: 10/20/2015 7:55:41 PM)
show user profile  9krausec
I'm not a scientist man... I just play one on TV.

Most metals have this dip -

Edit: " Other materials don't have it" - Sorry, I misread your post.. Thought you said "other metals don't have it."

- Portfolio-

read 648 times
10/20/2015 8:13:50 PM (last edit: 10/20/2015 8:17:40 PM)
show user profile  herfst1
All good, just wanted to tie in the matrix reference... though it does fascinate me why it does this.
read 644 times
10/20/2015 8:33:12 PM (last edit: 10/20/2015 8:33:12 PM)
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