Hey guys, my first post.
About that custom BRDFs and GGX reflections, I gave it a go for Gold, since it may be trickier than non colored metals such as Platinum or Silver.
SUPER cool looking gold setup for V Ray. As you can see you need to overkill and blend 3 materials (or more) with different glossiness: 0.8 + 0.9 + 0.99. It's what I call the Grant Warwick BRDF (although he compiled it from others on forums, etc, all credit towards everybody, can't remember their names), I was not smart enough to create this method though I made something similar (yet crappier) years ago for Maxwell Render.
How does he do it?
1.Wikipedia Red + Green + Blue (see attachments.) Those gives us the wavelength of these colors. You can use min or max values, or equal them out. (for my gold I used max).
2.Then go to
http://www.refractiveindex.info, plug that in with a 1/1000 modifier (nm units vs µm, so 450 becomes 0.45 in the Wavelength parameter of the website). Then select AU (GOLD) under BOOK ( I kept Rakic method ).
3.OK then scroll all the way down to
REFLECTION CALCULATOR. Yeah it's a graph, only diff between it and max is that this one is from 0 to 1 up, 0 to 0.9 left-to-right. So I multiplied everything horizontally with 1.11111. Yes I am a freak. ONLY USE THE GREEN GRAPH.
4.Use
WARD not BLINN (better for metals). In your material reflection slot, use a
FALL-OFF map, use the GREEN only graphs for the RED, GREEN and BLUE calculations. That will give you a custom RGB fall-off like in this picture. I tried to be as close to reality as I could, but please take everything with a grain of salt, don't over tweak it! Minute differences probably can't even be sensed. You got the values roughly to put in 3ds max, a 0.05 difference won't kill your production. Just remember the 1.111 multiplier horizontally since the website goes from 0 to 0.9 and max goes from 0 to 1. See below:
5.Ok you created a base custom BRDF. To get it to GGX status, since it's only a WARD now, blend 2 to 4 materials together. 4 might be overkill unless your machine is really into computing power. Make a V Ray Blend - change
only the glossiness (BEWARE: Fresnel IOR turned off, you DON'T need it, you got a custom Fall-off born from physical calculations). So a
0.8 +
0.9 +
0.99 3 way blend should do fine. I used this as blend map:
So the result is:
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BOOM. GGX super shader for gold. I apologise for using mister Warwick's renders but since my video card exploded my 4770k goes up to 95 degrees so I can't render, I will use his scene:
This is the comparison, this is why you want a GGX and not a simple WARD:
6.I had slight problems recreating this with Corona, since I only got A6 literally 7-8 hours ago. But the script did translate to BLEND - 2 corona materials into a 2 way BLEND + another corona material. So I had all 3. So it looks like this:
Basically: BLEND-->BLEND-->Corona 1 glossiness minimum (still high, equivalent of V Ray's 0.8)
-->Corona 2 glossiness medium (still high, equivalent of V Ray's 0.9)
-->Corona 3 glossiness medium (still high, equivalent of V Ray's 0.99)
So far so good, no problems, 3 gold materials with 3 different glossiness factors. Victory! But wait...
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What bummed me out: A. Can't turn off IOR. And it translated to IOR value of 999.999. That can't be right, since most specialised websites say IOR of Gold is 0.47. So yeah, minor tweaking. Copied a gold material presented on the forum for Corona with IOR of 100 (still can't be right...).
So I need help here.B. Reflection Color. I don't know why this is there. My custom RGB enabled Fall-off does a fantastic job, why do I need to add another color here? Feels a bit cheap and linear, when I put all that work for a calculated, really close to reality custom fall-off...
So I need help here.C. For the blend map the falloff I made simply does not work.
So I need help here.Here are some screenshots of material previews so you can see what I'm saying here and maybe you can help me translate my bad-ass gold into corona:
1. Corona 3 way blend material: a.reflection level 0.95
glossiness 0.8
Fresnel IOR 4.7 and not 100 + Color + Fall-off RGB calculated above
b.reflection level 0.95
glossiness 0.9
Fresnel IOR 4.7 and not 100 + Color + Fall-off RGB calculated above
c.reflection level 0.95
glossiness 0.99
Fresnel IOR 4.7 and not 100 + Color + Fall-off RGB calculated above
2. Corona simple material: reflection level 0.95
glossiness 0.8
Fresnel IOR 100 + Color Black + Fall-off RGB calculated above
3. Corona 3 way blend material: a.reflection level 0.95
glossiness 0.8
Fresnel IOR 100 + Color Balck + Fall-off RGB calculated above
b.reflection level 0.95
glossiness 0.9
Fresnel IOR 100 + Color Black + Fall-off RGB calculated above
c.reflection level 0.95
glossiness 0.99
Fresnel IOR 100 + Color Black + Fall-off RGB calculated above
4. Corona 2 way blend material: a.reflection level 0.95
glossiness 0.8
Fresnel IOR 100 + Color Yellow (as close as what my eyes tell me gold is)
b.reflection level 0.95
glossiness 0.99
Fresnel IOR 100 + Color Yellow (as close as what my eyes tell me gold is)
OK enough detailing, this is what they look like:
Off the bat:
Fresnel IOR can't be 1.47, it has to be as close to 100, but I feel is gets way too close for chrome so...I don't fancy it in my production. This fresnel IOR definately works way different than V Ray. But how much different?
So I need help here.Blending 3 different glossiness materials achieves absolutely nothing.2 and 4 look exactly the same. Except a longer rendering time.
So I need help here.A black color in the reflection lets my custom fall-off calculated map shade the reflections so yay! on that achievement.
A custom color in the reflection is very crappy when trying to produce real material shaders.
So you can use this custom fall-off calculated method in Corona Render A6, but still blending different gossiness materials results in nothing. So can't really mimic a custom GGX shader for materials, although the result is WAY BETTER in some ways compared to a simple WARD or BLINN. So you may not need to, although I grew accustomed to the level of control it offers.
I know this is a big ass post, I know at least some may find it confusing, but I know there people a lot smarter than me lurking on these nice forums, so help me put this together, so we can render unbiased REAL WORLD calculated METALS of ANY kind. I think this is important.CONCLUSION:
That custom Falloff map that you can calculate on the website and recreate in 3ds max is really useful.
I am messing up something with my fresnel IOR or something, gold is no way near that close to chrome and my Camera IEV settings had to be dropped to -3 for this not to be nearly white renders.
I can't seem to blend 2-3 versions of the material to get that GGX flavored reflections, blending right now does nothing, all reflections are uniform which really pisses me off.
Here are some test renders, custom Falloff RGB calculated VS Simple Color in reflective slot, rest are the same: Fresnel IOR 100 / Level 0.95 / Glossiness 0.9:
Let's ignite this conversation! And please message me if I posted in the wrong section, I just wanted to show how you can achieve a GGX style shader in V Ray then translate that level of control to Corona which for now I simply can't. We can figure this out!
