Hello, noob here, how do we create iridescent shaders in vray for houdini?
somethign like this…
thanks
Hi @anthony_kyriazis ,
There’s a very easy and cheap way to achieve this by mapping a falloff to a gradient map that is then used as your reflection. You can map any color to that gradiend, and get the colors you need depending of the angle of view (falloff mapped to fresnel or towards/away).
Best,
David.
Hi, where do i find that thin film? i have downloaded this OSL Shaders but cannot get it to work…
thank you @david.anastacio giving it a try…
It is in the list of all other maps, called vray pluginnodetex. Use it in the reflection colour slot for the coat material. Set the blend to 'additive shellac mode.
Enable anisotropy of e.g. 0.9 or whatever looks good and make it somewhat glossy..0.5 to .9 seems good.
If you then vary the glossiness of the base material then you can get anythng from your example to an e.g. blurry car paint iridescent paint/pearlescent effect.
I don’t use Houdini but these settings I imagine will translate.
That OSL texture was crashing some weeks ago last we tried it. But yes, this should be a more accurate result.
But the one I showed can also be easily used as a coat on a blend material too.
Best
David.
Hmm, no crashes here using it over long periods to test other scenarios…but then that’s with Max, so maybe it’s something not playing well with Houdini
Your version sure does work just fine, so options 
This was Houdini issue only, I found a recent post of the bug:
https://forums.chaosgroup.com/forum/…2213-osl-error
But nothing in that post indicates that the issue has been fixed yet, and I haven’t tried it with the latest nightlies.
Best,
David.
Ah ok, that’s a shame.
Hmm…it’s hard to know what you are after, as your first example is very different to this one.
Can you explain more what you want to see, based on this much more abstract form?
Maybe just photoshop it to show the ideal effect…
"Iridescence (also known as goniochromism) is the phenomenon of certain surfaces that appear to gradually change color as the angle of view or the angle of illumination changes. Examples of iridescence include soap bubbles, feathers, butterfly wings and seashell nacre, as well as certain minerals."
“as the angle of view … changes” = Fresnel effect (Falloff map with Fresnel mode)
“gradually change color” = Gradient Ramp.
So with this two parameters we should be able to emulate our iridescence effect in any renderer. This is a bit simplification of course, things can get a bit more complicated that’s why you can find things like the thin film shader that account for more nuances of the effect. But in a general way, this should suffice.
The technique applied on a similar mesh used on a metal shader:
vs the example from your post in the Houdini artists Facebook group (discount lighting and shape):
The same technique in a sphere (soap), you can even add the common distortions of soap with noise maps:
P.S: This was 15 minutes of my time, it’s normal that my result is not super accurate to your example image. It’s just a friendly example scenario.
Best,
David.
@david.anastacio thank you SOOOOOOOO much!!! you super star!
@david.anastacio I got it to work, but only in CPU mode… as son as i try with GPU it does wired stuff.
No problem, happy to help.
True, I did notice that. That’s most likely a bug on the GPU implementation.
Best,
David.
what does it do in the GPU? maybe a bug worth reporting.
Totally. The cpu is the standard, any deviation from the cpu result is for sure a bug/limitation of the gpu.
I report way too many bugs already, and the gpu stuff is not something we use much, as the data sets we work with are way too large to fit in the gpu, maybe with “out-of-core” in vray 5 that changes a bit.
If this is a thing you would like to see fixed , you should post it in the issues section.
Best,
David.