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Hi there,
I've often wondered about a few aspects concerning VrayMtl IOR settings and 3dsmax falloffs but have never got round to asking about them. So here are a few points that some of you may be able to shed some light on.
1:
When working with the basic VrayMtl, fresnel reflections are set as default and locked to the refract IOR value. Unlocking the Fresnel IOR lock and supplying a separate IOR for the reflection seems to lead to some interaction between the refract IOR and reflect IOR. Here is an example with exaggerated settings to demonstrate:
Is this intended? I haven't tested that much yet, but adjusting the refract IOR to 1.0 seems to lead to the fresnel reflection being reduced to the base reflection level (0°) of the override IOR specified. Any view dependent reflection behaviour is no longer noticable. Adjusting both values to the identical IOR leads to the reflection IOR working as expected.
2:
We're currently working on a system, which will make use of reflection behaviour being supplied via a map rather than using checkboxes and spinners. The basic idea being that the Fresnel Reflections checkbox is unticked and the fresnel reflections are driven purely by the map supplied in the reflection slot. Unforuntely I wasn't able to recreate the same reflection distributions.
Here are some tests:
Mapping the reflection slot with a 3dsmax Falloff set to Fresnel with some IOR produces different results from using a VrayMtl with fresnel reflections and supplying the same IOR there (base reflection levels picked as reference):
Now I don't really trust 3dsmax Falloff map implementation since discussions like these (https://forums.chaosgroup.com/forum/...orrect-falloff). For those that haven't read that topic, here is a comparison of the 3dsmax Falloff and a linear falloff supplied by Wobi in the other thread. One color per 10 degree increment:
As an alternative I tried using the Complex Fresnel OSL shader supplied here (https://docs.chaosgroup.com/display/...Fresnel+shader), which we are also using for some metals. Now this may be down to my lack of understanding, but I always thought setting nr, ng, nb to the desired IOR and all k-values to 0 would result in basic fresnel reflection behaviour. Here is the comparison between a VrayMtl with fresnel reflections and a material with no fresnel reflections but the Complex Fresnel OSL texture plugged into the reflection slot:
Since all these methods (apart from the BerconGradient in normal-ior mode) display different reflection distributions, I was wondering, what the proper approach would be to enable mapping the fresnel reflections rather than using the Fresnel option in the default VrayMtl. Are there any other methods available? Currently still shying away from writing something in OSL, since I would have thought that something would already exist. Or maybe I'm missing something
I've often wondered about a few aspects concerning VrayMtl IOR settings and 3dsmax falloffs but have never got round to asking about them. So here are a few points that some of you may be able to shed some light on.
1:
When working with the basic VrayMtl, fresnel reflections are set as default and locked to the refract IOR value. Unlocking the Fresnel IOR lock and supplying a separate IOR for the reflection seems to lead to some interaction between the refract IOR and reflect IOR. Here is an example with exaggerated settings to demonstrate:
Is this intended? I haven't tested that much yet, but adjusting the refract IOR to 1.0 seems to lead to the fresnel reflection being reduced to the base reflection level (0°) of the override IOR specified. Any view dependent reflection behaviour is no longer noticable. Adjusting both values to the identical IOR leads to the reflection IOR working as expected.
2:
We're currently working on a system, which will make use of reflection behaviour being supplied via a map rather than using checkboxes and spinners. The basic idea being that the Fresnel Reflections checkbox is unticked and the fresnel reflections are driven purely by the map supplied in the reflection slot. Unforuntely I wasn't able to recreate the same reflection distributions.
Here are some tests:
Mapping the reflection slot with a 3dsmax Falloff set to Fresnel with some IOR produces different results from using a VrayMtl with fresnel reflections and supplying the same IOR there (base reflection levels picked as reference):
Now I don't really trust 3dsmax Falloff map implementation since discussions like these (https://forums.chaosgroup.com/forum/...orrect-falloff). For those that haven't read that topic, here is a comparison of the 3dsmax Falloff and a linear falloff supplied by Wobi in the other thread. One color per 10 degree increment:
As an alternative I tried using the Complex Fresnel OSL shader supplied here (https://docs.chaosgroup.com/display/...Fresnel+shader), which we are also using for some metals. Now this may be down to my lack of understanding, but I always thought setting nr, ng, nb to the desired IOR and all k-values to 0 would result in basic fresnel reflection behaviour. Here is the comparison between a VrayMtl with fresnel reflections and a material with no fresnel reflections but the Complex Fresnel OSL texture plugged into the reflection slot:
Since all these methods (apart from the BerconGradient in normal-ior mode) display different reflection distributions, I was wondering, what the proper approach would be to enable mapping the fresnel reflections rather than using the Fresnel option in the default VrayMtl. Are there any other methods available? Currently still shying away from writing something in OSL, since I would have thought that something would already exist. Or maybe I'm missing something
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