vray displacements

[cdavis]

Hi,

I have a head which ive sculpted in mudbox 2009. I have exported the OBJ & the 32bit displacement, if I render in mental ray with their approximation editor it is a perfect match to what I have in mudbox, if however i try & us eVRAY , which is what I really want to be using it looks like the midpoint is set wrong. Why is this different & how do I fix it.

Thanks

Chris

[Morbid Angel]

its not the mid point. Vray has a thing where it clips the float displacement values. Unlike mental ray where you can specify the clipping range in max and it autoclips in maya, vray just clips it between 0 and 1 (as far as I know)...pretty uncool huh? In any case this happens only for 3d displacement, but since vray does not have 2d displacement in maya makes things worse.
The only way I know of is to truncate the float range and then expand it in displacement. For example so if you were to set your alpha gain to 0.01, and then set your displacement intensity to 100, you should get your range back.
I really wish they would just put in a manual clip or some thing that fixes this very annoying issue.

[vladimir.nedev]

Actually newer V-Ray for Maya builds do have 2d displacement ( since December last year).

Greetings,
Vladimir Nedev

[cdavis]

thanks for the reply. So where should i set my disp value to 100?

Also ive noticed that if im coming from zb3.5r3 & save a .ma it seems to render ok in vray, but it seems to set up the alpha gain & offset each time , where as from mudbox i have to do it manually & the ag is always at 1.

[Morbid Angel]

i suppose its different for maya. In maya you would have to run the displacement through either multiply divide or set range, im not sure.
But for the zbrush, it cannot export 32 bit map which contains both directions, it only exports positive, so that is why its working since its not a 32 bit float image, vray does not clip it, and zbrush auto sets the negative offset.
Idea with 32 bit displacement is that you just plug the map in (in mental ray that is) and it works with the default value, provided your scene is in the same unit scale.

Vladimir, any reason not to make a manual clip range for 32 bit float?

[vlado]

its not the mid point. Vray has a thing where it clips the float displacement values. Unlike mental ray where you can specify the clipping range in max and it autoclips in maya, vray just clips it between 0 and 1 (as far as I know)...

No, actually V-Ray for Maya does not clip the displacement values - please do some research before postsing. This is only a 3ds Max thing. In Maya, since we have control over all the textures, V-Ray can guess the correct displacement bounds automatically, even if they are negative or larger than 1.0.

Best regards,
Vlado

[cdavis]

ok, so what should i be doing to get it to work. It seems i'm just entering random numbers all over the place to get it to work & it still isnt ! i would like it to "just work" like mental ray does . Could you give me some direction please?

Thanks

Chris

[vlado]

Sure, can you get me your scene (or a part of it) to vlado@chaosgroup.com ?

Best regards,
Vlado

[cdavis]

ok great. when i get home from work ill mail it over.

Thanks

Chris