I think this is a problem....

[Morbid Angel]

Guess how long this rendered for?



14 hours...
reason?
I dont know....setup is: displaced frost object over the displaced pipe. The frost is refracting....the scene is lit by 1 light and hdri is reflecting.
Gi is quasi. Everything else is procedural textures with some other textures...in my opinion this has to render in no longer then few minutes, well with quasi maybe more, but not 14 hours.
the scene is here if anyone cares to pick at it (Vlado please)
http://www3.telus.net/public/vinnik8...ural_Frost.rar

I think vray has a problem with calculating displacement and any type of refraction. This is second time this week i get into such situation. First time was with sss, but I thought that sss/displacement just dont like eachother.

[percydaman]

what version of max is the file?

[Morbid Angel]

max is 6, vray is 10

[jacksc02]

Dmitry, I just tried to render your file and slow it is!
I turn the indirect illumination off and it rendered in a minute.
Have you tried it without the SciAnaComp maps?

[Morbid Angel]

hmm...that might be part of it...
i will reasearch it soon. So far I only know and noticed, that rendering speed drops when it renders the part where the two maps blend between eachother. In any instance where blending occurs vray has hard time.

[Morbid Angel]

ok here is what i got: partially i think the problem lies within 3ds max itself. I am using blend material to blend between two shaders as the frost progresses. When i setup a simple test where there was a blend between max standard and vray mtl i rightaway noticed that second blending material (max standard) would take some time to render. I couldnt understand why, then i made vray mtl glass (reflective/refractive) and the rendering on the max standard material increased even more. So I thought - vray has some problem with blend. Then i tried same setup with brazil and...brazil rendered it 10 times slower then vray. Same fell for scanline and mental.
So my conlusion is that I dont know why but blend is very slow when compositing against refractive/reflective object.

[jacksc02]

hmmmmm might be a good question for either Vlado or Discreet/Autodesk/whatevertheyarecallednow

Keep me posted

[vlado]

This is because for a Blend material, all lighting calculations must be performed twice - once for each material. This is not such a problem normally, but when you consider GI and refractions, things get very problemmatic. If you have nested Blend materials, the situation deteriorates rapidly. VRay tries to avoid this issue to some extent, but there is no good work-around.

Instead of using a Blend material, you can use just 1 material and vary the corresponding properties of the surface - e.g. a map for the refraction color/glossiness/whatever. Often, you can get the same effect, and it will render a lot faster.

This goes for other materials too. Instead of using a compound material, use one material with maps to vary its properties.

BTW Dmitry, I have looked at the sss/displacement thingy, but I didn't have much time to tinker with it; hope to have some today.

Best regards,
Vlado

[vlado]

Oh, also when using opacity, it might be better use a VRay material with opacity mapping.

Best regards,
Vlado

[CCS]

Don't mean to hijack the thread, but I've never heard this about a blend material. As to your mapping workaround, I don't follow. Do you mean using mix maps in each slot as necessary?

[vlado]

Don't mean to hijack the thread, but I've never heard this about a blend material. As to your mapping workaround, I don't follow. Do you mean using mix maps in each slot as necessary?

Yes, this is what I meant.

Best regards,
Vlado

[Morbid Angel]

Vlado thanks...
I will also continue working on that scene. As to this one, I think per pass is the solution.
However we should not need to do this. Maybe later when vray 1.5 is out (this could turn into a wish thread) but you guys can script some nice vray shaders to allow blending and other composit modes with fast performance and all.
On the other hand, max 8 is going to be around soon. Who knows what it will bring.

[PixelJockey]

What about Multi/Sub-Object materials? Do they also require more computing time? I've got a scene that uses one big Muti/Sub material and just a few single materials and it renders quite slow.

[CCS]

Man, I hope not.

[Morbid Angel]

dont think so...in multi subobject there is no blending.