Vray Fur strands appears and disappears when there are shorter

[Mathieu_1980]

Hello everybody,

I'm facing a strange problem with my Vray Fur's strands. When there are shorter, the strands comes and goes with no reason.
In the Vray Fur settings, I've a black and white map to change the Fur lenght (shorter) and another one to decrease the density when it's close to the eye. No level of detail according the camera distance.
When the camera is far I can't see the problem, but when the camera gets closer, the smaller strands appears and disappears, looking like a glitter effect I really do not want.
Here is a preview attached to make it clear to you :

I've tried a lot to identy the problem and I am sure that :
- it's not a GI problem (same result with or wihout GI)
- it's not a AA problem (same result when I change the Min shade rate)
- it's not a Image sampler problem (same result when I increase the Max subdivs or decrease the Nose threshold value)
- it's not a Global DMC problem (same result when I change the sample, amount and threshold values)
- it's not a Hair shader problem (same result with a very basic material)

Does anyone has an idea to fix the problem ?


Thanks in advance... and have a nice week-end !
Mathieu

[tashko.zashev]

Hi,

Can you attach this max file ? Are you rendering animation or you can see the missing strands just re-rendering the current frame ?

[joconnell]

This type of thing wouldn't be a shade rate or max aa issue, it'd be a min aa issue if anything - for really skinny objects like hair / fur / grass, if vray doesn't hit anything on it's first camera ray (first aa ray) then it thinks a bucket is empty and moves on - you see the same problems with heavy depth of field or motion blur - if you're not lucky enough to hit something you end up with an empty bucket. To prevent this from happening you have to tell vray to be more thorough at the very start and rather than using 1 aa ray (min aa 1) you've to raise it up to min aa 2 or 3. Min aa of 3 give vray 9 chances to find a small object and work from there!

[Mathieu_1980]

joconnell Hello and thanks for your message but I've already try to change the aa settings without success, even with a lot of min sample result is strictly the same.

tashko.zashev Hi ! Thanks for your answer, due to some confidentiality problem i'm sending the file to support@chaosgroup.com with the link of this thread as ref. Answering your question : I'm rendering animation and when I'm re-rendering the same frame the strand's layout and disposition is exactly the same, same strands are missing, same strands are correctly rendered.
Just a last word to tell you I won't be able to be reactive due to long distance between me and my computer (also called holydays) but i'm very impatient to find out more about this Fur mystery when I'll be back.
Thanks again and best regards !