shave hair renders slow

[sharktacos]

I'm getting really slow renders of Shave & a Haircut in Vray. Here's a speed comparison

(1 spot, no shadows, 20,000 hairs):

Maya software: 6 seconds
Renderman: 6 seconds
Mental ray: 11 seconds
Vray: 50 seconds

Is that normal? Are there any tricks to speed this up I need to know about? Also I don't see a Render Element pass for hair/fur...

[alainfx]

Hi,

Last time I tried, the main factor that can reduce Shave's speed is GI.
If you need GI, try to turn off "tip fade", and don't use too much passes.

The best source of information on that subject is Joe Alter, the Shave's author, his e-mail address is indicated here :
http://www.joealter.com/newSite/company.htm

Cheers.

[sharktacos]

I have GI off. I'll send a parallel mail to Joe and see what he has to say too.

[alainfx]

I have sent this thread link to Joe Alter, he will have registered access to this forum very soon.
Until then, he asked me to tell you this :

grab current versions of both shave and the vray shader (shave's current build is 5.5v15)
We made some real efficiency improvements for global illum.
It'll also speed any illumination in general.
Our hairs have transparency in the tips to aid with antialiasing, maya fur's do not.
Vray's ray casts are really slow with transparency, so for illumination calculation we now treat the hairs as fully opaque - much faster.

[sharktacos]

So I installed 5.5v15 and it was still slow. But when I started with a clean scene, and created the hair from scratch it renders out fast now (yippie!).
So there seems to be a problem somewhere with older scenes. In my case it was easier to just make it again rather than trouble shooting the old scene.

[vlado]

Ok then. I should probably make sure that Joe recompiles against a newer version of the V-Ray SDK - hair rendering is much faster there.

Best regards,
Vlado

[joealterinc]

no - that's just an old version of the shader/shave. Maya's shader doesn't do any transparency by default - ours does. Ray casting on transparency is slow, we now turn it off for all illumination bounces, so it should be up to speed.

joe

[joealterinc]

(don't know why creating the hair fresh would make any difference, unless maybe he had maya open when he installed the new shader)

[sharktacos]

It's not the shave node. I tried just deleting everything in the scene (including non-DAG nodes) so that I just had the head mesh and the shave hair with 1 new light, and it rendered out really fast. So there was some left over garbage from who knows what in there that was slowing it down.

[joealterinc]

oh - you might have had a pre-release beta version of 5.5 that left some kruft in there.

[joealterinc]

glad you got it sorted

[sharktacos]

Yeah, thanks for the help!

[sharktacos]

Okay, I figured out exactly why the hair was rendering so slow in Vray:

(drum roll please...)

Because I had an occlusion pass.

I delete the pass, and it goes from 40 seconds to 4 seconds.

That of course makes a lot of sense. in fact, that's pretty fast for occlusion on hair, but raises a question for me:

if I want occlusion to render on my geometry, but do not want to have hair included in that pass (since it means a big hit in render speed), but do want it to be in other passes (diffuse, spec, raw light, etc.) what would be a good strategy for that?