Particle hair slow to render? Tweet

[tapanojum]

Hi, I've started using Octane this past week so have no point of reference to prior builds. Rendering hair in Octane is taking me 3-4x longer than in Cycles. Has this always been the case or am I neglecting some settings?

I believe I've kept the same settings with only the Octane Hair Settings section being touched. the hair shader in Cycles is using the Principled Hair BDSF. In Octane I've tried both the Hair Material as well as a Glossy Material with both performing extremely slow.

Is there something I could have possible missed?

[linograndiotoy]

It may depend on the hair material settings you're using, especially roughness settings.
Do you have a scene you can share showing the slowness?
Thanks!

[tapanojum]

Sorry for the late response, I've been without access to my computer for two weeks.
It looks like the build time for the hair is slower in Octane than in Cycles, at least in my experience. Even hair with no shader took longer than it took to render in Cycles.

I've attached a file with just the haircap + particle hair. This one has multiple particle hair systems using interpolated children, however the slower build time issue has been consistent among all of my characters even those using single particle hair systems with simple children. Really hoping it's simply user error on my end.

[linograndiotoy]

I've tried here and rendering the image using 200 samples took one minute with 2 1080s, with about 22 seconds dedicated to setup time.
It looks pretty normal to me, especially because you're using 9 steps for the subdivision, which is quite a lot.
A trick to make the setup super fast, would be to use the same number of steps for both Render and Display. That reduced the setup time to 6 seconds here on my laptop.
I hope this helps.

[tapanojum]

Thanks for looking into it, Lino. I was more comparing Octanes to Cycles for the same hair settings, which Octane 2021 seems to be performing slower than Cycles but your assurance that this performance is expected puts me at ease. I was worried I was simply doing something wrong on my end. I believe Octane 2022 notes mentioned faster particle hair rendering so I'm looking forward to that.

[tapanojum]

I'm definitely seeing issues with Octane and particle hair. The huge build times aside, rendering particle hair seems to be consuming an insane amount of memory. With Cycles, I can render 7 characters with particle hair. In Octane, using the exact same characters/texture maps, I can only render 3 before running out of memory. If I turn off Max Child Particles through Simplify, I can render at least 5 characters. I didn't have the additional two characters converted to Octane to test if I could render all 7 just like Cycles.

With Child Particles turned off, Octane build time is as fast or even faster than Cycles. With Child Particles turned on, the build times are 3-4x longer in comparison.

Linograndiotoy, do you know if hair particle performance is the same in the upcoming standalone version?

[tapanojum]

Can we have any insight on Octane particle hair performance in Blender for the 2022 addon version? I don't mean to be annoying but I'm struggling to make sense of this performance.

Using the latest version of 26.3, the attached render used 30gb ram and only 18gb without hair.
Octane standalone rendered with hair using 18gb.
Cycles with hair took 15gb.

I understand that standalone is more efficient and that Octane is more memory intensive than Cycles but do these numbers pass a sanity test?

edit: Tested on 2022.1XB1, same thing.