Scattervolume vs environment fog

[Macker]

Hey guys,

Just rendering a scene here and I'm using the vrayenvironmentfog to create volumetric light rays/scatter GI; I was just wondering if there's any performance increase to be had by using the vrayscattervolume instead? I only ask as I seem to recall that in a previous release there was a speed increase in rendering sss/scattervolume (I could have just imagined that though).

[Undersky]

Haven't done any tests regarding speed, but you have way more control over it, since you can phase the scattering towards or away from the camera, creating more refined volumes.

[ben_hamburg]

I´ve recently switched to VrayVolumeGrid (or an empty phoenix grid) and I had massive speedups. Just use an empty grid and raise the first point above zero, the more you raise it, the denser the fog.
You have also a lot of options to map stuff there (mainly color and density).
if you´re getting weird results (haven´t quite figured out why, but mostly I got this when using too many lights), try turning off "light cache speedup", although your render times will suffer.

[Macker]

Thanks for the info guys.

Out of curiousity; does the scattervolume work with caustics? Also; does it work when you are "inside" it (like the environment fog), if that makes any sense?

[Macker]

I´ve recently switched to VrayVolumeGrid (or an empty phoenix grid) and I had massive speedups. Just use an empty grid and raise the first point above zero, the more you raise it, the denser the fog.
You have also a lot of options to map stuff there (mainly color and density).
if you´re getting weird results (haven´t quite figured out why, but mostly I got this when using too many lights), try turning off "light cache speedup", although your render times will suffer.

I'm about to try this (having never used the volumegrid before) and am a touch confused.

There doesn't appear to be any size to the volume grid(?) to constrain it to the area I'm trying to render. Is this normal? I would have thought it was a box with x dimensions?

Also when you say just raise the first point above zero; which point?

Forgive me if these are extremely basic questions; totally unfamiliar with this part of VRay.

[ben_hamburg]

I´m a bit more familiar with it, since I´ve been using phoenix for quite a while now.
I must confess, I used the phoenix grid instead, so I´m not sure, but I think as long as you don´t load a sequence in the Vrayvolumegrid it doesn´t have a size.
But I think you don´t need to worry about this, just open the render options, go to the smoke opacity rider, switch from simple to smoke based, and there you get the aforementioned curve:

https://docs.chaosgroup.com/display/...pacity+Rollout.

[Macker]

I've just tried it but it only appears to give me a (what looks like) 1x1m cube of smoke?

[Jiri.Matys]

I do some test while back and for me it doesnt matter. Looks pretty similar and speed was similar too.

[ben_hamburg]

I've just tried it but it only appears to give me a (what looks like) 1x1m cube of smoke?

Hm, not sure, maybe someone from chaosgroup can chime in? Can you post a screenshot of the scene and the opacity curve settings?

I do some test while back and for me it doesnt matter. Looks pretty similar and speed was similar too.

With volume grid and light cache speedup I get around 5 times faster render times than with standard Vrayenvironment fog, depending on the density and light setup.

[vlado]

To answer the original question, the scatter fog calculations are maybe a bit simpler and it may be slightly faster in certain situations compared to the environment fog, but there won't be a whole lot of difference.

Best regards,
Vlado