Is Environment Fog outdated?

[dgruwier]

I did some quick tests with using textures to shape environment fog, and then using the same textures to shape a completely filled up volume grid. I was able to get faster render times on the volume grid in some situations.
Is there any reason, other than convenience, to ever use environment fog if you can achieve the same thing with a filled volume grid?

[vlado]

The volume grid caches the textures and the lighting in the voxels of the grid, which makes it much faster to render. The environment fog doesn't do that, and if the textures are especially hard to evaluate (i.e. procedural noise, fractals etc), it can be quite a bit slower.

Best regards,
Vlado

[vfx_film_televsion]

Hey dgruwier!

Environment Fog is one great feature. We used it on one of our Earth-Shots to "simulate" clouds. It was a duplicated Earth, a small extrusion and then we used different noise types and real clouds textures to feed this into the density and on top of that we displaced the cloud geo to get different heights in our clouds. Try to get nice looking bended vdb's around a sphere and "real" looking clouds vdb's.... it's a pain

[dgruwier]

Thank you Vlado. Would it make sense to give us the option to fill up the VRayVolumeGrid by specifying grid and cell size? That way we could skip the step of caching a generic smoke filled cube in Phoenix FD or FumeFX, and just use it directly to replace Environment Fog in cases where the voxel rendering and other features of the volume grid come in handy. For example, to create individual clouds using distance tex and noises, or like what vfx_film_televsion did for their planet cloudcover.

[Svetlin.Nikolov]

Hey guys,

We didn't dedicate much time on making the Volume Grid a more independent tool for procedural creation of volumetrics - it's more of a loader right now. In the context of Phoenix, you can do more stuff with it, since you can brush volumes or use an empty grid and drop the opacity curve below zero in order to fill the container box with smoke even without a cache. We should eventually allow an empty container for the volume grid, with which you can control the voxel resolution. Note that when using textures for modulating the volumetric, the Volume Grid or Phoenix shader does not voxelize them to the grid resolution - they are kept with their original detail and the sampling interval is controlled by the Step size param.

Hope we can add more possibilities over time.. Cheers

[dgruwier]

Thank you for the explanation Svetlin, that makes sense. Good to know that you're aware of the potential

[dgruwier]

Looks like I am having some problems with using the volume grid in this way though. In my scene, I have a large area covered by a volume grid to create low hanging fog. I'm using distance tex with some spheres to create the shapes. But any geometry that is visible through the volume grid renders many times slower, even if viewed through an area of the grid that has no visible smoke. A region render on just the geometry goes from 1m25s 8s to when I turn off primary visibilty on the volume grid. Also happens when I make the geometry a matte surface. Doesn't happen when I hide the geometry and render the background dome light texture. All GI is off. Sample rate pass is identical between the slow and the fast render.

Any ideas? Is this because of the distance tex or is it something in the volume grid I can optimize?

[flat]

Is it possible to use Phoenix FD grid without using cache?
Like the VRay environment fog.

[Svetlin.Nikolov]

Sure, you can load a texture for the surface if you are in Mesh or Isosurface render mode from the Rendering rollout, or you can load a texture for the fire/smoke color/smoke opacity from the Volumetric Settings, when you switch Based On to Texture.

Cheers!

[flat]

Thank you for info!
fun 3d procedure volumetric with IPR.

Expect to improve the sample speed of 3D texture. (ex: VRayDistanceTex)

[Svetlin.Nikolov]

I think the V-Ray guys already did quite a few optimization for the distance tex, but they can tell exactly if they are already in V-Ray 3 or 4.

[japetus]

I'd like to know more...trying to do some sorta flying through clouds/fog. Don't need anything really detailed, but something to get something passing by camera quickly and get some volume light going...I can do it with a Phoenix grid w/o simming? Do I have to fill up the grid with smoke first? I get loading the texture, but I assume I need to start with a full grid.

[japetus]

Oh man, I get it....i had no idea you could just toss a texture into Surface and smoke and use that! Very cool!!