Blending/sorting between VRayVolumeGrid and VRayEnvironmentFog fails

[Dan Andersen]

Hello,

We often deal with a lot of Houdini-generated VDB volumes, that need to be rendered together with EnvironmentFog (think simulated smoke plumes in a hazy/foggy environment f.e.). Problem is, this doesn't really work. The two node-types don't really blend/sort properly, unless we switch the VolumeGrids to the "Volumetric Geometry"-mode (which we'd like to avoid, for various reasons).

Is this a known issue?

Maya 2018, VRay 4.3, Ubuntu 16.04

/Dan

[Svetlin.Nikolov]

Hey,

This is not an issue technically. It's a heritage from 3ds max where all atmospheres are rendered one in front of the other, so aerial perspective, environment fog, sphere fade and grid volume like the volume grid can not blend with one another or with other atmospheres. This is why you must switch Phoenix or the Volume Grid into Volumetric Geometry in order to make it behave like a mesh, so it would blend properly with other atmospheres, at the cost of render speed, because volumes render faster when they do not pretend to be meshes.

In V-Ray GPU, where the architecture is newer, such atmospheric volumes blend with one another without the need for Volumetric Geometry mode, and there is special code for handling V-Ray's own volumes together.

In CPU, this is not likely to change soo. Instead, if your fog is homogenous and not mapped by a texture, you could use a scaled volume grid with a cache with uniform density, which would act like fog and will blend properly with other volume grids in Volumetric mode.

Cheers!

[Dan Andersen]

Hey Svetlin,

Thanks for the explanation. It's nice to know why this doesn't work as I would expect it to.

Your workaround makes sense, and we have actually been doing that on a few occasions. But it's a bit of a hassle with the static, uniform density cache that requires an output from FX + the resolution requirements of the grid seem to vary from case to case (in our limited experience), so there's some back-and-forth involved.

Would it make sense to be able to define this on the VRayVolumeGrid itself? So for grids not pointing to a cache, we could declare an x/y/z resolution and a uniform density would be set for all voxels "on-the-fly"?

Cheers,
Dan

[Svetlin.Nikolov]

Yess, this is exactly what I was thinking. We already have this in 3ds Max's Volume Grid - a Grid rollout with xyz sizes and voxel size. This would allow you to just lift the leftmost point of the opacity curve and get uniform fog. It would also allow you to render a texture mapped grid in volumetric or even mesh mode, so it's much more procedural. I will try to get this working over the next few days and will ping you.

Cheers!

[Dan Andersen]

That sounds perfect, thanks!

[Svetlin.Nikolov]

Ah, was just gonna update you that this will be in tomorrow's V-Ray 5 nightlies and then I'm going to pick it for the V-Ray 5 stable nightly builds, but I just saw you are using V-Ray Next I'm afraid the code has changed a huge lot for the past years since V-Ray Next, so this won't be able to get backported...

[Dan Andersen]

That's good news! No worries about the missing VRay Next backport. Last I heard, we're moving to VRay 5 within a matter of weeks, so I should be able to take advantage of this on upcoming projects. It should really make life easier.

I'll let you know how we get on, once we've had the chance to use it for bit. Thanks for the stellar support.

Cheers,
Dan

[Svetlin.Nikolov]

Ah, whew! Just picked the code to the stable V-Ray 5 nightlies as well and it will be there starting with tomorrow's nightlies.

Please ping us when you've had the chance to check it

Cheers!

[Dan Andersen]

Hi Svetlin.Nikolov . I've recently started using the "cacheless" VolumeGrid functionality in VRay 5, as a replacement for VrayEnvironmentFog. It works beautifully so far. Thumbs up

[Svetlin.Nikolov]

Woooo, sweet! Thank you!