Distance Tex Map In VolumeGrid Stops Working with Dense Grid

[Joelaff]

Please have a look at the attached test scene.

Note that the large squashed sphere shaped area of "smoke" renders fine with the settings in the scene.

Now decrease the cell size of the VRayVolumeGrid such that there are now about 300-400K cells. When you render that large sphere is no longer visible.

Have a look at the shading network. I am using a pair of DistanceTex nodes to control the falloff of the effect independently per DistanceTex node (so the different objects can have independent falloffs).

Not sure if I am doing something wrong (or there is a better approach), or if this is a bug. It feel bug like to me.

Max 2021 Win 10, The latest release Vray5.20.23 build 000001 - PHX = Phoenix 4.41.02 Nightly, Build ID: 2022031131297 for 3ds Max 2021 from Mar 11 2022

Thoughts?

Thanks.

[georgi.zhekov]

Hey,

Thanks a lot for the scene. Since the distance measurement and the smoke opacity depend on the cells, changing the grid resolution will have an impact on your final look.

In your case if you increase the color of the V-Ray Color texture a bit and adjust the distance for the squished sphere it should look better.

Cheers!

[Joelaff]

Thanks for the reply. I will have a look at what you suggested.

When used like this what unit is the distance parameter measured in? I had thought it was going to be scene units and thus be independent of the grid. Is there a way to set this up such that we can change the grid size without having to adjust the other settings? It’s nice to be able to use a less dense grid for previews or shots that require less detail for other reasons.

As you probably guessed, the VrayColor is there to keep the smoke thin and transparent. Perhaps I need to lower the cutoff (Minimum Visible Opacity) as well.

Is there a better way to adjust the overall opacity of the smoke in a setup like this?

Thanks again.

EDIT: Also, I see I forgot to make Inside Separate and a white Inside Color.

[georgi.zhekov]

Ah, sorry for the late answer. I confused the distance in the Voxel tuner (which is the distance from the current voxel to the surface of the specified object) with the one in the V-Ray distance texture. This one should be in scene units.

In your case if you set the minimum visible opacity to 0, you should be able to get a lot more predictable behavior when changing the grid resolution.

As for adjusting the overall opacity of the smoke, you just can move up/down the first curve point for the smoke opacity.

[Joelaff]

Thanks for the reply. I did end up using that first point to control it (to avoid the extra multiply CompTex). Also, lowering the Minimum Visible Opacity indeed got me to where I wanted to be. I ended up only lowering it a small amount. It does slow things down of course.