VolumeGrid - scatter color / anisotropy / sampling questions

[Bruce Allen]

1. Can we set scatter color independent of diffuse color? I'm Trying to get some Arnold-esque volumes (see attached)... working around it by using a color ramp on Smoke, but it's not quite the same.

2. How do you set anisotropy (back-scatter vs forward-scatter)? Or should I just adjust the diffuse & scatter multipliers?

3. Even with the Spherical sampler, I sometimes get stair-stepping effects. Can I increase the radius of the filter / apply a blur (eg specify a radius in voxels or scene or object units) or median?

4. The manual doesn't explain how the Step(%) and Shadow Step(%) behave differently with Volumetric vs Volumetric Geometry. With low step values in Volumetric Geometry mode, I get strange-looking renders and thin wisps illuminate strangely. I thought low step values = higher quality?

Bruce Allen
Senior Theatrical Designer & TD - mOcean

[Svetlin.Nikolov]

Hey,

No control over the scattering right now, it's something we need to look at with higher priority.

You could use smoothing from the Input rollout if you get grid artifacts, but it would be good to send an example cache to Support. FFX and Houdini have advection issues which produce linear artifacts along grid axes.

When decreasing the steps in volumetric geometry mode, make sure to watch out that you don't run out of V-Ray's max transparency levels - the volumetric geometry mode represents the fluid as a collection of semi-transparent layers in order to get the RE working and workaround for blending between volumetrics. You can easily calculate how many layers you need based on the number of voxels and the step %. You need more steps than layers, the back side of fluids will not be rendered. Also, note that there is no Approximate Scattering in volumetric geom mode - this resets to Disabled, so there will be visible differences between smoke in Volumetric and Volumetric Geometry if you are using this scattering mode, which is the default.

Hope this helps, cheers!

[Bruce Allen]

Friendly check-in!

Houdini 18.5 has some really nice smoke with this built in...
https://youtu.be/1p_8eSaUfJM?t=268

Bruce