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Volumes 101: Volume Gradient (Patreon)

Published:
2017-09-21 06:50:48
Imported:
2026-06
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  • VDB_advection_001.hipnc

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Content

This is the beginning of a multi-part tutorial in which we'll build the setup used in most of our title cards for the Volumes 101 course.

We'll start by exploring two simple yet powerful tools here: The volume gradient and VDB advection.

Let's start by going over what a volume gradient ist, how it can be generated and why it is so useful.

Files

Previews only

Volumes 101 pt. 6: Volume Gradient

Comments

wang

can't understand why the sphere would inflate, the gradient vector is outwards?

Clinton Chang

Can anyone explain roughly why the 2 spheres don't penetrate initially, then eventually they do penetrate (when looking at the volume slice before adding the smoothing)?

nouhad

@Entagma Hi there, does anyone know why the SOP errors out and says "Missing velocity grid" ? I thought it's because I didn't add a switch to Input 1 and do a condition to check for $F==1 but it still doesn't work.. any feedback would be greatly appreciated

entagma
>>21422968

Hi nouhad, did you check your setup against the provided scene file? Does that scene file work for you? If so, please check if you can spot anything you might have set up differently. If that doesn't solve it please let us know :) Cheers, Mo

Lukasz Pason

I was trying to figure out how to get the tetra to be a cage for the volume so it holds them all in but I'm a bit at a loss, any tips there?

Justin Kirk
>>67956864

Try connecting the platonic>vdbfromPoly into the 2 input of the Solver. Then use a VDB SDF Union set to SDF intersection after the VDB Advect.

Dag Kjetsa

Awesome! This is precisely the kind of stuff I have been looking for. Finding information about how to deal with, and properly use the volume gradient and volume sample together seems somehow hard to find, so this is gold to me. If anyone could tell me if/how it is possible to use these tools and principles to control densities in a fog vdb ( inside/out directional control)... :)

entagma

Thanks :) For directional control of SDFs - that's gonna be the topic of the next tutorials. What would you like to achieve by controlling a fog vdb with a gradient?

Dag Kjetsa

Oh, cheers for the fast feedback! :) In my specific case I am looking for good, fast ways to have control over the density levels within a cloud. Gradients according to the bounding box and via the use of other volumes (as masks) to control for example mixing of looks I have sort of figured out, but it would be super helpful be able to control density levels according to the gradient within such an object that has a complex structure. And also to be able to more precisely control where to apply more advection, or where to add/create finer details, like tendrils and "whispyness". Again thank you so much for these tutorials!

entagma

Ok, understood - thx for the clarification. I'd suggest to try and adapt the techniques we're gonna show in the upcoming tuts for fog volumes, they seem pretty close. Yet I'll think about if it makes sense to do a specific tut about that topic. Thanks :)

Dag Kjetsa

Wow! That would be amazing if that would be possible :-)

entagma

Just checked - you'll be able to use the exact same techniques that we'll be using in our upcoming tuts on your fog VDBs as well without heavy modification :)

Dag Kjetsa

Cool! Sounds really great. I am looking forward to the tutorials already then :-)

paul silcox

It's a really great technique, opens up all kinds of possibilities! Can't wait to see how you apply the gradients to the fog volumes.

Samm Hodges

excited to learn about integrating geometry collisions with this setup. So powerful and adaptable!

Orson favrel

That's really interesting. I was wondering how would you do if your inout source volume was a moving one. For exemple A Vdb from particles Source. Would it be possible to use to Vdb Advect node ? Thanks

Ahmad Q

nice, I was trying to do something similar and my mistake was using merge instead of vdb combine