Karma default clouds versus Redshift Standard Volume

So in my challenge to start using Karma / Solaris more in Houdini I went and did some cloud tests one a cloud I modeled back for the guitar project. Same scale height and settings as close as I could get them. Karma volume settings are just default, no changes. I had to tweak the Redshift Standard Volume Shader a good deal to get it this far. Rendered both out at 1920x 1080. The Karma one looks more like a cloud though while the Redshift one still feels more like smoke to me. Karma on left, Redshift on right. Using Houdini 20.5.410 and Redshift 2025.1.1.

Houdini Doodle

And todays doodle sticks with motion blur as the primary component with some volumetric scattering added in.

Houdini Doodle: Motion Blur Study

After testing out some extreme caustics the other day, I kinda wanted to get into some crazy motion blurs. I made three different kinds of motions here to get these effects. The biggest hiccup I had was that my render window in Redshift was showing the blur but the final Render wih Mplay was not. Turns out if you have a motion vector AOV turned on, it won’t render out. Dunno if that’s a bug or not. But was odd to trouble shoot.

Houdini 20.5 MPM - what is that?

Really good write up on Reddit about what MPM actually is in Houdini 20.5. Really good explainer here.

“When it comes to simulation currently in the industry there are a few major kinds of solvers - 1. Grid based (Eulerian solvers) 2. Particle based (Lagrangian solvers) 3. A mix of both (Hybrid / semi Lagrangian solvers) 4. There’s also a 4th kind, mostly point or geometry based (PBD solvers, Bullet, NVIDIA PHYSX). Although PBD can be categorised as Lagrangian too.

So what are Eulerian and Lagrangian solvers? In very simple words if you’re calculating and storing your velocities on the grid like bounding box that you use in FLIP fluids or pyro solvers basically solvers that use a voxel grid then it’s Eulerian. Example of such solvers are FLIP fluid and pyro solver in Houdini.

On the other hand if you compute and store velocities and forces on the particles instead of any VDB grid etc then it’s Lagrangian. Example of Lagrangian solver can be SPH (smooth particle hydrodynamics) probably was used in old versions of Bifrost, Real Flow etc. Currently not very famous or used. Probably the most common example of this method in Houdini is vellum which uses PBD (position based dynamics) or XPBD (extended position based dynamics) where velocities and forces are computed and stored in the grid.

As you may already know in both the methods you can simulate various materials to some extent like cloth, soft bodies, fluids, grains etc.

When I worked in Dune 2 we used FLIP solver extensively to create some of the sand shots while in other shots where it wasn’t necessary we used vellum grains or even particles.

But here comes the major problem. You can’t make Eulerian and Lagrangian solver talk to each other easily without creating a custom bridge.

So in order to do that, the solution is MPM or material particle method based solver. MPM uses both the characteristics of Eulerian solver and Lagrangian solver.

How?

In MPM you store the forces and velocities of a particle in the particle like you do in Lagrangian but then you interpolate that velocity back into a grid , solve the forces and then interpolate the forces / velocities back to the particles and move the particles.

Whereas is FLIP the whole velocity projection / Pressure projection stage happens in the grid itself.

MPM is sort of a hybrid solver. It was built as an extension of FLIP solver. While FLIP is very good at handling fluid behaviours by keeping the simulation divergence free, MPM is more of a general purpose solver that can handle stretch, strain, granular sims a lot better however it can also do fluids.

Now through MPM you can have a good interaction between various materials that you didn’t have before like cloth and fluid, grain and fluid etc.

Not only that in some cases like snow accumulation etc MPM can give a lot better results than PBD based solvers like vellum. However one drawback is that with MPM you’ll have to make bounding boxes like FLIP or Pyro solver which might not always be very memory efficient.”- Icy-Acanthisitta3299

Houdini 20.5 Keynote

It’s nice that there is still a technology / program that I am actually excited to use and learn about new stuff in. Houdini is STILL really interesting tech. Digi cameras are boring, Photoshop is a pile of broken glass, windows is bloatware and macs are boring. But this stuff still gets me excited.

Houdini Doodles: Cassette

Just messing around with some clouds and voronoi fracture which was not really working for me. So I shifted it up and went into doing a caustics study which I like more. Works pretty good now in Redshift and renders fast.

Houdini show camera frustum in view port

Happy I found this little nugget when I was scattering trees on the doodle from the other day. You can turn on and leave on the camera frustum in Houdini. Frustum is a fancy way of saying field of view or to dumb it down more, what the camera can see.

RMB click on the camera and click on “Frustum Handle“ (Or click F). Then RMB Camera again and hit the check box, “Persistent”.

Houdini Doodle

Some more water explorations going on and playing with displacement.

Lops Lighting Quickstart

Great post from Reddit about trying to get into USD and Solaris in Houdini. I keep bouncing off of Solaris and Karma so hard. I see the advantages but I can’t crack it. Hoping reading these things will help. This page seems particularly interesting.

“Overview

You have a scene that you're just about to start rendering in Redshift/Mantra/Arnold, but you're keen to give Karma a try? Don't wanna learn all that prim/reference/sublayer/delegate stuff all the USD nerds talk about?

Hopefully this will get you started. USD jargon is unavoidable at some point, but I think its possible to dive in without getting too caught in the weeds. The aim here is to take a /obj, /mat, /rop setup, and port it to Lops as painlessly as possible, while picking up some basic USD concepts on the way.

This whole thing should be 20 mins at the max. Lets gooooo!“

Houdini Doodle: Water and Wax

Was messing around with water and cutting it up into different groups for some abstract stuff here. Working with Poly to VDB and back, groupings, and the new SSS in Redshift, which I am really liking. So much easier to work with since the update to random walk.

Wheee!

Tinkering with some FLIP stuff with help from a tut. Thought I just throw thi sup here cause it’s fun. Hopefully will develop it a bit further.

Some R&D that died

Was working up some stuff with the ripple solver that missed the mark, but it’s kinda interesting. The tricky bit with water and glass is that it is defined by it’s reflections. Anyways, onward…

Houdini Doodle- Cloth study

I am trying to do a deeper dive into vellum in Houdini when I catch a break between jobs and today I did a quick study on some cloth shapes that is kinda interesting. And purple. Very purple.

Houdini Hive

Was watching these in the background while working on the doodles yesterday. Good place to bookmark these things I guess, lol!

There is also one on USD lighting up a robot bar scene I need to watch. I keep bouncing off of USD and Karma every time I try it. I can see all the benefits, especially with LOPs and Solaris. But good lord, I can just whip something out with Redshift and when I have to import to the stage and convert, then is it Karma or Material X? It just sorts spins out and I bounce. Anyways, it's something to work towards.

Here is Rich Lord giving his talk on creepy things. So many useful bits in here.

Jakub Spacek makes these amazing particle / liquid sims that are really beautiful.

And here is the USD / Karma thing I wanna watch tonight after work.

Houdini Doodles

Messing around with some Houdini stuff today. Starts off with something abstract and simple and slowly worked up an idea.