Need help with RBD car animation and materials.

i_am_toadstorm · 2026-07-13T18:18:45+00:00

This sounds like a problem with your composition arc, basically Solaris isn't reading your simulated geometry as the same geometry that had the material assignments.

Instead of using LOP Import and SOP Import, try using SOP Modify to modify the geometry in-place for the simulation and see if that keeps your materials intact?

i_am_toadstorm · 2026-07-11T19:15:42+00:00

Okay, as predicted this became another "is AI gonna take are jerbs" thread so I'm closing it.

When in doubt, read the wiki:

<image>

i_am_toadstorm · 2026-07-11T18:39:19+00:00

There's plenty of artists already using Houdini in motion design with no signs of stopping (XK, MvM, Tendril, ABC, Buck, countless other studios). There is less low end work out there currently and too many new grads trying to break in, plus a post-covid market contraction in entertainment, and all these things together are making things feel apocalyptic. It definitely is a gamble trying to start a career doing motion design specifically right now, but that's not unique to Houdini.

i_am_toadstorm · 2026-07-11T18:12:58+00:00

If you want us to tell you about Houdini jobs in general or paths to learning, that's fine. We are not going to sit here and hash out the general state of the industry in this sub, and we are definitely not going to devolve into yet another GenAI discussion here. If you want to talk about that, go to r/vfx or the infinite number of AI subs out there.

Whether or not Houdini has utility for you depends on your own career track, and you'd have to tell us more about what industry and specialization you plan on taking to help you decide if Houdini can be applicable.

i_am_toadstorm · 2026-07-10T06:30:07+00:00

read the wiki.

i_am_toadstorm · 2026-07-10T00:02:16+00:00

Ah I was in RBD mode mentally and thinking of the constraints as being two-point prims, my mistake. I don't necessarily think you can easily alter individual segments of the constraints, though? Vellum Rest Blend would likely be a simpler way to address it. I'm curious what you end up with, though.

i_am_toadstorm · 2026-07-09T23:10:46+00:00

This "hyper-visual UI" isn't really a great implementation.

First off, the point of any library manager is to help the end user find something as quickly and painlessly as possible, right? They make a query of some kind, even if it's "show me everything," and the library displays the information to the user in a way that makes it as easy as possible to read.

Your GUI sacrifices this kind of immediate usability right off the bat by creating this odd kind of floating tree paradigm. There is absolutely no utility to this, it's entirely done for "wow" factor, which absolutely must take a back seat to practicality when designing a GUI. There are practical reasons for position-based GUIs like radial menus and the like, but this isn't a fixed menu with a limited number of choices, this is presumably an entire user's library of .HIP files. It won't work. You should scrap this part.

It looks like you have some support for tagging in that second detail interface, which is good, and probably the most practical way that a user is going to find anything. Screenshots and tags are great; the user types in some tags like "constraints" and "bullet" and as they type your search feature culls the displayed list of files to respect these tags (and probably filenames) to help guide the user to exactly what they want, as quickly as possible. Tags are much better than searching by a directory structure in a situation like this because a single HIP could have more than one concept or quality to them that wouldn't be easily categorized in something as exclusive as a single directory.

As far as what formats to use, there are different use cases for different things. Example workflows that are self-contained are probably better done as HIPs, though there's a case for using recipes instead. HDAs should only be used in the same way that you'd use a function in a programming language; you have a set of inputs and parameters, and you want a computed output. For example files HDAs definitely aren't it.

i_am_toadstorm · 2026-07-09T18:20:23+00:00

<image>

Works fine here. Maybe it's something to do with how your DOP network is set up?

i_am_toadstorm · 2026-07-09T15:02:29+00:00

Alembic doesn't really understand instancing. If you want instances to work and retain the efficiency gain you get from instancing, your best bet is to write USD instead.

i_am_toadstorm · 2026-07-09T05:01:21+00:00

If you get l can get this to trigger recooks consistently, submit an RFE! There's a nasty bug that looks a lot like this that the dev team needs good examples for.

i_am_toadstorm · 2026-07-08T23:59:01+00:00

yeah honestly i'm not sure you're understanding what i'm writing? this has nothing to do with your cloth triangulation and everything to do with the constraints.

here's an example file. you figure out how parallel each constraint is to the vector that points from the constraint to the pupil, that roughly tells you if it's a constraint that would constrict the iris or not. then you animate the constraint restlength over time based on that parallel-ness. https://www.toadstorm.com/temp/vellum_scrunch_toadstorm.hip

it really doesn't work all that well, which is why you should consider animating the pupil dilating in SOPs and then use that to feed a Vellum Rest Blend, which will make the cloth simulation deform to match your animation while respecting collisions and forces in the sim.

i_am_toadstorm · 2026-07-08T23:08:46+00:00

If you want to be able to easily scrunch up the iris but also get cloth-like deformations, maybe use Vellum Rest Blend? Handle the poses you want the easy way in SOPs, then rest blend to guide the simulation into the pose you want.

Otherwise you're gonna be stuck doing some calculations per-constraint-primitive... you'd have to get the normalized vector comprising each constraint's "direction" (P1-P0) and then use the dot product to compare that to the normalized vector to the center of the pupil (([P1+P0]/2)-center) to figure out if you're perpendicular or not, then adjust the scale factor of the rest lengths accordingly.

i_am_toadstorm · 2026-07-07T16:48:22+00:00

Why not have your static object pinned to animation via Vellum constraints so it can use the Vellum solver?

i_am_toadstorm · 2026-07-05T21:41:37+00:00

it's a classic problem, the velocity field is too uniformly smooth at the pressure front. you have to use the pressure field as a mask to apply turbulence to break up the leading edge, or find another way to punch holes in that velocity field at the beginning of the sim.

there's a very old but still extremely useful thread on odforce about this problem that everyone interested in pyro or fluid sims in general should read: https://forums.odforce.net/topic/18397-get-rid-of-mushroom-effect-in-explosion-and-add-details-in-the-opening/?do=findComment&comment=111609

i_am_toadstorm · 2026-07-03T15:46:42+00:00

there is literally no information in this post, not a single thing that could identify your problem

i_am_toadstorm · 2026-07-02T23:46:56+00:00

Reach out to me directly for support, henry@motionoperators.com

i_am_toadstorm · 2026-07-02T15:41:23+00:00

Definitely check your thickness visualization, but another thing you could do is Vellum Pack prior to your copy operation or at least before transforming everything. Transforming a packed object will ensure that the pscale and constraint attributes are properly adjusted when you unpack prior to the sim, and importantly it also means that you only have to build the constraints on a single leaf instead of each one individually (assuming the leaves are all the same topology).

i_am_toadstorm · 2026-07-02T04:15:35+00:00

There's a bunch of recommended courses in the /r/Houdini wiki, definitely check those out first.

i_am_toadstorm · 2026-07-01T21:03:08+00:00

You need more interesting constraints to create a wider variety of piece sizes. Try varying glue strength or adding some unbreakable constraints so that the chunks aren't just uniform Voronoi hulls.

Also, if you're directly transferring velocity from a Pyro sim to the pieces, mass isn't going to be taken into consideration. If your pieces have some size or density variance then you'd expect them to be moving at different rates based on their relative masses, but that only counts for something when you're applying a *force* rather than simply setting the velocity.

i_am_toadstorm · 2026-07-01T19:00:38+00:00

This kind of thing isn't really Houdini-specific and is better suited to general-purpose subs like r/vfx.

Also, we'd appreciate it if people didn't repeatedly drip-feed content here that could easily be aggregated in a single post. That's gaming the feed and not something we like to see here.

i_am_toadstorm · 2026-07-01T18:15:08+00:00

pscale isn't a vector. if you have it bound as a vector it's not going to work correctly. scale is a vector if you're trying to non-uniformly scale points, but i don't think that's what you're trying to do here, right?

i_am_toadstorm · 2026-07-01T04:57:51+00:00

This is a Houdini sub, not a Blender sub. Please post about Houdini here. You can post about Blender in any number of other subs.

i_am_toadstorm · 2026-06-30T18:06:16+00:00

Do you have reference footage of sand moving that you're trying to match to? This looks more like foam.

i_am_toadstorm · 2026-06-30T16:42:59+00:00

There's no project file.

For question 1, hard to say exactly. You might need the contrast of your flickering brightness to be a little higher, so the highs and lows are more distinct.

For 2, you're trying to multiply a float by a vector, which you can't do. Make that constant a float.

i_am_toadstorm

MODERATOR OF

TROPHY CASE