Whatsinaname

You might want to check out the documentation on grains and POPs, many attributes are shared.

You just need a more advanced intersection test, checking if any particular primitive or edge is intersecting the volume.

Although you could export each of them as a single object, I'd strongly advise against doing so. Apart from that, exporting an OBJ sequence would probably destroy any velocity data etc, so you might want to stick with Alembic. Alembic can be a bit of a pain when it comes to transporting data into your desired target application (maybe it would be easier if we knew what that is). However, it allows you to write attributes to your points and there are numerous ways to read these attributes in your target application.

According to Jeff lait from SideFX, PBD in its current installment won't allow any bouncy behaviour. So Karl's solution might be the only viable one, deactivating PBD behaviour in order to make the particles bounce. (He says it in this video, at about 27:40)

You might also try applicating a force towards the inverse normal direction, using SOP Solver inside DOPs or some POP wrangle. I did that successfully in the old pre- Vellum days to create a crumpling effect.

The problem is you are not supposed to be doing any commercial work with the nonCom license. This includes setting up a scene. What you might want to do is getting yourself a Houdini Indie license...which allows you to be doing commercial work unless you are making more than 100k$/year... It's a fully functional Houdini license for $269USD https://www.sidefx.com/buy/#houdini-indie

You can use the Volume SOP > From Camera to create a volume out of your camera view frustrum and then do a quick check if something is inside the volume (e.g. create group from Volume and delete everything inside that group).

Thanks, Karl, but unfortunately that is not the solution I am looking for. Setting ispbd to 0 will turn off Position Based Dynamics, which is what separates Houdini particles from grains. I was wondering if any bouncing behavior can be achieved with Houdini grains/PBD at all. It seems like grains and Vellum grains in their current implementation are incapable of bouncing.

Particles will bounce off a collision object, and I can influence that using the collider's Bounce parameter. Great. However, if I change my particles to grains, they will not bounce anymore, but slide. No matter what I do and this goes for pop grains as well as for Vellum grains. Settting ispbd to 0 is not a real solution, as this means I am not using PBD/Grains, anymore. Any idea? Here's a very simple test scene, using a pighead. Just activate/deactivate the POP Grains node in DOPs. collision_grains.hipnc

I presume you have been looking into the struts constraint? Also use weld, as this will update the rest position of your constraints. You might also want to look at constraint iterations and substeps, you need a good amount of iterations to get anything look stiff.

Stupid question: Why don't you just keyframe it?

In my sim, everything is behaving nicely, apart from the cloth reacting too strongly to the character's movements. Speaking in real-world terms, it feels like the air density was really high, almost as if it was underwater. Even small movements in the underlying animation are affecting the cloth way too much. I tried playing with the Normal Drag/Tangent Drag attributes in the Vellum Constraint, but these parameters didn't seem to have any effect at all. POP Drag on the solver also didn't affect the simulation, so I was wondering if anybody has been successfully dampening vellum behavior in the past?

Yes, that works nice and fine. I was only wondering if there is a way to make it work without localising as it does so in nCloth.

You could use targetweight on your points, which is a float variable, and animate that (see the help on grains for that matter). I tend to create a Pin to Target constraint, setting Stretch>Stiffness to Scale by Attribute and targetweight as control attribute. Also set Pin Type > Soft, Orientation Pin Type > None and activate Pin to Animation. This should allow you to control the pin strength by animating the targetweight attribute.

Did anybody have any success with vellum cloth on fast moving objects? I'm doing cloth on a character, who is free falling. It's done by an animator and speed-wise, it might be slightly overdone, but there's no way to change that. Simulating cloth on the character using Maya nCloth, I got proper results, but it was still nCloth and therefore slow and painful. I recreated the setup using vellum, but no matter how much I increase substeps, everything is exploding right away. It is working fine with a localised version, but I was wondering if there is a special trick or anything worth considering when using Vellum with fast moving objects? (Unfortunately, I cannot post the scene file)