Grains - how to make 'em bounce off surfaces

[Whatsinaname]

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

Edited May 31, 2019 by Whatsinaname

[KarlRichter]

Set the attribute "ispbd" to 0. See attached.

collision_grains_v02.hipnc

[Whatsinaname]

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.

[KarlRichter]

Look closer. I know it seems like setting ispbd to 0 would disable the grains entirely, but it doesn't! The particles bounce, but still maintain distance. It's hard to see in your test scene so I made one that illustrates this better.

ispbd_test.hipnc

The ispdb flag does not disable grains, it is there to tell the pop solver that a given particle is under control of pdb, so don't apply all the regular pop physics. Indecently,  before I was aware of this flag I would fake a bounce by giving each particle a random upward velocity on the first impact.

 

Edited June 3, 2019 by KarlRichter

[Whatsinaname]

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)