Jump to content
sebkaine

Bullet Soft Bodie in Houdini ?

Recommended Posts

Hi Guys,

 

I would like to know if any H expert have try to use bullet soft bodies inside H ?

 

The bullet API has a bullet soft bodie object / solver class 

http://bulletphysics.org/Bullet/BulletFull/classbtSoftBody.html

http://bulletphysics.org/Bullet/BulletFull/classbtDefaultSoftBodySolver.html

 

Maya has an implementation of this :

http://help.autodesk.com/view/MAYAUL/2016/ENU/?guid=GUID-6FA1B885-DF4C-45A8-B7E3-B0991449471C

 

I have not seen this yet in H ?

So i would like to know if it is possible and how you would proceed ?

 

My goal is to have interaction beetween RBD (Cube) and SBD (Sphere) directly inside bullet without using an other solver.

 

Thanks for your time

 

Cheers

 

E

Edited by sebkaine

Share this post


Link to post
Share on other sites

Well it looks after some more search that all the soft bodie part of the bullet solver is not implemented in H

http://www.sidefx.com/docs/houdini15.0/nodes/dop/bulletrbdsolver

 

I guess that 2 only way to get RBD cube interacting with SBD sphere with bullet is to use either a combo of :

- bullet / wire solver

- bullet / cloth solver

 

EDIT:

well it looks that bullet soft bodie is basically a PBD implementation

http://www.bulletphysics.org/Bullet/phpBB3/viewtopic.php?t=7990

http://matthias-mueller-fischer.ch/publications/posBasedDyn.pdf

http://image.diku.dk/kenny/download/kelager.niebe.ea10.pdf

 

 

So i guess the best way to mimic this would be a bullet / POP grain combo

Edited by sebkaine
  • Like 1

Share this post


Link to post
Share on other sites

Thanks for your answer Remi ! :)

 

Yes it looks that bullet use a PBD implementation for his soft bodies component. As H does have PBD implemented with the grain solver it doesn't have any sense to repeat this.

So i will dig the Bullet / POP grain path !

 

Cheers

 

E

 

EDIT :

 

This solver can use simplified representation of the objects, such as boxes or spheres, or a composite of these simple shapes to make-up a more complex shape. This solver can use arbitrary convex shapes based on the geometry points of the object, and can also collide objects against affectors that are cloth, solid, or wire objects.

 

POP grain is not mention explicitly in the doc so i will double check that both solver can affect each others ...

Edited by sebkaine

Share this post


Link to post
Share on other sites

I can add there's a point where grain based soft bodies get very hard to control and it starts getting easier with FEM... Here's a grains setup I was doing RnD for that just wouldn't play along trying to balance bouncyness with dampening, ets...

 

 

And here's the FEM version in a slapcomp...

 

  • Like 1

Share this post


Link to post
Share on other sites

Thanks for your feedback Johnny !

 

I have play quickly with a bullet / pop grain combo. It look ugly and it's slow as hell.

I am certainly the one to blame , as i have not use the grain solver very much ... but the fact that the connection are build in a esoteric way is really weird for me.

 

i just want that each point of my object became a particle and that each particle get a bend / shear / tear spring at each connection like nCloth.

 

I will also need to put some inflating pressure in the sphere, i'm mot sure i could get this with POP grain solver , so i will now try the bullet / FEM combo ...

 

i've attach a hip that roughly describe what i'm trying to do !

 

Cheers 

 

E

test_v001.hiplc

Edited by sebkaine

Share this post


Link to post
Share on other sites

Slow? It's not even a second per frame on my old computer...

 

As for it being ugly, I don't know what you're trying to achieve, you may want to increase the resolution and change the explicit constraints values in the grain update node

Share this post


Link to post
Share on other sites

yes it's pretty slow for a bunch of small cube and a sphere imo !  :)

 

i have done this 5 min test with nCloth just to illsutrate the idea.

 

basically :

 

- the cube are RBD 

- the sphere are SBD with a water balloon behavior 

- both collide together inside spherical object that rotate

 

Thanks again for your help Remi ! 

 

Cheers

 

E

nCloth_test.mov

Share this post


Link to post
Share on other sites

Here's a quick tweak to get it working better, but this type of setup is all about tweaking - 5 minutes to set up - 6 months to get it looking good. ;)

test_v001.FFv1.hiplc

Edited by Farmfield
  • Like 1

Share this post


Link to post
Share on other sites

 5 minutes to set up - 6 months to get it looking good. ;)

 

Exactly :)  The kind of stuff you try to avoid like the plague ...

 

You're test is far better johnny what are the main stuff you modify to avoid the collision problems with the container ?

 

I will also give cloth a try with this one !

Share this post


Link to post
Share on other sites

For the penetration issues, just increase the collision padding, then I also decreased the grain separation a tad, I also changed the grains from sheet to solids, decreased the constraint iterations to get them a bit spongier, and in SOPs, something that should be on from the start, I activated the "compute mass" (with a low number) in the grain source as, without it, the solver just has a tendency to do weird stuff (though more important with loose grain setups than using them as sheet/solid).

 

Personally, I would say - to paraphrase Donald Trump - the grain update node is a mess. You really have no idea what stuff does and if you read the help section about it and think you understand what they do, it's still not gonna do what you want, sadly. This is actually a type of setup that is easier to control in PFlow where it's all about the constraints while Houdini's grains are their own constraints, if I understand it correctly - either way, they seem to work more like FLIP than as particles with constraints. It's not the easiest feature to setup and get predictable results from, that's for sure. ;)

Edited by Farmfield
  • Like 2

Share this post


Link to post
Share on other sites

Hi Pavel,

thanks for file, great idea and it's quite fast.

At first I thought that constrained spheres would collapse and loose their volume but they didn't fortunately :)

 

Juraj

Share this post


Link to post
Share on other sites

You are a JEDI Pavel ! 

 

This is EXACTLY what i have in mind 

- 100% bullet solver 

- VERY fast solve 

- each point of the object represent a collision point 

- each point of the object are linked with a constrain

- Simple / Concise / Controlable 

 

Thanks for your magic Pavel ! :)

 

 
@Johnny
 

 to paraphrase Donald Trump - the grain update node is a mess. You really have no idea what stuff does and if you read the help section about it and think you understand what they do, it's still not gonna do what you want, sadly

 

This is exactly what i think of this POP grain node ... my personnal word to describe it would be esoteric :

1 - either you have spend times and know every weird controller

2 - either you make some incantation , cross as much finger as you have on both hand and pray to get the good enough presets 

 

unfortunatly i'm actually in the second category ... you look to be somewhere in the middle of the two ! ...  Lucky guy ! :)

Edited by sebkaine
  • Like 1

Share this post


Link to post
Share on other sites

@Pavel

 

This is way more like I would have set it up in Max using Pflow, where you use the constraints to build (thus pretty easily control-) the soft body shell - though I wouldn't have known how to do this until I saw how you've set it up here. Very cool.

 

Not often I miss Max but for particles, there's parts in Pflow and TP I just love the simplicity of.

 

@Emmanuel

 

My biggest problem is I'm often on autopilot, so I'm not really conscious about what I'm doing, tweaking stuff, even when I get it to work - and it's not that I don't know, I'm just not overly aware of that knowledge, hehe... There's just something with Houdini that just clicks with my mind, I guess, this last Monday, the 18th, was my 1 year anniversary of officially migrating from Max to Houdini, so it's not that I've using it for that long... ;)

Edited by Farmfield

Share this post


Link to post
Share on other sites

Hello, Guys.

I wanted to share this with you.

Here I am using @Pavel's awesome method. I am building the constraints using the geometry edges. I am really surprised how well this works!

For the initial rollup, I am using a VEX method from a fellow from this thread:  http://forums.odforce.net/topic/25760-curling-hair-curves-with-vex/#comment-149896

Thanks alot!

 

bullet_cloth.hipnc

bullet_cloth.gif

bullt_wire.gif

  • Like 7

Share this post


Link to post
Share on other sites

great examples,  is somewhat ironic and sad that constraint relationships works a lot better than cloth in terms of collisions,   :mellow::mellow::mellow:  

i was thinking that houdini was the best in terms  of cloth <_<

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

×