hello there,

i'm actually a softimage-xsi user but still looking over to sidefx since long ago and watching how this great piece of software is coming along. but due to my interests & environment i'm focused mainly on xsi.

anyway, i came here to ask if you guys could tell me if it's difficult to setup a procedural system for a destruction of an object. imagine a building or a skyscraper that is collapsing (also this radiohead musicvideo by the mill could be an inspiration). - right now i can't do this really in xsi (also the mill did most of the rigid dynamics & fragments in maya), because xsi 3.5 has no rigid bodies (now 4.0 is not yet shipping, but in a few weeks). and neither it has something i could use for fragmenting or shattering my object with a lot of detail. actually there is a script, but if you try to do detailed shattering it just freezes.

more or less i'm just intrested to know how this works in houdini to see if it's worth looking deeper into it (because i've only apprentice and can't throw out a lot of money again for another 3d program)…

thanks in advance

Well simulating fracture, or general destruction is a large subject….

Depending on how precise you want it to be, there's many approach to that.
It depends on, for exqmple: if you want solid shards or not, how many shards you want, do you want to see a progressive fracture, do you want to make shards real rigidbodies, or instances of geometry driven by a particle system, allow them to re-collide.
Animating 1000 rigid bodies with inter-collisions can be hardly manageable
(i think it is on any software…)

About Houdini: there's no built-in “fracture fonctions”. There are several ways to achieve interesting destructions FX: to break a piece of geometry in all its primitives ( but in this case all the shards look the same).
-> Look at the breakingice tutorial in the Community section at sidefx.com

You can, with some coding, break an object in parts that are not single primitives but pre-defined groups of primitives ( i'm creating an digital asset like that, that would allow the user to use a texture to define groups of primitive -> thus you pre-paint or pre-shade procedurally your surface to create all the different zones…).
Animating each shard is then almost OK, but make it collide with the ground ( as a piece of geometry and not a particle) is abit complicated.
(and it means not to use inter-shards collisions…)

Houdini handle rigidbodies in a bizarre way ( i've never seen any tutorial on it).

It depends on the experience you have with houdini ( expression and vex-scripting, OTL creation), but as Houdini doesn't like pre-made FX, the setup can be difficult for great realism!
It depends on your project. Maybe it's worth it.

hey FrenchOP

i was wondering if u could explain or maybe redirect me to somewhere where i can find information out about shattering an object using RBD.

I have achieved this using pops and a primitive sop, which is really great for large scale shatters, however that doesnt have intershard collisions, and im looking for a very intimate close up realistic effect. of course u dont need too achive that for me, however i have no idea how one can take facets of an object and get them to intercollide.

and as u were saying, theres almost no information online about RBD and it would be great if u could throw me a few pointers.

thanks in advance

aracid

I cannot redirect you to some info on the web for the simple reason that there isn't any.
( i don't understand why).

So, i cannot make all the things, and i dont usually use RBD but i'm gona try to give you some help.

First, i would say that you must think of a rigid body like a softbody in houdini.
The rigid body is represented in Houdini by a single particle ( whose “instance” attribute is the name of the OBJit refers to) and not by all the points of its geometry.
Now, how to create a RBD.
There's two types of rigid body: active and passive (active can be affected, passive only affect (like walls),
the way i make a passive RBD is by setting its mass attribute to 0. (i don't remember where is the special POP for that but just use an attributePOP ( name: mass, value 0)

To create all the stuff you must begin in OBJ mode.
Use the RIGID BODY DYNAMICS operation. Select the OBJ you want to make a RBD ( RBD work at OBJ mode, that is a problem, i will explain later).
It creates a RBD_pop popnet and a RBD_Chop chopnet.
Let's say it's a cube falling onto a plane

To add other RBD, stay in POPS, create another RBDPOP
which refer to the wall OBJ , withe the AttributePOP, set its mass to 0.

Add a velocity POP to the cube.
For the moment the two POPs are not connected together.
Now just wire all your RBD pops to a CollectPOP ( that's the key).
That's it. There will be intercollisions and anything you want…

What is painstaking is that RBD refer to OBJ, so if you have 20 shards, that means that you must have 20 objects and that you must repeat 20 times the RBDcreation operation. ( unlessthere's another way but….)

- > Here comes the scripting part. I never did it, but it's doable.

I hope RBD will be re-thought in next houdini versio.

Hey FrenchOP

thanks alot for the explanation

one thing u make clear was that one needs to have separate objects when doing something like a shard collision RBD.

its strange cause when i was reading up in the pdfs on RBD, it said one can easily shatter objects.

its a bit of a pity, however i suppose with a bit of scripting it can become quiet an easy task.

anyways

thanks once again for clearing things up :-)

all the best

aracid

I'm actually trying to figure out rigid body dynamics as well at the moment to try to simulate a realistic pool break. I've posted a question over in the online course at www.3dbuzz.com.

A patron by the name of Moose has replied with a really good example file for it although there are a few issues.

to see the thread you need to register at 3dbuzz.com and then sign up for the houdini 101 online courses. Then go into the virtual classroom.

Unsure if it will help but…..

Cheers
Starkhorn

hey starkhorn

thanks alot for the address, Im definately gonna take a look,
new infos always great :-)

all the best

aracid

there's also reactor, which can be a pain but is
quite fast. I've seen someone successfully use it
to collapse a house with all its individual roofiles
and structural elements behaving convincingly.
However I think it took him a few days of trial
and error (he hadn't used reactor before).

-cpb

hey cpb

yeah, ive seen reactor, if its the max dynamics engine you talking about, its really impressive.
real time dynamics is something i've seldom seen.

all the best

aracid