Fetch creation frame of RBD fractured object

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Is there a way to use the creation frame of a Breakable RBD object?
Ive been looking around for a while, and could not seem to find it.

I would like to use frame this to trigger multiple events at the same time.

At the moment Im just keyframing, it would be alot nicer if I am able to reuse the creation frame value..
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#1
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you might wanna have a look at the local variables
$OBJCF and $OBJCT (object created at simulation frame / simulation time).
You can read about local variables if you click on the help symbol in your RBD fractured obj or RBD object!

cheers,

Manu
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Manuel Tausch
Senior FX TD - Industrial Light and Magic Vancouver
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#2
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Thanks I will check it out as soon as possible!

Do you also happen to know if I can fetch veclocity from objects?
Or do I need to create a script comparing the current frame with the previous one?
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#3
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If you want to fetch data from dops objects, check out this expression:
http://www.sidefx.com/docs/houdini11.1/expressions/dopfield [sidefx.com]

If you have an object in sops and you want to compute it's velocity then put down a trail sop and change it's “Result Type” to compute velocity.
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#4
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Wow thanks!

Cant wait to test it out..
Ill let you know what happens.

Cheers
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#5
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Hi guys, just tested out some stuff but theres still something in Houdini which I dont quite understand.

When I take a look in the detail view of my object I can see vx, vy, vz these three variables should be velocity if Im correct.

How can I use one of these variables to drive, lets say my particle constant birth rate?

I tried using ch(“../../trial1/vy”), im obviously doing something wrong here, I tried looking around in the manual but im not quite sure what im looking for..

I appreciate all help!
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#6
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Check out the help for dopfield expression funciton:

http://www.sidefx.com/docs/houdini11.1/expressions/dopfield [sidefx.com]

In your case should be something like this:

dopfield(“/obj/dopnet1”, “obj0”, “Position”, “Options”, 0, “vely”)

The ch() function retrieves the value of a parameter. I think you might be mistaking the initial velocity in the RBD Object, which is always set by the user and only used to initialize the simulation. If you want data generated by DOPs you'll have to look into the dopoption and dopfield expression functions.

Cheers
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#7
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Ah yes that seems to be working!

Houdini is quite hard when you're a beginner, I have much to learn..

Ok.. but how would this work out inside SOP's? When I generate velocity trough the trail SOP?

Or am I talking madness right now?
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#8
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johnnycore
but how would this work out inside SOP's? When I generate velocity trough the trail SOP?

Or am I talking madness right now?

MADNESS?!?! You bring the heads of conquered kings to my city steps! You insult my queen!! You threaten my people with slavery and DEATH!!!

Sorry… I couldn't resist…

It all depends on how you're using this. What is your intention? The trail sop doesn't require any DOPs and it calculates the velocity of each point in your geometry, while the vel attribute from DOPs is the global object velocity… Does it make sense?

Cheers
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#9
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Yes I was aiming that the MADNESS reaction..

Uhm I think I understand, the one from DOPS has been given free because of the DOP environment, I dont know exactly why.. if you would like to explain this.. please..

I still dont really understand the trail SOP's velocity, when I emit particles from the surface afterwards I noticed it inherits the velocity of my object. Which is pretty neat..

But my main goal was actually using a velocity variable inside anything I like, for example I would like to increase the amount of particles emitted from an object with the value of my velocity.

Trough the DOP's velocity it works out, now my next challenge would be through a SOP local variable (if it is a local variable).

Ive got this scene in front of me, an Utah teapot, Ive generated some noise in its Y axis so I have a little varience in the animation.
Then I've generated particles from the surface by connecting it as a first imput.

What I want to do now is inside the popnet, there's a source node using the first imput connection, now In this node there should be a Const Birth Rate parameter. I would like to use my Y velocity as a value.

Many thanks again for your time and patience!

Attachments:
attachment grabVelocityVar_01.hipnc (51.5 KB)

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#10
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You can think of the trail sop like this: when you have some animated geometry that came from another package and your fx depends on the velocity of that geometry that's a good place to use. Or if your geometry is not translating but deforming and you want to find te fastest moving points of that geometry… See what I mean? Of course you can use instead of the dop expressions, it's all up to you and as long as it gives you the result you need on that specific case: it's all good!
Houdini is flexible enough that you can build your own trail sop of you wish. There's always another way to get the same result or data.

For what you want, you can just plug the dopoption straight in the birth rate parameter or use a point() expression (if you're using the trail sop) to find the velocity of a specific point in the geometry, which would be relatively fine for rigid body (non deforming).
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#11
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Aah yes I think I understand now..

I've also noticed what I was doing wrong, when I created the trail sop and took a look in the details view I saw some variables called vx, vy, and vz and I tought this was one value in total but it actually is a velocity value per point.

I will try out some stuff as soon as I get home!
It all seems a bit more logical now I think about it..

Thanks again, and I'll let you know how it goes!
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#12
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Looking forward to it!
:-)
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#13
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Hmm somehow the point() expression inside the popnetwork fetching velocity from my trail SOP does not seem to work..


point(“/obj/geo1/trail1” 189, “vy”, 1)


At the meanwhile Ive been trying some other stuff, Ive been able to group my velocity with the group SOP's filter by expression and used it to trigger emission. Which had a quite fun result, the only downside to this is that its feels more like an on/off switch instead of a smooth 0 to 100 gradient.

Do you happen to know what I can do to smooth this out?
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#14
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Hey, sorry for the silence, I haven't had a break at all these days… Can you post your file or some of it so I can take a look?

Cheers
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“As technology advances, the rendering time remains constant.”
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#15
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No problem for your late response, mine is also quite late sorry for that.
Windows 8 + Houdini 12 have been released so I've been messing around with those two for a while..

But just before I installed those it seemed I got it to work, turned out to be a typo..

Thanks anyways!
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#16
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I figured, seems like you're missing a comma there in your expression.
I tried to upload a file this weekend and the server kept timing out so I got fed up and threw it all in the trash can! Sorry for the lack of self control and persistence!

cheers
Toronto - ON
My Houdini playground [renderfarm.tumblr.com]
“As technology advances, the rendering time remains constant.”
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#17
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