Alembic Fracture

[theviolator]

Hey guys,

I was wondering if it's possible to voronoifracture and have an RBD sim of an animated object brought into Houdini using the Alembic import (which means geo cache). My problem is that after I fracture it the pieces change randomly over time. Is there any solution fo that?

So, basically you import an alembic animated (deforming) object and dynamically fracture it over time and still retain its animation throughout the timeline?

I was trying to find something like that online, but so far haven't seen if its even possible.

[Nerox]

Hi James,

Well what is happening is that the voronoi noise that scatters the points is driven by P. When your character moves/deforms, P does as well.

Depending on what you're after you have to figure out a way to deform your voronoi points along with the character. I think the easiest way would be to scatter at the first frame and then use the cloth capture and cloth deform SOP's. The tools are build to deform static highres piece of cloth with a simulated lowres piece of cloth, avoiding the need to sim very dens geometry.

You can apply the same idea on your setup, where your voronoise points are the highres geo, the characters geo on the scatter frame is the rest geo and the animated geometry of the character goes in to the last input. Just look at the example file that comes with the help file for Cloth capture.

http://www.sidefx.com/docs/houdini12.5/nodes/sop/clothcapture

Another method could be to import your character as an FBX and have Houdini rebuild the rig, scatter on the first frame and then deform the scatter points with the rig like you do on the mesh. But I'm not sure that would actually work.

Good luck,

[theviolator]

Thanks Nick, I think the cloth capture/deform is the way to go, importing FBX crashes Houdini every time! The only part I wasn't sure is how to connect the cloth deform node to the rest, I can't seem to find the example files online

Thanks for the tip!

[Nerox]

You'll find them in the local help, just go the the help in Houdini and copy past the last part of the url

[theviolator]

Ok, I think I got it, but it has some weird results. When I sim the fractured object, some pieces fall to the ground and some are still affected by its geo cache animation and also trying to act as dynamic objects which results in some weirdness.

Its definitely tricky

Edited April 28, 2013 by theviolator

[Nerox]

As for reference, this setup deforms a set of points, that are scattered inside a box, by deforming the same box. Mimicking the lowres simulated cloth to highres cloth workflow.

deform_scatter_points_v01.hipnc

[theviolator]

Thanks man, but here's my problem:

Check out this setup, it works e.i. fractures the geo cached object, but the problem is that when it moves its pieces start flying around because are driven by the RBD and the geo cache animation at the same time.

I'll try activating/ deactivating them, hopefully that works. Let me know if you have any ideas though.

Thanks!

[bloomendale]

Maybe you can fracture geo at 1st frame (use timeshift node) and then deform this fractured geo using initial one as deformer (with mentioned cloth capture and deform nodes).

EDIT: something like in attached file (i don't have alembic geo, sorry)

3ak_deform_fractured.hipnc

Edited April 28, 2013 by bloomendale

[Nerox]

If you look closely at my setup you can see that the fracture and rest geo are from 'the first frame', so you should slip in a timeshift SOP, deleting the expression and set it to 1. On the cloth deform node you should never have the same rest geo as the deforming geo (2nd, 3rd inputs) same applies to the cloth capture, the second one should always be your 'first frame'.

None of this is rocket science, just read the network and don't expect any magic its just common sense. Every node has a very specific task.

You can also simplify your network, first make sure your scatter points are correctly deforming with the character, then move to DOP's.

Edited April 29, 2013 by Nerox

[theviolator]

Yeah, I think I got it. Not as complicated like you said. I wanted to somehow still drive the geometry using the alembic cache and slowly transition into the RBD sim, was going look nicer that way. Right now I just write out the frame I want to shatter, read it back in and activate the pieces with activevalue, - not ideal but it works. The rest of the geometry is deformed with cloth capture/deform.

Thanks for the tip!