Fracture Examples Like Blender's New Modifier?

[Atom]

HI All,

 

I am wondering if anyone knows how to re-create the fracture effects in Blenders new fracture reel in Houdini?

Mainly the one around 0:58 seconds.

How do I setup Houdini so a RBD cube can rip through another object and tear only small portions out of the target surface?

 

I have been playing around with using Magnet Forces to trigger effects within a fracture object but it seems so coarse compared what I see in the Blender reel which has a finer effect.

 

[pezetko]

Look at Constraints.

This looks like simple Glue Contraint, it's quickly available from the shelf tool.

 

Attached example is something like 0:53 in your video but same stuff could be used for scene with cubes.

pz_glue_constraint.hipnc

[Juraj]

You could also do 2 simulations. One without fracturing to just capture impact points and second sim using same colliders and pre-fractured geometry based on previous impact points.

[Farmfield]

The methodology of doing multiple sims is very useful as you can actually do a sim, then sim other things on top of that while still having the already simulated stuff feed into the RBD to be resimulated. Imagine simulating a sphere falling on top of a pre-fracured element, breaking it, and you cache that sim. Now you set up a new sim with the simulated pieces as static objects and the sphere fracturing but you set it up so any piece of the original simulation colliding with any of the fractured parts of the sphere is switched from static to active, thus from that point being resimulated. These two sims together will be less computationally heavy compared to simulating everything in one go while still maintaining two way interaction between the objects.

 

And a setup like this will of course not work for everything, but it will work for a lot of stuff and not only is it lighter to simulate, it's easier to control as you're setting this up, step by step.

 

Edit:

 

Oh, and this methodology of stacking simulations also works for combining different solvers, like pyro and RBD. You can simulate an explosion, then use those velocities for driving an RBD sim for ejecting debris, fracturing stuff, baking that out, then you'd redo the original sim, feeding the baked objects back into the Pyro sim for edvecting the smoke from the explosion, etc... And it doesn't really matter what we're talking about, FLIP, FEM, grains, it's all stackable like this. 

Edited January 10, 2016 by Farmfield

[Atom]

Thanks for the feeback, I am really interested in how those cubes tear up a surface, however. I want to achieve a similar effect for the side of a building but I have been stuck now for a week. I can't seem to figure out how to concentrate a fracture on a certain area with enough detail. I know how to setup a prefractured object. I know how to fracture on the fly using the VoronoiFractureControl node and magnetic forces but none of those techniques produces enough detail chunks to make the simulation look 'real'. It just looks like "Oh that's some Voronoi chunks".

 

@Juraj: When you talk about two sim steps and reprocessing the second sim control points how do I do that? What file format stores impact points and how would I re-use them in the second sim? What node fetches and records impact points?

 

@Johnny: When you talk about SIMs are you talking about .sim files? Or just simulations in general?

I guess I ask because I can't find a way to playback .sim files. I can write them out from an AutoDOPNetwork but what do I do with them? In what conexts do I read .sim files for re-use?

 

@pezetko:

Here is an example of trying to re-create the Blender style fracture effect. I have pre-fractured the box and glued it together. However, I have to set the glue strength very high to keep the pieces from falling off the edge. Then when the rotating blue box hits the green box it does not cut into it, it lifts it up as if it weighs nothing. I am computing the mass automatically and I have turned that off and tried manual mass values as well. I have also tried turning off the propagation of force through the glue network. We have all of these 'features' but none of them seem to have any affect. Each time I change the values in the sim it always ends up looking the same as the image.

 

ap_cubes_rip_through_board_1a.hipnc

Edited January 10, 2016 by Atom

[Juraj]

Hi, hope it helps.

fracture_by_impacts.hipnc

[Farmfield]

@Atom

 

I say "sim" I mean simulation, I seldom cache to sim-files, I almost always cache to alembic.

 

@Juray

 

Cool setup, something to dissect when I get time. Tnx!

[Atom]

@Juraj: Thanks for the example, that is one complex setup but it still does not do what I am looking for. I need some objects to rip parts out of another object for some time before the rest of the system start collapsing. In your system as soon as an impact occurs all the pieces start sliding off. Is there any way to prevent that sliding for some time? Think of it as Wolverine's claws. He simply rips particles out of the wall when he drags his claws down them but the wall always remains intact.

 

Also, how would I add materials to the various pieces in this work flow? I have never used packed rbd objects or assemble nodes. These seem to defy colorization or materials.

Edited January 11, 2016 by Atom

[Juraj]

Hi,

I modified my setup a bit to support Wolverine's tearing. Important attribute on constraint network is f@treshold. With this you can control how strongly pieces are attached to "world space". You can set this procedurally through noise or paint it. In previous setup treshold value was small and that's why it collapsed after some time.

 

Assigning colors and materials is same as with ordinary geometry. You just need to unpack geometry.

Assemple SOP is convenient way of packing geometry. It's basically mix of partition and pack sops.

 

Juraj

fracture_by_impacts.hipnc

[Atom]

Thanks again for the example file. I think I am starting to understand how the first simulation points are getting used in the second simulation.

[alksndr]

Juraj's file is super cool. I've done it before in kind of a simpler way, have your rbd sim just cache out the say cube in this instance, super basic low res collision with ground, then color it and transfer (within solver using max Cd to save attr) to your high res voronoi'd ground. Then you can drive the active attribute in your real sim from color and only those pieces would ever get activated. Super controllable, super fast. I like Juraj's more though