Flicker on RBD sim when rested (Lighting?)

[Eucalyptus]

Hey guys,

I haven't stopped by the forums in several months but picked up an old simple project I was working on and finished it this weekend. I'm relatively new to Houdini, but know my way around the program quite well.

I've made an RBD simulation with some glue effects (link to video below), but I seem to have a problem with the lighting and shadows "Flickering" once one of the object pieces comes to rest. It's not the pieces still moving, as they often do, it's actually something with the shader or lighting. But I don't know what?

Any idea what might cause this and how I can fix it?

Things to note:

The Torus pieces are using a Glass shader - no object/environment reflecting - Refraction model (Translucency) - otherwise pretty default settings I think

I tried lowering the opacity limit to 0.75 in render... it made the render take like 12 hours, and still did not fix the issue. (Physically Based Rendering)

No motion blur, No depth of field.

Rendered as PNG's with a gaussian 2 2 filter.

** I don't know what the random red glare on the pieces is either, but it looks kinda neat so don't care about that. heh.

Video Link: https://vimeo.com/67014605

Any replies appreciated!

Edited May 27, 2013 by Eucalyptus

[Eucalyptus]

Any ideas on this?

It's using ray-traced shadows with default settings. Even if I could narrow it down to a lighting, shader or shadow problem I could tweak at least.

Scene uses a single light, nothing fancy. Area light I think, not at home so can't check.

[Solitude]

Can't tell for sure, but it looks likethe pieces are actually jittering from the sim. I only say this because the two pieces that get stuck in the box at the top aren't jittering, but the ones resting on the ground are. Are you using bullet by any chance?

[Hudson]

Hey man! Are you sure they are completely rested?

Because I had the same problem as you altough I don't think my pieces were completely "rested" since I had a geometry growing beneath the ground almost during the whole simulation. I started getting the flickering once I used that geometry to lift up the pieces on the ground. So Houdini is maybe preventing the pieces to get rested? I am not sure but I would be glad to hear the answer from someone experienced.

Here is my sim.on the breakdown you can easily see that the flickering only appears on the ground pieces (where my growing geometry is placed) and not on the pieces from teh wall or maybe my sim isn't long enougth to compare..

https://vimeo.com/64965593

I was using bullet

Edited May 27, 2013 by Hudson

[Eucalyptus]

Hmm... interesting point. A few of the pieces on the far left are not flickering (minus the small one spinning like crazy), as well as the two that get stuck on the ramp top.

I'm still at work now but will have a look when I get home. I believe it was Bullet though, yes. Any known fixes or ways to force them to freeze position once they reach a certain movement threshold?

[Hudson]

I am a meganoob and I really hope it is a better and suitable solution for this

But from the top of my head I would go thru the simulation in dops. Import back the pieces into SOPs, compute the average velocity of the points for each piece( you can probably use the piece group created before the sim) in your fractured object. then apply a threshold value which decides when the average point volocity of a piece is to low and set the point vel for all that piece to 0... it is tricky and maybe unnecessary but it should work with a bit of keyframing(keyframe after 4 seconds when all the pieces are on the ground) and also tweaking the threshold value. After that you could go thru the "special" cases when some piece has zero velocity but should be kept in the simulation.

Well, as I said I hope it is another solution but this might help

/Cheers

[Eucalyptus]

Turns out there's an RBD AutoFreeze node which seems to be what I need. Been tweaking it a bit and it seems to be working, just need to get it right. It works on a Decay of calculated motion, and then allows you to input a minimum threshold and freeze threshold, exactly as I was describing what I needed.

Clearly this was a foreseen problem by SideFX