Bifrost collider issue...

[Anonymous]

Hi guys.

I have an Issue that I can't really wrap my head around.

I did a fracture of an object in Houdini, saved that out as an Alembic file, and importet it into maya. The fracture bake worked fine, and the whole animation of the fracture is imported without problems, and I can play it and everything works.

 now I want that object to be a passive collider for my bifrost simulation.

So far when I have, through the bifrost menu, told maya that my object should be a passive collider, my maya is ending up crashing. Is there something specific I have to do when I have basically an animated object from another software package, and I want to use that as an collision object.

I played around with trying to cache out that animation after importing it to maya, to maybe help bifrost not computing so much data, but I haven't to achieve that.

Any help would be appriciated.

Cheers

[Anonymous]

I have attached a link to a  playblast to show exactly the problem.

https://dl.dropboxusercontent.com/u/31242707/Playblast_Wineglass_Collider.mp4

notice how, when my fracture sim, which is baked into my imported Alembic, starts, my bifrost liqiuid sim stops. Why is this? all my pieces from my fracture sim is separated and I have added them as a collider in the fracture sim. still it does not work.

Any help would be appreciated...

Cheers

[agraham]

Weird that your sim disappears at a certain frame. Are you sure your Playback Speed preference is set to 'Play Every Frame'?

One thing to remember about collisions (or emitters or accelerators) is that the source geometry has to be resolved correctly as a solid. You may want to change your collision mode on the colliders (both the bottle and the wineglass) to 'shell' rather than 'solid', which is the default.

Also, your sim resolution is very low. Reduce your MVS to get more FLIP particles. You may also need to increase your step adaptivity in order to get a more accurate simulation.

[Anonymous]

Yes, my PlayBack Speed is the to Play Every Frame, I checked that twice already.

My theory is that because I am using a Switch node in houdini, to switch from the none fractured model to the fractured model when the cork hit, Bifrost does not know how to solve the collision and there just stops. I did break out the different object from houdini, meaning that the fractured object is seperate pieces. I then made them to a Collision set through the bullet menu, and changed the collision to concave instead of convex to get the original shape on each piece. But it still just dissappear.

I think my next step is to test if it is better that I do the switch of the geometry within maya instead of baked down in the alembic file from houdini.

If I set my collision mode to shell I have no collision at all from the bottle geometry. I do know that my sim resolution is low, but for know I just want some collision on the glass before I up res it. step adaptivity is the same as substeps in houdini? meaning that 0.5 is calculation twice per frame?

[syracoj]

Can you send me the scene and alembic files?

john.syracopoulos@autodesk.com

[agraham]

Ah, I meant to reply to this but it dropped off my radar. Sorry.

What's happening is that you're switching the source geometry under Bullet's nose at the non-start frame.

The Bullet solver evaluates all geometry and potential collisions at the start frame. This is why there is sometimes a lag when you rewind your scene. This is also what makes Bullet so fast; it only evaluates once, then runs the compiled sim. The side effect of this is that you cannot simulate deforming geometry or, as in your case, geometry that changes topologically.

At the point of impact, you're swapping one piece of geo, with a specific vertex count for another. Bullet doesn't know what to do with the geo, so it kind of barfs.

Here's what I would do: simulate your fracture in its entirety in Houdini without using the switch node. Then bring in this baked geo into Maya and run your sim with the fractured pieces as passive colliders (kinematic, that is). When you render, you can show/hide the unbroken/broken bottle.

Actually, no, THIS is what I would do: run the entire sim in Maya using Bullet rigid sets! Yes, fracture in Houdini, but bring that static geo into Maya and sim it there.