View Full Version : Bullet and Object Replacement

04-18-2012, 04:45 PM
My original thought was to do a Bullet sim with cocktail glasses (dielectric node). But once you fracture glass, all the breaks show up because of the surface's transparent refractive nature. So I thought I would use object replacement, such as Object List or Object Sequence. I set up my sim with 3 non-fractured objects, ran the sim and noted the frame numbers that each of them hit the ground, and switched objects to the fractured versions at those frame numbers.

But ...

It seems Bullet doesn't like replaced objects. The sim changes completely each time an object is replaced. As soon as the second objects hits the ground and is replaced by its fractured counterpart, the first glass, which is well into being shattered, instantly looks totally different.

:( The crazy thing is that object 1 didn't change at the offending frame, only object 2, and so on.

See the damage here: http://www.youtube.com/watch?v=wc63XyfhYt0

Any thoughts on how to beat this?

04-18-2012, 05:22 PM
no LW11 here, but be sure to FogBugz it though (see my signature)

Mr. Wilde
04-18-2012, 05:33 PM
As a workaround you could try to animate "Object Dissolve" in "Object Properties". So instead of replacing the glasses, you just let them disappear when the fractured glasses appear.

04-18-2012, 09:05 PM
Object dissolve won't work with Bullet either, since the extra objects, although invisible, all affect the simulation, particularly being in exactly the same place as the visible ones. So it's not an option. Believe me, it's the first thing I tried. :)

04-18-2012, 10:01 PM
Fog-Bugz'd it, my new daily hobby ... :)

04-19-2012, 10:31 AM
NT Dev team is FAST these days. I get a clear response, whether I like it or not :D, within a day!

Regarding Bullet and Object Replacement, here is their response: "Changing the mesh during the simulation is not supported at this time. It sees that as a modification to the scene and recalculates the simulation. This is not a bug but a limitation."

:( I guess it's Feature Request time ...

04-19-2012, 11:05 AM
You could run the simulation then bake it and apply the motion to the different objects with a combination of dissolve...
I've not tried, just an idea.

04-19-2012, 11:46 AM
You could run the simulation then bake it and apply the motion to the different objects with a combination of dissolve...
I've not tried, just an idea.

Not a bad idea ... one potential shortcoming with that idea is that the various sims could not react to one another. But the bigger issue is that Bullet Envelopes would have to work perfectly, for things like Glue Strength (start at 100%, then instantly lower to normal level at impact, for the fractured objects). So far, enveloping Glue Strength has not worked AT ALL here -- Glue Strength acts exactly as it is set at frame 0, for the entire sim, no matter what the envelope does. :(

But I'll give it a try. Who knows, maybe I'll get lucky. :)

04-19-2012, 11:59 AM
I stand happily corrected. :) Enveloping Glue Strength does work as expected on Fractured parts objects (just apparently not on stacked parts objects ?).

Edit: This works beautifully. :)