Complex Collision Compounds (1.53 and 2.0)

[Cote-Duke]

Hi again,

This time I have some notes about my work with collision compounds. Application that I'm currently working on requires very precise collision geometry. Moreover, bodies using those collision should be fully dynamic. So, naturally, I use compound collisions made of convex hulls.

Here's the setup. Several objects each of which consists of a single rigid body using a compound collision. Each compound is approximately using 10-80 convex hulls. Convex hulls basically are two frustums symmetrically inverted. (Hulls are extruded from a quad along its normal in both directions).





However under the only force of gravity it literally explodes on 2.0, while on 1.53 it continues to work just fine.

Here's how this setup behaves on 1.53: http://www.youtube.com/watch?v=hsUtngIrPJc
And that's 2.0: http://www.youtube.com/watch?v=oNgV-ua76pQ

Tolerance parameter on convex hull creation in 2.0 seems to affect this behaviour - the smaller it is, the more violent the explosion gets.

The problem in 2.0 case seems to come from excessive inter-penetration of above-mentioned hulls. Contacts with impossibly huge forces are constantly being generated. Killing those contacts makes things a bit more stable - but it's clearly not the way to go.

[JernejL]

Do the hull objects themselves penetrate each other in hulls?

I actually had a similar problem very early when making my spaceship engine prototype, i placed a bunch of complex ships onto a big cube with gravity. when the pile went very big it had a tendency to explode, but that was a non-issue in spaceship sim as that would be a very rare thing to happen in such a game so i didnt pay attention to it anymore - but it looks like you are having the same problem.

[Cote-Duke]

Do you mean do the hulls penetrate each other inside the compound? If so, then yes. A bit. Well, it's very hard to prevent and I didn't think it may cause much trouble.

[JernejL]

Do you mean do the hulls penetrate each other inside the compound? If so, then yes. A bit. Well, it's very hard to prevent and I didn't think it may cause much trouble.

I dont know if that could cause it, but it might be important issue for julio when he sees your problem.

I also suggest you make a example exe that he can try out.