Problems with BulletSim

Tips and discussions about using OpenSim
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Kayaker Magic
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Problems with BulletSim

Post by Kayaker Magic » Sat Dec 01, 2018 6:40 pm

A long time ago (August 2017) I submitted several Mantis bug reports about BulletSim (Mantis #8010 and #8011). These were reports that Bulletsim often does not call the collsion_start() event even when it obviously DID detect a collision because you see one object bounce off the other. Mr Blue looked into the problem, says he fixed it (or made it a lot better) and eventually submitted a new version of BulletSim, which eventually made it into the OpenSim release.
Today in Kitely, I saw a bunch of objects bouncing off other ones without reporting collision_start() events. Has the version of bulletSim here on Kitely been updated to include the fixes done for those Mantis reports?
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Ilan Tochner
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Re: Problems with BulletSim

Post by Ilan Tochner » Sat Dec 01, 2018 6:49 pm

Hi Kayaker,

No, they haven't. We're using the same BulletSim code that is included with OpenSim 0.8.2.1.
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Kayaker Magic
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Re: Problems with BulletSim

Post by Kayaker Magic » Sun Dec 02, 2018 5:21 am

So, from my other thread this weekend, ODE has problems. And from this thread BulletSim has problems. Many BulletSim problems have been fixed in newer versions of OpenSim. ODE is never going to be fixed, unless you count ubODE as the fixed version of ODE. And ubODE will never work on OpenSim 0.8, only 0.9 and better. There are also many other bugs fixed in 0.9 that will never be fixed in 0.8. Finally, 0.9 has been in use on OSGrid and several commercial grids for quite some time.

I think it is almost time for Kitely to consider upgrading to OpenSim 0.9. They did release 0.9.0.1 some time ago, but several important improvements have been added since then. I would recommend waiting until the next "official release" and upgrading to that one. But I would recommend that you start getting ready for it!
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Re: Problems with BulletSim

Post by Ilan Tochner » Sun Dec 02, 2018 6:14 am

Thank you Kayaker.

Our general recommendation for OpenSim has always been, and still is: don't set anything to be Physical, regardless of which physics engine the region is using. None of the OpenSim physics engines (even the most updated ones) are problem free. They all have some issue that can easily bring down a sim. If you want to do anything physics based in OpenSim then simulate it via scripts without relying on the physics engine.
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Kayaker Magic
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Re: Problems with BulletSim

Post by Kayaker Magic » Wed Dec 05, 2018 8:30 pm

I’m the LAST person who should be recommending Physics Engines. Most people think they need a physics engine to make vehicles, but I have made many vehicles that use llSetKeyframedMotion instead. Unfortunately the physics engine does other things besides vehicles, like detect collisions and implement the llCastRay function (which can replace physical bullets in weapons). I gave a talk at OSCC last year suggesting that we need a “collision engine” separate from a “physics engine” and may not really need physics at all.

But we are stuck with the architecture that we have, and the OpenSim developers have fixed problems with collisions and llCastRay by fixing them in the physics engine. So even though I never use the vehicle API in the physics engine, that engine needs to be there for the other things it does.

In OpenSim 0.8 I would like llCastRay to work faster, to work the way it is supposed to and NOT detect phantom objects. But the only version of OpenSim with this fix is OpenSim 0.9 with the ubODE physics engine. I’d like for non-physical objects to tell my scripts when they collide, but this doesn’t work unless at least one of the objects is physical. If you can’t use llCastRay for weapons then you have to throw physical bullets around. This apparently can crash the ODE engine. Switching to the BulletSim engine can cause unusually high CPU usage, so Ilan does not recommend using it. Where can we go? I think the new version of OpenSim 0.9 has reached the point where it is now more reliable than living with 0.8 and crash modes like the one in ODE I discovered.

And there have been a lot of other fixes in OpenSim besides the physics engine. For example the HTTP stack has been completely re-written. This can make loading textures and mesh twice as fast as they were before.
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Re: Problems with BulletSim

Post by Ilan Tochner » Wed Dec 05, 2018 9:30 pm

Hi Kayaker,

Kitely's version of OpenSim is currently 0.8.2.1 with over 400 proprietary patches of our own that are better than some of the changes made to OpenSim 0.9. Thus, while our OpenSim system is not currently based on the latest OpenSim version it is still better performing and more stable than that newer version in some regards. For example, our assets system sits outside OpenSim and uses an optimized HTTP server that performs better than what OpenSim 0.9 includes, thus asset handling won't be improved in Kitely by us switching to OpenSim 0.9.

I agree that it would be good to switch our physics engine to something more capable, but that is just one of a long list of things we could do to improve our service, and it isn't at the top of the list in terms of impact it will have on our offering. As you know, we have a lot on our plate and some of the things we're currently working on can be beneficial to our users much more than improved physics handling. I wish we had the resources to do everything at once, but we're not there yet and until we are we have to constantly prioritize what we work on.
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Re: Problems with BulletSim

Post by Trouble Ahead » Thu Dec 06, 2018 12:43 am

Hello Ilian,

I totally understand you need to make choices what your priorities are. In my opinion, Kitely could provide people a great place for players and scripters who are interested in building vehicles ( and designing games with them), for its excellent sim performance . I know communities in SL who are waiting until this grid is ready to go for that. ( Maybe better not underestimate the amount of players in virtual who are interested in this feature.. seeing the SL planing and sailing communities suffering from high prices and lots of lag... the grid that offers better performance will get the customers .. )
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