BULLET PHYSICS FIXED

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Snoots Dwagon
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BULLET PHYSICS FIXED

Post by Snoots Dwagon »

Okay I just discovered this today. May have been fixed for some time. But for some folks this may be a major thing.

For quite some time the major drawback to Bulletsim physics was that Bullet didn't recognize cut prims. If you hollowed a doorway in a prim, Bullet would treat it as solid and you couldn't walk through it.

I just discovered (by random testing, out of curiosity) that apparently this has been fixed. Hollowed and cut prims appear to work fine... which removes THE major issue of Bullet physics.

This is good news, because Ubode, while purportedly a "better" physics engine, has significant problems with older meshes. It doesn't recognize the mesh shape (because "proper" meshes must have mesh hulls and mesh physics shapes). So one can't enter the doorways of homes, can't walk through caves, etc unless the mesh is "done right". (In other words, Ubode isn't compatible with either ODE or Bullet.)

The solution has been to turn the mesh phantom and add invisible prim floors (which frankly is probably a good idea anyway, from a physics standpoint)... but that can be a lot of work if one has dozens and dozens of old mesh structures... or complex-shape caves and caverns.

So if one doesn't get along well with Ubode or if you have a bunch of Bullet vehicles... Bullet now works.

For this Dwagon, that was very good news.

(Note: if you're a sailing fan and have an SPD ship, doesn't work on Bulletsim unless it says it does. That's something to be aware of.)
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Snoots Dwagon
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Re: BULLET PHYSICS FIXED

Post by Snoots Dwagon »

Well, a follow-up caveat.

I said Bullet Physics is fixed... and in the aspect mentioned above it is. Cut prims now work.

However in testing out Bullet over a week or two, there are still many issues that are problematic in Bullet physics. As a minor-but-inconvenient example: In both ODE and UBode you can double-click while flying to increase your speed. You cannot do that in Bullet. You have to wear a special HUD to enable "fast flying" in Bullet physics. (I'm not sure if this is fixed in Kitely. I couldn't find a Bullet world so had to do Bullet testing elsewhere.)

Vehicles work, but not as smoothly. The slightest bump can cause the vehicle to rock or even flip. So while in ODE I can run an (ODE) ATV across rough terrain, in Bullet physics trying to do that would almost certainly flip the vehicle. There are scripted ways to work around this, but not all vehicles have that extra-stabilization built in.

While cut prims work... they don't work as well as they should. For example, dropping a ball down a hollowed tube may result in the ball sticking partway down. A physical tower tipping over may only tip halfway and then freeze mid-air. Knock over a line of dominoes and that line may stop falling partway through.

So Bullet physics are still quite a ways from quality. Someone did fix the cut prim issue and that at least allows doorways to be entered, so kudos for that. But still in most cases, either ODE (which is a bit slower but seems to be the most stable of the three), or Ubode (which is fast but...*) is probably the answer for most world owners.


* Ubode works, but is incompatible with both ODE and Bullet. Ubode does not recognize the surfaces of hundreds (thousands?) of existing mesh object, so unless it's Ubode-compatible... building doorways can't be walked through, caves and caverns can't be traversed, Bullet and ODE vehicles don't work, and lots of mesh items will have to be significantly modified. If it's a no-mod item... outta luck. For example I have two mesh race tracks-- really nice ones-- which don't work because Ubode places the car 3m above the track surface.) On the other hand, SPD ships require Ubode, so if you're a sailing enthusiast or enjoy tallship battles... Ubode may be your only choice.

Wouldn't it be nice if we had one physics engine that works with everything, rather than three physics engines that don't meet user needs and just confuse the works considerably? This is something I would surely like to see Opensim correct. It's a major issue. The concept behind Ubode was certainly valid (make meshes the "right way"), but ignoring existing meshes was not the answer. Had Ubode been backward-compatible with ODE and Bullet... all of Opensim could have gone with Ubode and there would be no "Why doesn't this work on my world?" physics issues.

Just my outspoken dwagony opinion. :lol:
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