Max phys objects

I'm really not sure if this is right forum to post really but anyway. I'm a bored scripter and I was wondering if anyone knows the reccomended and/or theoretical maximum number of physical objects a "clean" sim can handle? As I was thinking about setting up a very large number in a physics objects in some kinda playing card structure and watch it fall apart. Anyone would be welcom to come and watch and I'll probably film it and slap it up on the net.

I ask live help and didn't get much of an answer, but to be fair the lindens probably have more important stuff todo.

Thanks in advance.

not sure what the max is, but if you get alot of things colliding on a SIM your pretty much guaranteed a visit from a Linden.. I think all the griefing lately has them on pins and needles when things start going bump in the night..

14,996.

Determined by going to a private sim, left-clicking on the land name in the toolbar, left-clicking objects tab. Simulator Object Usage value.

errr I dunno, isn't that the max number of prims it can handle rather than physical objects? I'm sure if you set that many physical objects off the sim would surely crash.

I wanna see!

It's not empty - there were 4 prims in it. An empty full sim can handle, according to the specs 15,000 items.

Somewhere around 100 - 200 physical items would be my guess. Certainly at around the 75 mark the sim is really struggling, but stays alive more or less. I *don't* advocate repeating the experiment though.

It depends on what those physical objects are, and what they are doing.

Try rezzing 100 physical twisted toruses - your sim will likely crash. 100 simple bullets, not so much problem. Or 20 complex particle-spewing collision-detecting bullets, you'll get a serious slowdown, where you can't do anything except move the camera.

Yes, you can fill a sim with 15,000 objects and not lag the sim at all. Place 15,000 cubes on the ground spaced .2 meters apart and with physics enabled, and all will be well.

However, stack up a pile of about 200 spheres and the sim is going to start lagging.


This is a complex question because there is a CPU-saving feature in SL to reduce physics load.

Any physics object that has not moved or rotated beyond a certain amount within a certain short span of time is considered to be not moving. The motionless object is silently changed from physics enabled to physics disabled to eliminate it from sim processing overhead, and save processing power for objects that ARE in motion.

So the cubes are rezzed physical, fall to the ground, and sit there for a second or two with physics enabled. The engine determines they are not moving any further and silently changes them to physics-disabled. All 15,000 physical cubes will be treated as if they are nonphysical after the engine has determined none of them are moving, and physics load is minimized.

The stack of spheres may be sitting inside a ring to keep them from rolling away, and so are not moving around. But physics-enabled objects touching other physics-enabled objects impart impacts on those neighboring objects that cause them "jitter" subtely, similar to Brownian motion of real-life molecules. This jitter prevents the objects from being set to non-physical by the engine, and so the stack of spheres will continuously consume physics processing power.


The physics-disabling system does save power, but leads to weird effects:

1. A physics-enabled ball on a pedestal is disabled by the sim to save CPU power. If the pedestal is pulled downward or removed completely, the ball sits there in midair because it is not being treated as physical.

2. A pendulum-like swinging object can get stuck on the upswing, where the object slows down, stops, and then reverses and accelerates. The engine assumes the upswing pause to mean the object has stopped moving, and so disables physics, leaving the object awkwardly "hanging" in the upswing position.


In either case, physics can be forced to stay enabled by llpushing the object with zero force. This prevents the sim from detecting the object's physics as motionless.

I did a small test last night, as part of a test of a conversation with Ms. Chance Takashi, where I created a (large) number of prims that all hung in the air, and that enabled physics on themselves on command...

Then they fell...

With 200+ prims, the affect on the sim was non-noticeable.


- d.

With 1200 prims, the effect was very noticeable.

I strongly recommend against anyone repeating this experiment.


- d.

It does depend on other things. It didn't crash the sim at all, but I made a sort of "ball-pool" like you see in kid's play areas. The balls were physical, the container not.

Somewhere between 1 and 200 all those collision crucified the sim (TD<0.1, often MUCH less).

Just being physical doesn't appear to add much load, but colliding, especially multiple on-going collisions is messier.

I suspect that, once the prims started landing, the collision rate was along the lines of >50% ...

It still was... ouch.


- d.