Stacked boxes slide and topple when they should stay still

[Defcronyke 0]

I am using CannonJS with BabylonJS, and I want to make a stack of 3 boxes, all the same size, but when I do, they slowly slide around until the stack topples. I have tried setting restitution to 0, and various values for gravity, mass, and friction, and regardless, the stack always topples itself undesirably. I only want them to topple when rammed with some other object. How can I achieve this?

[fenomas 204]

We can't find the bug in code you don't post  

Here's a sample for what you're describing - how does your code differ from it?

http://www.babylonjs-playground.com/#3AFJJ8

[aWeirdo 338]

@fenomas 

I bet he's using square boxes, http://www.babylonjs-playground.com/#3AFJJ8#1
leave it for a minute and the boxes will have slided out of place by a little bit, leave it for 20+  5'ish  minutes and i bet they will have fallen down.

i remember a simular post not so long ago, i believe it had something to do with gravity, but even at 0 gravity they slide, although it's much much slower than the above PG.

[fenomas 204]

5 minutes ago, aWeirdo said:

5'ish  minutes and i bet they will have fallen down.

i remember a simular post not so long ago, i believe it had something to do with gravity

Nothing to do with gravity, that's just due to the imprecise nature of integrated physics engines. The fix is:

scene.getPhysicsEngine().getPhysicsPlugin().world.allowSleep = true

 

Unless there's a known specific reason not to, BJS should probably set this by default... @Deltakosh

[aWeirdo 338]

21 minutes ago, fenomas said:

Nothing to do with gravity, that's just due to the imprecise nature of integrated physics engines. The fix is:

scene.getPhysicsEngine().getPhysicsPlugin().world.allowSleep = true

 

Unless there's a known specific reason not to, BJS should probably set this by default... @Deltakosh

i don't think they are being "allowed" to sleep, gravity is pushing on them and they are in constant collision with the other boxes, http://www.babylonjs-playground.com/#3AFJJ8#2 (increased gravity to speed up the effect)

whatever it is, something isn't quite right  

 

edit;

Ok, at around normal gravity with your line including the effect is almost gone, i can still see a very slight edge being made,
but it's close to none, so unless it's a scene they will run for hours i think it's reasonable  
it could ofcourse also be from the first collision when the boxes were made, makes sense.

[fenomas 204]

Yeah, physics engines are inherently not quite precise. If you drop one perfectly level box onto another, in general it still may shift a teeny bit due to, say, which order the vertices are processed in, or whatever. This is just part of how things work - in general the only thing that makes the simulation more precise is using smaller timesteps.

As for sleep, all it does is suspend the simulation for bodies whose velocity/acceleration is smaller than some threshhold. So the simulation itself doesn't get any more precise, it just stops getting calculated when not needed.

[Defcronyke 0]

13 hours ago, fenomas said:

Nothing to do with gravity, that's just due to the imprecise nature of integrated physics engines. The fix is:

scene.getPhysicsEngine().getPhysicsPlugin().world.allowSleep = true

 

Unless there's a known specific reason not to, BJS should probably set this by default... @Deltakosh

This fixed the issue, thank you!

Additionally, to have my sphere player able to still move and not fall asleep along with the boxes, I had to do:

sphere.physicsImpostor.physicsBody.allowSleep = false;

 

[fenomas 204]

@Defcronyke 

The player body should wake up automatically if you move it in physics-friendly ways (like applying forces to it or moving it with joints). If you're manually changing its position property or similar, yeah, you may need to disable sleep for it - but this may cause other issues depending on what you're trying to do. If you have issues, there have been a couple of threads in the past about how best to move a player in a physics scene that might be helpful.