PhysX constraints disintegrate in UE4.8, was OK in 4.7 and 4.6

Development World Creation
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1

Hi,
in my project there are PhysX constraints which, after I opened it in 4.8 are now very jittery and disintegrate very easily in linear directions even though all linear motions are locked. It is the situation where medium/high forces are put on the constrained actors and I know this is always to be handled with care, but it was running very solid in 4.7 and 4.6 without any problems. I just opened it as a copy in 4.8 and now it is unplayable. As mentioned, there were no any problems in 4.6 or 4.7.

Were any new physics features implemented in UE 4.8 or any thresholds changed in the source code or something like this that could be an explanation?

Does anyone else experience physics problems when converting a project to 4.8?

2

It just checked a few other projects with PhysX constraints that where running fine in 4.6 and 4.7. They all do not work anymore. They all have constraints driven by angular/linear motors in common. (no Phat, but constraint actors and rigid bodies).

Could you ask developers what precisely was changed between version to cause such an behavior. It only occurs since 4.8.0. All other version before were fine.

3

I have a similar issue. After debugging, I have found out that in 4.8.1 my code doesn’t enter blocks surrounded by

#if WITH_PHYSX
...
#endif //WITH_PHYSX

however it works fine with 4.7.6.

As a result, it breaks pretty much everything in those blocks including ComponentSweepMulti which is what made me notice and test this.

4

Oh doesn’t actually seem to be WITH_PHYSX.
Seems that

if (PxRigidActor* PRigidActor = PrimComp->BodyInstance.GetPxRigidActor()){ ...code... }

was replaced with

ExecuteOnPxRigidActorReadOnly(&PrimComp->BodyInstance, [&] (const PxRigidActor* PRigidActor)
{ ...code... });

which seems to have broken ComponentSweepMulti. Not sure if it’s related to your problem.

5

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