[4.8P1] Physics bugs

I have found two strange physics bugs in the 4.8 Preview 1.

One is if you spawn a physics actor which has simulate physics disabled at location x, then set the location to y and then enable simulate physics, it is again at location x.

Another bug is, if you set simulate physics to off in the details panel, and additionally set simulate physics off in event begin play, then you can’t enable physics later, it just stays disabled.

Here you have a clean repro project for both bugs:

Just hit play, you see the stone falls correctly. Then go into the “Stones” blueprint and connect the exec wire from EventBeginPlay to the stuff inside of the “DoesNotWork” Comment. Then hit play, you see you can’t see the Stone because it’s at location 0/0/0.

For the other bug, connect the wire in Stones back to working and open the Stone blueprint and connect the wire at EventBeginPlay to the SetSimulatePhysics Node. Then hit play, you see the Stone does not move because physics is disabled, even though SetSimulatePhysics(true) gets called in the Stones blueprint.

Hi John,

Thank you for the report.

Issue #1: I created JIRA UE-15268 and our developers will be investigating it further. We will post back here with updates as we have them.

Issue #2 : Is actually the intended functionality. What you are seeing is how the events stack.

  1. The ‘Spawner’ blueprint spawns the ‘Stone’ bp

  2. The 'Spawner sets ‘Simulate Physics’ to Enabled

  3. Then the ‘Stone’ bp’s ‘Event Begin Play’ kicks off and disables physics

I hope that helps clear up what is going on. Thanks again for the report.



Hi TJ, I saw this commit: https://github.com/EpicGames/UnrealEngine/commit/ff3784b50de9f582eecaac3aef2cfb68b7128409
It seems to be like a fix for UE-15268 except that it’s about destructibles, not physics actors. If this commit related to UE-15268?

Hi John,

No that commit is for another JIRA. It is specifically for the SetWorldLocation node not working for destructible actors.

It seems very similar in origin to your issue so it will likely help him narrow down the fix.