[4.5.1 Physics Crash] Setting AttachTo and Simulate Physics causes instant crash, Repro Content-Only Project for you!

Rama · October 30, 2014, 9:27pm

Dear Friends at Epic,

Please see my pic below!

I’ve created a easy repro case for you as a downloadable content-only project!

#Download Size 20 mb

#Pic

If you want you can repro whole thing without download, it is all contained in this one picture!

#Issue

Setting AttachTo with new body welding code involved (even though it is not even checked!) and turning physics simulating off

is causing an instant crash for me in a BP-only project!

Hourences and I encountered this crash in Solus but my repro project is reliably crashing every time I press B key

I am not even getting to try and press CTRL B to then detach object!

Just pressing B crashes editor every time.

#This Has to be Addressed, cost me 6 hours of debugging time

I spent 6 hours debugging this issue, starting in c++, only to realize it was BP, to then realize I could even repro it outside of Solus.

Please take this very seriously, it is a major engine instability issue!

#Second Crash

I tried using component level version of attach to and set simulate,

I still get crash!

If I disconnect attach to node, then crash does not happen.

So it is interaction of Set Simulate and Attach To that is causing crash!

PS:

Again you can simply download my 4.5.1 repro project I made for you during this 6 hour ordeal

#Download Size 20MB

Rama · October 30, 2014, 9:31pm

#Better Picture

Here’s a better picture in case you want to repro without downloading

anonymous_user_33800a51 · October 31, 2014, 6:29pm

Hey ,

Thanks for setting up test project and providing these details. I was able to reproduce issue in 4.5.1 as well as our internal build, so I have entered a bug report for developers (UE-4873). I will let you know when I see any updates on it. Thanks for report!

Rama · November 1, 2014, 2:40am

Thanks !

This has made Solus very unstable so it is really important that a fix come along for 4.6, because 4.5 is causing other crashes for me I’ve never seen in 4.4 and prior, and related parts of code base are same! I am quite convinced its all related to body welding / attaching of actors!

Have fun today !

_Epic_Ori_Cohen · November 3, 2014, 4:35pm

Hi ,

This is actually unrelated to attachment or welding code. problem here seems to be a PhysX bug with way CCD flag works. For example if you remove your attachment code and replace it with a call to SetActorLocation you’ll get same crash.

I’ve submitted a temporary fix for this while I await NVIDIA’s response to make sure we’re not doing something else wrong. You could avoid this issue by turning CCD off on your simulated object, or you can grab my change from github.

Thanks for repro steps.

Rama · November 4, 2014, 9:33pm

#Yay For Ori!

I can verify that turning off CCD on my static meshes does remove crash!

Great detective work Ori!

Thanks for this info and near future fix!

Rama · January 1, 2015, 8:36pm

“I’ve submitted a temporary fix for this while I await NVIDIA’s response to make sure we’re not doing something else wrong. You could avoid this issue by turning CCD off on your simulated object, or you can grab my change from github.”

Any update on this matter? Sjoerd is reporting Solus is still getting crashes due to attachments, just wondering if anything new has happened on your end

anonymous_user_33800a51 · January 3, 2015, 12:07am

Hey ,

Ori won’t get back until Monday, so I’ll ask him then. Does turning off CCD not work anymore?

anonymous_user_33800a51 · January 6, 2015, 7:56pm

Hi ,

I checked with Ori, and he said temporary fix is in 4.7 and he thinks NVIDIA fix will be in 4.8.

Rama · January 7, 2015, 7:11am

Thank you for info !

#

nopunintendo · January 24, 2015, 9:10pm

I believe that I’m encountering this bug as well, is temporary fix available in current 4.7 preview?

anonymous_user_33800a51 · January 26, 2015, 9:05pm

It should be. You can create a copy of your project to test it in 4.7 Preview 4. Let us know if you still have this problem!

nopunintendo · June 3, 2015, 9:03pm

Hey there, sorry I missed your response. Before you responded, I was still encountering bug in 4.7 preview 4. I’ve just now converted my project to 4.8 preview 4, and bug seems to be fixed!!

I can finally continue working on my game! Woohoo!