Inconsistent gravity behaviour when fracturing Geometry Collection

Development World Creation
, , ,
1

Getting familiar with the subject so I might be missing something crucial.

This Geometry Collection simulates physics but is not affected by gravity:

image
image1338×420 70.7 KB

I slam the actors into the ground :point_up:, the smaller chunks break off and fly away convincingly:

However, the large chunks that did not fully fracture are now affected by gravity all of a sudden.

  • is this intended?
  • is this a bug?

I was expecting the large chunks to remain unaffected by gravity. Note this only manifests if the collection breaks. If the damage threshold is not exceeded, the component remains floaty, indeed.

Zeroing Default Gravity Z in the Project Settings does fix the issue, but that’s a global setting. UE v5.5.1

Apologies for tagging you in @CedUE but you’ve been an invaluable source of insight.

2

Hi

I just repro-ed the issue on my side and this is indeed a bug
This is happening because the gravity settings are not transferred properly over to the newly created partial cluster ( the one that contains the remains of the original cluster )

I’m going to fix that for the next release

if you are building from source code you can write a quick fix by adding this to FRigidClustering::CreateClusterParticleFromClusterChildren after the SetIsAnchored call

NewParticle->SetIsAnchored(false); // << existing line 
if (Parent)
{
	NewParticle->SetGravityEnabled(Parent->GravityEnabled());
	NewParticle->SetGravityGroupIndex(Parent->GravityGroupIndex());
}

Thanks for reporting this issue :slight_smile:

1 Like
3

Interesting.

I assume this isn’t a proper simulation either way?

Or do Larger pieces attract smaller pieces into orbit?

4

With the fix, all pieces will remain unaffected by gravity and will float as expected

However Chaos Physics does not simulate attraction between pieces

2 Likes
5

I have submitted the fix in the main development branch for those who have access to the Unreal Engine Github here’s the link to the commit

https://github.com/EpicGames/UnrealEngine/commit/5b6abe44b57dd4d8e4d8ace214e77eeae8f79be8

1 Like