Nans in FPBDCollisionConstraint::AccumulatedImpulse followed by a crash.

Development Programming & Scripting
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I hit a nan ensure in the picture attached.

The problem is that I can’t extract anything useful from this.

Can’t even establish what collides with what (perhaps masses or inertias are crazy).

Either I’m blind or it’s just not anywhere in the data available.

Any advice on how to debug this would be much appreciated.

EDIT: Turned out to be due to the normal of collision point being nearly 0.

We could turn off this collision but if we couldn’t, I wouldn’t know what to do about it.

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Morning Wojciech,

Thanks for the update - the advice before seeing this would have been to see what info there was in the contact handle - but without having more context (or a full memory dump) it is difficult to add much context.

I’d be curious to know why the collision normal is nearly 0 though - have you run a quick check to verify your assets all have normalized normals? If so - it could be floating point error - but this is fairly rare, and I’d always check the assets first.

Best

Geoff Stacey

Developer Relations

EPIC Games

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>have you run a quick check to verify your assets all have normalized normals?

Is there a test for this somewhere or would I have to write it myself?

PS. The fishy part of the situation is that we started to see issues in the chaos code after

upgrading from 5.5 to 5.6. Are there any hotfixes pending maybe ?

Thanks

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Hi Wojchiech,

Checking for the validity of an asset would likely be something implemented by TechArt as part of the export pipeline. That being said, adding it into the loading side shouldn’t be too difficult.

If you can trap the crash at runtime, you should be able to tell if it is junk data, or if not, which assett it is.

There aren’t any further hotfixes planned for either as far as I’m aware, but it is interesting that this has appeared as part of a version bump. This is the first I’ve heard of this particular issue though so I’d be keen to know if there is an issue lurking.

Best

Geoff

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