Geometry Collections and Distance-Fields / Ray Tracing

[Loux_xavier]

Good morning,
I use the Unreal Engine destruction system. But I have problems with rendering Geometry Collections.
Currently it is not possible to generate Distance-Fields for Geometry Collections so rendering with Lumen is bad.

There is also a problem with Path Tracing. All Geometry Collections in my scene become invisible in Path Tracing rendering.
I can’t find any information about its limitations in the Unreal Engine docs.

About the Distance-Fields since each small element of the hierarchy are static I imagine it should be possible to manage them as Static Meshes?

I imagine for game performance it’s not great but it would be nice to have an option for animations or cinematics.

Small note: I notice that for Skeletal Meshes the problem of Distance-Fields can be corrected by using Hardware Ray Tracing. This does not work with Geometry Collections.
Also the Geometry Collections have no shadows at all if Ray Traced Shadows is active.
I think it’s related to the Path Tracing issue.

What do you think and do you have any techniques to work around this problem?

-Bleu

[Arkiras]

@Loux_xavier

There is also a problem with Path Tracing. All Geometry Collections in my scene become invisible in Path Tracing rendering.

This may be because geometry collections are hidden from hardware raytracing by default. You can try enabling it with this cvar: r.RayTracing.Geometry.GeometryCollection 1

[Loux_xavier]

Wow, thank you so much!

[Arkiras]

Just keep in mind, they’re hidden from the raytracing view by default because the raytracing accelleration structure needs to be rebuilt every frame for them which is extremely expensive. Probably fine for cinematics though.

Regarding mesh distance fields, I asked about this in early access and this is the response i got:

@Daniel_Wright

I would really like to know if there are any plans to improve support for chaos geometry collections, currently they don’t appear to generate distance fields and as a result have no representation in the Lumen scene.

We’d like to implement distance fields for Geometry Collections but it would be pretty far down the priority list. Hardware Ray Tracing already supports Geometry Collections, however as a dynamically deforming mesh, it will cause an acceleration structure rebuild every frame so you’ll have to watch out for the performance cost.

[Loux_xavier]

I understand better why, thanks. I hope this will move up the priority list.

[PerryDawg32]

Thanks. This just saved my music video. Cheers!

[Crackbundle]

@Arkiras

r.RayTracing.Geometry.GeometryCollection 1

DUDE! You’re the man!!! I was pulling my hair out trying to figure out why my chaos geometry collection wasn’t showing up in path tracer. I was so frustrated lol. Thank you bro!

[bashfulfruits (bash)]

Did the normal maps start flickering dark self contact shadow artifacts after the geometry collection is fractured? In lit mode it’s fine but not in path tracing and I used the Ray tracing CVAR so it’s visible but with shadow artifacts, but it’s only once I turn off all shadows being casted that the artifacting goes away, like it’s only taking into account the original normals even after using the recompute normals utility in the fracture mode.