UpdateInstanceTransform causes all instances to be rebuilt?

Development Platform & Builds Debugging, Optimization, & Profiling
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1

I have a UHierarchicalInstancedStaticMeshComponent with 321489 instances. If I do an UpdateInstanceTransform(…) on around 10000 instances the game freezes for a second and I get the following output after it’s finished.

LogStaticMesh:Display: Discarded foliage hierarchy of 321489 elements build due to concurrent removal (0.2s)
LogStaticMesh:Display: Copied 321489 transforms in 0.022s.
LogStaticMesh:Display: Built a foliage hierarchy with 321489 of 321489 elements in 0.3s.

To me it looks like it rebuilds all the instances after a UpdateInstanceTransform. I’m not sure how, but would it be possible to only apply the transform on the affected instances?

PS: It would be nice to have the ability to add a GroupIndex to an instance, and this way group the instances based on your own index. This way only the affected groups would rebuild.

Here is a video showing the problem: https://www.youtube.com/watch?v=6xeiXoR3uYg

2

I’m not sure how, but would it be possible to only apply the transform on the affected instances?

Nope.

If you want “groups” or “partial updates”, use multiple components.

3

The log message tricked me a bit. It was the marking of the render state that caused the freezing. Ref: https://github.com/EpicGames/UnrealEngine/pull/1037

But I also ended up splitting stuff into multiple components.