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Hierarchical Instanced Static Meshes no longer distance cull individually, in 4.15?

It seems hierarchical instanced static meshes are now distance culled all at once rather than individually. Getting close enough for one instanced mesh to be rendered makes all of them render at once. Testing HISMs it seems that the individual behavior is still sporadically present when moving the actor they are a component in.

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This simple test setup should reveal what I'm talking about. If things are the same on your end, the erratic behavior should become clear.

I assume this is a bug, if not I would very much like to hear what needs to be done differently to reliably distance cull instances individually again, as it provides significant performance improvements.

Product Version: UE 4.15
culltestbp.png (518.8 kB)
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asked Feb 21 '17 at 10:04 AM in Bug Reports

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avatar image AndrewHurley Feb 24 '17 at 05:45 PM

Hey SkyHigh,

I have tried to reproduce the issue you are reporting, but all of my HISMC are culling as expected. Perhaps I overlooked a minor detail, but instead of us going back and forth, could you provide me with a minimal test project in which this issue occurs so I can see it on my end and add the to the bug report if/when necessary.

Let me know if you have further questions.


Andrew Hurley

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Hey Andrew,

After noticing that different meshes gave different culling behavior, I plugged in meshes until one behaved as expected. Digging in we found that it was the material that made the difference. As it turns out, it is now required for meshes to have a material with the Use dithered LOD transition option to be enabled, for HISM distance culling to work correctly. Found the following answer confirming the solution: https://answers.unrealengine.com/questions/564333/my-foliage-will-not-cull-since-4150.html

What made this hard to grasp was the erratic behavior of the culled HISMs when having the incorrect material setting. Culling was taking place in a way, but unpredictable. Perhaps HISMs with bad materials could render as solid black, as is the case with other incorrect material settings, indicating a material issue.

But very good that the system still works!


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answered Feb 27 '17 at 11:07 AM

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