HISM performance very strange

Development Programming & Scripting
1

I’ve been trying to use HISM, but I’ve noticed that the performance is strange. Adding a large amount of instances is fine. Once they are loaded, the performance is great. There is lag on the game thread when adding initially, but I understand that adding a large amount of collision enabled things would lag the game thread.

What I do not understand, is once I have added about 20,000 HISM planes to the scene, removing or adding just a single instance lags the game thread significantly. But how can this make sense?

Doesn’t UE use HISM for foliage? With the foliage tool I can have a million instances in the scene, and removing a couple or adding a few more doesn’t cause noticeable lag.

So why is there a massive performance cost when adding just one or two instances, or removing a couple instances, to a HISM component, once that component has 20k+ instances? And why does this same lag not occur with foliage, where the instance counts can be much much higher?

What is going on here?

Unreal 5.1

Thanks

2

I’m not entirely sure ( I don’t know how you’re making these instances ), but if you’re doing it in construction, then the whole script has to run every time you make a change.

IE, re-make all 20k instances, just to remove one.

I just made 20K cubes ( HISMs ), and I can remove one without any hit ( if I don’t remake them all ).

1 Like