rdBPtools Tutorial 22 – ISMs, HISMs and Foliage Culling

Last Updated: 2nd September 2023

With the advent of UE5, the way Instances are culled has changed considerably.

Software occlusion culling has been removed in favor of shader based culling. Foliage has a cluster system for culling.

To start with, if you’re unfamiliar with the various culling types, a good reference is the Epic documentation:


And here’s another page with a good run down on them:


And here’s one describing Nanites culling:


Another topic that’s relevant here is Virtual Shadow Maps – the tests below show performance with and without VSMs – but to get the best looking scenes, it’s good to stick with Nante, Lumen and VSMs.

The link here has the Epic documentation on VSMs:


So, let’s start with the testing! (Distance culling works well for all types, so no tests have been done on that.)

In a real game, of course there will be a lot more going on in your scene and it will be larger – this test is concentrating on the occlusion culling, there are many more techniques for optimizing those, just out of scope.

There’s a lot of different configurations you can use, so there’s quite a number of different configs, each testing the occlusion culling by rendering the scene with and without occlusion – it’s simply done by placing planes in front of the camera.

UE5.3 introduces a number of optimizations with Nanite rendering and VSMs, more tests will be done when it reaches maturity.