Customize which actors affect navmesh generation

#unreal

1. Extend ARecastNavMesh, have its constructor set bUseVirtualGeometryFilteringAndDirtying = true and override CreateGeneratorInstance
2. Extend FRecastNavMeshGenerator, override ShouldGenerateGeometryForOctreeElement
3. Have your custom ShouldGenerate function do checks on the FNavigationOctreeElement, it contains the component which is being considered for the navmesh. Can do anything there like check if it’s from a certain actor type or such
4. Have CreateGeneratorInstance return an instance of your custom Nav Mesh Generator class
5. In project settings under navigation system, set up an agent type which uses your custom recast nav mesh instead of the default one

bUseVirtualGeometryFilteringAndDirtying needs to be set to true or the function on the nav mesh generator won’t be called.

The default ShouldGenerateGeometryForOctreeElement uses Element.ShouldUseGeometry(NavDataConfig), but calling Super would probably work.

To pull component/actor out of the FNavigationOctreeElement:

//This is (probably always?) a UPrimitiveComponent
UObject* Owner = Element.Data->GetOwner();
 
//since it's a primitive comp you can get the actor...
AActor* OwnerActor = Cast<AActor>(Owner->GetOuter());