Blueprint: How to listen to nav mesh changes

Development Programming & Scripting Blueprint
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1

I’m part way through creating a hybrid navmesh/hex grid world - e.g. I lay out a normal level using whatever primitives I like, calculate the nav mesh as normal, then using a BP I fill the bounds with a hex grid - then I project each grid location to the nav mesh and see if it exists or not (if it doesn’t exist in the nav mesh it is either out of bounds or blocked by some collider in some way and I assume it to be a blocked grid location).

The problem I have is that I can force re-generate my grid (which happens during the construction script of a BP) by moving about the blueprint in the world, but I do not know how to bind to nav mesh changes such that it is re-calculated anytime I add a new cube or sphere to my level in the editor.

I tried nodes: ‘Get navigation system → Bind event to OnNavigationGenerationFinished’ but it does not fire as I would expect (or at all from my experience) and I cannot see any other events I could bind to that seem to fit.

So short version: How do I listen to nav mesh recalculation or rebuild events inside of a blueprint?

2

You could try implementing Navigation Invokers to your AI. Navigation Invokers are Blueprint Actor components that generate the Navigation Mesh around the Agent at runtime. Using Navigation Invokers removes the need to build the Navigation Mesh in the editor and can also limit the number of tiles generated at runtime.

3

To trigger a navmesh rebuild on a particular instanced mesh component:

#include "AI/NavigationSystemBase.h"
FNavigationSystem::OnComponentUnregistered(YourInstancedStaticMeshComponent);
FNavigationSystem::OnComponentRegistered(YourInstancedStaticMeshComponent);