Weird behaviour with separate meshes, collisions & navmesh

[RoNin1971]

Here's something that's been bugging me for some time:

This is one of my vault pieces, the red lines being the collision (a "compound rigid body" pre-elric). 2 of these gets you a "hall" with a (half) floor between. As you can see, the collision does not block the passage. As player you can walk right thru.

 

NPC's however do not. The floor piece has a navmesh and works on its own, but they refuse to go there in combi with the above wall.

 

If I navmesh the small strip of floor they will walk there. Combined within 1 mesh (add floor part to nif + collision) then it works just fine too. 2 separate objects (wall+ceiling & floor), no go. unless... I cut the collision up in 2 separate parts (2 bhkCollision objects inside nif) for the wall & ceiling.

 

Any ideas on whats going on and possibly solve this issue? Am I missing something, a setting, a flag, or is it a bug?

 

Note:

For the image above I used the mesh to create the collision. Usually however I use a few boxes to keep it simple for the engine.

No difference there.

[South8028]

If I run havok animations on a wall... For example, an actor is climbing a rope/horizontal ladder/Spiderman... Etc... In places where the walls meet, the camera, for unknown reasons, falls into a collision (falls into the plane of the wall). The collision plane is conditionally infinite. This has no effect on the actor's movement, but the camera picks it up. Perhaps the npc also registers an invisible infinite plane. Havok feature. Actually, I don't know... It's just a guess.

[pepperman35]

RoNin1971, I don't know if this is related or not but back in 2023 kinggath posted some info regarding a Shared Interior Cell Navcutting bug.  Don't know if this got resolved or not.  Also, Ethreon post a short tutorial ref 3ds max and navcuts and stair helper collisions.  Don't know if either of these are helpful but I had them booked marked for reference.

[RoNin1971]

On 12/8/2024 at 7:01 PM, pepperman35 said:

RoNin1971, I don't know if this is related or not but back in 2023 kinggath posted some info regarding a Shared Interior Cell Navcutting bug.  Don't know if this got resolved or not.  Also, Ethreon post a short tutorial ref 3ds max and navcuts and stair helper collisions.  Don't know if either of these are helpful but I had them booked marked for reference.

It does look related, but not directly. The problem occurs everywhere. However: "It does so by taking the bounding box of the mesh*, and forcing the navmesh that intersects it to reform a new shape around that bounding box." sounds about right. I've tested inside V88, my own interior cell and down main street Sanctuary. The overhanging part will block any navmesh below, that isn't part of the same mesh/nif if it all is a single collision (data). It's as if the engine uses a convex-hull or bounding box around it. which would block that part of the passage way and as the top of the floor is above the meshes bottom (so, inside the "navcut"). Its the only way I can explain why it does work with 2 separate parts of collision data.

 

* = instead of the mesh, it looks to me like it uses the collision data instead, in this case.

 

edit:

Yes. It explains a lot. Including why it appeared to work normal at first. As the pieces where just above ground (so, above the navmesh of the floor = no navcut) & without the floor piece in my initial test.

So, it almost certainly uses a bounding box based on the collision data as a navcut. Which is not a bug but a feature. An annoying & buggy feature...

[RoNin1971]

By the looks of it the engine is pretty dumb in the way it handles this.

One of my pieces is the 'wrecked wall'. Which has a bunch of bend plates on the floor. I assigned it the "Clutter NoNavcut" collision type, but that is completely ignored and the navmesh gets cut anyway. (so I just didn't add a collision for those parts in the finall version)

 

...Wonder what happens if the collision is something like 'smoke' ... It wouldn't surprise me by now if that too gets cut.