Npc's that can climb: up and down ladders (to start with)

[Bikerdude]

I did do a quick search for this but wasn’t able to find anyone asking the question - 

@stgatilovDoes the engine have any code to allow NPC's to climb up and down ladders..?  if not how hard would it be to implement?

@ArcturusI assume the climbing animation and then blend blending animations would be doable?

And on a related note, what is the steepest incline/stairs NPC's can currently pathfind up/down..?
 

Edited October 19, 2025 by Bikerdude

[Zerush]

I rememner an mission where the NPC also climbed up a ladder. It was a mission in which I had to recover an old pocal in an old church. To access I had to recover first a key from the crypt on the roof of this church and recover an scull from the crypt of an old evil beeing and throw it in holy water in the basement. With this a secret door open and downstairs I could recover the old pocal. But this also respawn the evil beeing which killed everybody in the church. Only possible escape was over the roof of the church over an ladder, but also this evil NPC could use the ladder to the roof following me.

The only mission I know where an NPC can use a ladder.

No remember well the name of this old small and pretty creepy mission

[thebigh]

That mission is "Exhumed" by Airship Ballet and Kyyrma. But I don't recall that the baddie could follow you up the ladder. IIRC it can follow you up the winding tower staircase but not onto the roof.

[Arcturus]

@Bikerdude There's a lot of missions I haven't played but I don't remember this ever being implemented. Animations aren't the biggest problem, I think.

[AluminumHaste]

There's no code for climbing up ladders AFAIK. All the edge cases would be a nightmare.

[Bikerdude]

Fair enough, was worth an ask.

[demagogue]

I think it's similar with the problem of flying AI.

It'd be a fundamental rewiring of pathfinding to add z-axis motion completely separate from the x-y plane, as in they're not walking on a surface.

If I were going to try to rig it though, I'd probably do it in a hack-y way, like you just tweak the pathfinding a little so that the nodes at the top and bottom of a ladder connect, and when the AI wants to traverse it, it approaches the bottom, "triggers" the ladder like a switch, and it transports him already to the top, then throws in some stock climbing animation in between. Maybe not too different to the way elevators work. Actually I wouldn't trust the normal pathfinding to do it (not least b/c of edge cases like AH said), but it'd be even better if the mapper designated the bottom and top with some kind of marker object, and let the code take it from there. 

Anyway, I think there are some ways it could be rigged, but it'd still be a lot of work & would need a lot of testing and tweaking. But it really comes down to a very motivated & competent coder actually making the thing. 

[Zerush]

On 10/20/2025 at 12:57 AM, thebigh said:

That mission is "Exhumed" by Airship Ballet and Kyyrma. But I don't recall that the baddie could follow you up the ladder. IIRC it can follow you up the winding tower staircase but not onto the roof.

Ah yes, but to the windy tower there is a ladder, not a staircase, on which the NPC followed me up of the roof of the tower. I made this screenshot just now, going with noclip from start to show the ladder, but I'm going to replay the mission, and I later make a screenshot with the NPC on the roof of the tower if I can repeat the situation.

 

Edited October 21, 2025 by Zerush

[Zerush]

On 10/20/2025 at 12:57 AM, thebigh said:

That mission is "Exhumed" by Airship Ballet and Kyyrma. But I don't recall that the baddie could follow you up the ladder. IIRC it can follow you up the winding tower staircase but not onto the roof.

Voila, NPC fucked off on the roof, over the ladder, if he see you, he follow you even to the top, where is the skeleton (I didn't see it how, maybe floating up) when you exape over the church roof. Creepy

Edited October 21, 2025 by Zerush

[Arcturus]

I installed "Exhumed" and couldn't get the revenant to climb on the roof. There doesn't seem to be anything special about that ladder.

[datiswous]

In fm Winter Harvest spiders can climb trees. which looks quite scary. But maybe this is unrelated.

[Arcturus]

Elevators can be made quite narrow.

I replaced main idle animation.

There are several issues to tackle with with this approach.

• NPCs feel strong urge to turn while they are on the lift, one would have to force them to always face the same way.
• Force them to play only one selected animation while they are on the lift.
• Somehow solve the issue of calling and waiting for the elevator.

 

[Arcturus]

 

[thebigh]

"Someone's been gassed? Welp, better jump off a cliff then."

hehe

[STRUNK]

On 10/24/2025 at 10:20 AM, Arcturus said:

Elevators can be made quite narrow.

NPC's opening doors looks fake also, so having a ladder climbing NPC looking fake in a mission wouldn't be too bad. If it adds to the gameplay I wouldn't care.

[demagogue]

Just jumping in to applaud Arcturus for coming up with that. That's exactly the kind of thing I was thinking about in my post, thinking outside the box, and looking back on it, I'm almost surprised I didn't think of it myself, although I was hilariously close to it. But anyway, it's a bit buggy, but that can be tweaked, but probably more important is that it's better than what we have now (no climbing at all).

The big issue that I see is that it's more of a solution for mappers to do themselves, rather than fit for a general solution for the core package, which I guess is symptomatic of using a hacky approach. But as a hacky solution, it does the job pretty well!

I think it'd prove pretty robust, won't it? Wherever the elevator is (if it falls off mid-way like in the 2nd video), the AI will always call it up or down to themselves, it's just a bit more delay. And the mapper should take care of the geometry, in terms of being able to step on and off properly. 

As for being oriented the wrong way, you know a button can also trigger a script, and I think such a script can just turn the AI pushing it by fiat. (Now I have to remember if the AI ID passes to the script when you push a button. I remember talking about that ages ago, and I think it was dealt with in some way.) 

[Arcturus]

The reason why NPC falls down when knocked out is because I used monster_clip texture on the elevator. It blocks alive NPCs but the moment they become rag dolls they fall through.

However when you make an elevator out of monster_clip only, there's a weird glitch that I haven't noticed before:

It can be mitigated however by using monster_clip and ik_clip together. Here a func_static with textures/common/ik_clip is bound to the elevator which has monster_clip. That way there are no weird glitches when NPC gets lifted, and when it gets knocked out it's no longer supported by the elevator.

ik_clip blocks the player too unfortunately. Player can walk on it, but is prevented from jumping.

 

[grodenglaive]

plus there's the extra cheap hacky way of just making very steep and shallow stairs out of monster clip. Limits, Max, Min, Stats, etc - The DarkMod Wiki

The animation doesn't look very convincing though, especially coming down

https://imgur.com/a/810fy5Q

 

Edited October 30, 2025 by grodenglaive

[Arcturus]

The moment they start running they turn into lemmings.

You would have to make new walk animation for climbing with minimal forward motion.

 

You can't make it too slow or they refuse to climb.

In this example steps are 0.5 wide.

[Arcturus]

Them rotating chaotically is some quirk of the path-finding system.

 

[Arcturus]

edit

 

[datiswous]

On 10/31/2025 at 5:55 PM, Arcturus said:

The moment they start running they turn into lemmings.

So I could make a Lemmings game in tdm? Neat!

 

I think the elevator approach looks more convincing.

Edited November 6, 2025 by datiswous

[Arcturus]

On 11/6/2025 at 12:19 PM, datiswous said:

I think the elevator approach looks more convincing.

Both approaches would probably require additional coding to make them work.

[BoilerDunce]

Once NPCs can mantle its a wrap

[demagogue]

I think practically speaking the stairs approach is something mappers can do that'll just work. The AI should follow the player in tandem, so I think if they weren't specifically directed to go opposite directions on the stair by path nodes, then I don't think that problem will happen too often if at all in practice.