Hostile Survivor NPC

HOSTILE SURVIVOR NPC

This is a random addon I originally made for myself because I wanted hostile human NPCs wandering around in Left 4 Dead 2.

After a lot of experimenting, I managed to get something working surprisingly well, so I figured I'd publish it in case anyone else wanted to mess around with it.

Is it perfect? Absolutely not.

Could someone probably make this significantly better? Almost certainly.

Am I going to completely rewrite everything to find out? Probably not. I'm lazy.

But hey, it works!

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WHAT DOES IT DO?

Adds a hostile human NPC that can randomly appear while progressing through campaigns.

The Survivor/Bandit can:

- Wander around the map independently. - Detect and engage nearby survivors. - Chase survivors and disengage when appropriate. - Fire actual weapons, reload, and move while shooting. - Attack Common and Special Infected. - Take damage from players and infected. - Fight friendly survivor bots, who can retaliate. - Damage and potentially incapacitate survivors. - Die from accumulated damage or certain infected abilities. - Return to wandering when combat ends.

The idea is to introduce occasional encounters with another armed human rather than yet another infected.

It's primarily been developed and tested in single-player. Multiplayer compatibility is largely unknown, and I wouldn't be surprised if there are still bugs.

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NATURAL ENCOUNTERS

The Bandit can now appear naturally throughout campaigns, but he is NOT guaranteed to spawn!

The addon tracks map progression and performs a 25% encounter roll at each new 10% checkpoint, from 10% through 90%.

If a roll fails, another opportunity occurs at the next checkpoint.

When successful, the addon searches for a navigable location ahead of the survivors, preferably outside their line of sight.

- Only one Bandit encounter per chapter attempt. - No respawning after being killed. - Backtracking won't generate additional chances. - Spawn placement depends on the map's navigation mesh. - A successful roll doesn't guarantee a suitable spawn location. - Restarting a chapter resets the encounter system.

Sometimes he'll appear early, sometimes late, and sometimes not at all.

I personally prefer this over having him spawn every chapter. That would get predictable rather quickly.

FINALE EXCLUSIONS

Natural spawning is disabled on official finale maps.

The addon also attempts to detect custom finales using finale entities and map names. However, unusual custom campaigns may bypass detection.

Manual spawning remains available on finales.

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HOW DOES IT WORK?

Here's the interesting part for anyone curious about how this thing was put together.

The Bandit isn't actually a completely new NPC.

It uses a modified version of the game's existing Survivor AI, specifically the Team 4 / Passing survivor system, spawned using techniques similar to those found in Admin System.

The problem is that survivor bots aren't designed to treat other survivors as enemies.

To get around that, the addon uses an invisible Hunter that follows the survivor being targeted.

This tricks the Bandit's native AI into believing it's fighting a Special Infected, allowing it to aim, shoot, reload, and move much more naturally than a manually animated prop.

VScript handles wandering, engagement conditions, damage calculations, and other behavior.

Because hostile survivor combat isn't natively supported, some damage is simulated using weapon events and custom calculations.

This also allows Common and Special Infected to damage the Bandit. Certain Special Infected abilities can even kill him outright.

The AI itself has also undergone a substantial rewrite, replacing thousands of lines of experimental code with a much cleaner implementation.

It's a pretty ridiculous workaround, but it works better than I expected.

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KNOWN LIMITATIONS

Because of how this addon works, there are some unavoidable (or at least currently unfixed) issues:

- Invisible Hunter: The proxy can occasionally interfere with bullets or other interactions, particularly while crouching. If a shot seems to hit nothing, this is probably why.

- Special Infected Slot: The Hunter occupies an actual infected slot while active, potentially affecting normal spawning.

- Audio: Some Hunter alert sounds and music cues can still play despite attempts to suppress them.

- Survivor AI: Friendly survivor bots may occasionally react to the invisible Hunter.

- Animations: The Bandit may occasionally animate or navigate strangely.

- Damage: Some combat interactions use simulated damage. Unusual behavior may occur, especially with certain infected abilities.

- Natural Spawning: Some custom maps may lack suitable navigation locations, preventing encounters.

- Finales: Unusual custom finales may not be recognized correctly.

- Compatibility: Other VScript-heavy addons could interfere with this one.

- Multiplayer: Primarily developed for single-player. Some multiplayer considerations were attempted, but functionality isn't guaranteed.

I'm aware some of these problems could probably be fixed with enough effort.

I've spent enough time fighting the Source engine for now.

Also, I can't guarantee smooth compatibility with every addon or custom campaign.

If something breaks, please mention the map and what happened. It makes troubleshooting much easier.

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COMMANDS

You can manually manage the Bandit through chat commands.

!t4 help Display available commands.

!t4 spawn Manually spawn a Bandit.

!t4 status Display Bandit information.

!bandit natural status Check natural encounter information.

!bandit natural on Enable random encounters.

!bandit natural off Disable random encounters.

!bandit natural chance 100 Force successful encounter rolls for testing.