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anpc - Advanced NPCs for minetest

What is anpc?

anpc, short for advanced NPCs or non-playable-character, is a Minetest mod that allows you to create animals, enemies (so-called mobs) and any other kind of computer-controlled character. anpc is the spiritual successor to my other mod, advanced_npc. anpc inherits the "computer-like" structure of entities in advanced_npc, but takes it to a whole new level.

NOTE anpc is still on development. This is not even an alpha version - but close. The mod is very stable, but functionality is missing. This mod also doesn't contain any real playable content: you can fiddle around with the included vegetarian.lua NPC, which will be taken out of the release version of the mod.

For more information about how to use anpc, please see anpc_dev

How does it works?

The main concept behind anpc is that each NPC is an independent, programmable computer.

The NPC programming model

Each NPC has a "CPU" and a memory space. The "CPU" runs instructions inside a program. The instructions are Lua functions, while programs are collections of instructions. The CPU also supports timers, interruptions and low-latency tasks.

Instructions, as said before, are Lua functions. This is the lowest level of operation in anpc. Each instruction is condered "atomic", and therefore should run on one entity step.

Programs are collections of instructions, implemented as a Lua array. Each element in the array contains the name of the instruction and the arguments of it. This is useful for the "CPU" (think binary code), but it is very annoying to use for a human. Therefore, a special script-kind of language was developed, anpc-script, which can be used by humans to code and it is translated to the Lua-array format by menas of a interpreter.

anpc comes built-in with instructions and programs that supports:

  • Environment interactions (e.g. place node, dig node, use node)
  • Movement (e.g. walk to a certain position, rotate)

NOTE: More documentation on the programming model coming soon.

Each NPC also has a memory space, which can be local to its program or global, shared among programs.

To make a Minetest entity use anpc, simply set the following functions in your entity registration:

  • on_step: npc.do_step
  • on_activate: npc.on_activate
  • get_staticdata: npc.get_staticdata

And that's it! You can then execute a program by doing:

npc.proc.execute_program(entity:get_luaentity(), "vegetarian:init")

Replacing vegetarian:init with whatever name your program actually has.

Why anpc?

anpc is different from many other "mobs mods" in Minetest. The #1 difference is that in anpc each NPC is essentially an independent, programmable computer. Each NPC has a CPU that supports timers and interrupts, and have its own memory. Other differences are:

  • anpc is strictly an API mod - no NPCs are defined
  • anpc is not opinionated about what features and entity should have
    • anpc does include pre-built programs that are considered basic, e.g. follow something, attack. However these are not defined in your entity - you use them if you need them
  • anpc is very lightweight: you add features to the entities as you need

And you may be asking again, why? Why build NPCs like a CPU? The idea of a programmable NPC API came first with the previous mod, advanced_npc, and my attempt to create smart NPCs that could roam around villages, use chests, furnaces, beds, and trade with players. At that time I understood that a minimal, generic-enough mobs mod for Minetest would essentially support the infrastructure to perform certain actions, without forcing them on the entities. That's why everything is programmable, from how your NPC walks to how it attacks if(!) it does.

How to use anpc

If you are user and don't want to create any NPC and just play Minetest, you should use a mod that uses anpc to implement its mobs. Currently there are no mods that do that, but I will be developing one soon.

Testing

If you are really eager to test this out, the included vegetarian.lua is a testing grounds NPC. A couple of testing items are included that can let you play around with some features of anpc.

  • Vegetarian Spawner: use this to spawn the dull and boring vegetarian NPC. By himself, he will:
    • Wander around and sometimes look at you or other objects around him
    • When he gets hungry, he will find grass and eat it, until he's satisfied
    • When it is night, he will try to find a bed and sleep on it
  • Follower: while having this in hand, punch a NPC with it. It will follow you wherever you go, until you punch him again.
  • Feeder: punch a NPC while having this in hand and he will go around searching for grass, even if he's not hungry.
  • Jumper: punch a NPC while having this in hand to make him jump
  • Owner: while having this in hand, punch a node. Then, punch a NPC. You will be giving him "ownership" of that node, e.g. their bed. When they go to sleep, they will search first for their "owned" bed.
  • Walk-to-owned: punch a NPC while having this in hand and he will walk to one of his "owned" nodes. Notice that you must first use the Owner item to give him an owned node.

OK, I actually want to create a NPC. What should I do?

Go to anpc's helper mod, anpc-dev, in order to get started to create NPCs. anpc-dev contains development tools and documentation to help you get started and create NPCs with anpc.