NPCs breathe life into any game world:

• villagers with schedules
• merchants with stock
• guards who patrol
• hostile factions
• relationships
• dialogue that reacts to story flags
• simulation (hunger, work, needs)
• towns that evolve over time

Lua is perfect for simulation layers:

• lightweight logic
• hot reload
• easy-to-edit behavior packages
• clean data-driven content
• integrates with quests, story, and world triggers

This chapter builds:

1. NPC definitions
2. Behavior packages (wander, talk, patrol, work)
3. Daily schedules (day/night cycles)
4. Merchant system
5. Factions & reputation
6. Town simulation
7. Social interactions

1. NPC Definitions (Data-Driven)

npcs/
villagers.lua
merchants.lua
guards.lua

1.1 Example NPC Definition

return {
  elder = {
    name = "Village Elder",
    sprite = "npc_elder",
    faction = "village",
    behaviors = {"talk", "idle"},
    dialogue = "elder_intro",
    schedule = {
      {time=0,   state="sleep"},
      {time=6,   state="idle"},
      {time=12,  state="walk_square"},
      {time=18,  state="home"},
      {time=22,  state="sleep"},
    }
  },
}

NPC = data + behaviors + dialogue + schedule.

All real-time multiplayer games—from shooters to MOBAs—depend on one core mechanism:
the game loop, also known as the simulation loop.

The game loop is the server’s “heartbeat.”
It controls how often:

• Player inputs are processed
• The world updates
• Physics and collisions resolve
• Timers and cooldowns advance
• NPCs and AI behave
• State is broadcast to players

Understanding the game loop is essential for building fair, predictable, real-time gameplay.

1. What Is a Game Loop?

A game loop is a repeating cycle that advances the simulation one step at a time.