Ai Overview

Ai Overview

This article is about helping to understand how the Ai in Shards Online works.

Some Basics:

The Artificial Intelligence for NPCs follows a general Ai Principle which is the cycle of

• Sense
• Think
• Act

The model of implementation is a Finite State Machine(FSM). [Wikipedia Article Finite State Machine]

To understand how an FSM would transition from one state (e.g. "Idle") to another state (e.g. "Combat") in Shards Online (SO) it is important to understand the first step: "Sense".

How does an NPC sense the world?

There are several ways:

Messages

Messages using the Sendmessage function tell the NPC someone or something sent it a message. To understand Messages the NPC needs to have the appropriate EventHandlers.

Views

Views are added to objects by using the AddView function. A view is basically a search function performed on a configurably regular basis which triggers an event if something matching that search function enters its configured range. Mobiles can carry around views with them.

FindObjects

The FindObjects function can be executed whenever an NPC needs to find something.

Each of these sensing mechanisms can call functions provided by the core Ai which lives in base_ai_state_machine.lua.

SchedulePulse()
AI.StateMachine.Init(initialState)
AI.StateMachine.Shutdown()
AI.StateMachine.ChangeState(newState)
AI.StateMachine.ChangeSubState(newState)
AI.StateMachine.EndSubStates(success,reason)
HandleAiPulse()

Especially important is function AI.StateMachine.ChangeState(newState) which could be called when something happens our NPC needs to react to, e.g. a wolf entering the perception range of a turkey.

In base_ai_mob.lua we find the following line of code in the initialization part:

AddView("chaseRange",SearchMobileInRange(chaseViewRange,false,false,true))