Utility AI for GameMaker

Quickly add life to NPCs in complex gameplay situations

Simple settings produce robust results

AI adapts to changing game situations

Optional custom interrupt logic

Introduction

1. Create Behavior Sequences, re-usable lists of methods each with an optional delay:

idleSeq = new behavior_sequence([
    new behavior(0,function(){
        goto(x,y)
    }),
    new behavior(4,function(){
        goto(random_range(-sprite_width*2,sprite_width*2),random_range(-sprite_height*2,sprite_height*2),self)
    }),
    new behavior(2,function(){
        utilityModule.satisfy("Idle")
    })
])

2. Create a Utility Module, a high-level decisionmaker that tries to satisfy needs called directives:

utilityModule = new utility_module([
    new directive("Idle", idleSeq,0.2,0.05),
    new directive("Gather", gatherSeq,0,0.1,function(){return instance_exists(ResourceObj)},function(){return !collision_point(tgtX+8,tgtY+8,ResourceObj,false,true)}),
    new directive("Return", returnSeq),
    new directive("Recoup",recoupSeq,0,-0.001,function(){return instance_exists(HourglassObj)})
])

3. Feed that Utility Module some updates. These don't need to be in the "step" event but they can be!

utilityModule.update()

That's it! The ai will check it's directives from first to last (in order!) and pick the one with the highest priority.

Predicates

This module has two predicates:

1. _predicate is checked before a directive is selected, and must return true for the directive to be selected
2. _breakoutPredicate is checked during update and must return false otherwise the directive will abort and the AI will reconsider

Here we can see an example of both of these predicate definitions in this Directive definition:

new directive(
  "Gather",//name
  gatherSeq,//sequence
  0,//valence
  0.1,//rate
  function(){//predicate
    return instance_exists(ResourceObj)
  },
  function(){//breakout predicate
    return !collision_point(tgtX+8,tgtY+8,ResourceObj,false,true)
  }
),