zaplmm/pomelo-bt

behavior tree implementation for pomelo ai

#pomelo-bt - behavior tree for node.js

pomelo-bt is a Behavior-Tree module for pomelo project to implement AI. More information about Behavior-Tree please refer other articles from Internet, such as Understanding Behavior Trees.

• Tags: node.js

##Installation

npm install pomelo-bt

##Behavior tree nodes

###Node The base class of all the behavior tree node classes. Its constructor receives a blackboard instance as parameter.

Each node class provides a doAction method to fire the behavior of current node instance. All the children should implement their own doAction. And the doAction method sould report a result code to the parent when it return. The result code is one of below:

• RES_SUCCESS: the behavior finished successfully.
• RES_FAIL: the behavior fails.
• RES_WAIT: the behavior is running and should be continued in next tick. The parent node makes its decision based on the result code.

###Composite The base class of all the composite nodes. A composite node has arbitrary child nodes and it has a addChild method to add child node.

###Decorator The base class of all the decorator nodes. A decorator node has the ability to decorate the result for its child node. A decorator node has only one child node and has a setChild method to set the child node.

Followings are some behavior node types provided in pomelo-bt.

##Composite nodes ###Sequence Implementation of sequence semantics. ####Sequence(opts)

• opts.blackboard - blackboard instance for the behavior node.

###Parallel Implementation of parallel semantics. ####Parallel(opts)

• opts.blackboard - blackboard instance for the behavior node.
• opts.policy - Failure strategy for Parallel node: Parallel.POLICY_FAIL_ON_ONE(default) return RES_FAIL if one child node fail, Parallel.POLICY_FAIL_ON_ALL return RES_FAIL only on all the child nodes fail.

###Selector Implementation of selector semantics. ####Selector(opts)

• opts.blackboard - blackboard instance for the behavior node.

###Decorator nodes ###Loop Implementation of loop semantics. ####Loop(opts)

• opts.blackboard - blackboard instance for the behavior node.
• opts.child - child node for the decorator node。
• opts.loopCond(blackboard) - loop condition function. return true to continue the loop and false to break the loop.

###Condition Return RES_SUCESS if the condition is true otherwise return RES_FAIL. ####Condition(opts)

• opts.blackboard - blackboard instance for the behavior node.
• opts.cond(blackboard) - condition function, return true or false.

##Other nodes ###If Implementation of loop semantics. If the condition is true, then fire the child node. ####If(opts)

• opts.blackboard - blackboard instance for the behavior node.
• opts.action - child node.
• opts.cond(blackboard) - condition function, return true or false.

##Usage

var util = require('util');
var bt = require('pomelo-bt');
var Sequence = bt.Sequence;
var Node = bt.Node;

// define some action nodes
var HelloNode = function(blackboard) {
  Node.call(this, blackboard);
};
util.inherits(HelloNode, Node);

HelloNode.prototype.doAction = function() {
  console.log('Hello ');
  return bt.RES_SUCCESS;
};


var WorldNode = function(blackboard) {
  Node.call(this, blackboard);
};
util.inherits(WorldNode, Node);

WorldNode.prototype.doAction = function() {
  console.log('World');
  return bt.RES_SUCCESS;
};

var blackboard = {};

// composite your behavior tree
var seq = new Sequence({blackboard: blackboard});
var hello = new HelloNode(blackboard);
var world = new WorldNode(blackboard);

seq.addChild(hello);
seq.addChild(world);

// run the behavior tree
seq.doAction();