基于Unity行为树设计与实现的尝试
查阅了一些行为树资料，目前最主要是参考了这篇文章，看完后感觉行为树实乃强大，绝对是替代状态机的不二之选。但从理论看起来很简单的行为树，真正着手起来却发现很多细节无从下手。
总结起来，就是：
1、行为树只是单纯的一棵决策树，还是决策+控制树。为了防止不必要的麻烦，我目前设计成单纯的决策树。
2、什么时候执行行为树的问题，也就是行为树的Tick问题，是在条件变化的时候执行一次，还是只要对象激活，就在Update里面一直Tick。前者明显很节省开销，但那样设计的最终结果可能是最后陷入事件发送的泥潭中。那么一直Tick可能是最简单的办法，于是就引下面出新的问题。目前采用了一直Tick的办法。
3、基本上可以明显节点有 Composite Node、 Decorator Node、 Condition Node、 Action Node，但具体细节就很头疼。比如组合节点里的Sequence Node。这个节点是不是在每个Tick周期都从头迭代一次子节点，还是记录正在运行的子节点。每次都迭代子节点，就感觉开销有点大。记录运行节点就会出现条件冗余问题，具体后面再讨论。目前采用保存当前运行节点的办法。4、条件节点（Condition Node）的位置问题。看到很多设计都是条件节点在最后才进行判断，而实际上，如果把条件放在组合节点处，就可以有效短路判断，不再往下迭代。于是我就采用了这种方法。
设计开始
在Google Code上看到的某个行为树框架，用的是抽象类做节点。考虑到C#不能多继承，抽象类可能会导致某些时候会很棘手，所以还是用接口。虽然目前还未发现接口的好处。
在进行抽象设计的时候，接口的纯粹性虽然看起来更加清晰，不过有时候遇到需要重复使用某些类函数的时候就挺麻烦，让人感觉有点不利于复用。public enum RunStatus
{
Completed,
Failure,
Running,
}
public interface IBehaviourTreeNode
{
RunStatus status { get; set; }
string nodeName { get; set; }
bool Enter(object input);
bool Leave(object input);
bool Tick(object input, object output);
RenderableNode renderNode { get; set; }
IBehaviourTreeNode parent { get; set; }
IBehaviourTreeNode Clone();
}
/************************************************************************/
/* 组合结点 */
/************************************************************************/
public interface ICompositeNode : IBehaviourTreeNode
{
void AddNode(IBehaviourTreeNode node);
void RemoveNode(IBehaviourTreeNode node);
bool HasNode(IBehaviourTreeNode node);
void AddCondition(IConditionNode node);
void RemoveCondition(IConditionNode node);
bool HasCondition(IConditionNode node);
ArrayList nodeList { get; }
ArrayList conditionList { get; }
}
/************************************************************************/
/* 选择节点 */
/************************************************************************/
public interface ISelectorNode : ICompositeNode
{
}
/************************************************************************/
/*顺序节点 */
/************************************************************************/
public interface ISequenceNode : ICompositeNode
{
}
/************************************************************************/
/* 平行(并列)节点 */
/************************************************************************/
public interface IParallelNode : ICompositeNode
{
}
//////////////////////////////////////////////////////////////////////////
/************************************************************************/
/* 装饰结点 */
/************************************************************************/
public interface IDecoratorNode : IBehaviourTreeNode
{
}
/************************************************************************/
/* 条件节点 */
/************************************************************************/
public interface IConditionNode
{
string nodeName { get; set; }
bool ExternalCondition();
}
/************************************************************************/
/* 行为节点 */
/************************************************************************/
public interface IActionNode : IBehaviourTreeNode
{
}
public interface IBehaviourTree
{
}
很多节点的接口都是空的，目前唯一的作用就是用于类型判断，很可能在最后也没有什么实际的作用，搞不好就是所谓的过度设计。如果最终确定没有用再删掉吧。
接口里出现了一个渲染节点，目的是为了能够更方便的把这个节点和负责渲染的节点联系到一起，方便节点的可视化。
如果只有接口，每次实现接口都要重复做很多工作，为了利用面向对象的复用特性，就来实现一些父类
public class BaseNode
{
public BaseNode() { nodeName_ = this.GetType().Name + "\n"; }
protected RunStatus status_ = RunStatus.Completed;
protected string nodeName_;
protected RenderableNode renderNode_;
protected IBehaviourTreeNode parent_;
public virtual RunStatus status { get { return status_; } set { status_ = value; } }
public virtual string nodeName { get { return nodeName_; } set { nodeName_ = value; } }
public virtual RenderableNode renderNode { get { return renderNode_; } set { renderNode_ = value; } }
public virtual IBehaviourTreeNode parent { get { return parent_; } set { parent_ = value; } }
public virtual IBehaviourTreeNode Clone() {
var clone = new BaseNode();
clone.status_ = status_;
clone.nodeName_ = nodeName_;
clone.renderNode_ = renderNode_;
clone.parent_ = parent_;
return clone as IBehaviourTreeNode;
}
}
public class BaseActionNode : IActionNode
{
public BaseActionNode() { nodeName_ = this.GetType().Name + "\n"; }
protected RunStatus status_ = RunStatus.Completed;
protected string nodeName_;
protected RenderableNode renderNode_;
protected IBehaviourTreeNode parent_;
public virtual RunStatus status { get { return status_; } set { status_ = value; } }
public virtual string nodeName { get { return nodeName_; } set { nodeName_ = value; } }
public virtual RenderableNode renderNode { get { return renderNode_; } set { renderNode_ = value; } }
public virtual IBehaviourTreeNode parent { get { return parent_; } set { parent_ = value; } }
public virtual IBehaviourTreeNode Clone()
{
var clone = new BaseActionNode();
clone.status_ = status_;
clone.nodeName_ = nodeName_;
clone.renderNode_ = renderNode_;
clone.parent_ = parent_;
return clone as IBehaviourTreeNode;
}
public virtual bool Enter(object input)
{
status_ = RunStatus.Running;
return true;
}
public virtual bool Leave(object input)
{
status_ = RunStatus.Completed;
return true;
}
public virtual bool Tick(object input, object output)
{
return true;
}
}
public class BaseCondictionNode {
protected string nodeName_;
public virtual string nodeName { get { return nodeName_; } set { nodeName_ = value; } }
public BaseCondictionNode() { nodeName_ = this.GetType().Name+"\n"; }
public delegate bool ExternalFunc();
protected ExternalFunc externalFunc;
public static ExternalFunc GetExternalFunc(BaseCondictionNode node) {
return node.externalFunc;
}
}
public class Precondition : BaseCondictionNode, IConditionNode{
public Precondition(ExternalFunc func) { externalFunc = func; }
public Precondition(BaseCondictionNode pre) { externalFunc = BaseCondictionNode.GetExternalFunc(pre); }
public bool ExternalCondition()
{
if (externalFunc != null) return externalFunc();
else return false;
}
}
public class PreconditionNOT : BaseCondictionNode, IConditionNode
{
public PreconditionNOT(ExternalFunc func) { externalFunc = func; }
public PreconditionNOT(BaseCondictionNode pre) { externalFunc = BaseCondictionNode.GetExternalFunc(pre); }
public bool ExternalCondition()
{
if (externalFunc != null) return !externalFunc();
else return false;
}
}
public class BaseCompositeNode : BaseNode{
protected ArrayList nodeList_ = new ArrayList();
protected ArrayList conditionList_ = new ArrayList();
protected int runningNodeIndex = 0;
protected bool CheckNodeAndCondition() {
if (nodeList_.Count == 0)
{
status_ = RunStatus.Failure;
Debug.Log("SequenceNode has no node!");
return false;
}
return CheckCondition();
}
protected bool CheckCondition() {
foreach (var node in conditionList_)
{
var condiction = node as IConditionNode;
if (!condiction.ExternalCondition())
return false;
}
return true;
}
public virtual void AddNode(IBehaviourTreeNode node) { node.parent = (IBehaviourTreeNode)this; nodeList_.Add(node); }
public virtual void RemoveNode(IBehaviourTreeNode node) { nodeList_.Remove(node); }
public virtual bool HasNode(IBehaviourTreeNode node) { return nodeList_.Contains(node); }
public virtual void AddCondition(IConditionNode node) { conditionList_.Add(node); }
public virtual void RemoveCondition(IConditionNode node) { conditionList_.Remove(node); }
public virtual bool HasCondition(IConditionNode node) { return conditionList_.Contains(node); }
public virtual ArrayList nodeList { get { return nodeList_; } }
public virtual ArrayList conditionList { get { return conditionList_; } }
public override IBehaviourTreeNode Clone()
{
var clone = base.Clone() as BaseCompositeNode;
clone.nodeList_.AddRange(nodeList_);
clone.conditionList_.AddRange(conditionList_);
clone.runningNodeIndex = runningNodeIndex;
return clone as IBehaviourTreeNode;
}
}
public class SequenceNode : BaseCompositeNode, ISequenceNode
{
public SequenceNode(bool canContinue_ = false) { canContinue = canContinue_; }
public bool canContinue = false;
public bool Enter(object input)
{
var checkOk = CheckNodeAndCondition();
if (!checkOk) return false;
var runningNode = nodeList_[runningNodeIndex] as IBehaviourTreeNode;
checkOk = runningNode.Enter(input);
if (!checkOk) return false;
status_ = RunStatus.Running;
return true;
}
public bool Leave(object input)
{
if (nodeList_.Count == 0)
{
status_ = RunStatus.Failure;
Debug.Log("SequenceNode has no node!");
return false;
}
var runningNode = nodeList_[runningNodeIndex] as IBehaviourTreeNode;
runningNode.Leave(input);
if (canContinue)
{
runningNodeIndex++;
runningNodeIndex %= nodeList_.Count;
}
status_ = RunStatus.Completed;
return true;
}
public bool Tick(object input, object output)
{
if (status_ == RunStatus.Failure) return false;
if (status_ == RunStatus.Completed) return true;
var runningNode = nodeList_[runningNodeIndex] as IBehaviourTreeNode;
var checkOk = CheckCondition();
if (!checkOk)
{
return false;
}
switch (runningNode.status)
{
case RunStatus.Running:
if (!runningNode.Tick(input, output))
{
runningNode.Leave(input);
return false;
}
break;
default:
runningNode.Leave(input);
runningNodeIndex++;
if(runningNodeIndex >= nodeList_.Count)break;
var nextNode = nodeList_[runningNodeIndex] as IBehaviourTreeNode;
var check = nextNode.Enter(input);
if (!check) return false;
break;
}
return true;
}
public override IBehaviourTreeNode Clone()
{
var clone = base.Clone() as SequenceNode;
clone.canContinue = canContinue;
return clone;
}
}
这就是序列节点的设计，但是明显看起来很不爽，里面还出现了一个别扭的变量canContinue 。为什么会出现这个？因为序列节点的特点就是遇到一个子节点FALSE，就会停止并返回FALSE，但是这里我想用序列节点来做根节点，如果是根节点遇到这种情况，那么就不会执行下一个节点，而我看了很多种对于几大节点的描述，似乎都没提到这个。很多都用序列节点做根节点，有些就直接说是根节点。那么要么根节点另外实现，要么改一下序列节点。因为如果序列节点是非根节点的情况下，如果不是每次都从头开始，似乎又会引来新的问题，虽然目前还没想到会出什么问题。不过最后实现执行起来之后发现，用选择节点其实是一样的。所以目前这样的设计，可能是有根本上的问题。希望哪位大神可以指点一下。
然后是选择节点，根据了所有FALSE才返回FALSE的特点设计了
public class SelectorNode : BaseCompositeNode, ISelectorNode
{
public bool Enter(object input)
{
var checkOk = CheckNodeAndCondition();
if (!checkOk) return false;
do
{
var runningNode = nodeList_[runningNodeIndex] as IBehaviourTreeNode;
checkOk = runningNode.Enter(input);
if (checkOk) break;
runningNodeIndex++;
if (runningNodeIndex >= nodeList_.Count) return false;
} while (!checkOk);
status_ = RunStatus.Running;
return true;
}
public bool Leave(object input)
{
var runningNode = nodeList_[runningNodeIndex] as IBehaviourTreeNode;
runningNode.Leave(input);
runningNodeIndex = 0;
status_ = RunStatus.Completed;
return true;
}
public bool Tick(object input, object output)
{
if (status_ == RunStatus.Failure) return false;
if (status_ == RunStatus.Completed) return true;
var checkOk1 = CheckCondition();
if (!checkOk1) return false;
var runningNode = nodeList_[runningNodeIndex] as IBehaviourTreeNode;
switch (runningNode.status)
{
case RunStatus.Running:
if (!runningNode.Tick(input, output))
{
runningNode.Leave(input);
return false;
}
break;
default:
runningNode.Leave(input);
runningNodeIndex++;
if (runningNodeIndex >= nodeList_.Count) return false;
bool checkOk = false;
do
{
var nextNode = nodeList_[runningNodeIndex] as IBehaviourTreeNode;
checkOk = nextNode.Enter(input);
if (checkOk) break;
runningNodeIndex++;
if (runningNodeIndex >= nodeList_.Count) return false;
} while (!checkOk);
break;
}
return true;
}
}
目前对于我的简单DEMO，组合节点只需要这两个就够了，实际上只需要选择节点、条件节点、动作节点就够了。所以说设计是不完全的，虽然能够实现目标需求，但是实际工作量仍挺大，具体接下来会说明。
行为节点
先放一些渲染节点的代码。实际上我基本上是第一次接触自己去渲染一种数据结构，看完网上的大牛们随随便便就能写出个数据结构的示意图，不得不佩服。我一时半会没想出怎么渲染出树状结构，于是就简单的把树按层分组，一层一层渲染，缺点就是不能很好的表现树的样子，父子关系不能很好的表示。这里放出来希望能抛砖引玉。我以后可能会去完事它，但是现在首先是要搞清楚行为树。实现这个完全是为了看看节点是否正确放置，以方便调试。
public class RenderableNode
{
public RenderableNode parent;
public IBehaviourTreeNode targetNode;
public Rect posRect = new Rect();
public string name;
public int layer;
public RunStatus staus;
public override string ToString()
{
return name + "\n" + staus.ToString();
}
public virtual void Render()
{
bool running = staus == RunStatus.Running;
var rect = posRect;
rect.y -= (posRect.height / 2);
var oldColor = GUI.color;
if (running)
{
GUI.color = Color.green;
}
GUI.Box(rect, ToString());
GUI.color = oldColor;
if (parent == null && targetNode != null && targetNode.parent!=null)
{
parent = targetNode.parent.renderNode;
}
if (parent != null)
{
Vector2 parentPos = new Vector2();
parentPos.x = parent.posRect.x + parent.posRect.width;
parentPos.y = parent.posRect.y;
GUIHelper.DrawLine(new Vector2(rect.x, rect.y + rect.height / 2), parentPos, running?Color.green:Color.yellow);
}
}
}
public class RenderableCondictionNode : RenderableNode
{
public IConditionNode targetCondictionNode;
public override string ToString() { parent = null; return name; }
public override void Render()
{
var rect = posRect;
rect.y -= (posRect.height / 2);
var oldColor = GUI.color;
if (targetCondictionNode.ExternalCondition())
GUI.color = Color.green;
else
GUI.color = Color.blue;
GUI.Box(rect, ToString());
GUI.color = oldColor;
}
}
public class EmptyNode : RenderableNode { public override void Render() { } }
public class NodeBox
{
public Rect posRect = new Rect();
public List<RenderableNode> nodeList = new List<RenderableNode>();
public void AddNode(RenderableNode node)
{
nodeList.Add(node);
}
public void Render()
{
posRect.y = Screen.height / 2;
Rect rect = new Rect();
foreach (var node in nodeList)
{
var n = node;
rect.height += (n.posRect.height + 1);
rect.width = n.posRect.width + 10;
}
rect.height += 10;
rect.x = posRect.x - rect.width / 2;
rect.y = posRect.y - rect.height / 2;
//GUI.Box(rect, "");
posRect.width = rect.width;
posRect.height = rect.height;
float height = 0;
for (var i = 0; i < nodeList.Count; i++)
{
var n = nodeList[i];
n.posRect.y = rect.y + height + n.posRect.height / 2 + 5;
n.posRect.x = rect.x + 5;
n.Render();
height += n.posRect.height + 1;
}
}
}
放一张渲染出来的效果
虽然每一组都只是简单的居中，不过效果看起来还可以接受
然后从图中就可以看到问题了。所有正条件，都会有一个反条件，不这么做就无法在条件改变时，让当前节点返回FALSE，从而让行为树去寻找其他节点。而如果用状态机来做的话，条件肯定只用判断一次，比如
if(run){
Run();
}
else{
Walk();
}那么可能就回到最初的组合节点的设计了，组合节点就不得不每次都扫描条件。其实本质上我是在担心开销问题，因为变成节点后，就不在是if else那么简单，而是变成了函数调用的开销。简单的AI还好，如果大量复杂的AI，每次对整棵树进行扫描估计够呛。但是目前的设计，条件节点就会非常多，条件不完备就会出现BUG，似乎也不是非常好的情况。
最后放出一些细节
class PatrolAction : BaseActionNode {
public PatrolAction() { nodeName_ += "巡逻行为"; }
public override bool Tick(object input_, object output_)
{
// var input = input_ as WarriorInputData;
var output = output_ as WarriorOutPutData;
output.action = WarriorActon.ePatrol;
return true;
}
}
class RunAwayAction : BaseActionNode {
public RunAwayAction() { nodeName_ += "逃跑行为"; }
public override bool Tick(object input_, object output_)
{
// var input = input_ as WarriorInputData;
var output = output_ as WarriorOutPutData;
output.action = WarriorActon.eRunAway;
return true;
}
}
class AttackAction : BaseActionNode {
public AttackAction() { nodeName_ += "攻击行为"; }
public override bool Tick(object input_, object output_)
{
// var input = input_ as WarriorInputData;
var output = output_ as WarriorOutPutData;
output.action = WarriorActon.eAttack;
return true;
}
}
class CrazyAttackAction : BaseActionNode {
public CrazyAttackAction() { nodeName_ += "疯狂攻击行为"; }
public override bool Tick(object input_, object output_)
{
// var input = input_ as WarriorInputData;
var output = output_ as WarriorOutPutData;
output.action = WarriorActon.eCrazyAttack;
return true;
}
}
class AlertAction : BaseActionNode
{
public AlertAction() { nodeName_ += "警戒行为"; }
public override bool Tick(object input_, object output_)
{
// var input = input_ as WarriorInputData;
var output = output_ as WarriorOutPutData;
output.action = WarriorActon.eAlert;
return true;
}
}
private ICompositeNode rootNode = new SelectorNode();
private WarriorInputData inputData = new WarriorInputData();
private WarriorOutPutData outputData = new WarriorOutPutData();
// Use this for initialization
public void Start()
{
inputData.attribute = GetComponent<CharacterAttribute>();
rootNode.nodeName += "根";
//条件
var hasNoTarget = new PreconditionNOT(() => { return inputData.attribute.hasTarget; });
hasNoTarget.nodeName = "无目标";
var hasTarget = new Precondition(hasNoTarget);
hasTarget.nodeName = "发现目标";
var isAnger = new Precondition(() => { return inputData.attribute.isAnger; });
isAnger.nodeName = "愤怒状态";
var isNotAnger = new PreconditionNOT(isAnger);
isNotAnger.nodeName = "非愤怒状态";
var HPLessThan500 = new Precondition(() => { return inputData.attribute.health < 500; });
HPLessThan500.nodeName = "血少于500";
var HPMoreThan500 = new PreconditionNOT(HPLessThan500);
HPMoreThan500.nodeName = "血大于500";
var isAlert = new Precondition(() => { return inputData.attribute.isAlert; });
isAlert.nodeName = "警戒";
var isNotAlert = new PreconditionNOT(isAlert);
isNotAlert.nodeName = "非警戒";
var patrolNode = new SequenceNode();
patrolNode.nodeName += "巡逻";
patrolNode.AddCondition(hasNoTarget);
patrolNode.AddCondition(isNotAlert);
patrolNode.AddNode(new PatrolAction());
var alert = new SequenceNode();
alert.nodeName += "警戒";
alert.AddCondition(hasNoTarget);
alert.AddCondition(isAlert);
alert.AddNode(new AlertAction());
var runaway = new SequenceNode();
runaway.nodeName += "逃跑";
runaway.AddCondition(hasTarget);
runaway.AddCondition(HPLessThan500);
runaway.AddNode(new RunAwayAction());
var attack = new SelectorNode();
attack.nodeName += "攻击";
attack.AddCondition(hasTarget);
attack.AddCondition(HPMoreThan500);
var attackCrazy = new SequenceNode();
attackCrazy.nodeName += "疯狂攻击";
attackCrazy.AddCondition(isAnger);
attackCrazy.AddNode(new CrazyAttackAction());
attack.AddNode(attackCrazy);
var attackNormal = new SequenceNode();
attackNormal.nodeName += "普通攻击";
attackNormal.AddCondition(isNotAnger);
attackNormal.AddNode(new AttackAction());
attack.AddNode(attackNormal);
rootNode.AddNode(patrolNode);
rootNode.AddNode(alert);
rootNode.AddNode(runaway);
rootNode.AddNode(attack);
var ret = rootNode.Enter(inputData);
if (!ret)
{
Debug.Log("无可执行节点！");
}
}
// Update is called once per frame
void Update () {
var ret = rootNode.Tick(inputData, outputData);
if (!ret)
rootNode.Leave(inputData);
if (rootNode.status == RunStatus.Completed)
{
ret = rootNode.Enter(inputData);
if (!ret)
rootNode.Leave(inputData);
}
else if (rootNode.status == RunStatus.Failure)
{
Debug.Log("BT Failed");
enabled = false;
}
if (outputData.action != inputData.action)
{
OnActionChange(outputData.action, inputData.action);
inputData.action = outputData.action;
}
}
void OnActionChange(WarriorActon action, WarriorActon lastAction) {
// print("OnActionChange "+action+" last:"+lastAction);
switch (lastAction)
{
case WarriorActon.ePatrol:
GetComponent<WarriorPatrol>().enabled = false;
break;
case WarriorActon.eAttack:
case WarriorActon.eCrazyAttack:
GetComponent<WarriorAttack>().enabled = false;
break;
case WarriorActon.eRunAway:
GetComponent<WarriorRunAway>().enabled = false;
break;
case WarriorActon.eAlert:
GetComponent<WarriorAlert>().enabled = false;
break;
}
switch (action) {
case WarriorActon.ePatrol:
GetComponent<WarriorPatrol>().enabled = true;
break;
case WarriorActon.eAttack:
var attack = GetComponent<WarriorAttack>();
attack.revenge = false;
attack.enabled = true;
break;
case WarriorActon.eCrazyAttack:
var crazyAttack = GetComponent<WarriorAttack>();
crazyAttack.revenge = true;
crazyAttack.enabled = true;
break;
case WarriorActon.eRunAway:
GetComponent<WarriorRunAway>().enabled = true;
break;
case WarriorActon.eAlert:
GetComponent<WarriorAlert>().enabled = true;
break;
case WarriorActon.eIdle:
GetComponent<WarriorPatrol>().enabled = false;
GetComponent<WarriorAttack>().enabled = false;
GetComponent<WarriorRunAway>().enabled = false;
break;
}
}