行为树详解（5）——事件驱动

【分析】

如果行为树的节点很多，那么会存在要经过很多节点才会走到动作节点的情况。显然，性能上不如状态机。

每帧都需要重新遍历一系列节点才会走到动作节点，而实际上很多条件节点在数帧内不会有变化，这是造成性能问题的重要原因。

行为树每帧的Update其实就是在轮询这些条件，为避免轮询，我们自然而然的希望在一帧直接执行动作节点。

为此，需要将在Running状态的动作节点缓存，直接执行直到成功。

这种方式引起的问题是动作节点不一定总是会执行成功，可能在某一帧，某些条件改变了，动作需要被打断。

为了解决该问题，就需要给动作节点引入一些事件，当特定事件发生时，在动作节点内接收该事件，直接结束动作节点的运行，返回失败。

随后重新开始整个行为树的轮询，找到下一个动作节点。

这就是事件和轮询混合驱动的行为树。

事件本质上就是直接调用，当经过动作节点的路径较长，也即影响该动作节点的条件过多时，不可避免要通过代码调用发多种消息,这就失去了配置的意义。

需要将打断动作节点及节点的逻辑做成单独的Conditional节点，这些节点接收消息或监听变化，以决定是否打断其子节点。

通过轮询这些Conditional节点以简化发多种消息的调用。

当打断发生时，需要重新运行被打断节点的父节点确定新的分支走向。为此，需要将路径上所有节点做缓存。

这里要对控制节点做特殊处理，控制节点会控制自身的子节点运行，其状态受子节点影响，当打断存在时，子节点可能不需要再次运行，因此控制节点在控制子节点运行前需要知道当前是否被打断。

【代码实现】

    public class BehaviorTree{public string btName;public int btId;public UpdateType updateType;public DrivenType drivenType;public float updateTime;private float curTime;public GameObject owner;private Node rootNode;private List<Node> allNodes = new List<Node>();private Dictionary<int,Node> id2Node = new Dictionary<int,Node>();private Dictionary<int,NodeInfo> id2NodeInfo = new Dictionary<int,NodeInfo>();private Dictionary<Type, Dictionary<string, Delegate>> eventDic = new Dictionary<Type, Dictionary<string, Delegate>>();private Node curActionNode;private Stack<Node> activeNodes = new Stack<Node>();private List<ConditionalNode> conditionalNodes = new List<ConditionalNode>();  public static Func<string, BehaviourTreeData> loadFunc = null;public void Init(GameObject owner, string path, Func<string, BehaviourTreeData> loadFunc){this.owner = owner;//这里省略部分边界情况检查的逻辑，if (!string.IsNullOrEmpty(path)){var data = loadFunc?.Invoke(path);btId = owner.GetInstanceID();updateType = data.updateType; updateTime = data.updateTime;drivenType = data.drivenType;//通常初始化有两种写法，一种是在管理者中完成管理者自身以及被管理者的数据初始化；另一种是管理者完成自身的初始化后将被数据传递给被管理者，被管理者自身完成初始化//第二种方式更加灵活可变，且不需要关注行为树结构是怎么样的，只需每个节点做好自身的初始化//在第二种方式下涉及如何将数据递归传递的问题，为统一获取，将数据记录在管理者上，被管理者根据Id从管理者中获取，初始化后可选择将数据释放foreach (var item in data.nodes){id2NodeInfo[item.nodeId] = item;}var rootData = data.nodes[0];//默认第一个是rootNode数据rootNode = new RootNode();rootNode.Init(rootData, this);id2NodeInfo.Clear();//也可以保留}}public void Update(float time){if(drivenType == DrivenType.Polling){PollingUpdate(time);}else if(drivenType == DrivenType.PollingAndEvent){if (curActionNode != null){var actionStatus = curActionNode.Update();if(actionStatus != NodeStatus.Running){curActionNode = null; PollingUpdate(time);}else{if (updateType == UpdateType.FixedTime){curTime += time;}}}else{PollingUpdate(time);}}else if(drivenType == DrivenType.EventDriven){EventUpdate(time);}}private void PollingUpdate(float time){if (updateType == UpdateType.EveryFrame){Update();}else if (updateType == UpdateType.FixedTime){curTime += time;if (curTime > updateTime){curTime = 0;Update();}}}private void EventUpdate(float time){int index = -1;for (int i = 0; i < conditionalNodes.Count; i++){if (conditionalNodes[i].ConditionChanged()) //当条件节点条件改变，其后所有节点都需要重新计算,动作节点需要被打断{index = i;break;}}if (index != -1){              while(activeNodes.Count> 0 && activeNodes.Peek().nodeId != conditionalNodes[index].nodeId)//移除其后所有Active节点{PopNode(activeNodes.Peek());}conditionalNodes[index].Update();//重新运行该节点if (conditionalNodes[index].StatusChanged(out var curStatus)){                    var curNode = (Node)conditionalNodes[index];var parent = conditionalNodes[index].parent;while (parent is ControlNode)//如果父节点是控制节点，其状态会与子节点相关,这里简化处理，直接重新运行{curNode = parent;parent = parent.parent;}if(curNode != conditionalNodes[index]){while (activeNodes.Count > 0 && activeNodes.Peek().nodeId != curNode.nodeId){PopNode(activeNodes.Peek());}curNode.Update();}}}else{var state = activeNodes.Peek().Update();//没有打断，再次运行末尾的动作节点if(state != NodeStatus.Running)//运行结束，重新从根节点开始运行，也可以选择回退到上一个节点开始运行{activeNodes.Clear();conditionalNodes.Clear();rootNode.Update();}}}public void PushNode(Node node){if (drivenType != DrivenType.EventDriven)return;activeNodes.Push(node);if(node is ConditionalNode conditionalNode){conditionalNodes.Add(conditionalNode);}}private void PopNode(Node node){if (drivenType != DrivenType.EventDriven)return;node.End();activeNodes.Pop();if(node is ConditionalNode conditionalNode){conditionalNodes.Remove(conditionalNode);}}public NodeStatus Update(){var status = rootNode.Update();if(status != NodeStatus.Running){rootNode.End();}return status;}public void Destroy(){foreach (var item in allNodes){item.Destroy();}allNodes.Clear();id2Node.Clear();id2NodeInfo.Clear();}public NodeInfo GetNodeInfo(int nodeId){return id2NodeInfo[nodeId];}public void AddNode(Node node){allNodes.Add(node);id2Node[node.nodeId] = node;}public void SetActionNode(Node node){curActionNode = node;}private void RegisterEvent(string eventName, Delegate handler){if (drivenType == DrivenType.Polling)return;if (!eventDic.TryGetValue(handler.GetType(), out var dic)){dic = new Dictionary<string, Delegate>();eventDic[handler.GetType()] = dic;}if (!dic.TryGetValue(eventName, out var value)){dic[eventName] = handler;}else{dic[eventName] = Delegate.Combine(value, handler);}}public void RegisterEvent(string eventNmae,Action action){RegisterEvent(eventNmae, (Delegate)action);}public void RegisterEvent<T>(string eventNmae, Action<T> action){RegisterEvent(eventNmae, (Delegate)action);}public void RegisterEvent<T1,T2>(string eventNmae, Action<T1,T2> action){RegisterEvent(eventNmae, (Delegate)action);}public void RegisterEvent<T1, T2,T3>(string eventNmae, Action<T1, T2,T3> action){RegisterEvent(eventNmae, (Delegate)action);}private Delegate GetDelegate(string eventName,Type type){if (drivenType == DrivenType.Polling)return null;if (eventDic.TryGetValue(type, out var dic)){if (dic.TryGetValue(eventName, out var handler)){return handler;}}return null;}public void SendEvent(string eventName){            if(GetDelegate(eventName, typeof(Action)) is Action action){action();}}public void SendEvent<T>(string eventName, T t){if (GetDelegate(eventName, typeof(Action<T>)) is Action<T> action){action(t);}}public void SendEvent<T1,T2>(string eventName, T1 t1,T2 t2){if (GetDelegate(eventName, typeof(Action<T1,T2>)) is Action<T1,T2> action){action(t1,t2);}}public void SendEvent<T1, T2,T3>(string eventName, T1 t1, T2 t2,T3 t3){if (GetDelegate(eventName, typeof(Action<T1, T2,T3>)) is Action<T1, T2,T3> action){action(t1, t2,t3);}}}public enum DrivenType{Polling,PollingAndEvent,EventDriven}

    public class Node{public string nodeName;public int nodeId;public NodeStatus status;public BehaviorTree owner;public Node parent;public void Init(NodeInfo nodeInfo, BehaviorTree owner){this.owner = owner;this.nodeName = nodeInfo.nodeName;this.nodeId = nodeInfo.nodeId;OnInit(nodeInfo);owner.AddNode(this);//对于字段的配置可以通过字段名反射获取字段然后设置值，但这里允许的值是有限的，我们直接在每个节点写对应的处理}public NodeStatus Update(){owner.PushNode(this);return OnUpdate();}public void End()//方法名字叫Exit也是一样的{OnEnd();}protected virtual void OnInit(NodeInfo nodeInfo){}protected virtual NodeStatus OnUpdate(){return NodeStatus.Success;}protected virtual void OnEnd(){}public virtual void Destroy(){}}public class ConditionalNode:Node{public Node subNode;protected override void OnInit(NodeInfo nodeInfo){if (nodeInfo.subNodes.Count > 0){var subNodeInfo = owner.GetNodeInfo(nodeInfo.subNodes[0]);Type type = Type.GetType(subNodeInfo.nodeType);subNode = (Node)Activator.CreateInstance(type);subNode.Init(subNodeInfo, owner);subNode.parent = this;}}protected override NodeStatus OnUpdate(){return subNode.Update();}public virtual bool ConditionChanged(){return false;}public virtual bool StatusChanged(out NodeStatus status){status = NodeStatus.Success;return false;}public class ActionNode:Node{private bool start;private bool stop;protected override NodeStatus OnUpdate(){if (!start){Start();start = true;}var res = base.OnUpdate();if(stop){res = NodeStatus.Failure;}if (res == NodeStatus.Running){owner.SetActionNode(this);}return res;}private void Start(){OnStart();}protected virtual void OnStart(){//各动作节点自定义注册事件}protected override void OnEnd(){start = false;stop = false;}}