[Unity插件]Lua行为树(三)：组合节点Sequence

Sequence的继承关系如下：

Sequence->Composite->ParentTask->Task

上一篇已经实现了简单版本的ParentTask和Task(基于Behavior Designer的源码)，那么接下来看下Composite和Sequence。

1.Composite：表明该节点是组合节点，无特殊作用。

2.Sequence：

成员：

currentChildIndex：当前运行的子节点索引

executionStatus：当前运行的子节点状态

方法：

CanExecute：当有可运行的子节点并且子节点不返回失败时，返回true

OnChildExecuted：当一个子节点运行完后调用，将当前索引指向下一个节点，同时更新当前运行的子节点状态

OnEnd：Sequence运行结束时调用，重置变量

 namespace BehaviorDesigner.Runtime.Tasks
 {
     [TaskDescription("The sequence task is similar to an \"and\" operation. It will return failure as soon as one of its child tasks return failure. " +
                      "If a child task returns success then it will sequentially run the next task. If all child tasks return success then it will return success.")]
     [HelpURL("http://www.opsive.com/assets/BehaviorDesigner/documentation.php?id=25")]
     [TaskIcon("{SkinColor}SequenceIcon.png")]
     public class Sequence : Composite
     {
         // The index of the child that is currently running or is about to run.
         private int currentChildIndex = ;
         // The task status of the last child ran.
         private TaskStatus executionStatus = TaskStatus.Inactive;

         public override int CurrentChildIndex()
         {
             return currentChildIndex;
         }

         public override bool CanExecute()
         {
             // We can continue to execuate as long as we have children that haven't been executed and no child has returned failure.
             return currentChildIndex < children.Count && executionStatus != TaskStatus.Failure;
         }

         public override void OnChildExecuted(TaskStatus childStatus)
         {
             // Increase the child index and update the execution status after a child has finished running.
             currentChildIndex++;
             executionStatus = childStatus;
         }

         public override void OnConditionalAbort(int childIndex)
         {
             // Set the current child index to the index that caused the abort
             currentChildIndex = childIndex;
             executionStatus = TaskStatus.Inactive;
         }

         public override void OnEnd()
         {
             // All of the children have run. Reset the variables back to their starting values.
             executionStatus = TaskStatus.Inactive;
             currentChildIndex = ;
         }
     }
 }

当然，因为Behavior Designer源码的代码量比较多，所以不可能完全地实现一个Lua版本的BD，不过可以参考里面的一些设计思想去实现一套行为树。

以Sequence节点为例：

1.如果当前节点返回Failure，则Sequence返回Failure，结束执行Sequence

2.如果当前节点返回Running，则Sequence返回Running，下一帧继续执行当前节点

3.如果当前节点返回Success，那么Sequence将会执行下一个节点，这里会出现两种做法，一是Sequence返回Running，等下一帧再执行下一节点；二是在同一帧下继续执行。这里我采用的是第二种，因为在早期的AI中，逻辑都是在Update中进行的，也就是逻辑都在同一帧中，因此我觉得放在同一帧中执行效率会高一些。

代码如下：

BTParentTask.lua

 BTParentTask = BTTask:New();

 local this = BTParentTask;

 function this:New()
     local o = {};
     setmetatable(o, self);
     self.__index = self;
     o.currentChildIndex = ;  --当前运行到第几个子节点
     o.currentChildTask = nil; --当前运行的子节点
     o.childTasks = {};        --子节点列表
     return o;
 end

 function this:AddChild(task)
     local index = #self.childTasks + ;
     task.index = index;
     task.layer = self.layer + ;
     task.parent = self;
     task.root = self.root;
     self.childTasks[index] = task;
 end

 --是否有子节点
 function this:HasChild()
     if (#self.childTasks > ) then
         return true;
     else
         return false;
     end
 end

 --获取下一个要执行的子节点
 function this:GetNextChild()
     if (#self.childTasks >= (self.currentChildIndex + )) then
         self.currentChildIndex = self.currentChildIndex + ;
         return self.childTasks[self.currentChildIndex];
     end
     return nil;
 end

 --重置
 function this:Reset()
     self.currentChildIndex = ;
     self.currentChildTask = nil;
 end

BTSequence.lua

 BTSequence = BTComposite:New();

 local this = BTSequence;

 function this:New()
     local o = {};
     setmetatable(o, self);
     self.__index = self;
     o.executionStatus = BTTaskStatus.Inactive;
     return o;
 end

 function this:OnUpdate()
     if (not self:HasChild()) then
         return BTTaskStatus.Failure;
     end

     if (not self.currentChildTask) then
         self.currentChildTask = self:GetNextChild();
         if (not self.currentChildTask) then
             return BTTaskStatus.Failure;
         end
     end

     while (self.currentChildTask) do
         self.executionStatus = self.currentChildTask:OnUpdate();
         if (self.executionStatus == BTTaskStatus.Failure) then --结束
             self:Reset();
             return BTTaskStatus.Failure;
         elseif (self.executionStatus == BTTaskStatus.Running) then --下一帧继续执行
             return BTTaskStatus.Running;
         else --继续执行下一节点
             self.currentChildTask = self:GetNextChild();
         end
     end

     --所有节点执行完毕
     self.executionStatus = BTTaskStatus.Success;
     self:Reset();
     return BTTaskStatus.Success;
 end

TestBehaviorTree.lua

 TestBehaviorTree = BTBehaviorTree:New();

 local this = TestBehaviorTree;

 function this:New()
     local o = {};
     setmetatable(o, self);
     self.__index = self;
     this:Init();
     return o;
 end

 function this:Init()
     local sequence = BTSequence:New();
     local log = BTLog:New("hello world!");
     local log2 = BTLog:New("This is a test");
     sequence:AddChild(log);
     sequence:AddChild(log2);
     this:PushTask(sequence);
 end

打印如下：