[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 = 0;
        // 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 = 0;
        }
    }
}

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 = 0;  --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 + 1;
    task.index = index;
    task.layer = self.layer + 1;
    task.parent = self;
    task.root = self.root;
    self.childTasks[index] = task;
end

--是否有子节点
function this:HasChild()
    if (#self.childTasks > 0) 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 + 1)) then
        self.currentChildIndex = self.currentChildIndex + 1;
        return self.childTasks[self.currentChildIndex];
    end
    return nil;
end

--重置
function this:Reset()
    self.currentChildIndex = 0;
    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：