How to create a BehaviorTree

How to create a BehaviorTree

行为树类似于状态机，只是一种机制，在正确的条件下，正确的时间来唤醒回调函数。

进一步，我们使用callback和tick来相互替换；

这些回调函数里面具体执行什么取决于你；

怎样创建你自己的ActionNodes

默认的方法是采用继承的方式来实现一个TreeNode：

//Example of custom SyncActionNode(synchronous action) without ports.class ApproachObject : public BT::SyncActionNode{ public: ApproachObject(const std::string& name) : BT::SyncActionNode(name, {}) {} //You must override the virtual function tick() BT::NodeStatus tick() override { std::out << "ApproachObject: " << this->name() <

任何一个TreeNode的实例需要有一个名字，但不要求是唯一的；

方法tick()是实际行为发生的地方。它必须总是返回一个节点状态，如RUNNING,SUCCESS或者FAILURE。

另外，也可以用依赖注入的方式创建一个TreeNode，给定一个函数指针(如functor)

对functor唯一的要求是具有如下之一的表示：

BT::NodeStatus myFunction() BT::NodeStatus myFunction(BT::TreeNode& self)

例如：

using namespace BT;// Simple function that return a NodeStatusBT::NodeStatus CheckBattery(){ std::cout << "[ Battery: OK ]" << std::endl; return BT::NodeStatus::SUCCESS;}// We want to wrap into an ActionNode the methods open() and close()class GripperInterface{public: GripperInterface(): _open(true) {} NodeStatus open() { _open = true; std::cout << "GripperInterface::open" << std::endl; return NodeStatus::SUCCESS; } NodeStatus close() { std::cout << "GripperInterface::close" << std::endl; _open = false; return NodeStatus::SUCCESS; }private: bool _open; // shared information};

我们可以构建一个SimpleActionNode从下面的functors中的任何一个：

CheckBattery()GripperInterface::open()GripperInterface::close()

用一个XML来动态创建一棵树

XML文件命名为my_tree.xml:

You can find more details about the XML schema ​​here​​.

首先比如注册我们自定义的TreeNodes到BehaviorTreeFactory中，然后从文件或者text中加载XML；

在XML中使用的标志符必须与注册TreeNodes中使用的一致；

属性name表示实例的名字，它是可选的；

#include "behaviortree_cpp_v3/bt_factory.h"// file that contains the custom nodes definitions#include "dummy_nodes.h"int main(){ // We use the BehaviorTreeFactory to register our custom nodes BehaviorTreeFactory factory; // Note: the name used to register should be the same used in the XML. using namespace DummyNodes; // The recommended way to create a Node is through inheritance. factory.registerNodeType("ApproachObject"); // Registering a SimpleActionNode using a function pointer. // you may also use C++11 lambdas instead of std::bind factory.registerSimpleCondition("CheckBattery", std::bind(CheckBattery)); //You can also create SimpleActionNodes using methods of a class GripperInterface gripper; factory.registerSimpleAction("OpenGripper", std::bind(&GripperInterface::open, &gripper)); factory.registerSimpleAction("CloseGripper", std::bind(&GripperInterface::close, &gripper)); // Trees are created at deployment-time (i.e. at run-time, but only // once at the beginning). // IMPORTANT: when the object "tree" goes out of scope, all the // TreeNodes are destroyed auto tree = factory.createTreeFromFile("./my_tree.xml"); // To "execute" a Tree you need to "tick" it. // The tick is propagated to the children based on the logic of the tree. // In this case, the entire sequence is executed, because all the children // of the Sequence return SUCCESS. tree.tickRoot(); return 0;}/* Expected output:* [ Battery: OK ] GripperInterface::open ApproachObject: approach_object GripperInterface::close*/

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