Composition of Behaviors with Subtree

可以构建将多个更小的可重复使用的行为到一个更大的树中；

换句话说，想构建分层的行为树；

通过在XML中定义多个树来实现；

CrossDoor behavior

This example is inspired by a popular article about behavior trees.

It is also the first practical example that uses Decorators and Fallback.

<root main_tree_to_execute = "MainTree">

    <BehaviorTree ID="DoorClosed">
        <Sequence name="door_closed_sequence">
            <Inverter>
                <IsDoorOpen/>
            </Inverter>
            <RetryUntilSuccesful num_attempts="4">
                <OpenDoor/>
            </RetryUntilSuccesful>
            <PassThroughDoor/>
        </Sequence>
    </BehaviorTree>

    <BehaviorTree ID="MainTree">
        <Fallback name="root_Fallback">
            <Sequence name="door_open_sequence">
                <IsDoorOpen/>
                <PassThroughDoor/>
            </Sequence>
            <SubTree ID="DoorClosed"/>
            <PassThroughWindow/>
        </Fallback>
    </BehaviorTree>

</root>

The desired behavior is:

• If the door is open, PassThroughDoor.
• If the door is closed, try up to 4 times to OpenDoor and, then, PassThroughDoor.
• If it was not possible to open the closed door, PassThroughWindow.

Loggers

一个Logger是一种用于显示，记录，或者发布在树中任何状态的改变的机制：

int main()
{
    using namespace BT;
    BehaviorTreeFactory factory;

    // register all the actions into the factory
    // We don't show how these actions are implemented, since most of the 
    // times they just print a message on screen and return SUCCESS.
    // See the code on Github for more details.
    factory.registerSimpleCondition("IsDoorOpen", std::bind(IsDoorOpen));
    factory.registerSimpleAction("PassThroughDoor", std::bind(PassThroughDoor));
    factory.registerSimpleAction("PassThroughWindow", std::bind(PassThroughWindow));
    factory.registerSimpleAction("OpenDoor", std::bind(OpenDoor));
    factory.registerSimpleAction("CloseDoor", std::bind(CloseDoor));
    factory.registerSimpleCondition("IsDoorLocked", std::bind(IsDoorLocked));
    factory.registerSimpleAction("UnlockDoor", std::bind(UnlockDoor));

    // Load from text or file...
    auto tree = factory.createTreeFromText(xml_text);

    // This logger prints state changes on console
    StdCoutLogger logger_cout(tree);

    // This logger saves state changes on file
    FileLogger logger_file(tree, "bt_trace.fbl");

    // This logger stores the execution time of each node
    MinitraceLogger logger_minitrace(tree, "bt_trace.json");

#ifdef ZMQ_FOUND
    // This logger publish status changes using ZeroMQ. Used by Groot
    PublisherZMQ publisher_zmq(tree);
#endif

    printTreeRecursively(tree.rootNode());

    //while (1)
    {
        NodeStatus status = NodeStatus::RUNNING;
        // Keep on ticking until you get either a SUCCESS or FAILURE state
        while( status == NodeStatus::RUNNING)
        {
            status = tree.tickRoot();
            CrossDoor::SleepMS(1);   // optional sleep to avoid "busy loops"
        }
        CrossDoor::SleepMS(2000);
    }
    return 0;
}