BrainTree

A C++ behavior tree single header library.

Features

behavior tree implementation
predefined composites
predefined decorators
(optional) rudimentary blackboard
(optional) behavior tree builders

Install

Include BrainTree.h in your project.

Example

// this example should print out "Hello, World!", four times
#include <iostream>
#include "BrainTree.h"

class Action : public BrainTree::Node
{
public:
    Status update() override
    {
        std::cout << "Hello, World!" << std::endl;
        return Node::Status::Success;
    }
};

void CreatingBehaviorTreeManually()
{
    BrainTree::BehaviorTree tree;
    auto sequence = std::make_shared<BrainTree::Sequence>();
    auto sayHello = std::make_shared<Action>();
    auto sayHelloAgain = std::make_shared<Action>();
    sequence->addChild(sayHello);
    sequence->addChild(sayHelloAgain);
    tree.setRoot(sequence);
    tree.update();
}

void CreatingBehaviorTreeUsingBuilders()
{
    auto tree = BrainTree::Builder()
        .composite<BrainTree::Sequence>()
            .leaf<Action>()
            .leaf<Action>()
        .end()
        .build();
    tree->update();
}

int main()
{
    CreatingBehaviorTreeManually();
    CreatingBehaviorTreeUsingBuilders();
    return 0;
}

Composites

Selector

The Selector composite ticks each child node in order.
If a child succeeds or runs, the selector returns the same status.
In the next tick, it will try to run each child in order again.
If all children fails, only then does the selector fail.

Sequence

The Sequence composite ticks each child node in order.
If a child fails or runs, the sequence returns the same status.
In the next tick, it will try to run each child in order again.
If all children succeeds, only then does the sequence succeed.

StatefulSelector

The StatefulSelector composite ticks each child node in order, and remembers what child it prevously tried to tick.
If a child succeeds or runs, the stateful selector returns the same status.
In the next tick, it will try to run the next child or start from the beginning again.
If all children fails, only then does the stateful selector fail.

StatefulSequence

The StatefulSequence composite ticks each child node in order, and remembers what child it prevously tried to tick.
If a child fails or runs, the stateful sequence returns the same status.
In the next tick, it will try to run the next child or start from the beginning again.
If all children succeeds, only then does the stateful sequence succeed.

Builder

The Builder class simplifies the process of creating a behavior tree. You use three methods to build your tree:

leaf<NodeType>()
composite<CompositeType>()
decorator<DecoratorType>()

Both composite() and decorator() require a corresponding call to end(), this marks where you are done adding children to a composite or a child to a decorator. At the very end you call build() which will then give you the finished behavior tree.

auto tree = Builder()
    .decorator<Repeater>()
        .composite<Sequence>()
            .leaf<SayHello>("Foo")
            .leaf<SayHello>("Bar")
        .end()
    .end()
    .build();

License

MIT (c) Pär Arvidsson 2015-2018

docwyatt2001/BrainTree