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

Composite	Behaviour	Success	Running	Failure
Selector	Ticks each child node in order, starting from the beginning each tick	If a child succeeds	If a child is running	If all children fail
Sequence	Ticks each child node in order, starting from the beginning each tick	If all children succeed	If a child is running	If a child fails
StatefulSelector	Ticks each child node in order, starting from the child ticked in previous tick	If a child succeeds	If a child is running	If all children fail
StatefulSequence	Ticks each child node in order, starting from the child ticked in previous tick	If all children succeed	If a child is running	If a child fails

Decorators

Decorator	Behaviour
Succeeder	Always returns success
Failer	Always returns failure
Inverter	Inverts the result of the child node
Repeater	Repeats until child node succeeds (infinitely or limited)
UntilSuccess	Repeats until child node succeeds
UntilFailure	Repeats until child node fails

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