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