BrainTree

A C++ behavior tree header-only library.

Features

• behavior tree
• 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!", six times
#include <iostream>
#include <BrainTree.h>

class Action : public BrainTree::Node
{
public:
    Action() {}

    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 actionOne = std::make_shared<Action>();
    auto actionTwo = std::make_shared<Action>();
    auto actionThree = std::make_shared<Action>();
    sequence.addChild(actionOne);
    sequence.addChild(actionTwo);
    sequence.addChild(actionThree);
    tree.setRoot(sequence);
    tree.update();
}

void CreatingBehaviorTreeUsingBuilders()
{
    auto tree = BrainTree::TreeBuilder()
        .composite<BrainTree::Sequence>()
            .leaf<Action>()
            .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 makes it easier to create a behavior tree. You use three methods to build your tree: leaf<NodeType>(), composite<CompositeType>() and 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 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) arvidsson