A lightweight behavior tree library in C++.

💥 Thanks to Davide Faconti there is now a more sophisticated version of the library. The new version of this library is available here. There is also GUI available here.

Our book Behavior Trees in Robotics and AI, published by CRC Press Taylor & Francis, is available for purchase (ebook and hardcover) on the CRC Press Store or Amazon. The Preprint version (free) is available here: https://arxiv.org/abs/1709.00084

Tutorials available at https://btirai.github.io/

Please refer to the following paper when using the library:

How Behavior Trees Modularize Hybrid Control Systems and Generalize Sequential Behavior Compositions, the Subsumption Architecture, and Decision Trees. Michele Colledanchise and Petter Ogren. IEEE Transaction on Robotics 2017.

bibtex entry:

@ARTICLE{TRO17Colledanchise,
author={M. Colledanchise and P. Ögren},
journal={IEEE Transactions on Robotics},
title={{How Behavior Trees Modularize Hybrid Control Systems and Generalize Sequential Behavior Compositions, the Subsumption Architecture, and Decision Trees}},
year={2017},
volume={33},
number={2},
pages={372-389},
keywords={Computer architecture;Decision trees;High definition video;Robot control;Switches;Behavior trees (BTs);decision trees;finite state machines (FSMs);hybrid dynamical systems (HDSs);modularity;sequential behavior compositions;subsumption architecture},
doi={10.1109/TRO.2016.2633567},
ISSN={1552-3098},
month={April},}

Regarding visualization purposes:

• OpenGL
• Glut

Regarding tests:

• GTests

Fallback: Fallback nodes are used to find and execute the first child that does not fail. A Selector node will return immediately with a status code of success or running when one of its children returns success or running. The children are ticked in order of importance, from left to right.

Sequence: Sequence nodes are used to find and execute the first child that has not yet succeeded. A sequence node will return immediately with a status code of failure or running when one of its children returns failure or running. The children are ticked in order, from left to right.

Parallel: The parallel node ticks its children in parallel and returns success if M ≤ N children return success, it returns failure if N − M + 1 children return failure, and it returns running otherwise.

Decorator: The decorator node manipulates the return status of its child according to the policy defined by the user (e.g. it inverts the success/failure status of the child). In this library the decorators implemented are the two common ones: Decorator Retry which retries the execution of a node if this fails; and Decorator Negation That inverts the Success/Failure outcome.

Action: An Action node performs an action, and returns Success if the action is completed, Failure if it can not be completed and Running if completion is under way.

Condition: A Condition node determines if a desired condition c has been met. Conditions are technically a subset of the Actions, but are given a separate category and graphical symbol to improve readability of the BT and emphasize the fact that they never return running and do not change any internal states/variables of the BT.

A user manual is available in the project folder (BTppUserManual.pdf).

The first step to use BT++ is to retrieve its source code. You can either download it here (https://github.com/miccol/Behavior-Tree) or clone the repository:

$ cd /path/to/folder
$ git clone https://github.com/miccol/Behavior−Tree.git

Once you have the repository, compile the library:

$ cd /path/to/folder/
$ mkdir ./build
$ cd build
$ cmake ..
$ make

NOTE In case you get the following error:

CMake Error: The following variables are used in this project, but they are set to NOTFOUND. Please set them or make sure they are set and tested correctly in the CMake files: GLUT_Xmu_LIBRARY (ADVANCED)

please see solution here. Thanks miquelramirez for this.

Check the installation by running a sample example.

$ cd /path/to/folder/
$ cd build/sample
$ ./btpp_example

If you would like to install the library system-wide, then run:

$ cd /path/to/folder/
$ cd build
$ sudo make install

On Ubuntu, this will install the library (libbtpp.so) in /usr/local/lib.
In an external project, just call in your CMakeLists 'find_package(BTpp)' to find the library.
The include directory is defined as BTpp_INCLUDE_DIRS and the libraries to link as BTpp_LIBRARIES.
The repository my-behavior-tree-project shows an example on how to use the library once system-wide installed.

1. Implement your action node class extending the abstract class BT::ActionNode.
2. Implement the method BT::ReturnStatus Tick() with the code you want to execute while the action is running. Use the method is_halted() to check if the action has been prempted. When the execution of your action finished, return BT::SUCCESS or BT::FAILURE accordingly.
3. Implement the method void Halt() with the code you want to execute when the action gets preempted (halted). See the file src/example.cpp for an example.

1. Implement your condition node class extending the abstract class BT::ConditionNode.
2. Implement the method BT::ReturnStatus Tick() with the code you want to execute to check the condition. Return BT::SUCCESS or BT::FAILURE accordingly.
   See the file src/example.cpp for an example.

In case you are puzzled about why a sequence (or fallback) node with 2 or more actions as children never get past the first action, see this discussion.

The MIT License (MIT)

Copyright (c) 2014-2018 Michele Colledanchise

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.