NEWS!

The Preprint of our book titled "**Behavior Trees in Robotics and AI**" is available here: https://arxiv.org/abs/1709.00084

<img width="100" alt="portfolio_view" src="http://michelecolledanchise.com/BTPPLOGO.png"> BT++

  <img src="https://travis-ci.org/miccol/Behavior-Tree.svg?branch=master"/>

<br/>

A behavior tree library in `C++`.

REFERENCE

DEPENDENCIES

Regarding visualization purposes:

* [OpenGL](https://www.opengl.org/)

* [Glut](https://www.opengl.org/resources/libraries/glut/)

Regarding tests:

* [GTests](https://github.com/google/googletest)

BT NODES SUPPORT

**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](https://github.com/miccol/Behavior-Tree/blob/master/BTppUserManual.pdf)).

SETUP

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:

Once you have the repository, compile the library:

`$ cd /path/to/folder/` <br/>

`$ mkdir ./build` <br/>

`$ cd build` <br/>

`$ cmake ..` <br/>

`$ make` <br/>

**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](https://ubuntuforums.org/archive/index.php/t-1703770.html). Thanks [miquelramirez](https://github.com/miquelramirez) for this.

Check the installation by running a sample example.

`$ cd /path/to/folder/` <br/>

`$ cd build/sample` <br/>

`$ ./btpp_example` <br/>

INSTALL THE LIBRARY SYSTEM-WIDE (tested on Ubuntu 14.04 and 16.04)

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

`$ cd /path/to/folder/` <br/>

`$ cd build` <br/>

`$ sudo make install` <br/>

On Ubuntu, this will install the library (libbtpp.so) in `/usr/local/lib`. <br/>

In an external project, just call in your CMakeLists 'find_package(BTpp)' to find the library. <br/>

The include directory is defined as `BTpp_INCLUDE_DIRS` and the libraries to link as `BTpp_LIBRARIES`.<br/>

The repository [my-behavior-tree-project](https://github.com/miccol/my-behavior-tree-project) shows an example on how to use the library once system-wide installed.

CREATE YOUR OWN ACTION NODE

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.

CREATE YOUR OWN CONDITION NODE

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.

NOTES

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](https://github.com/miccol/ROS-Behavior-Tree/issues/16) discussion.