Advanced: Where is the code?


Intro

Welcome to the Advanced Module! This module will guide you through the process of making a contribution to Gazebo's codebase! We will cover topics such as:

  • Using Mercurial and Bitbucket to manage source files
  • Understanding the source code structure
  • Finding an issue to fix
  • Testing and documenting your code
  • Getting your code integrated into Gazebo!

Each tutorial builds upon the last, so we recommend following the tutorials in order.

These tutorials are intended for those with basic experience using Gazebo, Ubuntu Linux, and writing C++ code.

Note: It's possible to contribute to Gazebo if you're using a different operating system, but for simplicity, this tutorial is focusing on Ubuntu users.

Where is Gazebo's source code?

Gazebo is an open source project, and as such, its source code is publicly available online. It is currently hosted on a mercurial repository at Bitbucket:

https://bitbucket.org/osrf/gazebo/

If none of that makes sense to you, let's go through some important concepts:

Mercurial

Mercurial is a version control software used to keep track of changes made to source code. Some might be familiar with a similar tool called Git.

This tutorial series won't be going into detail about how mercurial works, but each mercurial command (hg) used will be explained.

If you're completely new to version control, there's a lot of good information available online, such as this tutorial series.

Bitbucket

Bitbucket is the website used to host the mercurial repository so that the source code has a central place to live.

In order to contribute to Gazebo, you'll need to create an account there, by following this link.

Where is the rest of the code?

You might be asking, is this it, is that all the code needed to bring Gazebo to life? Well, not exactly. Gazebo, as most software, takes advantage of other existing libraries to perform specific tasks. These are called dependencies.

For example, Gazebo uses Ogre for rendering, Qt for the graphical user interface and supports a few physics engines, such as ODE and Bullet. That's only to name a few.

Among Gazebo's dependencies, there are some dependencies which are maintained by the Gazebo core team. Gazebo development is often tied to the development of these libraries, so everything that will be discussed on this series also applies to those libraries. All these libraries are hosted on Bitbucket using mercurial. They are the following:

SDFormat

SDF is an XML file format that describes worlds used by simulators such as Gazebo. The SDF library is used to parse these files and provide a C++ interface.

Ignition Math

Ignition Math is a small, fast, and high performance math library. This library is a self-contained set of classes and functions suitable for robot applications.

Ignition Transport

Ignition Transport combines ZeroMQ with Protobufs to create a fast and efficient message passing system. Asynchronous message publication and subscription is provided along with service calls and discovery.

Ignition Messages

Ignition Messages provides a standard set of message definitions, used by Ignition Transport, and other applications.