godot_ros

This repo is a GDExtension meant to connect Robotic Operating System 2 (ROS 2) and the Godot Game Engine.

Uses cases for this extension could range from creating a control UI for a robot to creating a simulator to validate some algorithms.

Concept

This GDExtension's core concept is hooking into Godots existing MainLoop concept and its default MainLoop implementation - the SceneTree.

Within the SceneTree::initialization() method we can call our typical ROS 2 rclcpp::init() and within the SceneTree::finalize() method we can call rclcpp::shutdown(). With this approach, every Godot game or application will be operating within a valid ROS 2 environment.

With the ROS 2 environment up and running, we now need ROS 2 nodes so that we can create publishers and subscribers. Luckily, Godot also has a node concept and we can hook directly into it by placing a rclcpp::Node shared pointer as a member variable within a Godot::Node. This approach allows almost any Godot node (or any derivative) to also be a ROS 2 node.

The foundation described above lays the ground work - but to actually do something useful we need to implement conversion functions between Godot data types and ROS 2 data types.

Publish (Godot type to ROS 2 messages)

• Godot::String => std_msgs::msg::String
• Godot::Image => sensor_msgs::msg::Image
• Godot::Array => sensor_msgs::msg::PointCloud

Additional types can be added.

Feel free to contribute additional type conversions or create an issue here in this repository with what you think is missing.

Subscribe (ROS 2 messages to Godot Type)

• Godot::String => std_msgs::msg::String
• Godot::Image => sensor_msgs::msg::Image
• Godot::Array => sensor_msgs::msg::PointCloud

Additional types can be added.

Feel free to contribute additional type conversions or create an issue here in this repository with what you think is missing.

Building

For now, refer to the CI script for the most up-to-date information on how to build this extension.

Examples

Refer to the demos for examples of GDScript using this extension.

Running Godot with the godot_ros GDExtension

source /opt/ros/<distro>/setup.bash
godot

Sourcing of the ROS 2 underlay is extremely important, otherwise you will see an error something like:

Error: librcutils.so: cannot open shared object file: No such file or directory.

Determining dependencies of godot_ros extension

If for whatever reason you want to fork and extend this package and additional features are added - additional dependencies may be introduced to the extension that will need to be declared in the demo/godot_ros.gdextension file.

To determine what dependencies are required:

readelf -d libgodot_ros.linux.template_debug.x86_64.so

Dynamic section at offset 0xced28 contains 31 entries:
  Tag        Type                         Name/Value
 0x0000000000000001 (NEEDED)             Shared library: [librcutils.so]
 0x0000000000000001 (NEEDED)             Shared library: [librclcpp.so]
 0x0000000000000001 (NEEDED)             Shared library: [libstdc++.so.6]
 0x0000000000000001 (NEEDED)             Shared library: [libm.so.6]
 0x0000000000000001 (NEEDED)             Shared library: [libgcc_s.so.1]
 0x0000000000000001 (NEEDED)             Shared library: [libc.so.6]
 0x0000000000000001 (NEEDED)             Shared library: [ld-linux-x86-64.so.2]
 0x000000000000001d (RUNPATH)            Library runpath: [$ORIGIN]
 ...

At the top of the list you'll see all the dependency shared libraries that are needed to run the extension. Keep in mind you'll also need to run the same readelf command on each dependency library in order to get a complete list of all required dependencies.