.. _example-ros-1-app:

Example ROS 1 app
=================

This how-to guide covers the steps, decisions, and implementation details that
are unique when crafting a `ROS 1 <https://wiki.ros.org/noetic>`_-based snap.
We'll work through the aspects unique to ROS 1 apps by examining an existing
recipe.

There are two supported bases for ROS 1 -- core20 and core18.

.. tip::

  Often, ROS developers rely on the *devel* space of their ``catkin``
  workspace. As a result, it's easy to forget the importance of complete
  install rules, such as rules for installing every component of the package
  necessary to run, or every component necessary to use a given library.

  The ``catkin`` packages you're building must have install rules, or else
  Snapcraft won't know which components to place into the snap. Make sure
  you install necessary binaries, libraries, header files, and launch files.


Example recipe for ROS Talker/Listener
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

.. tabs:: ROS Talker/Listener example

  .. group-tab:: core20

    The following code comprises the recipe for the `core20 version of ROS
    Talker/Listener
    <https://github.com/snapcraft-docs/ros-talker-listener-core20>`_.

    .. collapse:: Code

      .. code:: yaml

        name: ros-talker-listener
        version: '0.1'
        summary: ROS Talker/Listener Example
        description: |
          This example launches a ROS talker and listener.

        confinement: devmode
        base: core20

        parts:
        ros-tutorials:
          plugin: catkin
          source: https://github.com/ros/ros_tutorials.git
          source-branch: noetic-devel
          catkin-packages: [roscpp_tutorials]
          stage-packages:
              - ros-noetic-roslaunch

        apps:
        ros-talker-listener:
          command: opt/ros/noetic/bin/roslaunch roscpp_tutorials talker_listener.launch
          extensions: [ros1-noetic]

  .. group-tab:: core18

    The following code comprises the recipe for the `core18 version of ROS Talker/Listener
    <https://github.com/snapcraft-docs/ros-talker-listener>`_.

    .. collapse:: Code

      .. code:: yaml

        name: ros-talker-listener
        version: '0.1'
        summary: ROS Talker/Listener Example
        description: |
          This example launches a ROS talker and listener.

        confinement: devmode
        base: core18

        parts:
          ros-tutorials:
            plugin: catkin
            source: https://github.com/ros/ros_tutorials.git
            source-branch: melodic-devel
            source-space: roscpp_tutorials/

        apps:
          ros-talker-listener:
            command: roslaunch roscpp_tutorials talker_listener.launch


Add an ROS 1 app based on core20
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

To add an ROS 1 app based on core20:

#. Declare the general app keys, such as ``command``.
#. For ``extensions``, list ``ros1-noetic``. See
   `The ROS 1 Noetic Extension <https://snapcraft.io/docs/ros-noetic>`_ for a
   description of what the extension does during build.


Add a part written for ROS 1
~~~~~~~~~~~~~~~~~~~~~~~~~~~~

ROS 1 parts are built with the `catkin plugin
<https://snapcraft.io/docs/catkin-plugin>`_.

To add an ROS 1 part:

#. Declare the general part keys, such as ``source``, ``override-build``,
   ``build-packages``, and so on.
#. Set ``plugin: catkin``.
#. If the snap is based on core20, for ``catkin-packages``, list any ROS
   package dependencies.