.. _project-structure:


Project Structure
=================

There are four nested structures you need to be aware of when working in the direct workflow with an Isaac Lab template
project: the **Project**, the **Extension**, the **Modules**, and the **Task**.

.. figure:: ../../_static/setup/walkthrough_project_setup.svg
    :align: center
    :figwidth: 100%
    :alt: The structure of the isaac lab template project.

The **Project** is the root directory of the generated template.  It contains the source and scripts directories, as well as
a ``README.md`` file. When we created the template, we named the project *IsaacLabTutorial* and this defined the root directory
of a git repository.   If you examine the project root with hidden files visible you will see a number of files defining
the behavior of the project with respect to git. The ``scripts`` directory contains the ``train.py`` and ``play.py`` scripts for the
various RL libraries you chose when generating the template, while the source directory contains the python packages for the project.

The **Extension** is the name of the python package we installed via pip. By default, the template generates a project
with a single extension of the same name. A project can have multiple extensions, and so they are kept in a common ``source``
directory. Traditional python packages are defined by the presence of a ``pyproject.toml`` file that describes the package
metadata, but packages using Isaac Lab must also be Isaac Sim extensions and so require a ``config`` directory and an accompanying
``extension.toml`` file that describes the metadata needed by the Isaac Sim extension manager. Finally, because the template
is intended to be installed via pip, it needs a ``setup.py`` file to complete the setup procedure using the ``extension.toml``
config. A project can have multiple extensions, as evidenced by the Isaac Lab repository itself!

The **Modules** are what actually gets loaded by Isaac Lab to run training (the meat of the code). By default, the template
generates an extension with a single module that is named the same as the project. The structure of the various sub-modules
in the extension is what determines the ``entry_point`` for an environment in Isaac Lab. This is why our template project needed
to be installed before we could call ``train.py``: the path to the necessary components to run the task needed to be exposed
to python for Isaac Lab to find them.

Finally, the **Task** is the heart of the direct workflow. By default, the template generates a single task with the same name
as the project. The environment and configuration files are stored here, as well as placeholder, RL library dependent ``agents``.
Critically, note the contents of the ``__init__.py``! Specifically, the ``gym.register`` function needs to be called at least once
before an environment and task can be used with the Isaac Lab ``train.py`` and ``play.py`` scripts.
This function should be included in one of the module ``__init__.py`` files so it is called at installation. The path to
this init file is what defines the entry point for the task!

For the template, ``gym.register`` is called within ``isaac_lab_tutorial/source/isaac_lab_tutorial/isaac_lab_tutorial/tasks/direct/isaac_lab_tutorial/__init__.py``.
The repeated name is a consequence of needing default names for the template, but now we can see the structure of the project.
**Project**/source/**Extension**/**Module**/tasks/direct/**Task**/__init__.py