Application Development

Application Development#

Extensions#

Extensions are the recommended way to develop applications in Isaac Sim. They are modularized packages that formulate the Omniverse ecosystem. Each extension provides a set of functionalities that can be used by other extensions or standalone applications. A folder is recognized as an extension if it contains an extension.toml file in the config directory. More information on extensions can be found in the Omniverse documentation.

Each extension in Isaac Lab is written as a python package and follows the following structure:

<extension-name>
├── config
│   └── extension.toml
├── docs
│   ├── CHANGELOG.md
│   └── README.md
├── <extension-name>
│   ├── __init__.py
│   ├── ....
│   └── scripts
├── setup.py
└── tests

The config/extension.toml file contains the metadata of the extension. This includes the name, version, description, dependencies, etc. This information is used by Omniverse to load the extension. The docs directory contains the documentation for the extension with more detailed information about the extension and a CHANGELOG file that contains the changes made to the extension in each version.

The <extension-name> directory contains the main python package for the extension. It may also contains the scripts directory for keeping python-based applications that are loaded into Omniverse when then extension is enabled using the Extension Manager.

More specifically, when an extension is enabled, the python module specified in the config/extension.toml file is loaded and scripts that contains children of the omni.ext.IExt class are executed.

import omni.ext

class MyExt(omni.ext.IExt):
   """My extension application."""

   def on_startup(self, ext_id):
      """Called when the extension is loaded."""
      pass

   def on_shutdown(self):
      """Called when the extension is unloaded.

      It releases all references to the extension and cleans up any resources.
      """
      pass

While loading extensions into Omniverse happens automatically, using the python package in standalone applications requires additional steps. To simplify the build process and avoiding the need to understand the premake build system used by Omniverse, we directly use the setuptools python package to build the python module provided by the extensions. This is done by the setup.py file in the extension directory.

Note

The setup.py file is not required for extensions that are only loaded into Omniverse using the Extension Manager.

Lastly, the tests directory contains the unit tests for the extension. These are written using the unittest framework. It is important to note that Omniverse also provides a similar testing framework. However, it requires going through the build process and does not support testing of the python module in standalone applications.

Custom Extension Dependency Management#

Certain extensions may have dependencies which require installation of additional packages before the extension can be used. While Python dependencies are handled by the setuptools package and specified in the setup.py file, non-Python dependencies such as ROS packages or apt packages are not handled by setuptools. To handle these dependencies, we have created an additional setup procedure described in the next section.

There are two types of dependencies that can be specified in the extension.toml file under the isaac_lab_settings section:

  1. apt_deps: A list of apt packages that need to be installed. These are installed using the apt package manager.

  2. ros_ws: The path to the ROS workspace that contains the ROS packages. These are installed using the rosdep dependency manager.

As an example, the following extension.toml file specifies the dependencies for the extension:

[isaac_lab_settings]
# apt dependencies
apt_deps = ["libboost-all-dev"]

# ROS workspace
# note: if this path is relative, it is relative to the extension directory's root
ros_ws = "/home/user/catkin_ws"

These dependencies are installed using the install_deps.py script provided in the tools directory. To install all dependencies for all extensions, run the following command:

# execute from the root of the repository
# the script expects the type of dependencies to install and the path to the extensions directory
# available types are: 'apt', 'rosdep' and 'all'
python tools/install_deps.py all ${ISAACLAB_PATH}/source/extensions

Note

Currently, this script is automatically executed during the build process of the Dockerfile.base and Dockerfile.ros2. This ensures that all the ‘apt’ and ‘rosdep’ dependencies are installed before building the extensions respectively.

Standalone applications#

In a typical Omniverse workflow, the simulator is launched first, after which the extensions are enabled that load the python module and run the python application. While this is a recommended workflow, it is not always possible to use this workflow.

For example, for robot learning, it is essential to have complete control over simulation stepping and all the other functionalities instead of asynchronously waiting for the simulator to step. In such cases, it is necessary to write a standalone application that launches the simulator using AppLauncher and allows complete control over the simulation through the SimulationContext class.

The following snippet shows how to write a standalone application:

"""Launch Isaac Sim Simulator first."""

from omni.isaac.lab.app import AppLauncher

# launch omniverse app
app_launcher = AppLauncher(headless=False)
simulation_app = app_launcher.app


"""Rest everything follows."""

from omni.isaac.lab.sim import SimulationContext

if __name__ == "__main__":
   # get simulation context
   simulation_context = SimulationContext()
   # reset and play simulation
   simulation_context.reset()
   # step simulation
   simulation_context.step()
   # stop simulation
   simulation_context.stop()

   # close the simulation
   simulation_app.close()

It is necessary to launch the simulator before running any other code because extensions are hot-loaded when the simulator starts. Many Omniverse modules become available only after the simulator is launched. To do this, use the :class:~omni.isaac.lab.app.AppLauncher class to start the simulator. After that, the :class:~omni.isaac.lab.sim.SimulationContext class can be used to control the simulation. For further details, we recommend exploring the Isaac Lab tutorials.