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.

Isaac Lab in itself provides extensions for robot learning. These are written into the source/extensions directory. Each extension 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.

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.

[isaaclab_settings]
apt_deps = ["example_package"]
ros_ws = "path/from/extension_root/to/ros_ws"

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.

"""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()

The source/standalone directory contains various standalone applications designed using the extensions provided by Isaac Lab. These applications are written in python and are structured as follows:

• demos: Contains various demo applications that showcase the core framework omni.isaac.lab.

• environments: Contains applications for running environments defined in omni.isaac.lab_tasks with different agents. These include a random policy, zero-action policy, teleoperation or scripted state machines.

• tools: Contains applications for using the tools provided by the framework. These include converting assets, generating datasets, etc.

• tutorials: Contains step-by-step tutorials for using the APIs provided by the framework.

• workflows: Contains applications for using environments with various learning-based frameworks. These include different reinforcement learning or imitation learning libraries.