Extensions in-depth

What is an Extension?

An extension is, in its simplest form, just a folder with a config file (extension.toml). The Extension system will find that extension and if it’s enabled it will do whatever the config file tells it to do, which may include loading python modules, Carbonite plugins, shared libraries, applying settings etc.

There are many variations, you can have an extension whose sole purpose is just to enable 10 other extensions for example, or just apply some settings.

Extension in a single folder

Everything that an extension has should be contained or nested within its root folder. This is a convention we are trying to adhere to. Looking at other package managers, like those in the Linux ecosystem, the content of packages can be spread across the filesystem, which makes some things easier (like loading shared libraries), but also creates many other problems.

Following this convention makes the installation step very simple - we just have to unpack a single folder.

A typical extension might look like this:

[extensions-folder]
└── omni.appwindow
    │──bin
    │  └───windows-x86_64
    │      └───debug
    │          └─── omni.appwindow.plugin.dll
    │───config
    │   └─── extension.toml
    └───omni
        └───appwindow
            │─── _appwindow.cp37-win_amd64.pyd
            └─── __init__.py

This example contains a Carbonite plugin and a python module (which contains the bindings to this plugin).

Extension Id

Extension id consists of 3 parts: [ext_name]-[ext_tag]-[ext_version]:

[ext_name]: Extension name. Extension folder or kit file name.
[ext_tag]: Extension tag. Optional. Used to have different implementations of the same extension. Also part of folder or kit file name.
[ext_version]: Extension version. Defined in extension.toml. Can also be part of folder name, but ignored there.

Extension id example: omni.kit.commands-1.2.3-beta.1. Extension name is omni.kit.commands. Version is 1.2.3-beta.1. Tag is empty.

Extension Version

Version is defined in [package.version] config field.

Semantic Versioning is used. A good example of valid and invalid versions: link

In short, it is [major].[minor].[patch]-[prerelease]. Express compatibility with version change:

For breaking change increment major version
For backwards compatible change increment minor version
For bugfixes increment patch version

Use [prerelease] part to test a new version e.g. 1.2.3-beta.1

Extension Package Id

Extension package id is extension id plus build metadata. [ext_id]+[build_meta].

One extension id can have 1 or multiple packages in order to support different targets. It is common for binary extensions to have packages like:

[ext_id]+wx64.r - windows-x86_64, release config.
[ext_id]+lx64.r - linux-x86_64, release config.
[ext_id]+lx64.d - linux-x86_64, debug config.
…

Python version or kit version can also denote different target. Refer to [package.target] section of extension config.

Single File Extensions

Single file Extensions are supported - i.e. Extensions consisting only of a config file, without any code. In this case the name of the config will be used as the extension ID. This is used to make a top-level extension which we call an app. They are used as an application entry point, to unroll the whole extension tree.

The file extension can be anything (.toml for instance), but the recommendation is to name them with the .kit file extension, so that it can be associated with the kit.exe executable and launched with a single click.

[extensions-folder]
└── omni.exp.hello.kit

App Extensions

When .kit files are passed to kit.exe they are treated specially:

This: > kit.exe C:/abc/omni.exp.hello.kit

Is the same as: > kit.exe --ext-path C:/abc/omni.exp.hello.kit --enable omni.exp.hello

It adds this .kit file as an extension and enables it, ignoring any default app configs, and effectively starting an app.

Single file (.kit file) extensions are considered apps, and a “launch” button is added to it in the UI of the extension browser. For regular extensions, specify the keyword: package.app = true in the config file to mark your extension as an app that users can launch.

App extensions can be published, versioned, etc. just like normal extensions. So for instance if the omni.exp.hello example from above is published, we can just run Kit as:

> kit.exe omni.exp.hello.kit

Kit will pull it from the registry and start.

Extension Search Paths

Extensions are automatically searched for in specified folders.

Core Kit config kit-core.json specifies default search folders in /app/exts/foldersCore setting. This way Kit can find core extensions, it also looks for extensions in system-specific documents folders for user convenience.

To add more folders to search paths there are a few ways:

Pass --ext-folder [PATH] CLI argument to kit.
Add to array in settings: /app/exts/folders
Use the omni::ext::ExtensionManager::addPath API to add more folders (also available in python).

To specify direct path to a specific extension use the /app/exts/paths setting or the --ext-path [PATH] CLI argument.

Folders added last are searched first. This way they will be prioritized over others, allowing the user to override existing extensions.

Example of adding an extension seach path in a kit file:

[settings.app.exts]
folders.'++' = [
    "C:/hello/my_extensions"
]

Custom Search Paths Protocols

Both folders and direct paths can be extended to support other url schemes. If no scheme is specified, they are assumed to be local filesystem. The extension system provides APIs to implement custom protocols. This way an extension can be written to enable searching for extensions in different locations, for example: git repos.

E.g. --ext-folder foo://abc/def – The extension manager will redirect this search path to the implementor of the foo scheme, if it was registered.

Git URL as Extension Search Paths

Extension omni.kit.extpath.git implements following extension search path schemes: git, git+http, git+https, git+ssh. Optional URL query params are supported:

dir subdirectory of a git repo to use as a search path (or direct path).
branch git branch to checkout
tag git tag to checkout
sha git sha to checkout

Example of usage with cmd arg:

--ext-folder git://github.com/bob/somerepo.git?branch=main&dir=exts – Add exts subfolder and main branch of this git repo as extension search paths.

Example of usage in kit file:

[settings.app.exts]
folders.'++' = [
    "git+https://gitlab-master.nvidia.com/bob/some-repo.git?dir=exts&branch=feature"
]

After the first checkout, the git path is cached into global cache. To pull updates:

use extension manager properties pages
setting: --/exts/omni.kit.extpath.git/autoUpdate=1
API call omni.kit.extpath.git.update_all_git_paths()

The Extension system automatically enables this extension if a path with a scheme is added. It enables extensions specified in a setting: app/extensions/pathProtocolExtensions, which by default is ["omni.kit.extpath.git"].

Note

Git installation is required for this functionality. It expects the git executable to be available in system shell.

Extension Discovery

The Extension system monitors any specified extension search folders (or direct paths) for changes. It automatically syncs all changed/added/removed extensions. Any subfolder which contains an extension.toml in the root or config folder is considered to be an extension.

The subfolder name uniquely identifies the extension and is used to extract the extension name and tag: [ext_name]-[ext_tag]

[extensions-folder]
└── omni.kit.example-gpu-2.0.1-stable.3+cp37
            ├── extension.toml
            └── ...

In this example we have an extension omni.kit.example-gpu-2.0.1-stable.3+cp37, where:

name: omni.kit.example
tag: gpu (optional, default is “”)

The version and other information (like supported platforms) are queried in the extension config file (see below). They may also be included in the folder name, which is what the system does with packages downloaded from a remote registry, but that is not “the ground truth” for that data. So in this example anything could have been after the “gpu” tag, e.g. omni.kit.example-gpu-whatever.

Extension Dependencies

When a Kit-based application starts, it discovers all extensions and does nothing with them until some of them are enabled, whether via config file or API. Each extension can depend on other extensions and this is where the whole application tree can unroll. The user may enable a high level extension like omni.usd_viewer which will bring in dozens of others.

An extension can express dependencies on other extensions using name, version and optionally tag. It is important to keep extensions versioned properly and express breaking changes using Semantic Versioning.

This is a good place to grasp what tag is for. If extension foo depends on bar, you might implement other versions of bar, like: bar-light, bar-prototype. If they still fulfill the same API contract and expected behavior, you can safely substitute bar without foo noticing. In other words if the extension is an interface, tag is the implementation.

The effect is that just enabling some high-level extensions like omni.kit.window.script_editor will expand the whole dependency tree in the correct order without the user having to specify all of them or worry about initialization order.

One can also substitute extensions in a tree with a different version or tag, towards the same end-user experience, but having swapped in-place a different low-level building block.

When an extension is enabled, the manager tries to satisfy all of its dependencies by recursively solving the dependency graph. This is a difficult problem - If dependency resolution succeeds the whole dependency tree is enabled in-order so that all dependents are enabled first. The opposite is true for disabling extensions. All extensions which depend on the target extension are disabled first. More details on the dependency system can be found in the C++ unit tests: source/tests/test.unit/ext/TestExtensions.cpp

A Dependency graph defines the order in which extensions are loaded - it is sorted topologically. There are however, many ways to sort the same graph (think of independent branches). To give finer control over startup order, the order parameters can be used. Each extension can use core.order config parameter to define its order and the order of dependencies can also be overriden with order param in [[dependencies]] section. Those with lower order will start sooner. If there are multiple extensions that depend on one extension and are trying to override this order then the one that is loaded last will be used (according to dependency tree). In summary - the dependency order is always satisfied (or extensions won’t be started at all, if the graph contains cycles) and soft ordering is applied on top using config params.

Extension configuration file (extension.toml)

An Extension config file can specify:

Dependencies to import
Settings
A variety of metadata/information which are used by the Extension Registry browser (for example)

TOML is the format used. See this short toml tutorial. Note in particular the [[]] TOML syntax for arrays of objects and quotes around keys which contain special symbols(e.g. "omni.physx").

The config file should be placed in the root of the extension folder or in a config subfolder.

Note

All relative paths in configs are relative to the extension folder. All paths accept tokens. (like ${platform}, ${config}, ${kit} etc). More info: Tokens.

There are no mandatory fields in a config, so even with an empty config, the extension will be considered valid and can be enabled - without any effect.

Next we will list all the config fields the extension system uses, though a config file may contain more. The Extension system provides a mechanism to query config files and hook into itself. That allows us to extend the extension system itself and add new config sections. For instance omni.kit.pipapi allows extensions to specify pip packages to be installed before enabling them. More info on that: Hooks. That also means that typos or unknown config settings will be left as-is and no warning will be issued.

Config Fields

`[core]` section

For generic extension properties. Used directly by the Extension Manager core system.

`[core.reloadable]` (default: `true`)

Is the extension reloadable? The Extension system will monitor the extension’s files for changes and try to reload the extension when any of them change. If the extension is marked as non-reloadable, all other extensions that depend on it are also non-reloadable.

`[core.order]` (default: `0`)

When extensions are independent of each other they are enabled in an undefined order. An extension can be ordered to be before (negative) or after (positive) other extensions

`[package]` section

Contains information used for publishing extensions and displaying user-facing details about the package.

`[package.version]` (default: `"0.0.0"`)

Extension version. This setting is required in order to publish extensions to the remote registry. The Semantic Versioning concept is baked into the extension system, so make sure to follow the basic rules:

Before you reach 1.0.0, anything goes, but if you make breaking changes, increment the minor version.
After 1.0.0, only make breaking changes when you increment the major version.
Incrementing the minor version implies a backward-compatible change. Let’s say extension bar depends on foo-1.2.0. That means that foo-1.3.0, foo-1.4.5, etc.. are also suitable and can be enabled by extension system.
Use version numbers with three numeric parts such as 1.0.0 rather than 1.0.
Prerelease labels can also be used like so: 1.3.4-beta, 1.3.4-rc1.test.1, or 1.3.4-stable.

`[package.title]` default: `""`

User-facing package name, used for UI.

`[package.description]` default: `""`

User facing package description, used for UI.

`[package.category]` (default: `""`)

Extension category, used for UI. One of:

animation
graph
rendering
audio
simulation
example
internal
other

`[package.app]` (default: `false`)

Whether the extension is an App. Used to mark extension as an app in the UI. Adds a “Launch” button to run kit with only this extension (and its dependents) enabled. For single-file extensions (.kit files), it defaults to true.

`[package.feature]` (default: `false`)

Extension is a Feature. Used to show user-facing extensions, suitable to be enabled by the user from the UI. By default, the app can choose to show only those feature extensions.

`[package.toggleable]` (default: `true`)

Indicates whether an extension can be toggled (i.e enabled/disabled) by the user from the UI. There is another related setting: [core.reloadable], which can prevent the user from disabling an extension in the UI.

`[package.authors]` (default: `[""]`)

Lists people or organizations that are considered the “authors” of the package. Optionally include email addresses within angled brackets after each author.

`[package.repository]` (default: `""`)

URL of the extension source repository, used for display in the UI.

`[package.keywords]` (default: `[""]`)

Array of strings that describe this extension. Helpful when searching for it in an Extension registry.

`[package.changelog]` (default: `""`)

Location of a CHANGELOG.MD file in the target (final) folder of the Extension, relative to the root. The UI will load and show it. We can also insert the content of that file inline instead of specifying a filepath. It is important to keep the changelog updated when new versions of an extension are released and published.

For more info on writing changelogs refer to Keep a Changelog

`[package.readme]` (default: `""`)

Location of README file in the target (final) folder of an extension, relative to the root. The UI will load and show it. We can also insert the content of that file inline instead of specifying a filepath.

`[package.preview_image]` (default: `""`)

Location of a preview image in the target (final) folder of extension, relative to the root. The preview image is shown in the “Overview” of the extension in the Extensions window. A screenshot of your extension might make a good preview image.

`[package.icon]` (default: `""`)

Location of the icon in the target (final) folder of extension, relative to the root. Icon is shown in Extensions window. Recommended icon size is 256x256 pixels.

`[package.target]`

This section is used to describe the target platform this extension runs on - this is fairly arbitrary, but can include:

Operating system
CPU architecture
Python version
Build configuration

The Extension system will filter out extensions that doesn’t match the current environment/platform. This is particularly important for extensions published and downloaded from a remote Extension registry.

Normally you don’t need to fill this section in manually. When extensions are published, this will be automatically filled in with defaults, more in Publishing Extensions. But it can be overriden by setting:

package.target.kit (default: ["*"] – Kit version (major.minor), e.g. "101.0", "102.3".

package.target.kitHash (default: ["*"] – Kit git hash (8 symbols), e.g. "abcdabcd"

package.target.config (default: ["*"] – Build config, e.g. "debug", "release".

package.target.platform (default: ["*"] – Build platform, e.g. "windows-x86_64", "linux-aarch64".

package.target.python (default: ["*"] – Python version, e.g. "cp37" (cpython 3.7). Refer to PEP 0425.

Wildcards can be used. A full example:

[package.target]
config = ["debug"]
platform = ["linux-*", "windows"]
python = ["*"]

`[package.writeTarget]`

This section can be used to explicitly control if [package.target] should be written. By default it is written based on rules described in Extension Publishing. But if for some [target] a field is set, such as package.writeTarget.[target] = true/false, that tells explicitly whether it should automatically be filled in.

For example if you want to target a specific kit version to make the extension only work with that version, set:

[package]
writeTarget.kit = true

Or if you want your extension to work for all python versions, write:

[package]
writeTarget.python = false

The list of known targets is the same as in the [package.target] section: kit, config, platform, python.

`[dependencies]` section

This section is used to describe which extensions this extension depends on. The extension system will guarantee they are enabled before it loads your extension (assuming that it doesn’t fail to enable any component). One can optionally specify a version and tag per dependency, as well as make a dependency optional.

Each entry is a name of other extension. It may or may not additionally specify: tag, version, optional, exact:

"omni.physx" = { version="1.0", "tag"="gpu" }
"omni.foo" = { version="3.2" }
"omni.cool" = { optional = true }

Note that it is highly recommended to use versions, as it will help maintain stability for extensions (and the whole application) - i.e if a breaking change happens in a dependency and dependents have not yet been updated, an older version can still be used instead. (only the major and minor parts are needed for this according to semver).

optional (default: false) – will mean that if the extension system can’t resolve this dependency the extension will still be enabled. So it is expected that the extension can handle the absence of this dependency. Optional dependencies are not enabled unless they are a non-optional dependency of some other extension which is enabled, or if they are enabled explicitly (using API, settings, CLI etc).

exact (default: false) – only an exact version match of extension will be used. This flag is experimental and may change.

order (default: None) – override the core.order parameter of an extension that it depends on. Only applied if set.

`[python]` section

If an extension contains python modules or scripts this is where to specify them.

`[[python.module]]`

Specifies python module(s) that are part of this extension. Multiple can be specified. Take notice the [[]] syntax. When an extension is enabled, modules are imported in order. Here we specify 2 python modules to be imported (import omni.hello and import omni.calculator). When modules are scheduled for import this way, they will be reloaded if the module is already present.

Example:

[[python.module]]
name = "omni.hello"

[[python.module]]
name = "omni.calculator"
path = "."
public = true

name (required) – python module name, can be empty. Think of it as what will be imported by other extensions that depend on you:

import omni.calculator

public (default: true) – If public, a module will be available to be imported by other extensions (extension folder is added to sys.path). Non-public modules have limited support and their use is not recommended.

path (default: ".") – Path to the root folder where the python module is located. If written as relative, it is relative to extension root. Think of it as what gets added to sys.path. By default the extension root folder is added if any [[python.module]] directive is specified.

searchExt (default: true) – If true, imports said module and launches the extensions search routine within the module. If false, only the module is imported.

By default the extension system uses a custom fast importer. Fast importer only looks for python modules in extension root subfolders that correspond to the module namespace. In the example above it would only look in [ext root]/omni/**. If you have other subfolders that contain python modules you at least need to specify top level namespace. E.g. if you have also foo.bar in [ext root]/foo/bar.py:

[[python.module]]
name = "foo"

Would make it discoverable by fast importer. You can also just specify empty name to make importer search all subfolders:

[[python.module]]
path = "."

Example of that is in omni.kit.pip_archive which brings a lot of different modules, which would be tedious to list.

`[[python.scriptFolder]]`

Script folders can be added to IAppScripting, and they will be searched for when a script file path is specified to executed (with –exec or via API).

Example:

[[python.scriptFolder]]
path = "scripts"

path (required) – Path to the script folder to be added. If the path is relative it is relative to the extension root.

`[native]` section

Used to specify Carbonite plugins to be loaded.

`[[native.plugin]]`

When an Extension is enabled, the Extension system will search for Carbonite plugins using path pattern and load all of them. It will also try to acquire the omni::ext::IExt interface if any of the plugins implements it. That provides an optional entry point in C++ code where your extension can be loaded.

When an extension is disabled it releases any acquired interfaces which may lead to plugins being unloaded.

Example:

[[native.plugin]]
path = "bin/${platform}/${config}/*.plugin"
recursive = false

path (required) – Path to search for Carbonite plugins, may contain wildcards and Tokens).

recursive (default: false) – Search recursively in folders.

`[[native.library]]` section

Used to specify shared libraries to load when an Extension is enabled.

When an Extension is enabled the Extension system will search for native shared libraries using path and load them. This mechanism is useful to “preload” libraries needed later, avoid OS specific calls in your code, and the use of PATH/LD_LIBRARY_PATH etc to locate and load DSOs/DLLs. With this approach we just load the libraries needed directly.

When an extension is disabled it tries to unload those shared libraries.

Example:

[[native.library]]
path = "bin/${platform}/${config}/foo.dll"

path (required) – Path to search for shared libraries, may contain wildcards and Tokens.

`[settings]` section

Everything under this section is applied to the root of the global Carbonite settings (carb.settings.plugin). In case of conflict, the original setting is kept.

It is good practice to namespace your settings with your extension name and put them all under the exts root key, e.g.:

[settings]
exts."omni.kit.renderer.core".compatibilityMode = true

Note

Quotes are used here to distinguish between the . of a toml file and the . in the name of extension.

An important detail is that settings are applied in reverse order of extension startup (before any extensions start) and they don’t override each other. Therefore a parent extension can specify settings for child extensions to use.

`[[env]]` section

This section is used to specify one or more environment variables to set when an extension is enabled. Just like settings, env vars are applied in reverse order of startup. They don’t by default override if already set, but override behavior does allow parent extensions to override env vars of extensions they depend on.

Example:

[[env]]
name = "HELLO"
value = "123"
isPath = false
append = false
override = false
platform = "windows-x86_64"

name (required) – Environment variable name.

value (required) – Environment variable value to set.

isPath (default: false) – Treat value as path. If relative it is relative to the extension root folder. Tokens can also be used as within any path.

append (default: false) – Append value to already set env var if any. Platform-specific separators will be used.

override (default: false) – Override value of already set env var if any.

platform (default: "") – Set only if platform matches pattern. Wildcards can be used.

`[fswatcher]` section

Used to specify file system watcher used by the Extension system to monitor for changes in extensions and auto reload.

`[fswatcher.patterns]`

Specify files that are monitored.

include (default: ["*.toml", "*.py"]) – File patterns to include.

exclude (default: []) – File patterns to exclude.

Example:

[fswatcher.patterns]
include = ["*.toml", "*.py", "*.txt"]
exclude = ["*.cache"]

`[fswatcher.paths]`

Specify folders that are monitored. FS watcher will use OS specific API to listen for changes on those folders. You can use that setting that limit amount of subscriptions if your extensions has too many folders inside. Simple path as string pattern matching is used, where ‘*’ means any amount of symbols. Patterns like */123* will match abc/123/def, abc/123, abc/1234. ‘/’ path separator is used on all platforms. Matching paths are relative to extension root, they begin and end with ‘/’.

include (default: ["*/config/*", "*/./*"] and python modules) – Folder path patterns to include.

exclude (default: ["*/__pycache__/*", "*/.git/*"]) – Folder path patterns to exclude.

Example:

[fswatcher.paths]
include = ["*/config"]
exclude = ["*/data*"]

`[[test]]` section

This section is read only by the testing system (omni.kit.test extension) when running per-extension tests. Extension tests are run as a separate process where only the tested extension is enabled and runs all the tests that it has. Usually this section can be left empty, but extensions can specify additional extensions (which are not a part of their regular dependencies, or when the dependency is optional), additional cmd arguments, or filter out (or in) any additional stdout messages.

Each [[test]] entry will run a separate extension test process.

Extension tests run in the context of an app. An app can be empty, which makes extension test isolated and only its dependencies are enabled. Testing in an empty app is the minimal recommended test coverage. Extension developers can then opt-in to be tested in other apps and fine-tune their test settings per app.

Example:

[[test]]
name = "default"
enabled = true
apps = [""]
args = ["-v"]
dependencies = ["omni.kit.capture"]
pythonTests.include = ["omni.foo.*"]
pythonTests.exclude = []
cppTests.libraries = ["bin/${lib_prefix}omni.appwindow.tests${lib_ext}"]
timeout = 180
parallelizable = true
unreliable = false
profiling = false
pyCoverageEnabled = false
waiver = ""
stdoutFailPatterns.include = ["*[error]*", "*[fatal]*"]
stdoutFailPatterns.exclude = [
    "*Leaking graphics objects*",  # Exclude grahics leaks until fixed
]

name – Test process name. If there are multiple [[test]] entries, this name must be unique.

enabled – If tests are enabled. By default it is true. Useful to disable tests per platform.

apps – List of apps to use this test configuration for. Used in case there are multiple [[test]] entries. Wildcards are supported. Defaults to [""] which is an empty app.

args – Additional cmd arguments to pass into the extension test process.

dependencies – List of additional extensions to enable when running the extension tests.

pythonTests.include – List of tests to run. If empty, python modules are used instead ([[python.module]]), since all tests names start with module they are defined in. Can contain wildcards.

pythonTests.exclude – List of tests to exclude from running. Can contain wildcards.

cppTests.libraries – List of shared libraries with C++ doctests to load.

timeout (default: 180) – Test process timeout (in seconds).

parallelizable (default: true) – Whether the test processes can run in parallel relative to other test processes.

unreliable (default: false) – If marked as unreliable, test failures won’t fail a whole test run.

profiling (default: true) – Collects and outputs Chrome trace data via carb profiling for CPU events for the test process.

pyCoverageEnabled (default: false) – Collects python code coverage using Coverage.py.

waiver – String explaining why an extension contains no tests.

stdoutFailPatterns.include – List of additional patterns to search stdout for and mark as a failure. Can contain wildcards.

stdoutFailPatterns.exclude – List of additional patterns to search stdout for and exclude as a test failure. Can contain wildcards.

`[documentation]` section

This section is read by the omni.kit.documenation.builder extension, and is used to specify a list of markdown files for in-app API documentation and offline sphinx generation.

Example:

[documentation]
pages = ["docs/Overview.md"]
menu = "Help/API/omni.kit.documentation.builder"
title = "Omni UI Documentation Builder"

pages – List of .md file paths, relative to the extension root.

menu – Menu item path to add to the popup in-app documentation window.

title – Title of the documentation window.

Config Filters

Any part of a config can be filtered based on the current platform or build configuration. Use "filter:platform"."[platform_name]" or "filter:config"."[build_config]" pair of keys. Anything under those keys will be merged on top of the tree they are located in (or filtered out if it doesn’t apply).

filter	values
platform	`windows-x86_64`, `linux-x86_64`
config	`debug`, `release`

To understand, here are some examples:

[dependencies]
"omni.foo" = {}
"filter:platform"."windows-x86_64"."omni.fox" = {}
"filter:platform"."linux-x86_64"."omni.owl" = {}
"filter:config"."debug"."omni.cat" = {}

After loading that extension on a Windows debug build, it would resolve to:

[dependencies]
"omni.foo" = {}
"omni.fox" = {}
"omni.cat" = {}

Note

You can debug this behavior by running in debug mode, with --/app/extensions/debugMode=1 setting and looking into the log file.

Example

Here is a full example of an extension.toml file:

[core]
reloadable = true
order = 0

[package]
version = "0.1.0"
category = "Example"
feature = false
app = false
title = "The Best Package"
description = "long and boring text.."
authors = ["John Smith <jsmith@email.com>"]
repository = "https://gitlab-master.nvidia.com/omniverse/kit"
keywords = ["banana", "apple"]
changelog = "docs/CHANGELOG.md"
readme = "docs/README.md"
preview_image = "data/preview.png"
icon = "data/icon.png"

# writeTarget.kit = true
# writeTarget.kitHash = true
# writeTarget.platform = true
# writeTarget.config = true
# writeTarget.python = true

[dependencies]
"omni.physx" = { version="1.0", "tag"="gpu" }
"omni.foo" = {}

# Modules are loaded in order. Here we specify 2 python modules to be imported (``import hello`` and ``import omni.physx``).
[[python.module]]
name = "hello"
path = "."
public = false

[[python.module]]
name = "omni.physx"

[[python.scriptFolder]]
path = "scripts"

# Native section, used if extension contains any Carbonite plugins to be loaded
[[native.plugin]]
path = "bin/${platform}/${config}/*.plugin"
recursive = false  # false is default, hence it is optional

# Library section. Shared libraries will be loaded when the extension is enabled, note [[]] toml syntax for array of objects.
[[native.library]]
path = "bin/${platform}/${config}/foo.dll"

# Settings. They are applied on the root of global settings. In case of conflict original settings are kept.
[settings]
exts."omni.kit.renderer.core".compatibilityMode = true

# Environment variables. Example of adding "data" folder in extension root to PATH on Windows:
[[env]]
name = "PATH"
value = "data"
isPath = true
append = true
platform = "windows-x86_64"

# Fs Watcher patterns and folders. Specify which files are monitored for changes to reload an extension. Use wildcard for string matching.
[fswatcher]
patterns.include = ["*.toml", "*.py"]
patterns.exclude = []
paths.include = ["*"]
paths.exclude = ["*/__pycache__*", "*/.git*"]

[documentation]
pages = ["docs/Overview.md"]
menu = "Help/API/omni.kit.documentation.builder"
title = "Omni UI Documentation Builder"

Extension Enabling/Disabling

Extensions can be enabled and disabled at runtime using the provided API. The default Create application comes with an Extension Manager UI which shows all the available extensions and allows a user to toggle them. An App configuration file can also be used to control which extensions are to be enabled.

You may also use command-line arguments to the Kit executable (or any Omniverse App based on Kit) to enable specific extensions:

Example: > kit.exe --enable omni.kit.window.console --enable omni.kit.window.extensions

--enable adds the chosen extension to the “enabled list”. The command above will start only extensions needed to show those 2 windows.

Python Modules

Enabling an extension loads the python modules specified and searches for children of :class:omni.ext.IExt class. They are instantiated and the on_startup method is called, e.g.:

hello.py

import omni.ext

class MyExt(omni.ext.IExt):
    def on_startup(self, ext_id):
        pass

    def on_shutdown(self):
        pass

When an extension is disabled, on_shutdown is called and all references to the extension object are released.

Native Plugins

Enabling an extension loads all Carbonite plugins specified by search masks in the native.plugin section. If one or more plugins implement the omni::ext::IExt interface, it is acquired and the onStartup method is called. When an extension is disabled, onShutdown is called and the interface is released.

Settings

Settings to be applied when an extension is enabled can be specified in the settings section. They are applied on the root of global settings. In case of any conflicts, the original settings are kept. It is recommended to use the path exts/[extension_name] for extension settings, but in general any path can be used.

It is also good practice to document each setting in the extension.toml file, for greater discoverability of which settings a particular extension supports.

Tokens

When extension is enabled it sets tokens into the Carbonite ITokens interface with a path to the extension root folder. E.g. for the extension omni.foo-bar, the tokens ${omni.foo} and ${omni.foo-bar} are set.

Extensions Manager

Reloading

Extensions can be hot reloaded. The Extension system monitors the file system for changes to enabled extensions. If it finds any, the extensions are disabled and enabled again (which can involve reloading large parts of the dependency tree). This allows live editing of python code and recompilation of C++ plugins.

Use the fswatcher.patterns and fswatcher.paths config settings (see above) to control which files change triggers reloading.

Use the reloadable config setting to disable reloading. This will also block the reloading of all extensions this extension depends on. The extension can still be unloaded directly using the API.

New extensions can also be added and removed at runtime.

Extension interfaces

The Extension manager is implemented in omni.ext.plugin, with an interface: omni::ext::IExtensions (for C++), and omni.ext module (for python)

It is loaded by omni.kit.app and you can get an extension manager instance using its interface: omni::kit::IApp (for C++) and omni.kit.app (for python)

Runtime Information

At runtime, a user can query various pieces of information about each extension. Use omni::ext::IExtensions::getExtensionDict() to get a dictionary for each extension with all the relevant information. For python use omni.ext.ExtensionManager.get_extension_dict().

This dictionary contains:

Everything the extension.toml contains under the same path
An additional state section which contains:
- state/enabled (bool): Indicates if the extension is currently enabled.
- state/reloadable (bool): Indicates if the extension can be reloaded (used in the UI to disable extension unloading/reloading)

Hooks

Both the C++ and python APIs for the Extension system provide a way to hook into certain actions/phases of the Extension System to enable extending it. If you register a hook like this:

def on_before_ext_enabled(self, ext_id: str, *_):
    pass

manager = omni.kit.app.get_app_interface().get_extension_manager()
self._hook = self._manager.get_hooks().create_extension_state_change_hook(
    self.on_before_ext_enabled,
    omni.ext.ExtensionStateChangeType.BEFORE_EXTENSION_ENABLE,
    ext_dict_path="python/pipapi",
    hook_name="python.pipapi",
)

…your callback will be called before each extension that contain the “python/pipapi” key in a config file is enabled. This allows us to write extension that extend the Extension system. They can define their own configuration settings and react to them when extensions which contain those settings get loaded.

Extension API Code Examples

Enable Extension

# Extensions/Enable Extension
import omni.kit.app

manager = omni.kit.app.get_app().get_extension_manager()

# enable immediately
manager.set_extension_enabled_immediate("omni.kit.window.about", True)
print(manager.is_extension_enabled("omni.kit.window.about"))

# or next update (frame), multiple commands are be batched
manager.set_extension_enabled("omni.kit.window.about", True)
manager.set_extension_enabled("omni.kit.window.console", True)

Get All Extensions

# Extensions/Get All Extensions
import omni.kit.app

# there are a lot of extensions, print only first N entries in each loop
PRINT_ONLY_N = 10

# get all registered local extensions (enabled and disabled)
manager = omni.kit.app.get_app().get_extension_manager()
for ext in manager.get_extensions()[:PRINT_ONLY_N]:
    print(ext["id"], ext["package_id"], ext["name"], ext["version"], ext["path"], ext["enabled"])

# get all registered non-local extensions (from the registry)
# this call blocks to download registry (slow). You need to call it at least once, or use refresh_registry() for non-blocking.
manager.sync_registry()
for ext in manager.get_registry_extensions()[:PRINT_ONLY_N]:
    print(ext["id"], ext["package_id"], ext["name"], ext["version"], ext["path"], ext["enabled"])

# functions above print all versions of each extension. There is other API to get them grouped by name (like in ext manager UI).
# "enabled_version" and "latest_version" contains the same dict as returned by functions above, e.g. with "id", "name", etc.
for summary in manager.fetch_extension_summaries()[:PRINT_ONLY_N]:
    print(summary["fullname"], summary["flags"], summary["enabled_version"]["id"], summary["latest_version"]["id"])

# get all versions for particular extension
for ext in manager.fetch_extension_versions("omni.kit.window.script_editor"):
    print(ext["id"])

Get Extension Config

# Extensions/Get Extension Config
import omni.kit.app

manager = omni.kit.app.get_app().get_extension_manager()

# There could be multiple extensions with same name, but different version
# Extension id is: [ext name]-[ext version].
# Many functions accept extension id:
ext_id = manager.get_enabled_extension_id("omni.kit.window.script_editor")
data = manager.get_extension_dict(ext_id)

# Extension dict contains whole extension.toml as well as some runtime data:
# package section
print(data["package"])
# is enabled?
print(data["state/enabled"])
# resolved runtime dependencies
print(data["state/dependencies"])
# time it took to start it (ms)
print(data["state/startupTime"])

# can be converted to python dict for convenience and to prolong lifetime
data = data.get_dict()
print(type(data))

Get Extension Path

# Extensions/Get Extension Path
import omni.kit.app

manager = omni.kit.app.get_app().get_extension_manager()

# There could be multiple extensions with same name, but different version
# Extension id is: [ext name]-[ext version].
# Many functions accept extension id.
# You can get extension of enabled extension by name or by python module name:
ext_id = manager.get_enabled_extension_id("omni.kit.window.script_editor")
print(ext_id)
ext_id = manager.get_extension_id_by_module("omni.kit.window.script_editor")
print(ext_id)

# There are few ways to get fs path to extension:
print(manager.get_extension_path(ext_id))
print(manager.get_extension_dict(ext_id)["path"])
print(manager.get_extension_path_by_module("omni.kit.window.script_editor"))

Other Settings

`/app/extensions/disableStartup` (default: `false`)

Special mode where extensions are not started (the python and C++ startup functions are not called). Everything else will work as usual. One use-case might be to warm-up everything and get extensions downloaded. Another use case is getting python environment setup without starting anything.

`/app/extensions/precacheMode` (default: `false`)

Special mode where all dependencies are solved and extensions downloaded, then the app exits. It is useful for precaching all extensions before running an app to get everything downloaded and check that all dependencies are correct.

`/app/extensions/debugMode` (default: `false`)

Output more debug information into the info logging channel.

`/app/extensions/detailedSolverExplanation` (default: `false`)

Output more information after the solver finishes explaining why certain versions were chosen and what the available versions were (more costly).

`/app/extensions/registryEnabled` (default: `true`)

Disable falling back to the extension registry when the application couldn’t resolve all its dependencies, and fail immediately.

`/app/extensions/skipPublishVerification` (default: `false`)

Skip extension verification before publishing. Use wisely.

`/app/extensions/excluded` (default: `[]`)

List of extensions to exclude from startup. Can be used with or without a version. Before solving the startup order, all of those extensions are removed from all dependencies.

`/app/extensions/preferLocalVersions` (default: `true`)

If true, prefer local extension versions over remote ones during dependency solving. Otherwise all are treated equally, so it can become likely that newer versions are selected and downloaded.

`/app/extensions/syncRegistryOnStartup` (default: `false`)

Force sync with the registry on startup. Otherwise the registry is only enabled if dependency solving fails (i.e. something is missing). The --update-exts command line switch enables this behavior.

`/app/extensions/publishExtraDict` (default: `{}`)

Extra data to write into the extension index root when published.

`/app/extensions/fsWatcherEnabled` (default: `true`)

Globally disable all filesystem watchers that the extension system creates.

`/app/extensions/mkdirExtFolders` (default: `true`)

Create non-existing extension folders when adding extension search path.

`/app/extensions/installUntrustedExtensions` (default: `false`)

Skip untrusted-extensions check when automatically installing dependencies and install anyway.

`/app/extensions/profileImportTime` (default: `false`)

Replace global import function with the one that sends events to carb.profiler. It makes all imported modules show up in a profiler. Similar to PYTHONPROFILEIMPORTTIME

`/app/extensions/fastImporter/enabled` (default: `true`)

Enable faster python importer, which doesn’t rely on sys.path and manually scan extensions instead.

`/app/extensions/fastImporter/searchInTopNamespaceOnly` (default: `true`)

If true fast importer will skip search for python files in subfolders of the extension root that doesn’t match module names defined in [[python.module]]. E.g. it won’t usually look in any folder other than [ext root]/omni.

`/app/extensions/fastImporter/fileCache` (default: `false`)

Cache file existence checks in the fast importer. This speeds up startup time, but extensions python code can’t be modified without cleaning the cache.

`/app/extensions/parallelPullEnabled` (default: `false`)

Enable parallel pulling of extensions from the registry.

Extension Registries

The Extension system supports adding external registry providers for publishing extensions to, and pulling extensions from. By default Kit comes with the omni.kit.registry.nucleus extension which adds support for Nucleus as an extension registry.

When an extension is enabled, the dependency solver resolves all dependencies. If a dependency is missing in the local cache, it will ask the registry for a particular extension and it will be downloaded/installed at runtime. Installation is just unpacking of a zip archive into the cache folder (app/extensions/registryCache setting).

The Extension system will only enable the Extension registry when it can’t find all extensions locally. At that moment, it will try to enable any extensions specified in the setting: app/extensions/registryExtension, which by default is omni.kit.registry.nucleus.

The Registry system can be completely disabled with the app/extensions/registryEnabled setting.

The Extension manager provides an API to add other extension registries and query any existing ones (omni::ext::IExtensions::addRegistryProvider, omni::ext::IExtensions::getRegistryProviderCount etc).

Multiple registries can be configured to be used at the same time. They are uniquely identified with a name. Setting app/extensions/registryPublishDefault sets which one to use by default when publishing and unpublishing extensions. The API provides a way to explicitly pass the registry to use.

Publishing Extensions

To properly publish your extension to the registry use publishing tool, refer to: Publishing Extensions Guide

Alternatively, kit.exe --publish CLI command can be used during development:

Example: > kit.exe --publish omni.my.ext-tag

If there is more than one version of this extension available, it will produce an error saying that you need to specify which one to publish.

Example: > kit.exe --publish omni.my.ext-tag-1.2.0

To specify the registry to publish to, override the default registry name:

Example: > kit.exe --publish omni.my.ext-tag-1.2.0 --/app/extensions/registryPublishDefault="kit/mr"

If the extension already exists in the registry, it will fail. To force overwriting, use the additional --publish-overwrite argument:

Example: > kit.exe --publish omni.my.ext --publish-overwrite

The version must be specified in a config file for publishing to succeed.

All [package.target] config subfields are filled in automatically if unspecified:

If the extension config has the [native] field [package.target.platform] or [package.target.config], they are filled with the current platform information.
If the extension config has the [native] and [python] fields, the field [package.target.python] is filled with the current python version.
If the /app/extensions/writeTarget/kitHash setting is true, the field [package.target.kitHash] is filled with the current kit githash.

An Extension package name will look like this: [ext_name]-[ext_tag]-[major].[minor].[patch]-[prerelease]+[build]. Where:

[ext_name]-[ext_tag] is the extension name (initially coming from the extension folder).
[ext_tag]-[major].[minor].[patch]-[prerelease] if [package.version] field of a config specifies.
[build] is composed from the [package.target]] field.

Pulling Extensions

There are multiple ways to get Extensions (both new Extensions and updated versions of existing Extensions) from a registry:

Use the UI provided by this extension: omni.kit.window.extensions
If any extensions are specified in the app config file - or required through dependencies - are missing from the local cache, the system will attempt to sync with the registry and pull them. That means, if you have version “1.2.0” of an Extension locally, it won’t be updated to “1.2.1” automatically, because “1.2.0” satisfies the dependencies. To force an update run Kit with --update-exts flag:

Example: > kit.exe --update-exts

Pre-downloading Extensions

You can also run Kit without starting any extensions. The benefit of doing this is that they will be downloaded and cached for the next run. To do that run Kit with --ext-precache-mode flag:

Example: > kit.exe --ext-precache-mode

Authentication and Users

The Omniverse Client library is used to perform all operations with the nucleus registry. Syncing, downloading, and publishing extensions requires signing in. For automation, 2 separate accounts can be explicitly provided, for read and write operations.

User account read/write permissions can be set for the omni.kit.registry.nucleus extension. The “read” user account is used for syncing with registry and downloading extensions. The “write” user account is used for publishing or unpublishing extensions. If no user is set, it defaults to a regular sign-in using a browser.

By default, kit comes with a default read and write accounts set for the default registry.

Accounts setting example:

exts."omni.kit.registry.nucleus".accounts = [
    { url = "omniverse://kit-extensions.ov.nvidia.com", read = "[user]:[password]", write = "[user]:[password]" }
]

Where read - is read user account, write - is write user account. Both are optional. Format is: “user:password”.

Building Extensions

Extensions are a runtime concept. This guide doesn’t describe how to build them or how to build other extensions which mihht depend on another specific extension at build-time. One can use a variety of different tools and setups for that. We do however have some best-practice recommendations. The best sources of information on that topic are currently:

The example omni.example.hello extension (and many other extensions). Copy and rename it to create a new extension.

We also strive to use folder linking as much as possible. Meaning we don’t copy python files and configs from the source folder to the target (build) folder, but link them. This permits live changes to those files under version control to be immediately reflected, even at runtime. Unfortunately we can’t link files, because of Windows limitations, so folder linking is used. This adds some verbosity to the way the folder structure is organized.

For example, for a simple python-only extension, we link the whole python namespace subfolder:

source/extensions/omni.example.hello/omni – [linked to] –> _build/windows-x86_64/debug/exts/omni.example.hello/omni

For an extension with binary components we link python code parts and copy binary parts.

We specify other parts to link in the premake file: repo_build.prebuild_link { "folder", ext.target_dir.."/folder" }

When working with the build system it is always a good idea to look at what the final _build/windows-x86_64/debug/exts folder looks like, which folder links exist, where they point to, which files were copied, etc. Remember that the goal is to produce one extension folder which will potentially be zipped and published. Folder links are just zipped as-is, as if they were actual folders.

Extensions in-depth

What is an Extension?

Extension in a single folder

Extension Id

Extension Version

Extension Package Id

Single File Extensions

App Extensions

Extension Search Paths

Custom Search Paths Protocols

Git URL as Extension Search Paths

Extension Discovery

Extension Dependencies

Extension configuration file (extension.toml)

Config Fields

[core] section

[core.reloadable] (default: true)

[core.order] (default: 0)

[package] section

[package.version] (default: "0.0.0")

[package.title] default: ""

[package.description] default: ""

[package.category] (default: "")

[package.app] (default: false)

[package.feature] (default: false)

[package.toggleable] (default: true)

[package.authors] (default: [""])

[package.repository] (default: "")

[package.keywords] (default: [""])

[package.changelog] (default: "")

[package.readme] (default: "")

[package.preview_image] (default: "")

[package.icon] (default: "")

[package.target]

[package.writeTarget]

[dependencies] section

[python] section

[[python.module]]

[[python.scriptFolder]]

[native] section

[[native.plugin]]

[[native.library]] section

[settings] section

[[env]] section

[fswatcher] section

[fswatcher.patterns]

[fswatcher.paths]

[[test]] section

[documentation] section

Config Filters

Example

Extension Enabling/Disabling

Python Modules

Native Plugins

Settings

Tokens

Extensions Manager

Reloading

Extension interfaces

Runtime Information

Hooks

Extension API Code Examples

Enable Extension

Get All Extensions

Get Extension Config

Get Extension Path

Other Settings

/app/extensions/disableStartup (default: false)

/app/extensions/precacheMode (default: false)

/app/extensions/debugMode (default: false)

/app/extensions/detailedSolverExplanation (default: false)

/app/extensions/registryEnabled (default: true)

/app/extensions/skipPublishVerification (default: false)

/app/extensions/excluded (default: [])

/app/extensions/preferLocalVersions (default: true)

/app/extensions/syncRegistryOnStartup (default: false)

/app/extensions/publishExtraDict (default: {})

/app/extensions/fsWatcherEnabled (default: true)

/app/extensions/mkdirExtFolders (default: true)

/app/extensions/installUntrustedExtensions (default: false)

`[core]` section

`[core.reloadable]` (default: `true`)

`[core.order]` (default: `0`)

`[package]` section

`[package.version]` (default: `"0.0.0"`)

`[package.title]` default: `""`

`[package.description]` default: `""`

`[package.category]` (default: `""`)

`[package.app]` (default: `false`)

`[package.feature]` (default: `false`)

`[package.toggleable]` (default: `true`)

`[package.authors]` (default: `[""]`)

`[package.repository]` (default: `""`)

`[package.keywords]` (default: `[""]`)

`[package.changelog]` (default: `""`)

`[package.readme]` (default: `""`)

`[package.preview_image]` (default: `""`)

`[package.icon]` (default: `""`)

`[package.target]`

`[package.writeTarget]`

`[dependencies]` section

`[python]` section

`[[python.module]]`

`[[python.scriptFolder]]`

`[native]` section

`[[native.plugin]]`

`[[native.library]]` section

`[settings]` section

`[[env]]` section

`[fswatcher]` section

`[fswatcher.patterns]`

`[fswatcher.paths]`

`[[test]]` section

`[documentation]` section

`/app/extensions/disableStartup` (default: `false`)

`/app/extensions/precacheMode` (default: `false`)

`/app/extensions/debugMode` (default: `false`)

`/app/extensions/detailedSolverExplanation` (default: `false`)

`/app/extensions/registryEnabled` (default: `true`)

`/app/extensions/skipPublishVerification` (default: `false`)

`/app/extensions/excluded` (default: `[]`)

`/app/extensions/preferLocalVersions` (default: `true`)

`/app/extensions/syncRegistryOnStartup` (default: `false`)

`/app/extensions/publishExtraDict` (default: `{}`)

`/app/extensions/fsWatcherEnabled` (default: `true`)

`/app/extensions/mkdirExtFolders` (default: `true`)

`/app/extensions/installUntrustedExtensions` (default: `false`)

`/app/extensions/profileImportTime` (default: `false`)

`/app/extensions/fastImporter/enabled` (default: `true`)

`/app/extensions/fastImporter/searchInTopNamespaceOnly` (default: `true`)

`/app/extensions/fastImporter/fileCache` (default: `false`)

`/app/extensions/parallelPullEnabled` (default: `false`)