About OpenXR and Monado

Software that supports VR by using the OpenXR API requires two software packages to work:

OpenXR runtimes like Monado can be though of as “VR headset and VR controller drivers” and the OpenXR loader, analog to the Vulkan loader, is responsible for finding and connecting applications to this “driver” so that OpenXR applications do not need to interact directly with a runtime.
Applications link to only the libopenxr_loader.so or .dll library and use the C headers provided by the OpenXR SDK.

More general background information about OpenXR and OpenXR runtimes can be found at About Runtimes.

Monado Requirements

Monado currently runs on linux and android. A windows port is in progress.

The Monado compositor requires a Vulkan driver with certain Vulkan extensions. For example the compositor requires VK_KHR_external_memory_fd and VK_KHR_external_semaphore_fd to enable the most basic submission of textures from the application to the compositor.

A full list of required and optional Vulkan extensions is available in the doxygen documentation.

In particular reasonably modern versions of radv, intel anv and the nvidia proprietary driver are tested and confirmed to work.

OpenXR applications using OpenGL require an OpenGL driver with support for the GL_EXT_memory_object_fd OpenGL extension. OpenGL applications have been tested and are confirmed to work with radeonsi, intel i965 and iris (since mesa 21.2) and the nvidia proprietary driver.

Note that the intel drivers offer only limited support for GL_EXT_memory_object_fd: depth/stencil formats are not supported yet.

Running Monado with the amdvlk Vulkan driver generally works but may not render OpenXR applications using OpenGL correctly.

Monado Installation

There are no prebuilt generic binaries for monado available at this time.
If your distribution does not provide packages for the OpenXR SDK and Monado, you will have to build Monado from source.

Distribution packages

Packages for the OpenXR SDK and Monado are available for various distributions.

Up to date information can be found on repology.

Debian and Ubuntu packages

In Debian and Ubuntu the OpenXR SDK is split into several packages.

When using the precompiled debian packages, these packages are required to build and run OpenXR applications with Monado:

apt install libopenxr-loader1 libopenxr-dev libopenxr1-monado

Other useful packages:

Installation from Source

Install the CMake and ninja build tools

apt install cmake ninja-build

See https://gitlab.freedesktop.org/monado/monado#getting-started for a list of dependencies.

This command will install required and some optional dependencies that will enable most of the commonly used functionality of monado on Debian/Ubuntu. Some features and drivers are only compiled with additional dependencies like libsurvive or librealsense.

apt install build-essential git wget unzip cmake ninja-build libeigen3-dev curl patch python3 pkg-config libx11-dev libx11-xcb-dev libxxf86vm-dev libxrandr-dev libxcb-randr0-dev libvulkan-dev glslang-tools libglvnd-dev libgl1-mesa-dev ca-certificates libusb-1.0-0-dev libudev-dev libhidapi-dev libwayland-dev libuvc-dev libavcodec-dev libopencv-dev libv4l-dev libcjson-dev libsdl2-dev libegl1-mesa-dev libbsd-dev

then compile and install Monado. Monado can be built with either cmake or meson.

git clone https://gitlab.freedesktop.org/monado/monado.git
cmake -G Ninja -S monado -B build -DCMAKE_INSTALL_PREFIX=/usr
ninja -C build install

Monado Service

Since version 0.2, Monado can be built in two different modes: With monado-service (this is the default) and without monado-service.

The service can be disabled with cmake -DXRT_FEATURE_SERVICE=OFF or meson -Dservice=false.

With monado-service

When monado is built with monado-service, Monado’s compositor and drivers run in a separate service process that has to be started before running an OpenXR application. monado-service will be installed as /usr/bin/monado-service in a default installation.

monado-service can either be started manually by running the binary, or it can be run automatically by using systemd socket activation.

Most monado developers and users who want exact control over when Monado is running are expected to run monado-service manually.

A manually started monado-service is cleanly shut down by simply pressing enter in the terminal it was started in. An unclean shutdown (ctrl+c, crash) will leave a socket file /run/user/1007/monado_comp_ipc that gets deleted when Monado starts again.

If systemd is available (and it’s not configured to disable this), a monado.socket and monado.service user unit files are installed in /usr/lib/systemd/user or similar. systemctl --user enable monado.socket will have systemd open the domain socket at login. Running an OpenXR application will spin up the service, while systemctl --user stop monado.service will stop it. This is expected to mainly be used by end users installing a package.

Without monado-service

When monado is built with the service disabled, the monado-service binary is not built. Instead of connecting to a long running service instance, OpenXR applications load the entire monado runtime as a library, initialize it at startup and shut it down on exit.

This mode is very convenient for debugging the Monado runtime, but makes it impossible to run overlay applications with XR_EXTX_overlay.

Running OpenXR Applications

OpenXR SDK

Monado’s own tools run without the OpenXR loader, but running OpenXR applications requires the OpenXR loader provided by Khronos in the OpenXR SDK. Compiling OpenXR applications requires the OpenXR headers from the OpenXR SDK.

OpenXR SDK distribution packages

The OpenXR SDK is packaged in various distributions using different naming conventions. Check for availability of packages with names like openxr, openxr-loader, openxr-sdk or openxr-sdk-source.

OpenXR packages for various Ubuntu versions are also available in the Monado PPA.

Building the OpenXR SDK from source

If no package is available for your distribution or you want to use an updated version of the loader, you will have to compile the OpenXR loader from source. There are two repositories for the OpenXR SDK available.

See https://github.com/KhronosGroup/OpenXR-SDK#linux for a list of dependencies.

Build the OpenXR SDK with cmake, this example uses ninja.

git clone https://github.com/KhronosGroup/OpenXR-SDK.git
cd OpenXR-SDK
cmake . -G Ninja -DCMAKE_INSTALL_PREFIX=/usr -Bbuild
ninja -C build install

Selecting the Monado runtime for OpenXR applications

The OpenXR loader chooses the OpenXR runtime to load by first looking at the environment variable XR_RUNTIME_JSON. If this variable is not set, a file called active_runtime.json is searched in various locations.

Most installations of Monado will ship an active_runtime.json symlink in a systemwide xdg config path, which will make the OpenXR loader use Monado when starting OpenXR applications as described in the loader documentation. If the packager decided not to ship an active_runtime.json symlink, you can create it yourself:

sudo mkdir -p /etc/xdg/openxr/1/
sudo ln -s /usr/share/openxr/1/openxr_monado.json /etc/xdg/openxr/1/active_runtime.json

Alternatively the OpenXR Loader also knows user specific xdg config paths. Note that this will only be obeyed by applications that are not run as root.

mkdir -p ~/.config/openxr/1
ln -s /usr/share/openxr/1/openxr_monado.json ~/.config/openxr/1/active_runtime.json

The environment variable XR_RUNTIME_JSON can be used in absense of, or to override an active_runtime.json:

XR_RUNTIME_JSON=/usr/share/openxr/1/openxr_monado.json ./application

Driver Selection

Monado automatically initializes drivers in the order they appear in target_lists.c.

For example for a connected HTC Vive, Monado will first attempt to use the “survive” driver, then the “vive” driver, and at last the “ohmd” (OpenHMD) driver. In this example, to use the “ohmd” driver, the “survive” and “vive” drivers should be disabled.

Tools

Monado comes with a number of tools.

monado-service

See Running OpenXR applications with monado-service

monado-gui

monado-gui serves the important function of calibrating cameras for positional tracking. See Setting up Playstation Move Controllers for an example of using it for calibration.

monado-gui stores persistent configuration in $XDG_CONFIG_HOME, or by default ~/.config/monado/. A configuration file is only required for setups that require camera calibration (PSVR, PS Move).

monado-cli

monado-cli probe and the more verbose monado-cli test provide an easy way to test which supported devices monado finds and can open.

monado-ctl

Running concurrent non-overlay OpenXR applications will result in Monado only presenting the first started application. monado-ctl allows choosing the currently presented application. This command is only installed when the monado service is enabled at build time.

monado-ctl lists all applications connected to the current monado service instance and their status.

monado-ctl -p 1 switches monado to present the application with id 1 in the list reported by monado-ctl.

Environment Variables

Note: When compiling monado without monado-service, the environment variables that apply to the service can be used with the OpenXR application directly.

Either TRUE/FALSE or 1/0 can be used to set boolean variables.

General

Available for monado-service and OpenXR applications:

Available for OpenXR applications:

Available for monado-service:

Compositor

Available for monado-service:

Available for OpenXR applications

Logging

Various components and drivers in Monado use a logging system with well known logging levels trace, debug, info warn, error.

At this time the log level can only be changed for components individually by using environment variables. The default log level is warn. Environment variables that make use of the log level system typically end with _LOG. Examples:

Debug GUI

Available for monado-service and OpenXR applications (if build time option XRT_FEATURE_CLIENT_DEBUG_GUI is enabled):

SteamVR plugin

These variables should be set for SteamVR, for example when starting from command line: STEAMVR_EMULATE_INDEX_CONTROLLER=1 ~/.local/share/Steam/steamapps/common/SteamVR/bin/vrstartup.sh or in the Steam library properties for SteamvR: STEAMVR_EMULATE_INDEX_CONTROLLER=1 %command%

Instructions for setting up the SteamVR plugin can be found here

Developing with Monado

You can now start developing with Monado