getting-started.md

title: "Monado - Getting Started"
layout: main

• TOC {:toc}

About OpenXR and Monado

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

• The OpenXR Loader provided by Khronos
• An OpenXR runtime like Monado or SteamVR (with OpenXR support)

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.

The initial focus of Monado lies on desktop VR usage. In the future a main goal will be to bring Monado to mobile and standalone AR devices, but desktop VR support will remain an important aspect for Monado for the foreseeable future.

Monado Requirements

Monado currently runs on Linux. A Windows port is in progress.

The Monado compositor requires a Vulkan driver with the instance extensions:

• VK_KHR_external_fence_capabilities
• VK_KHR_external_memory_capabilities
• VK_KHR_external_semaphore_capabilities
• VK_KHR_get_physical_device_properties2
• VK_KHR_surface
• for direct mode on Linux/X11
  • VK_KHR_display
  • VK_EXT_direct_mode_display
  • VK_EXT_acquire_xlib_display

and the Device extensions:

• VK_KHR_dedicated_allocation
• VK_KHR_external_fence
• VK_KHR_external_fence_fd
• VK_KHR_external_memory
• VK_KHR_external_memory_fd
• VK_KHR_external_semaphore
• VK_KHR_external_semaphore_fd
• VK_KHR_get_memory_requirements2
• VK_KHR_swapchain

OpenXR applications using Vulkan are supported with all Vulkan drivers that support the listed extensions. In particular 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 are supported with radeonsi and the nvidia proprietary driver.\ Intel does not currently support this extension in mainline mesa but there are WIP MRs for mesa/iris and for mesa/i965 that have been tested to work with Monado.

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

OpenXR SDK and 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.

• Debian: releases in distro, Monado continuous builds in CI
• Ubuntu: releases in distro via Debian or through a PPA, Monado continuous builds in CI
• Archlinux AUR: openxr-loader-git and AUR: monado-git

Up to date information can be found on repology.

Debian and Ubuntu packages

{: #deb} In Debian and Ubuntu the OpenXR SDK is split into several packages.

The core packages are

• libopenxr-loader1
  • This is libopenxr_loader.so library. OpenXR applications link to this library and can not be compiled/run without it.
• libopenxr-dev
  • The OpenXR headers are required to compile OpenXR C/C++ applications.
• libopenxr1-monado
  • The Monado OpenXR runtime

Useful packages:

• xr-hardware
  • udev rules allowing users without root permissions to use XR hardware, installation is highly recommended
• libopenxr-utils
  • OpenXR applications and demos, including the hello_xr example
• openxr-layer-corevalidation
  • A validation layer for OpenXR. Can be enabled with the environment variable XR_ENABLE_API_LAYERS=XR_APILAYER_LUNARG_core_validation
• openxr-layer-apidump
  • Another layer that can dump all OpenXR calls an application makes to a file
• monado-cli, monado-gui
  • See Tools for a detailed description

Installation from Source

Install the meson and ninja build tools

apt install meson ninja-build

OpenXR SDK

The OpenXR SDK contains the OpenXR loader and the OpenXR headers.

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

Monado

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 meson 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

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

git clone https://gitlab.freedesktop.org/monado/monado.git
cd monado
meson --prefix=/usr build
ninja -C build install

Running OpenXR Applications

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 meson -Dservice=false or cmake -DXRT_FEATURE_SERVICE=OFF.

With monado-service

{: #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 /tmp/monado_comp_ipc around. The Monado compositor will refuse to start if this file is found with the message ERROR: Could not bind socket to path /tmp/monado_comp_ipc: is the service running already?. If monado-service is not running, it is safe to simply delete /tmp/monado_comp_ipc.

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.

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 or if this variable is not set for a file called active_runtime.json 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

{: #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:

• XRT_PRINT_OPTIONS=1: Print supported environment variables and current value during runtime

Available for OpenXR applications:

• OXR_DEBUG_ENTRYPOINTS=1: Print all OpenXR "entry point" function calls that the application performs. Note that XR_ENABLE_API_LAYERS=XR_APILAYER_LUNARG_api_dump performs a similar role and prints even more information.
• OXR_TRACKING_ORIGIN_OFFSET_X=0.5, OXR_TRACKING_ORIGIN_OFFSET_Y=1.0, OXR_TRACKING_ORIGIN_OFFSET_Z=0.1: The offset of the current tracking origin to the desired tracking origin. Moves everything (HMD, left and right controllers) in the opposite direction of this offset, e.g. a device calibrated to (0,0,0) on a table 1 meter above the floor with OXR_TRACKING_ORIGIN_OFFSET_Y=1.0 sets the tracking origin to the floor, and the device's resulting position will be (0,1,0).

Available for monado-service:

• PROBER_LOG=debug: Print information about devices that are found and opened.
• IPC_EXIT_ON_DISCONNECT=1: Exit the service whenever a client quits.

Compositor

Available for monado-service:

• XRT_COMPOSITOR_LOG=debug: Print compositor related debug information (selected GPU, driver, display mode, ...). See Logging.
• XRT_COMPOSITOR_PRINT_MODES=1: Like XRT_COMPOSITOR_LOG=debug, but only prints mode. Useful for XRT_COMPOSITOR_DESIRED_MODE.
• XRT_COMPOSITOR_DESIRED_MODE=2: Choose another mode than the default (highest resolution, then highest refresh rate). See XRT_COMPOSITOR_PRINT_MODES for a list of modes supported by the HMD.
• XRT_COMPOSITOR_FORCE_GPU_INDEX=3: Choose the GPU to run the compositor on. See XRT_COMPOSITOR_LOG=debug for the index of available Vulkan devices.
• XRT_COMPOSITOR_FORCE_CLIENT_GPU_INDEX=4: Choose the GPU recommended to OpenXR client to use. Defaults to the GPU the compositor runs on. Expect breakage when choosing a different GPU.
• XRT_COMPOSITOR_FORCE_WAYLAND=1: Run the Monado compositor on wayland. Usually this should not be necessary.
• XRT_COMPOSITOR_FORCE_XCB=1: Do not use direct mode and run the Monado compositor in a window.
• XRT_COMPOSITOR_XCB_FULLSCREEN=1: Only when using XRT_COMPOSITOR_FORCE_XCB: Start the compositor as a fullscreen window.
• XRT_COMPOSITOR_FORCE_NVIDIA=1, XRT_COMPOSITOR_FORCE_RANDR=1: Force the use of nvidia or mesa/amdvlk flavor of direct mode initialization. Usually this should not be necessary.
• XRT_COMPOSITOR_FORCE_NVIDIA_DISPLAY=PNP: Allows using direct mode on nvidia GPUs with a GPU not listed in NV_DIRECT_WHITELIST in comp_settings.h. See XRT_COMPOSITOR_LOG=debug for finding viable display strings.
• XRT_COMPOSITOR_SCALE_PERCENTAGE=100: Scale the render target size recommended to applications to render at. Affects all applications connecting to this service. Defaults to 140% supersampling.
• XRT_MESH_SIZE=64: Control the resolution of the meshes generated by distortion mesh computation (vive, psvr, openhmd, northstar).

Available for OpenXR applications

• OXR_VIEWPORT_SCALE_PERCENTAGE=100: Scale the render target size recommended to this application to render at. Affects only this application. Defaults to 100%. Applied on top of XRT_COMPOSITOR_SCALE_PERCENTAGE.
• OXR_DEBUG_IPD_MM=58: Change the default IPD (63mm) for drivers that do not support dynamic IPD adjustment.

Logging

{: #loglevel}

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:

• VIVE_LOG=debug
• XRT_COMPOSITOR_LOG=debug
• XRT_LOG=debug: Log messages from various systems around monado not hooked up to a more specific category.

Debug GUI

Available for OpenXR applications and monado-service:

• OXR_DEBUG_GUI=1: Open a separate debug window for observing and manipulating certain state. For example changing a tracking origin virtually moves devices tracked on that tracking origin.
  • the debug information shown for monado-service and OpenXR clients is different, for example monado-service shows a basic compositor frametiming graph.

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%

• STEAMVR_EMULATE_INDEX_CONTROLLER=1: Use SteamVR's Index controller profile with hardcoded bindings instead of monado's generated input profiles. May be useful to make legacy games work.
• XRT_COMPOSITOR_SCALE_PERCENTAGE=100: Scales SteamVR's render target size, like for the Monado compositor.

Instructions for setting up the SteamVR plugin can be found here

Developing with Monado

You can now start developing with Monado