Headless output

[robbins]

Does Niri have the ability to create headless outputs that aren't tied to any physical monitor? e.g. for programs like Moonlight/Sunshine?

e.g. https://wiki.archlinux.org/title/Sway#Create_headless_outputs

[YaLTeR]

Not at the moment.

[djmaze]

Not only for that, it is also needed for virtual desktops in VR / MR (which I am planning to do in the future). People reported successfully using headless outputs in Hyprland for use in the Immersed virtual desktop environment.

I have no deeper knowledge about this topic, but this sounds to me like the used smithay toolkit already somewhat supports these kind of usecases: Smithay/smithay#287

[YaLTeR]

I don't think anything is missing on the Smithay side for headless outputs.

[djmaze]

Talking about immersed, I just tried running it (on NixOS). On sway it works, but on niri it fails to start, outputting this message:

listener function for opcode 2 of wl_output is NULL

What could be the reason? Is this maybe a client problem as similarly reported here?

[djmaze]

Ah yes, client problem, just found this: pop-os/cosmic-epoch#1137

[FlyingWombat]

If you make support for headless output, please consider including a way to detach an existing session from its display and make it headless. A use case for this is starting a VM with VFIO gpu passthrough, without having to kill the user session.

[YaLTeR]

Interesting use case, could you link some more info about it?

[Quackdoc]

I have found a usecase for headless, I have found myself wanting to test niri on all sorts of different interaction methods and one of the more convenient ways of doing this is using streaming solutions such as sunshine + moonlight.

The goal would be to create a headless session at whatever output is desired, then stream that to whatever interface I am testing on. This isn't the nicest solution in the world, but it should work fine.

[Quackdoc]

As an appendage to this, not sure if this is a "headless" part or not, but I did find myself in a usecase where it would be nice to have a "pipewire only" output mode. I think this would be a "headless + always on pipewire". The case here is remote streaming use case where I only view the output over a network via gstreamer.

[isti115]

One more really nice use case that I've been relying on with other wayland compositors (Sway and River) is to repurpose other devices as extra monitors by piping the contents of headless outputs to theirs screens through VNC.

[hcoohb]

Oh, I would love this feature as well!

My use case is basically we have a media server at home, which output is constantly driving the TV and i am also remotely accessing it as a different user. I currently use a virtual x11 display coupled with VNC to use for everything as my laptop is not performant.

But it would be so much better to use niri with a "virtual" output!

[Hikiru]

i dont have a second monitor, and sunshine/moonlight with a headless display is a great way to use one of my other devices as one.

[myNicole98]

I second this, it would be really nice to have a headless display option in Niri

[envicious]

Third this! I love using vnc as a nice virtual monitor whenever i need some extra space :)
Would love to do this in Niri too

[zitongcharliedeng]

+1 for NixOS e2e tests

[clarkarch]

Any update on this? i need this for sunshine and moonlight streaming

[Vibricks]

Would love to also have this for using my devices as a second monitor with sunshine + moonlight

[QaidVoid]

I have implemented it on my fork: https://github.com/QaidVoid/niri/tree/feat/virtual. It's not polished but it works for my use case. Tested with moonlight/sunshine and wayvnc.

Disclaimer: most of this was written with the help of AI

[repparw]

Will you make a PR?

[QaidVoid]

I'm not 100% confident if the implementation is correct. It might be better if someone more knowledgeable picks it up.

[repparw]

someone will review it, better than start from scratch surely

[patroza]

sadly crashes on a laptop when closing the lid of my laptop.

[juliadin]

I'd love to see headless niri for running wayvnc without local graphics output

[subsy]

Another vote here - sunshine/moonlight being my primary use case

[aaronlauterer]

Definitely another vote here.
One more use case I have for headless displays is when giving presentations online where you have to share the screen. I don't want to or cannot share my main screen, as it is a high resolution widescreen monitor.
So the resolution would not work because of the aspect ratio and resolution. Additionally, switching a PDF or presentation tool into full screen on the main screen is a problem when you also need it for the video call.

[YaLTeR]

Windowed fullscreen + dynamic cast target set to the window. https://niri-wm.github.io/niri/Screencasting.html#windowed-fakedetached-fullscreen

[aaronlauterer]

Windowed fullscreen + dynamic cast target set to the window. https://niri-wm.github.io/niri/Screencasting.html#windowed-fakedetached-fullscreen

Thanks! I wasn't aware of that approach.

Unless I am missing something else, for more complex scenarios, like live demos or screen recordings involving multiple windows/applications, the headless display would be a great addition. As one could then set the resolution to a better-fitting one, usually full HD. :-)

[roufpup]

Would love to see this feature added for use with sunshine

[vinnavannewton]

it's very useful for me, so im casting a vote!

[rektide]

Sizable write-up for virtual outputs in #3101.