Bug 435631

Summary:	Support for Xinerama/RandR equivalent on Wayland for integrally-combined monitors
Product:	[Plasma] kwin	Reporter:	Maciej Poleski <d82ks8djf82msd83hf8sc02lqb5gh5>
Component:	wayland-generic	Assignee:	KWin default assignee <kwin-bugs-null>
Status:	RESOLVED DUPLICATE
Severity:	wishlist	CC:	kde, nate, xaver.hugl
Priority:	NOR
Version First Reported In:	5.20.5
Target Milestone:	---
Platform:	Compiled Sources
OS:	Linux
Latest Commit:		Version Fixed In:
Sentry Crash Report:

Description Maciej Poleski 2021-04-11 20:46:53 UTC

There are monitors out there (such as Dell UP3218K) which are implemented as two monitors in one casing, connected to the computer using two DisplayPort cables.

From software perspective we have to monitors with resolution 3840x4320. Only when combined together these give desired 7680x4320@60Hz. The problem is, from software perspective there are still two monitors, even though I have just one piece standing on my desk. This has unintended consequences on application behavior, such as having a panel on only half of the screen and being able to "maximize" window only up to half of the screen.

The solution I'm using right now to workaround this is xinerama. RandR (used as described in https://michael.stapelberg.ch/posts/2017-12-11-dell-up3218k/#linux-compatibility-configuration) fails to produce desired result (appears as nop, still seeing two "actual" monitors in KScreen instead of one "virtual"). But these both are specific for X.

What we need is an equivalent of Xinerama/RandR implemented for Wayland. According to earlier attempts on bringing RandR equivalent to Wayland
- https://lists.freedesktop.org/archives/wayland-devel/2013-March/007876.html
- https://fedoraproject.org/wiki/Wayland_features#XRandR_control_of_Wayland_outputs
- https://lists.freedesktop.org/archives/wayland-devel/2014-April/014091.html

the right place to implement this functionality would be the wayland compositor itself, kwin in our case.

I may be able to dedicate some time to this. I have experience in C++/Qt, but none in Wayland protocol nor kwin internals. I'd need someone to mentor me.

What do you think?

Comment 1 Nate Graham 2021-04-13 15:07:30 UTC

Seems like a legitimate use case. I'm not sure if directly replicating Xinerama would be the solution; perhaps some Wayland-specific thing would be appropriate instead.

Comment 2 Zamundaaa 2021-04-13 16:09:47 UTC

Definitely something we want to support. There are two things we need here:
1. Implement the ability for two outputs to be seen as one screen. This should be pretty easy and quick to do once https://invent.kde.org/plasma/kwin/-/merge_requests/808 and https://invent.kde.org/plasma/kwin/-/merge_requests/844 are in and is something I've been working towards. Most tiled monitors send information about their tiling and the kernel passes it down to us so they will work automatically.

If your monitor is recognized as two in X as well then your monitor probably doesn't announce its tiling though, so once 1 is done we'll also need

2. Add an option to kscreen-doctor that allows you to configure 1 even if the monitor doesn't announce itself as a single monitor, or if you want to setup something like Eyefinity. This should ideally be exposed in the system settings, too, even though I could see that needing a bunch of changes in the UI to be made nice.

While I don't think you can help for 1 (most of the code is already written), for 2 we'll need to extend the Plasma specific outputdevice and outputmanagement wayland protocols, implement and use it with a bunch of patches (see https://invent.kde.org/plasma/kwin/-/merge_requests/846 for a simpler example).
To discuss the specifics an issue for KWin or a chat program would probably be better than the bug tracker though :)

Comment 3 David Redondo 2022-04-19 13:58:31 UTC


*** This bug has been marked as a duplicate of bug 427545 ***