Red Hat Bugzilla – Bug 1289714
find a solution for XWayland games trying to set display resolution
Last modified: 2018-10-05 03:36:34 EDT
This is the year or Linux gaming. We now have thousands of games available for Linux thanks to Steam, and Steam machines running SteamOS (Linux) are sold worldwide. All of those games out there are X11-based. Some of them will get updated for Wayland, but most never will. If we want to push Wayland as the default display technology, we need to make sure those games work.
One of the core issues is display resolution. Game developers and players are used to games changing their display resolution (especially 3D games) in order to achieve satisfactory performance. That is no longer possible in Wayland, and there are good reasons for that, and solutions (scaling the ouput). However, we also need a solution for XWayland games, which is the majority.
Under XWayland, there seems to be only a single resolution available when querying display through xrandr - the current resolution - and no custom resolution can be set.
According to my short testing, there are several ways how games currently cope with that (all of this covers fullscreen behavior only, I haven't seen any issues when running in a windowed mode):
A) Run in a letterbox fixed to a single resolution - the game in enclosed in black bars around the screen (corresponding to the game's default resolution), no change can be made
B) Run in a letterbox, but allow different resolutions to be set, adjusting letterbox - different resolutions change the rendering size and the size of the black bars around it
Examples: Extreme Tux Racer, Battle for Wesnoth
C) Run in a desktop resolution - you can either see desktop resolution as the only available resolution, or you can see other resolutions available, but nothing happens when you try to set it, you stay fixed to the current one. This is basically the same case as A), only the game default resolution seems to be your desktop resolution. Internal game logic probably differentiates A) and C).
Examples: 0 A.D., Xonotic, Supertuxkart, Neverball
D) Run scaled in a desktop resolution - only single resolution is available, but the game output is scaled as opposed to letterboxing
E) Use internal scaling instead of relying on system resolutions - this is what some modern games do. Instead of changing the monitor resolution, keep it intact, just adjust the internal rendering resolution and then either scale up the output or display a smaller game area.
Examples: Pillars of Eternity, Gnomoria
F) Crash - when configuring the game in the better case, on startup in the worst case
Examples: Minecraft (according to bug 1287864, not tested)
Only E) is the ideal solution for users of Wayland desktop. A) and B) make the game screen small or tiny, C) and D) don't allow to tune the game performance to available hardware.
There is a simple yet tiresome workaround for B) and C) - switch desktop resolution manually to a desired size, run the game, switch resolution manually back afterwards. I don't know about any workarounds for A), D) and F).
Please try to find a solution for this. If we can't make the crushing majority of games work, Wayland will not convert a large portion of our user base (anyone who sometimes plays a game), they will stay with X11.
For example, could we fake the resolution list for XWayland apps and if they try to set a custom fullscreen resolution, could we tell them it succeeded, but scale their output instead? (similarly to what we intend to do with Wayland-based games)
*** Bug 1286217 has been marked as a duplicate of this bug. ***
(In reply to Kamil Páral from comment #0)
> F) Crash - when configuring the game in the better case, on startup in the
> worst case
> Examples: Minecraft (according to bug 1287864, not tested)
Bug 1287864 is a bug in Minecraft itself, not something we can fix.
(In reply to Olivier Fourdan from comment #2)
> Bug 1287864 is a bug in Minecraft itself, not something we can fix.
Actually, a workarround for this was just added to Xwayland, included in xserver 1.18.3 so Minecraft should start in Wayland now (upstream).
This is still an issue in F25 (e.g. with openarena I can't change its resolution at all).
Well, for games using Xwayland this feature was denied:
That comment said it should be implemented in mutter, not Xwayland.
(In reply to Olivier Fourdan from comment #5)
> Well, for games using Xwayland this feature was denied:
Yes, and I understand why. However, the purpose of this ticket was whether we can find a different solution to this (because X11-based games will be with us for a long time still). For example:
(In reply to Kamil Páral from comment #0)
> For example, could we fake the resolution list for XWayland apps and if they
> try to set a custom fullscreen resolution, could we tell them it succeeded,
> but scale their output instead? (similarly to what we intend to do with
> Wayland-based games)
Is that doable (or something similar)? Is there a will and time to implement it?
I just like to add that a scaling solution as mentioned above would also heavily benefit wine games, probably a big factor.
Ok I started tinkering on this for fun and it looks surprisingly simple.
I changed xwayland in the xserver so it allows 1024x768 as resolution and mutter plays along quite nicely.
When changing the resolution in Warcraft 3, it properly resizes to that.
When minimizing the game and selecting again (this is not 100% reproducibly atm and probably a bug in mutter), the output even gets scaled up!
The input handling is limited to the official size of the window (1024x768 instead of 1366x768) thought, so I can't move the mouse to the far right anymore.
I'll try if I can make that behavior explicit in mutter and fix the input.
For those interested, here's some screenshots:
If I understand everything correctly, mutter on X11 (or Xorg itself?) currently remembers randr settings for each application and sets them on focus change (e.g. taping out and back again).
We can maybe mirror that behaviour for xwayland, but instead of setting the resolution just apply a resize to the interface the application renders to and some sort of mouse coordinate wrapper.
I'll tinker on that a bit but I'm really slow as it's still hard for me how everything interacts and how many different ways there are to set the resolution.
The most clean solution would of course be to have one xwayland instance per application, but that will probably not happen anytime soon.
Ok I was totally wrong, the app always sets the resolution itself.
So the idea would be as follows:
- make xwayland accept randr mode setting (not really setting it but remembering and reporting it on future request).
- make mutter check the set resolution when it sets an x-window to fullscreen on wayland. If the resolution is not the native one, take only the output of the reported resolution and scale it up to native size
- create a shim layer for mouse input that reports the current mouse position accordingly
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Created attachment 1355915 [details]
xwayland patch to enable some common resolutions
This is a small patch for xwayland to enable some common resolutions make xwayland accept/save the settings.
The rest probably has to get handled by the compositor (I'm focusing on mutter)
With the patch above applied, most applications somewhat work.
When fullscreened by mutter, all 3d-games I tested so far get scaled up well. What remains to be done here:
- when a fake resolution is set, mutter often doesn't set the fullscreen flag for the corresponding windows (or unsets them)
- mouse input is somewhat broken, needs some translation layer
- black-bar mode for resolutions not fitting the screen (should be relatively easy)
The 2d-games I've tested don't get scaled up right now. But that might have to do with the fact that all of them use legacy fullscreening, therefore mutter doesn't know how big they're supposed to be. If mutter knew, it should be easy.
I don't think making up modes in Xwayland is the right approach, it should retrieve those from the wl_output::mode given by the Wayland compositor (gnome-shell in this case).
Right now, gnome-shell doesn't list any but the current one, so adding this in gnome-shell would be a start.
But then Xwayland as of now ignores all modes but the current one (!), so you'd need to fix Xwayland to take thoise into account and list them in the available modes in XRandR.
But even with that in place, Xwayland would need a way to notify the Wayland compositor that one of its X11 client with a surface fullscreen has requested a different mode. However, We do not want Xwayland to control the output mode though (see https://fedoraproject.org/wiki/Wayland_features#XRandR_control_of_Wayland_outputs) as any XRandR client (including the command xrandr itself) would be able to change the modes in Wayland.
PS: I think you'd get probably more feedback and traction by discussing this upstream on xorg-devel and wayland devel mailing lists rather than in a bug downstream.
@Olivier Fourdan: thanks for the feedback, the reason I'm tracking it here is mainly for the fakt that it's not yet clear which components need to get changed (only xwayland or also mutter/the window manager).
But you're right.
For the other part: what I'm currently trying is exactly not to set the screen mode, as that is not supposed to happen under wayland. So xwayland should not tell the compositor to do that but only fake it.
The idea is to just scale up the output. That in turn makes it independent from the real modes the screen supports.
This feature overall is mostly about legacy support (old games which don't detect the actual screen resolution or don't know anything bigger than say 1024x768).
So we could add all supported screen resolutions, but I think it's important to make sure the most common ones are in the list (640x480, 800x600, 1024x768), as those basically are the ones which will get used.
Think of games like Diablo 2, Age of Empires 2, Counter Strike and the like.
Created attachment 1356127 [details]
Translate the mouse position when fake resolution is set
This patch translates the mouse position accordingly to the fake resolution. It assumes that, when a fake resolution is set, the window is fullscreen (therefore scaled up to the full screen size).
That would be the usual case.
Alright, with the two patches above everything on the xwayland side should be done, the rest probably has to get figured out on the compositor side (properly detecting when a window should get fullscreened, resetting the fake resolution if the application does not itself on quit etc.).
With these patches, I can already play most 3d-games with lower resolutions, like starcraft 2, source-engine based shooters (only the menu, shooters don't yet work in gnome/wayland, but that's another story) or the talos principle.
As soon as I have some mutter patches ready, I'll create a copr for those interested to test.
Created attachment 1358665 [details]
Translate the mouse position when fake resolution is set
Created attachment 1358678 [details]
Hack to make mutter fullscreen all games (unclean solution)
FWIW, I have just posted a patch for Xwayland to list all the wl_output::mode(s) advertised by the compositor as available XRandR modes, so that you wouldn't need to fake modes in Xwayland.
That works with weston which lists multiple available modes, but gnome-shell/mutter only lists the current mode.
Created attachment 1364382 [details]
mutter patch to expose some common resolutions (WIP)
With Oliviers patch (https://patchwork.freedesktop.org/series/34628/), xwayland exposes modes send by mutter.
This makes mutter expose three hard-coded common modes. Actually it should expose all modes it would list in system-setting AND these modes (they are the most important modes for old games).
Created attachment 1364383 [details]
xwayland patch to accept fake modesetting
This makes xwayland fake/accept modes (WIP). Together with Oliviers patch and 1364382 (mutter patch to expose some common resolutions (WIP)), it makes it possible to launch games which don't work without modesetting, such as Diablo 2 over Wine.
Little status update of the todo list:
- make mutter expose all solutions it would in system-settings, in addition to some very import ones which are hard-coded so far
- implement wl_viewport. There's some old work here: https://mail.gnome.org/archives/commits-list/2014-November/msg00700.html
- make mutter add viewports to xwayland windows which don't have the screen resolution and want to become fullscreen
Created attachment 1364992 [details]
implement wp_viewporter (WIP)
This is based on old patches by Jasper St. Pierre, see
This makes it work with gnome 3.26.2 and stabilizes it as wp_viewporter instead of wl_scaler.
It's not tested yet, but it builds :)
External bug-tracker for wp_viewport: https://bugzilla.gnome.org/show_bug.cgi?id=791405
And the external bug tracker for the xwayland part: using wp_viewporter to actually scale things.
Just for information, people who need a minimal solution for the problem can use the following copr with a patched mutter/xwayland which expose certain modes in xwayland. It doesn't include ongoing work to use the wp_viewporter protocol to actually scale things up, but it lets you start many games that otherwise would not.
Thanks, Robert, for working on this, much appreciated. Hopefully this gets into upstream.