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Hans de Goede
22 May 2019 @ 06:25 pm
Thank you all for the large amount of feedback I have received after my previous Wayland Itches blog post. I've received over 40 mails, below is an attempt at summarizing all the mails.

Highlights

1. Middle click on title / header bar to lower the Window does not work for native apps. Multiple people have reported this issue to me. A similar issue was fixed for not being able to raise Windows. It should be easy to apply a similar fix for the lowering problem. There are bugs open for this here, here and here.

2. Running graphical apps via sudo or pxexec does not work. There are numerous examples of apps breaking because of this, such as lshw-gui and usbivew. At least for X11 apps this is not that hard to fix. But sofar this has deliberately not been fixed. The reasoning behind this is described in this bug. I agree with the reasoning behind this, but I think it is not pragmatic to immediately disallow all GUI apps to connect when run as root starting today.

We need some sort of transition period. So when I find some time for this, I plan to submit a merge-requests which optionally makes gnome-shell/mutter start Xwayland with an xauth file, like how it is done when running in GNOME on Xorg mode. This will be controlled by a gsettings option, which will probably default to off upstream and then distros can choice to override this for now, giving us a transition period

Requests for features implemented as external programs on X11

There are various features which can be implemented as external programs
on X11, but because of the tighter security need to be integrated into the
compositor with Wayland:

  • Hiding of the mouse-cursor when not used à la unclutter-xfixes, xbanish.

  • Rotating screen 90 / 270 degrees à la "xrandr -o [left|right]" mostly used through custom hotkeys, possible fix is defining bindable actions for this in gsd-media-keys.

  • Mapping actions to mouse buttons à la easystroke

  • Some touchscreen's, e.g. so called smart-screens for education, need manual calibration. Under X11 there are some tools to get the callibration matrix for the touchscreen, after which this can be manually applied through xinput. Even under X11 this currently is far from ideal but at least it is possible there.

  • Keys Indicator gnome-shell extension. This still works when using Wayland, but only works for apps using Xwayland, it does not work for native apps.

  • Some sort of xkill and xdotool utility equivalents would be nice

  • The GNOME on screen keyboard is not really suitable for use with apps which are not touch-enabled, as it lacks a way to send ctrl + key, etc. Because of this some users have reported that it is impossible to use alternative on screen keyboards with Wayland. Not being able to use alternative on screen keyboards is by design and IMHO the proper fix here is to improve GNOME's on screen keyboard.

App specific problems


  • Citrix ICA Client does not work well with Xwayland

  • Eclipse does not work well with Xwayland

  • Teamviewer does not work with Wayland. It needs to be updated to use pipewire for screencapturing and the RemoteDesktop portal to inject keyboard and mouse events.

  • Various apps lack screenrecording / capture support due to the app not having support for pipewire: gImageReader, green-recorder, OBS studio, peek, screenrecorder, slack

  • For apps which do support pipewire, there is not an option to share the contents of a window, other then the window making the request. On Xorg it is possible to share a random window and since pipewire allows sharing the whole desktop I see no security reason why we would not allow sharing another window.

  • guake window has incorrect size when using HiDPI scaling, see this issue

Miscellaneous problems


  • Mouse cursor is slow / lags

  • Drag and drop sometimes does not work, e.g. dragging files into file roller to compress or out of file roller to extract.

  • Per keyboard layouts. On X11 after plugging in a keyboard, the layout/keymap for just that one keyboard can be updated manually using xinput, allowing different keyboard layouts for different keyboards when multiple keyboards are connected

  • No-title-bar shell extension, X button can be hit unintentionally, see this issue

  • Various issues with keyboard layout switching

Hard to fix issues


  • Alt-F2, r equivalent (restart the gnome-shell)

  • X11 apps running on top of Xwayland do not work well on HiDPI screens

  • Push-to-talk (passive key grab on space) does not work in Mumble when using native Wayland apps, see this issue

Problems with other compositors then GNOME3 / mutter

I've also received several reports about issues when using another Wayland compositor as GNOME / mutter (Weston, KDE, Sway). I'm sorry but I have not looked very closely into these reports. I believe that it is great that Linux users have multiple Desktop Environments to choose from and I wish for the other DEs to thrive. But there are only so many hours in a day so I've chosen to mainly focus on GNOME.
 
 
Hans de Goede
First of all I do not want people to get their hopes up about $subject of this blogpost. Improving gaming support is a subjects which holds my personal interest and it is an issue I plan to spend time on trying to improve. But this will take a lot of time (think months for simple things, years for more complex things).

As I see it there are currently 2 big issues when running games under Wayland:

1. Many games show as a smal centered image with a black border (letterbox) around the image when running fullscreen.

For 2D games this is fixed by switching to SDL2 which will transparently scale the pixmap the game renders to the desktop resolution. This assumes that 2D games in general do not demand a lot of performance and thus will not run into performance issues when introducing an extra   scaling step. A problem here is that many games still use SDL1.2 (and some games do not use SDL at all).

I plan to look into the recently announced SDL1.2 compatibility wrapper around SDL2. If this works well this should fix this issue for all SDL1.2 2D games, by making them use SDL2 under the hood.

For 3D games this can be fixed by rendering at the desktop resolution, but this might be slow and rendering at a lower resolution leads to the letterbox issue.

Recently mutter has has grown support for the WPviewport extension, which allows Wayland apps to tell the compositor to scale the pixmap the app gives to the compositor before presenting it. If we add support to SDL2's Wayland backend for this then, this can be used to allow rendering 3D apps at a lower resolution and still have them fill the entire screen.

Unfortunately there are 2 problems with this plan:

  1. SDL2 by default uses its x11 backend, not its wayland backend. I'm not sure what fixes need to be done to change this, at a minimum we need a fix at either the SDL or mutter side for this issue, which is going to be tricky.

  2. This only helps for SDL2 apps, again hopefully the SDL1.2 compatibility wrapper for SDL2 can help here, at least for games using SDL.

2. Fullscreen performance is bad with many games.

Since under Wayland games cannot change the monitor resolution, they need to either render at the full desktop resolution, which can be very slow; or they render at a lower resolution and then need to do an extra scaling step each frame.

If we manage to make SDL2's Wayland backend the default and then add WPviewport support to it then this should help by reducing an extra memcpy/blit of a desktop-sized pixmap. Currently what apps which use scaling do is:

  1. render lower-res-pixmap;

  2. scale lower-res-pixmap to desktop-res-pixmap

  3. give desktop-res-pixmap to the compositor;

  4. compositor does a hardware blit of the desktop-res-pixmap to the framebuffer.

With viewport support this becomes:

  1. render lower-res-pixmap;

  2. give low-res-pixmap to the compositor;

  3. compositor uses hardware to do a scaling blit from the low-res-pixmap to the desktop-res framebuffer

Also with viewport support, the compositor could in the case of there only being the one fullscreen app even keep the framebuffer in lowres and use a hardware scaling drm-plane to send the low-res framebuffer scaled to desktop-res to the output while only reading the low-res framebuffer from memory saving a ton of memory bandwidth. But this optimization is going to be a challenge to pull off.