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Screen Sharing

Screensharing in Wayland is done with the help of Portals. Portals were initially designed to allow applications sandboxes via Flatpak to access resources of the desktop, but have since gained popularity outside of the realm of Flatpaks. In our case, we can use the screen sharing portal to allow applications to access the contents of the Wayland compositor.

Note

Please be aware that you will only be able to share a single screen with this method, not individual windows. Sharing individual windows requires the ext_foreign_toplevel_image_capture_source_manager_v1 protocol, which Mir does not implement yet.

Requirements

  • miracle-wm built against MirAL >= 5.6 (Mir >= 2.26), which provides the ext_image_copy_capture_v1 and ext_image_capture_source_v1 protocols
  • xdg-desktop-portal-wlr >= 0.8.0, which prefers those protocols when the compositor provides them
  • slurp, used as the output chooser

Note

Older versions of these instructions required building xdg-desktop-portal-wlr v0.5.0 from source, because later versions depended on dma-buf support in the compositor's zwlr_screencopy_manager_v1 implementation that Mir lacks. This is no longer necessary: with the versions above, the portal uses ext_image_copy_capture_v1 instead, so the package from your distribution works.

Setup

Installation

Install xdg-desktop-portal-wlr (>= 0.8.0) and slurp from your distribution, for example:

sudo apt install xdg-desktop-portal-wlr slurp

If your distribution only packages an older version, build the latest release from source:

git clone https://github.com/emersion/xdg-desktop-portal-wlr
cd xdg-desktop-portal-wlr
git checkout v0.8.2
meson setup builddir --prefix=/usr
cd builddir
ninja -j4
sudo ninja install

Configuration

First, tell xdg-desktop-portal to use the wlr backend for screenshots and screen casting by creating ~/.config/xdg-desktop-portal/portals.conf:

[preferred]
org.freedesktop.impl.portal.Screenshot=wlr
org.freedesktop.impl.portal.ScreenCast=wlr

Next, create a file at /etc/xdg/xdg-desktop-portal-wlr/config with: 

[screencast]
max_fps=30
chooser_type=simple
chooser_cmd=slurp -f %o -or

Running

Build miracle with the systemd cmake flag: -DSYSTEMD_INTEGRATION=1. Among other things, this ensures that WAYLAND_DISPLAY and XDG_CURRENT_DESKTOP are imported into the D-Bus activation environment at startup, which the portal needs in order to find the compositor.

Next, add the following startup application to miracle:

# ~/.config/miracle-wm/config.yaml

startup_apps:
    - command: systemd-run --user /usr/libexec/xdg-desktop-portal --replace
      in_systemd_scope: true

This will make it so that your regular screensharing mechanism is disabled at runtime in favor of our new one.

Finally, restart your compositor and then open up obs-studio or Google Meet and see that you are able to share your screen.

Troubleshooting

To verify that the portal is using the new capture path, kill any running instance of xdg-desktop-portal-wlr and start it manually with tracing:

xdg-desktop-portal-wlr -l TRACE -r

It should log wayland: using ext_image_copy_capture on startup.