This is the gtk3 version of !6722.
This fixes a problem that is apparent in
https://bugzilla.mozilla.org/show_bug.cgi?id=1869724, but that also
reproduces on any GTK application as described in
https://bugzilla.mozilla.org/show_bug.cgi?id=1869724#c16.
xdg_output sizes might be physical if the compositor doesn't scale them,
it seems. So to report the correct logical geometry in GDK pixels, we
need to detect this case. We do this by checking whether the wl_output
size matches the xdg_output size.
The xdg_output interface has a `name` property that reflects the output
name coming from the compositor.
This is the closest thing we can get to a connector name.
Fixes: #1961
Previously, the GDK backend for Wayland would deduce the logical size
of the monitors from the wl_output size and scale.
With the addition of fractional scaling which advertises a larger scale
value and then scale down the client surface, the computed logical size
of the monitors in GDK would be wrong and confuse applications which
insist on using the monitor size and position (like Firefox).
The xdg-output protocol aims at describing outputs in a way which is more
in line with the concept of an output on desktop oriented systems by
presenting the outputs using their logical size and position appropriately
transformed.
Add support for the optional xdg-output protocol so that the size and
position of the monitors as reported by GDK is correct even when using
fractional scaling.
Fixes: https://gitlab.gnome.org/GNOME/gtk/issues/1828
