The upper layers (OSDs basically) want to know the monitor that a
tablet is currently assigned to, not the monitor just as configured
through settings.
This broke proper OSD positioning for display-attached tablets since
commit 87858a4e01, as the MetaInputMapper kicks in precisely when
there is no configured monitor for the given device.
Consulting both about the assigned output will make OSDs pop up
again in the right place.
https://gitlab.gnome.org/GNOME/mutter/merge_requests/971
This object takes care of mapping absolute devices to monitors,
to do so it uses 3 heuristics, in this order of preference:
- If a device is known to be builtin, it's assigned to the
builtin monitor.
- If input device and monitor match sizes (with an error margin
of 5%)
- If input device name and monitor vendor/product in EDID match
somehow (from "full", through "partial", to just "vendor")
The most favorable outputs are then assigned to each device, making
sure not to assign two devices of the same kind to the same output.
This object replaces (and is mostly 1:1 with) GsdDeviceMapper in
g-s-d. That object would perform these same heuristics, and let
mutter indirectly know through settings changes. This object allows
doing the same in-process.
