We'll soon introduce a new gesture tracking framework which heavily
depends on ClutterActions seeing all events of a sequence. For this to
work, a larger change to event delivery is needed: Implicit grabbing of
all events for button and touch press->motion->release sequences to
ensure ClutterActions continue receiving events for the whole sequence.
This commit takes care of that: At the start of an event sequence we
collect all the event-handling actors and actions to a GArray that lives
in the PointerDeviceEntry, and then deliver all events belonging to
that sequence to the same actors/actions until the sequence ends.
To avoid events getting pulled from under our feet when mutters event
filter returns CLUTTER_EVENT_STOP, this also introduces private API
(maybe_lost_implicit_grab()) on ClutterStage so that we can't end up
with stale sequences.
Note that this also slightly changes behavior when it comes to event
delivery to actions: Because we now store actions separated from their
actors, any action returning CLUTTER_EVENT_STOP now stops event
propagation immediately. That was different before, where we'd emit
events to all actions of the actor and only then stop propagation.
Note that this isn't handling ClutterGrabs correctly right now,
this will be a little tricky, so we'll take care of that in a future
commit.
To handle actors getting destroyed or unmapped during a grab, listen to
notify::grab on the deepmost actor in the implicit grab tree. This gives
us a notification when any actor inside the tree goes unmapped.
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2342>
bac66fcbc4