Add the mechanism to integrate MetaWaylandEventInterface with grabs,
callers may now specify whether a grab is required, in which case
one is created, shared by all the event interface stack.
ClutterStage grab state is also tracked, so the MetaWaylandEventInterface
in charge will focus or unfocus depending on whether input should be
handled (if ungrabbed, or grabbed by the MetaWaylandInput itself), or
not (if grabbed by something else).
At the moment nothing uses this mechanism yet, later commits will add
the first users.
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/3420>
MetaWaylandInput is an object that will become in charge of handling
input events on their way to the Wayland socket. It keeps a stack
of event handlers, and propagates events and changes across them in
order to have them emit Wayland events, or change focus.
Each of these event handlers has a MetaWaylandEventInterface, this
is a vtable meant to replace MetaWaylandPointerGrabInterface and
MetaWaylandKeyboardGrabInterface in an unified manner, with the
following methods:
- get_focus_surface: to return the focus surface for a device/sequence.
Since several handlers will want to delegate logic on previous
handlers, it is optional to chain up with
meta_wayland_event_handler_chain_up_get_focus_surface().
- focus: To trigger a focus change for a device/sequence, since
event handlers are daisy chained by default, it is mandatory to
chain up with meta_wayland_event_handler_chain_up_focus(), either
with the given surface, or passing NULL to let later handlers
unset their state.
- press/motion/release: Unified handlers for pointer/touch/stylus
input, they chain up like event handlers do.
- key: Key event handler, propagates like event handlers do.
- other: Fallthrough for other events (pad, scroll, ...), propagates
like event handlers do.
Since there is a variety of expected behaviors, and the possibility
of stacking for some of the existing Wayland "grabs", this provides
the mechanism for that to happen.
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/3420>
