Create the device manager during the event initialization, where it
makes sense.
This allows us to get rid of the per-backend get_device_manager()
virtual function, and just store the DeviceManager pointer into the
ClutterBackend structure.
All the functionality that ClutterBackendCogl provided has been moved
into ClutterBackend itself, so there is no need to have this class
around in the source.
Cogl-based backends can derive directly from ClutterBackend.
Input backends are, in some cases, independent from the windowing system
backends; we can initialize input handling using a model similar to what
we use for windowing backends, including an environment variable and
compile-/run-time checks.
This model allows us to remove the backend-specific init_events(), and
use a generic implementation directly inside the base ClutterBackend
class, thus further reducing the backend-specific code that every
platform has to implement.
This requires some minor surgery to every single backend, to make sure
that the function exposed to initialize the event loop is similar and
performs roughly the same operations.
The Clutter backend split is opaque enough that should allow us to just
build all possible backends inside the same shared object, and select
the wanted backend at initialization time.
This requires some work in the build system, as well as the
initialization code, to remove duplicate functions that might cause
conflicts at build and link time. We also need to defer all the checks
of the internal state of the platform-specific API to run-time type
checks.
Previously, the Cogl backend was at times a subclass of the X11
backend, and at times a standalone one. Now it is the other way
round, with GDK and X11 backends providing the concrete classes,
layered on top of the generic Cogl backend. A new EglNative backend
was introduced for direct to framebuffer rendering. This greatly
simplifies the API design (at the expense of some casts needed)
and reduces the amount of #ifdefs, without duplicating code.
https://bugzilla.gnome.org/show_bug.cgi?id=657434
