mirror of
https://github.com/brl/mutter.git
synced 2024-09-20 14:35:48 -04:00
167 lines
6.1 KiB
Plaintext
167 lines
6.1 KiB
Plaintext
IMPLEMENTING BACKENDS
|
|
=====================
|
|
|
|
Clutter supports multiple backends for handling windowing systems and
|
|
GL/GLES API on different platforms.
|
|
|
|
The GL and GLES API are abstracted by the COGL library. The windowing
|
|
system is handled by the ClutterBackend implementations inside Clutter
|
|
itself.
|
|
|
|
Clutter, at the moment, supports only in-tree backends.
|
|
|
|
In order to write a new backend for a specific platform you should
|
|
create a new sub-directory under clutter/clutter containing:
|
|
|
|
<backend>/clutter-backend-<backend>.h
|
|
<backend>/clutter-backend-<backend>.c
|
|
|
|
-- The subclass of the ClutterBackend abstract class.
|
|
|
|
<backend>/clutter-stage-<backend>.h
|
|
<backend>/clutter-stage-<backend>.c
|
|
|
|
-- The implementation of the stage actor.
|
|
|
|
<backend>/clutter-event-<backend>.c
|
|
|
|
-- The event handling code (optional).
|
|
|
|
<backend>/clutter-<backend>.h
|
|
|
|
-- A header for the backend-specific API that should be installed
|
|
by Clutter inside the include directory along with the rest of
|
|
the public API headers (optional).
|
|
|
|
|
|
Implementing ClutterBackend
|
|
---------------------------
|
|
|
|
Each backend must implement the
|
|
|
|
GType
|
|
_clutter_backend_impl_get_type (void);
|
|
|
|
function declared inside clutter/clutter-private.h. The implementation
|
|
of the function must return the same GType of the backend implementation,
|
|
for instance:
|
|
|
|
GType
|
|
_clutter_backend_impl_get_type (void)
|
|
{
|
|
return CLUTTER_TYPE_BACKEND_GLX;
|
|
}
|
|
|
|
The ClutterBackend implementation is a singleton instance, and the
|
|
backend must ensure that every time g_object_new() is called the same
|
|
pointer is returned (with its reference count increased). The GObject
|
|
API reference describes how to use the ::constructor virtual function
|
|
to implement a singleton, so you should refer to that.
|
|
|
|
When implementing the ClutterBackend subclass these virtual functions
|
|
can be overridden:
|
|
|
|
ClutterBackend::add_options
|
|
-- Use this function to install new, backend-specific GOptionEntry
|
|
definitions to the Clutter GOptionGroup. This function is guaranteed
|
|
to be called just once.
|
|
|
|
ClutterBackend::pre_parse
|
|
-- Use this function to check for environment variables or setting
|
|
up default values before the command line arguments are parsed.
|
|
This function is guaranteed to be called just once.
|
|
|
|
ClutterBackend::post_parse
|
|
-- Use this function to prepare the backend with the values either
|
|
set inside the ::pre_parse virtual function or by the command
|
|
line options parsing code. This function is guaranteed to be
|
|
called just once.
|
|
|
|
ClutterBackend::init_events
|
|
-- Use this function to initialize the event handling. This function
|
|
is guaranteed to be called just once.
|
|
|
|
ClutterBackend::get_features
|
|
-- Use this function to retrieve the features detectable at runtime
|
|
from the GL or GLES implementation, plus the eventual backend-specific
|
|
features.
|
|
|
|
ClutterBackend::ensure_context
|
|
-- This function is used to ensure that the backend drawing context
|
|
is made current for passed ClutterStage, using the backend-specific
|
|
API.
|
|
|
|
ClutterBackend::redraw
|
|
-- This function is used to draw the passed ClutterStage; the backend
|
|
must call clutter_actor_paint() on the ClutterStage that has been
|
|
passed as a parameter and then perform backend-specific tasks, like
|
|
waiting for vertical blanking and swapping the buffers.
|
|
|
|
ClutterBackend::create_stage
|
|
-- This function is used to create the stage implementation. It will
|
|
receive as an argument the ClutterStage instance that is "wrapping"
|
|
the actual implementation being created. The backend must create
|
|
its stage implementation and call _clutter_stage_set_window() with
|
|
the wrapper and the stage implementation instance:
|
|
|
|
_clutter_stage_set_window (wrapper, CLUTTER_STAGE_WINDOW (impl));
|
|
|
|
The backend must also call clutter_actor_realize() on the stage
|
|
implementation, and then check if the stage has been realized, using
|
|
the CLUTTER_ACTOR_IS_REALIZED() macro; if the stage was not
|
|
realized, it must return NULL and set the passed GError.
|
|
|
|
Implementing the stage
|
|
----------------------
|
|
|
|
ClutterStage acts as a wrapper object relaying all the drawing operations
|
|
to the actual implementation. The implementation of the stage can be any
|
|
ClutterActor subclass, as long as it does not subclass ClutterStage and
|
|
it implements the ClutterStageWindow interface.
|
|
|
|
The ClutterStageWindow interface contains a set of virtual functions that
|
|
should be overridden by backends that support a windowing system, like
|
|
::set_title(), ::set_fullscreen(), ::set_cursor_visible(), etc.
|
|
|
|
The stage implementation actor must implement at least the ::realize and
|
|
::unrealize ClutterActor virtual functions. Inside the ::realize function
|
|
the stage implementation should:
|
|
|
|
- create a new native window handle
|
|
- create the drawing context (either GL or GLES) and assign it
|
|
to the backend, if it's not already present
|
|
- set the CLUTTER_ACTOR_REALIZED flag on *both* the wrapper and the
|
|
stage implementation
|
|
- call clutter_stage_ensure_current() with the wrapper instance
|
|
- set the private CLUTTER_ACTOR_SYNC_MATRICES flag on the stage wrapper
|
|
|
|
In case of failure, the CLUTTER_ACTOR_REALIZED flag should be unset on
|
|
both the wrapper and the stage implementation.
|
|
|
|
Inside the ::unrealize function the stage implementation should:
|
|
|
|
- unset the CLUTTER_ACTOR_REALIZED flag
|
|
- call _clutter_shader_release_all() if the backend supports shaders
|
|
and the GL programmable pipeline
|
|
- destroy the native window handle
|
|
- call clutter_stage_ensure_context() with the wrapper instance
|
|
|
|
|
|
NOTES
|
|
=====
|
|
|
|
If the platform is using X11 you should probably subclass ClutterBackendX11
|
|
and ClutterStageX11, which will provide you with a ready to use code
|
|
implementation for event handling and window management.
|
|
|
|
Usual points of failure for backends are:
|
|
|
|
- not setting the CLUTTER_ACTOR_REALIZED flag on the stage implementation
|
|
and the stage wrapper inside the ::realized virtual function;
|
|
- not setting the CLUTTER_ACTOR_SYNC_MATRICES on the stage wrapper
|
|
at the end of the ::realized virtual function;
|
|
- calling public API, like clutter_actor_paint(), or checking properties
|
|
on the stage implementation instead of the ClutterStage wrapper.
|
|
|
|
$LastChangedDate$
|