* swipe-action:
test-swipe-action: Clean up the test code
docs: Add the new actions to the API reference
gesture-action: Remove the multi-device entry points
swipe-action: Remove the required devices call
swipe-action: Clean up
gesture-action: Clean up
Add ClutterSwipeAction and ClutterGestureAction
This adds a virtual to ClutterActor so that an actor subclass can
report whether it has overlapping primitives. ClutterActor uses this
to determine whether it needs to use ClutterFlattenEffect to implement
the opacity property. The default implementation of the virtual
returns TRUE which means that most actors will end up being redirected
offscreen when the opacity != 255. ClutterTexture and ClutterRectangle
override this to return FALSE because they should never need to be
redirected. ClutterClone overrides it to divert to the source.
The values for the ClutterOffscreenRedirect enum have changed to:
AUTOMATIC_FOR_OPACITY
The actor will only be redirected if has_overlaps returns TRUE and
the opacity is < 255
ALWAYS_FOR_OPACITY
The actor will always be redirected if the opacity < 255 regardless
of the return value of has_overlaps
ALWAYS
The actor will always be redirected offscreen.
This means that the property can't be used to prevent the actor from
being redirected but only to increase the likelihood that it will be
redirected.
ClutterActor now adds and removes the flatten effect depending on
whether flattening is needed directly in clutter_actor_paint(). There
are new internal versions of add/remove_effect that don't queue a
redraw. This means that ClutterFlattenEffect is now just a no-op
subclass of ClutterOffscreen. It is only needed because
ClutterOffscreen is abstract. Removing the effect also makes it so
that the cached image will be freed as soon as an actor is repainted
without being flattened.
This adds a property which can be used to redirect the actor through
an FBO before painting so that it becomes flattened in an image. The
image can be used as a cache to avoid having to repaint the actor if
something unrelated in the scene changes. It can also be used to
implement correct opacity even if the actor has overlapping
primitives. The property is an enum that takes three values:
CLUTTER_OFFSCREEN_REDIRECT_NEVER: The default behaviour which is to
never flatten the actor.
CLUTTER_OFFSCREEN_REDIRECT_ALWAYS: The actor is always redirected
through an FBO.
CLUTTER_OFFSCREEN_REDIRECT_ONLY_FOR_OPACITY: The actor is only
redirected through an FBO if the paint opacity is not 255. This
value would be used if the actor wants correct opacity. It will
avoid the overhead of using an FBO whenever the actor is fully
opaque.
The property is implemented by installing a ClutterFlattenEffect.
ClutterFlattenEffect is a new internal class which subclasses
ClutterOffscreen to redirect the painting to an FBO. When
ClutterOffscreen paints, the effect sets an opacity override on the
actor so that the image will always contain the actor at full
opacity. The opacity is then applied to the resulting image before
painting it to the stage. This means the actor does not need to be
redrawn while the opacity is being animated.
The effect has a high internal priority so that it will always occur
before any other effects and it gets hidden from the application.
This adds a new public function to queue a rerun of an effect. If
nothing else queues a redraw then when the effect's actor is painted
the effect will be run without the CLUTTER_EFFECT_RUN_ACTOR_DIRTY
flag. This allows parametrised offscreen effects to report that they
need to redraw the image without having to redraw the underlying
actor. This will be used to implement the 'transparency' effect of
ClutterActor.
If multiple redraws are queued with different effects then redrawing
is started from the one that occurs last in the list of effects.
Internally the function is a wrapper around the new function
_clutter_actor_queue_redraw_full. This is intended to be the sole
point of code for queuing redraws on an actor. It has parameters for
the clip and the effect. The other two existing functions to queue a
redraw (one with a clip and one without) now wrap around this function
by passing a NULL effect.
This adds a new virtual to ClutterEffect which is intended to be a
more flexible replacement for the pre and post_paint functions. The
implementation of a run virtual would look something like this:
void
effect_run (ClutterEffect *effect,
ClutterEffectRunFlags flags)
{
/* Set up state */
/* ... */
/* Chain to the next item in the paint sequence */
clutter_actor_continue_paint (priv->actor);
/* Clean up state */
/* ... */
}
ClutterActor now just calls this virtual instead of the pre_paint and
post_paint functions. It keeps track of the next effect in the list so
that it knows what to do when clutter_actor_continue_paint is
called. clutter_actor_continue_paint is a new function added just for
implementing effects.
The default implementation of the run virtual just calls pre_paint and
post_paint so that existing effects will continue to work.
An effect is allowed to conditionally skip calling
clutter_actor_continue_paint(). This is useful to implement effects
that cache the image of an actor. The flags parameter can be used to
determine if the actor is dirty since the last paint. ClutterActor
sets this flag whenever propagated_one_redraw is TRUE which means that
a redraw for this actor or one of its children was queued.
This backend hasn't been used for years now and so because it is
untested code and almost certainly doesn't work any more it would be a
burdon to continue trying to maintain it. Considering that we are now
looking at moving OpenGL window system integration code down from
Clutter backends into Cogl that will be easier if we don't have to
consider this backend.
The OffscreenEffect class needs to expose a way for sub-classes to
track the size of FBO it creates, in case it has to do some geometry
deformations like the DeformEffect sub-classes.
Let's move the private symbol we used internally in 1.6 to fix
DeformEffect to the list of public symbols of OffscreenEffect.
http://bugzilla.clutter-project.org/show_bug.cgi?id=2570
Creating a synthetic event requires direct access to the ClutterEvent
union members; this access does not map in bindings to high-level
languages, especially run-time bindings using GObject-Introspection.
It's also midly annoying from C, as it unnecessarily exposes the guts of
ClutterEvent - something we might want to fix in the future.
http://bugzilla.clutter-project.org/show_bug.cgi?id=2575
Make sure users get the idea that clutter_init()
has a return value that needs to be checked.
These were fixed via sed magic:
sed -i -s -e "s/clutter_init (.*)/\
if (& != CLUTTER_INIT_SUCCESS)\n return 1/"\
doc/*/*/*.{c,xml} doc/*/*.xml
http://bugzilla.clutter-project.org/show_bug.cgi?id=2574
When synthesizing events coming from input devices it should be
possible to just call a setter function, to avoid a huge switch
on the type of the event.
Clutter should also store the device pointer inside the private
data, for faster access of the pointer in allocated events.
Finally, the get_device_id() and get_device_type() accessors should
just be wrappers around clutter_event_get_device(), to reduce the
amount of code duplication.
Allow the developer to set whether the Stage should receive key focus
when mapped. The implementation is fully backend-dependent. The default
value is TRUE because that's what we've been expecting so far.
http://bugzilla.clutter-project.org/show_bug.cgi?id=2500
Other frameworks expose the same functionality as "auto-reverse",
probably to match the cassette tape player. It actually makes sense
for Clutter to follow suit.
Since EGA colors are apparently all the rage in other toolkits, Clutter
should not be left out. On top of the usual CGA/EGA palette the static
colors also include the Tango Icon palette, which at least is more
pleasant to the eye.
Static colors are accessed through an enumeration by using
clutter_color_get_static(), or using the short-hand pre-processor
macros.
http://bugzilla.clutter-project.org/show_bug.cgi?id=2066
* wip/path-constraint:
docs: Add PathConstraint
tests: Add a PathConstraint interactive test
Add ClutterPathConstraint
actor-box: Add setters for origin and size
This function handles a single windows message. The idea is that it
could be used by clutter-gtk to forward on events from a
GdkEventFilter. The function replaces the old message_translate()
function. That function didn't translate the event anymore anyway and
instead it could generate multiple events so
clutter_win32_handle_event seems like a more appropriate name. The
function returns TRUE or FALSE depending on whether the event was
completely handled instead of setting call_window_proc.
The interpolate() method does what it says on the tin: it interpolates
between two colors using the given factor.
ClutterColor uses it to register a progress function for Intervals.
The internal copy of JSON-GLib was meant to go away right after the 1.0
release, given that JSON-GLib was still young and relatively unknown.
Nowadays, many projects started depending on this little library, and
distributions ship it and keep it up to date.
Keeping a copy of JSON-GLib means keeping it up to date; unfortunately,
this would also imply updating the code not just for the API but for the
internal implementations.
Starting with the 1.2 release, Clutter preferably dependend on the
system copy; with the 1.4 release we stopped falling back automatically.
The 1.6 cycle finally removes the internal copy and requires a copy of
JSON-GLib installed on the target system in order to compile Clutter.
The keysyms defines in clutter-keysyms.h are generated from the X11 key
symbols headers by doing the equivalent of a pass of sed from XK_* to
CLUTTER_*. This might lead to namespace collisions, down the road.
Instead, we should use the CLUTTER_KEY_* namespace.
This commit includes the script, taken from GDK, that parses the X11
key symbols and generates two headers:
- clutter-keysyms.h: the default included header, with CLUTTER_KEY_*
- clutter-keysyms-compat.h: the compatibility header, with CLUTTER_*
The compat.h header file is included if CLUTTER_DISABLE_DEPRECATED is
not defined - essentially deprecating all the old key symbols.
This does not change any ABI and, assuming that an application or
library is not compiling with CLUTTER_DISABLE_DEPRECATED, the source
compatibility is still guaranteed.
When animating an actor through clutter_actor_animate() and friends we
might want forcibly detach the animation instance from the actor in
order to start a new one - for instance, in response to user
interaction.
Currently, there is no way to do that except in a very convoluted way,
by emitting the ::completed signal and adding a special case in the
signal handlers; this is due to the fact that clutter_actor_animate()
adds more logic than the one added by clutter_animation_set_object(),
so calling set_object(NULL) or unreferencing the animation instance
itself won't be enough.
The right way to approach this is to add a new method to Clutter.Actor
that detaches any eventual Animation currently referencing it.
http://bugzilla.clutter-project.org/show_bug.cgi?id=2051
Intel CE3100 and CE4100 have several planes (framebuffers) and a
hardware blender to blend the planes togeteher to produce the final
image.
clutter_cex100_set_plane() lets you configure which framebuffer clutter
will use for its rendering.
*** This is an API change ***
The create_target() virtual function should return a CoglHandle to a
texture; clutter_offscreen_effect_get_target(), instead, returns a
CoglMaterial to be painted in the implementation of the paint_target()
virtual function.
Instead of equating textures with materials, and confusing the user of
the API, we should mark the difference more prominently.
First of all, we should return a CoglMaterial* (now that we have that
as a public type) in get_target(); having handles all over the place
does not make it easier to distinguish the semantics of the virtual
functions.
Then we should rename create_target() to create_texture(), to make it
clear that what should be returned is a texture that is used as the
backing for the offscreen framebuffer.
It can be useful to be able to forcibly break the grab set up by the
ClickAction. The newly added release() method provides a mechanism to
release the grab and unset the :held state of the ClickAction.
This removes all references to SDL in the build instructions as the
backend is no longer available. The OpenGL version required is only
1.2 not 1.4. The Windows build instructions were out of date and have
been replaced with a link to the wiki instead.
A TableLayout is a layout manager that allocates its children in rows
and columns. Each child is assigned to a cell (or more if a cell span
is set).
The supported child properties are:
• x-expand and y-expand: if this cell with try to allocate the
available extra space for the table.
• x-fill and y-fill: if the child will get all the space available in
the cell.
• x-align and y-align: if the child does not fill the cell, then
where the child will be aligned inside the cell.
• row-span and col-span: number of cells the child will allocate for
itself.
Also, the TableLayout has row-spacing and col-spacing for specifying
the space in pixels between rows and between columns.
We also include a simple test of the layout manager, and the
documentation updates.
The TableLayout was implemented starting from MxTable and
ClutterBoxLayout.
http://bugzilla.clutter-project.org/show_bug.cgi?id=2038
Signed-off-by: Emmanuele Bassi <ebassi@linux.intel.com>
Layout managers are using the same code to allocate a child while taking
into consideration:
• horizontal and vertical alignment
• horizontal and vertical fill
• the preferred minimum and natural size, depending
on the :request-mode property
• the text direction for the horizontal alignment
• an offset given by the fixed position properties
Given the amount of code involved, and the amount of details that can go
horribly wrong while copy and pasting such code in various classes - let
alone various projects - Clutter should provide an allocate() variant
that does the right thing in the right way. This way, we have a single
point of failure.
Some apps or some use cases don't need to clear the stage on immediate
rendering GPUs. A media player playing a fullscreen video or a
tile-based game, for instance.
These apps are redrawing the whole screen, so we can avoid clearing the
color buffer when preparing to paint the stage, since there is no
blending with the stage color being performed.
We can add an private set of hints to ClutterStage, and expose accessors
for each potential hint; the first hint is the 'no-clear' one.
http://bugzilla.clutter-project.org/show_bug.cgi?id=2058
* cally-merge:
cally: Add introspection generation
cally: Improving cally doc
cally: Cleaning CallyText
cally: Refactoring "window:create" and "window:destroy" emission code
cally: Use proper backend information on CallyActor
cally: Check HAVE_CONFIG_H on cally-util.c
docs: Fix Cally documentation
cally: Clean up the headers
Add binaries of the Cally examples to the ignore file
docs: Add Cally API reference
Avoid to load cally module on a11y examples
Add accessibility tests
Initialize accessibility support on clutter_init
Rename some methods and includes to avoid -Wshadow warnings
Cally initialization code
Add Cally
This adds a separate variable name "CLUTTER_SONAME_INFIX" to define the
infix for the clutter library that gets linked. Currently the WINSYS
corresponds to the directory we enter when building to compile the
window system and input support, but it is desirable to be able to
define multiple flavours that use the same WINSYS but should result in
different library names.
For example we are planning to combine the eglx and eglnative window
systems into one "egl" winsys but we will need to preserve the current
library names for the eglx and eglnative flavours.
* wip/deform-effect:
docs: Add DeformEffect and PageTurnEffect to the API reference
effect: Add PageTurnEffect
effect: Add DeformEffect
offscreen-effect: Traslate the modelview with the offsets
docs: Fix Effect subclassing section
It is often useful to determine if one actor is an ancestor of
another. Add a method to do that.
http://bugzilla.openedhand.com/show_bug.cgi?id=2162
Signed-off-by: Emmanuele Bassi <ebassi@linux.intel.com>
By default, ShaderEffect creates a fragment shader; in order to be able
to deprecate ClutterShader we need a way for ShaderEffect sub-classes to
create a vertex shader if needed - By using a write-only, constructor
only property.
ClutterShader has, internally, a ClutterShaderType enumeration that can
be used exactly for this. We just need to expose it and create a GObject
property for ClutterShaderEffect.
Various headers are build in builddirs (clutter-marshal.h, mkenums
headers and cogl-define.h) so we need to add the corresponding include
paths for gtk-doc to build its scanner.
ClutterInterval.compute_value() computes the new value given a progress
and copies it to a given GValue. Since most of the time we want to pass
that very same value to another function that copies it again, we should
have a compute_value() variant that stores that computed value inside
ClutterInterval and returns a pointer to it. This way we initialize the
result GValue just once and we never copy it, as long as the Interval
instance is valid.
The ClutterActor API should have modifier methods for adding, removing
and retrieving Actions and Constraints using the ClutterActorMeta:name
property - mostly, for convenience.
Add clutter_actor_has_allocation(), a method meant to be used when
deciding whether to call clutter_actor_get_allocation_box() or any
of its wrappers.
The get_allocation_box() method will, in case the allocation is invalid,
perform a costly re-allocation cycle to ensure that the returned box
is valid. The has_allocation() method is meant to be used if we have an
actor calling get_allocation_box() from outside the place where the
allocation is always guaranteed to be valid.
Signed-off-by: Emmanuele Bassi <ebassi@linux.intel.com>
We should explain what a "key frame" is for ClutterAnimator, possibly
with some sort of visual cue.
This allows me to demonstrate my poor skills at using Inkscape, as well
as my overall bad taste for graphics design.
It is conceivable that Container implementations might add children
outside of the Container::add() implementation - e.g. for packing at
a specific index. Since the addition (and removal) might happen outside
the common path we need to expose all the API that is implicitly called
by ClutterContainer when adding and removing a child - namely the
ChildMeta creation and destruction.
Embedding toolkits most likely will disable the event handling, so all
the input device code will not be executed. Unfortunately, the newly
added synthetic event generation of ENTER and LEAVE event pairs depends
on having input devices.
In order to unbreak things without reintroducing the madness of the
previous code we should allow embedding toolkits to just update the
state of an InputDevice by using the data contained inside the
ClutterEvent. This strategy has two obvious reasons:
• the embedding toolkit is creating a ClutterEvent by translating
a toolkit-native event anyway
• this is exactly what ClutterStage does when processing events
We are, essentially, deferring input device handling to the embedding
toolkits, just like we're deferring event handling to them.
* origin/cwiiis-stage-resize:
[stage-x11] Set the default size differently
[stage] Set default size correctly
Revert "[x11] Don't set actor size on ConfigureNotify"
[x11] Don't set actor size on ConfigureNotify
[stage] Now that get_geometry works, use it
[stage-x11] make get_geometry always get geometry
[stage] Get the current size correctly
[stage] Set minimum width/height to 1x1
[stage] Add set/get_minumum_size
ClutterAnimator is a class for managing the animation of multiple
properties of multiple actors over time with keyframing of values.
The Animator class is meant to be used to effectively describe
animations using the ClutterScript definition format, and to construct
complex implicit animations from the ground up.
Signed-off-by: Emmanuele Bassi <ebassi@linux.intel.com>
High level toolkits might wish to construct a PangoFontDescription and
then set it directly on a ClutterText actor proxy or sub-class.
ClutterText should have a :font-description property to set (and get)
the PangoFontDescription.
http://bugzilla.openedhand.com/show_bug.cgi?id=1960
* device-manager: (37 commits)
x11: Re-enable XI1 extension keyboards
x11: Always handle core device events before XI events
docs: Documentation fixes for DeviceManager
device-manager: Fix the signals definition
docs: Add sections for InputDevice and DeviceManager
docs: Add clutter_input_device_get_device_name()
tests: Print out the device details on motion
Always register core devices
device: Remove unused is_default member
win32: Experimental implementation of device support
tests: Print the device name, as well as its Id
x11: Fill out the :name property of the InputDevices
device: Add the :name property to InputDevice
x11: Store core devices on the X11 Backend singleton
device: Unset the cursor actor when leaving the stage
device: Add pointer actor getter
x11: Discard the LeaveNotify for off-stage ButtonRelease
device: Do not overwrite the stage for an InputDevice
event: Off-stage button releases have a click count of 1
event: Scroll events do not have click count
...
In the example for clutter_actor_animate the "x" and "y" properties
are floats so they need to be passed float values in the var args
otherwise it will crash. There was also a missing comma.
There were some other minor problems with the behaviours example which
would cause it not to compile.
Allow the user of the ClutterMedia interface to specify a Pango font
description to display subtitles. Even if the underlying implementation
of the interface does not natively use Pange, it must be capable of
parsing the grammar that pango_font_description_from_string() accepts.
Since asking for ARGB by default is still somewhat experimental on X11
and not every toolkit or complex widgets (like WebKit) still do not like
dealing with ARGB visuals, we should switch back to RGB by default - now
that at least we know it works.
For applications (and toolkit integration libraries) that want to enable
the ClutterStage:use-alpha property there is a new function:
void clutter_x11_set_use_argb_visual (gboolean use_argb);
which needs to be called before clutter_init().
The CLUTTER_DISABLE_ARGB_VISUAL environment variable can still be used
to force this value off at run-time.
At first, those symbols were called {get,set}_subtitles_uri() but were
renamed to {get,set}_subtitle_uri() without updating the
clutter-section.txt file.
This fix makes gtk-doc document those symbols again.
Allow the user of the ClutterMedia interface to specify an external (as
in not multiplexed with the audio/video streams) location of a subtitle
stream.
* animate-layout-manager:
layout-manager: Document the animation support
layout-manager: Rewind the timeline in begin_animation()
box-layout: Remove the allocations hash table
docs: Clean up the README file
layout: Let begin_animation() return the Alpha
box-layout: Add knobs for controlling animations
box-layout: Animate layout properties
layout: Add animation support to LayoutManager
Add ActorBox animation methods
* stage-use-alpha:
tests: Use accessor methods for :use-alpha
stage: Add accessors for :use-alpha
tests: Allow setting the stage opacity in test-paint-wrapper
stage: Premultiply the stage color
stage: Composite the opacity with the alpha channel
glx: Always request an ARGB visual
stage: Add :use-alpha property
materials: Get the right blend function for alpha
ClutterActor checks, when destroying and reparenting, if the parent
actor implements the Container interface, and automatically calls the
remove() method to perform a clean removal.
Actors implementing Container, though, might have internal children;
that is, children that are not added through the Container API. It is
already possible to iterate through them using the Container API to
avoid breaking invariants - but calling clutter_actor_destroy() on
these children (even from the Container implementation, and thus outside
of Clutter's control) will either lead to leaks or to segmentation
faults.
Clutter needs a way to distinguish a clutter_actor_set_parent() done on
an internal child from one done on a "public" child; for this reason, a
push/pop pair of functions should be available to Actor implementations
to mark the section where they wish to add internal children:
➔ clutter_actor_push_internal ();
...
clutter_actor_set_parent (child1, parent);
clutter_actor_set_parent (child2, parent);
...
➔ clutter_actor_pop_internal ();
The set_parent() call will automatically set the newly added
INTERNAL_CHILD private flag on each child, and both
clutter_actor_destroy() and clutter_actor_unparent() will check for the
flag before deciding whether to call the Container's remove method.
ClutterLayoutManager does not have any state associated with it, and
defers all the state to its sub-classes.
The BoxLayout is thus in charge of controlling:
• whether or not animations should be used
• the duration of the animation
• the easing mode of the animation
By adding three new properties:
• ClutterBoxLayout:use-animations
• ClutterBoxLayout:easing-duration
• ClutterBoxLayout:easing-mode
And their relative accessors pairs we can make BoxLayout decide whether
or not, and with which parameters, call the begin_animation() method of
ClutterLayoutManager.
The test-box-layout has been modified to reflect this new functionality,
by checking the key-press event for the 'a' key symbol to toggle the use
of animations.
In order to animate a fluid layout we cannot use the common animation
code paths as they will override the size request and allocation paths
that are handled by the layout manager itself.
One way to introduce animations in the allocation sequence is to use a
Timeline and an Alpha to compute a progress value and then use that
value to interpolate an ActorBox between the initial and final states of
the animation - with the initial state being the last allocation of the
child prior to the animation start, and the final state the allocation
of the child at the end; for every frame of the Timeline we then queue a
relayout on the layout manager's container, which will result in an
animation.
ClutterLayoutManager is the most likely place to add a generic API for
beginning and ending an animation, as well as the place to provide a
default code path to create the ancillary Timeline and Alpha instances
needed to drive the animation.
A LayoutManager sub-class will need to:
• call clutter_layout_manager_begin_animation() whenever it should
animate between two states, for instance: whenever a layout property
changes value;
• eventually override begin_animation() and end_animation() in case
further state needs to be set up, and then chain up to the default
implementation provided by LayoutManager;
• if a completely different implementation is required, the layout
manager sub-class should override begin_animation(), end_animation()
and get_animation_progress().
Inside the allocate() implementation the sub-class should also
interpolate between the last known allocation of a child and the newly
computed allocation.
ClutterActorBox should have an interpolate() method that allows to
compute the intermediate values between two states, given a progress
value, e.g.:
clutter_actor_box_interpolate (start, end, alpha, &result);
Another utility method, useful for layout managers, is a modifier
that clamps the members of the actor box to the nearest integer
value.
When getting signals from higher level toolkits, occasionally
one wants access to the underlying event; say for a Button
widget's "clicked" signal, to get the keyboard state.
Rather than having all of the highlevel widgets emit
ClutterEvent just for the more unusual use cases,
add a global function to access the event state.
http://bugzilla.openedhand.com/show_bug.cgi?id=1888
Signed-off-by: Emmanuele Bassi <ebassi@linux.intel.com>
* text-direction:
docs: Add text-direction accessors
Set the default language on the Pango context
actor: Set text direction on parenting
tests: Display the index inside text-box-layout
box-layout: Honour :text-direction
text: Dirty layout cache on text direction changes
actor: Add :text-direction property
Use the newly added ClutterTextDirection enumeration
Add ClutterTextDirection enumeration
The ClutterLayoutMeta instances should be created on demand, whenever
the layout manager needs them - if the layout manager supports layout
properties.
This removes the requirement to call add_child_meta() and
remove_child_meta() on add and remove respectively; it also simplifies
the implementation of LayoutManager sub-classes since we can add
fallback code in the base abstract class.
Eventually, this will also lead to an easier to implement ClutterScript
parser for layout properties.
With the new scheme, the ClutterLayoutMeta instance is created whenever
the layout manager tries to access it; if there isn't an instance
already attached to the container's child, one is created -- assuming
that the LayoutManager sub-class has overridden the
get_child_meta_type() virtual function and it's returning a valid GType.
We can also provide a default implementation for create_child_meta(),
by getting the GType and instantiating a ClutterLayoutMeta with all the
fields already set. If the layout manager requires more work then it can
obviously override the default implementation (and even chain up to it).
The ClutterBox actor has been updated, as well as the ClutterBoxLayout
layout manager, to take advantage of the changes of LayoutManager.
