The repaint functions list can (and should) be manipulated from
different threads, but it currently doesn't prevent multiple threads
from accessing it concurrently. We should have a simple lock and take it
when adding and removing elements from the list; the invocation is still
performed under the Big Clutter Lock™, so it doesn't require special
handling.
Because we have had several reports about significant performance
regressions since we enabled offscreen redirection by default for
handling correct opacity we are now turning this feature off by default.
We feel that clutter should prioritize performance over correctness in
this case. Correct opacity is still possible if required but the
overhead of the numerous offscreen allocations as well as the cost of
many render target switches per-frame seems too high relative the
improvement in quality for many cases.
On reviewing the offscreen_redirect property so we have a way to
disable redirection by default we realized that it makes more sense for
it to take a set of flags instead of an enum so we can potentially
extend the number of things that might result in offscreen redirection.
We removed the ability to say REDIRECT_ALWAYS_FOR_OPACITY, since it
seems that implies you don't trust the implementation of an actor's
has_overlaps() vfunc which doesn't seem right.
The default value if actor::redirect_offscreen is now 0 which
effectively means don't ever redirect the actor offscreen.
If an actor using a LayoutManager has attributes like margin or padding
then it'll have to shave them from the available allocation before
passing it to the LayoutManager::allocate() implementation. Layout
managers should, thus, not assume that the origin of the allocation is
in (0, 0), but take into account that the passed ActorBox might have a
different origin.
https://bugzilla.gnome.org/show_bug.cgi?id=649631
The actor is in charge of providing to the LayoutManager the available
allocation. ClutterBox should not just pass the box it got from its
parent: it should, instead, provide a normalized box, with an origin in
(0, 0) and the available size.
https://bugzilla.gnome.org/show_bug.cgi?id=649631
This adds experimental API to be able to get the CoglContext associated
with the ClutterBackend. The CoglContext is required to use some of the
experimental 2.0 Cogl API.
Note: Since CoglContext is itself experimental API this API should
considered experimental too. This patch introduces a
CLUTTER_ENABLE_EXPERIMENTAL_API #ifdef guard which anyone wanting to use
this API must define so it's explicitly clear to developers that they
are playing with experimental API.
Note: This API is not yet supported on OSX because OSX still uses the
stub Cogl winsys and the Clutter backend doesn't explicitly create a
CoglContext.
Note: even though this is experimental API we still promise that it
wont be changed during a stable release cycle. This means for example
that you can depend on this for the lifetime of the clutter-1.8 stable
release cycle.
The :fontconfig-timestamp is a write-only property that will get updated
by the underlying platform whenever the fontconfig configuration has
been changed — i.e. when the fontconfig caches should be rebuilt after
the user has installed a new font.
This makes ClutterText implement the Scriptable interface so that we can
have a custom property parser and setter for the font-description
property. This works by simply passing the string description through
to clutter_text_set_font_name.
Reviewed-by: Emmanuele Bassi <ebassi@linux.intel.com>
Actually this change has two notable effects; firstly we no longer
perform culling during picking and secondly we avoid updating the
last-paint-volume of an actor when picking.
We shouldn't perform culling during picking until clutter-stage.c is
updated to setup the clipping planes appropriately.
Since the last-paint-volume is intended to represent the visible region
of the actor the last time it was painted on screen it doesn't make
sense to update this during off screen pick renders since we are liable
to end up with a last-paint-volume that maps to an actors new position
when we next come to paint for real.
This fixes a bug in gnome-shell with dragging dash icons leaving a
messy trail on the screen.
Reviewed-by: Emmanuele Bassi <ebassi@linux.intel.com>
All 2D coordinate spaces in Cogl have their origin at the top-left so we
shouldn't be flipping the coordinates we pass to
cogl_framebuffer_swap_region to be relative to the bottom of the
framebuffer.
This bumps the Cogl version requirement to 1.7.5 since we've had to fix
a bug in the semantics of cogl_framebuffer_swap_region.
Reviewed-by: Neil Roberts <neil@linux.intel.com>
Since commit 38b67e2884 of Cogl the naming scheme for winsys-specific
API has changed to be cogl_win32_onscreen_* instead of
cogl_onscreen_win32_* so it wouldn't build on Windows.
Added isHiding field to _ClutterStageOSX to allow windowDidResignKey
delegate to not order full screen window back whilst the full screen
window was being hidden. This caused other application windows to be
hidden. Also added code to keep hidden stage windows from being listed
in the application's Windows menu.
https://bugzilla.gnome.org/show_bug.cgi?id=655311
Added -windowDidChangeScreen: delegate to handle condition where moving
host window to a different screen would cause pick errors to be output.
The delegate just causes the stage to be redrawn which re-creates the
pick buffer.
https://bugzilla.gnome.org/show_bug.cgi?id=655306
The Animatable interface allows object classes to provide and animate
properties outside of the usual GObject property introspection API.
This change allows ClutterState to defer to the animatable objects the
property introspection and animation, just like ClutterAnimation does.
The animate_property() method of the Animatable interface is far less
than optimal:
• it has a direct reference to ClutterAnimation;
• it has an interval decomposed as two values.
These issues tie the Animatable interface with the Animation object,
even though it's neither necessary nor future-proof.
Let's introduce a new method, interpolate_value(), which does not
reference ClutterAnimation and uses a ClutterInterval to express the
initial and final states.
All ClutterModelIter virtual functions have a default implementation,
and G_TYPE_INSTANCE_GET_CLASS cannot return NULL unless in case of a
catastrophic event in the type system - which will most likely blow up
any application code way before you could call a ModelIter method.
Thus, the idiom:
klass = CLUTTER_MODEL_ITER_GET_CLASS (instance);
if (klass && klass->vfunc)
klass->vfunc (instance);
is utterly useless complication, and it can be perfectly replaced by:
CLUTTER_MODEL_ITER_GET_CLASS (instance)->vfunc (instance);
without any loss of safety.
Currently, only clutter_model_iter_set_valist() is in charge of emitting
the ClutterModel::row-changed signal. Both the set() and the
set_valist() functions can be called with multiple columns, so we
coalesce the signal emission at the end of the set_valist(), to have a
single ::row-changed emission per change.
The clutter_model_iter_set_value() function is just a thin wrapper
around the set_value() virtual function, but since it's called
internally we cannot add the signal emission there as well, as we'd
break the signal coalescing.
For this reason, we need some code refactoring inside the various set()
variants of ClutterModelIter:
- we only use the internal va_arg variant for both the set() and
set_valist() public functions, to avoid multiple type checks;
- the internal set_valist() calls an internal set_value() method
which calls the virtual function from the iterator vtable;
- a new internal emit_row_changed() method is needed to retrieve
the ClutterModel from the iterator, and emit the signal;
Now, all three variants of the value setter will call an internal
ClutterModelIter::set_value() wrapper, and emit the ::row-changed
signal.
To check that the intended behaviour has been implemented, and it's not
going to be broken, the test suite has grown a new unit which populates
a model and changes a random row.
Cally was initially created with Clutter 0.6 in mind. To check
recursively the visibility of a actor a custom method was added.
Since 0.8.4 clutter_actor_get_pain_visibility provides
the same functionality.
Also removed a dummy method. Lets add methods that provide a real
functionality.
Keeping the backing Cairo surface of a CairoTexture canvas in sync with
the actor's allocation is tedious and prone to mistakes. We can
definitely do better by simply exposing a property that does the surface
resize and invalidation automagically on ::allocate.
The current "create context/draw/destroy context" pattern presents
various problems. The first issue is that it defers memory management to
the caller of the create() or create_region() methods, which makes
bookkeeping of the cairo_t* harder for language bindings and third party
libraries. The second issue is that, while it's easier for
draw-and-forget texturs, this API is needlessly complicated for contents
that have to change programmatically - and it introduces constraints
like calling the drawing code explicitly after a surface resize (e.g.
inside an allocate() implementation).
By using a signal-based approach we can make the CairoTexture actor
behave like other actors, and like other libraries using Cairo as their
2D drawing API.
The semantics of the newly-introduced ::draw signal are the same as the
one used by GTK+:
- the signal is emitted on invalidation;
- the cairo_t* context is owned by the actor;
- it is safe to have multiple callbacks attached to the same
signal, to allow composition;
- the cairo_t* is already clipped to the invalidated area, so
that Cairo can discard geometry immediately before we upload
the texture data.
There are possible future improvements, like coalescing multiple
invalidations inside regions, and performing clipped draws during
the paint cycle; we could even perform clipped redraws if we know the
extent of the invalidated area.
ClutterTexture relies too much on GError, even for things that are
clearly programmer errors. Also, no error message passed to GError
is marked for translation as it should.
We should move the programmer errors, like passing the wrong bpp
value with regards to the presence of the alpha channel, to real
warnings; we should also try and harmonize all the error messages,
and not mention Cogl — especially in the ones marked for translation.
This avoids explicitly including gl or egl headers in
clutter-egl-headers.h. We were getting build failures when building
clutter against a libcogl that has runtime support for GL and GLES
because cogl-defines.h was including gl.h and then clutter-egl-headers.h
was later including GLES2/gl.h with typedef conflicts. Clutter relies on
Cogl to abstract GL and GLES and the winsys APIs like EGL and GLX so
Clutter should just rely on cogl.h to include the appropriate egl.h in
clutter-egl-headers.h.
Reviewed-by: Emmanuele Bassi <ebassi@linux.intel.com>
Reviewed-by: Neil Roberts <neil@linux.intel.com>
Setting up the call and calling the GClosure was showing up in profiles
and seemed an easy one to remove.
Instead of calling the closure, let's remember the alpha func and the
user_data when possible (ie set_mode() and set_func()) and use it in
get_alpha().
https://bugzilla.gnome.org/show_bug.cgi?id=654727
The "editable" property is documented to default to TRUE, but is
initialized to FALSE in the _init() function.
Third party code would be affected if we changed the default to be
TRUE, so we have to change the default value in the GParamSpec.
https://bugzilla.gnome.org/show_bug.cgi?id=654726
When emitting a new-frame signal, priv->elapsed_time is passed as a
parameter. This is a gint64. The closure marshal uses an INT. On some
platforms, this is not received correctly by signal handlers (they
receive 0). One solution is to cast priv->elapsed_time to a gint when
emitting the signal.
We cannot change the signature of the signal without breaking ABI.
https://bugzilla.gnome.org/show_bug.cgi?id=654066
If the meta for the animation property is not found, the name of the
property to look for is still from the token, and we need to free the
memory allocated for it.
https://bugzilla.gnome.org/show_bug.cgi?id=654656
Clutter may be used together with GTK+, which indirectly may use
XInput2 too, so the cookie data must persist when both are handling
events.
What happens now in a nutshell is, Clutter is only guaranteed to allocate
the cookie itself after XNextEvent(), and only frees the cookie if its
XGetEventData() call allocated the cookie data.
The X[Get|Free]EventData() calls happen now in clutter-event-x11.c as
hypothetically different event translators could also handle other set
of X Generic Events, or other libraries handling events for that matter.
When picking we need to disable dithering to be sure that the hardware
will not modify the colors we use as actor identifiers. Clutter was
manually calling glEnable/Disable GL_DITHER to handle this, but that was
a layering violation since Cogl is intended to handle all interactions
with OpenGL. Since we are now striving for GL vs GLES to be a runtime
choice we need to remove this last direct usage of GL from Clutter so it
doesn't have to be linked with GL at build time.
Signed-off-by: Neil Roberts <neil@linux.intel.com>
This updates _clutter_paint_volume_get_stage_paint_box to try and
calculate more stable paint-box sizes for fixed sized paint-volumes by
not basing the size on the volume's sub-pixel position.
So the aim is that for a given rectangle defined with floating point
coordinates we want to determine a stable quantized size in pixels that
doesn't vary due to the original box's sub-pixel position.
The reason this is important is because effects will use this API to
determine the size of offscreen framebuffers and so for a fixed-size
object that may be animated across the screen we want to make sure that
the stage paint-box has an equally stable size so that effects aren't
made to continuously re-allocate a corresponding fbo.
The other thing we consider is that the calculation of this box is
subject to floating point precision issues that might be slightly
different to the precision issues involved with actually painting the
actor, which might result in painting slightly leaking outside the
user's calculated paint-volume. This patch now adds padding to consider
this too.
Signed-off-by: Neil Roberts <neil@linux.intel.com>
Signed-off-by: Emmanuele Bassi <ebassi@linux.intel.com>
Instead of relying on C to round the floating point allocation to
integers by flooring the values we now use CLUTTER_NEARBYINT to round
the allocation's position and size to the nearest integers instead. Using
floor leads to rather unstable rounding for the width and height when
there may be tiny fluctuations in the floating point width/height.
Signed-off-by: Neil Roberts <neil@linux.intel.com>
Signed-off-by: Emmanuele Bassi <ebassi@linux.intel.com>
This is a replacement for the nearbyint function which always rounds to
the nearest integer. nearbyint is a C99 function so it might not always
be available but also it seems in glibc it is defined as a function call
so this macro could end up faster anyway. We can't just add 0.5 because
it will break for negative numbers.
Signed-off-by: Neil Roberts <neil@linux.intel.com>
Signed-off-by: Emmanuele Bassi <ebassi@linux.intel.com>
The implementation of _clutter_actor_set_default_paint_volume which
simply uses the actor's allocation to determine a paint-volume was
needlessly using the allocation rounded to integers by internally using
clutter_actor_get_allocation_geometry instead of
clutter_actor_get_allocation_box. This was introducing a lot of
instability into the paint-volume due to the way rounding was done.
The code has now been updated to use clutter_actor_get_allocation_box
so we are dealing with the floating point allocation instead.
Signed-off-by: Neil Roberts <neil@linux.intel.com>
Signed-off-by: Emmanuele Bassi <ebassi@linux.intel.com>
If we're building on/for Windows, set 'win32' as the default flavour; if
we're building on OS X, set 'osx' as the default flavour. For everything
else, use 'glx'.
This adds a public function to get the bounds of the current clipped
redraw on a stage. This should only be called while the stage is being
painted. The function diverts to a virtual function on the
ClutterStageWindow implementation. If the function isn't implemented
or it returns FALSE then the entire stage is reported. The clip bounds
are in integer pixel coordinates in the stage's coordinate space.
http://bugzilla.clutter-project.org/show_bug.cgi?id=2421
Cogl recently renamed symbols with the form
cogl_onscreen_<platform>_blah to be consistent with other platform
specific APIs so they are now named like cogl_<platform>_onscreen_blah.
This makes the corresponding change to clutter.
Cogl changed has changed the name of cogl_context_egl_get_egl_context to
cogl_egl_context_get_egl_context to be consistent with other platform
specific symbols.
The class is of dubious utility, now that we have a complex animation
API in ClutterAnimator and ClutterState, as opposed to a simple one
in ClutterBehaviour. The Score API also suffers from some naïve design
issues that made it far less useful than intended.
Commit 0ede622f51 inadvertently made it so that shaders are applied
during picking. This was making test-shader fail to respond to clicks.
The commit also makes it so that culling is applied during
picking. Presumably this is also unintentional because the commit
message does not mention it. However I think it may make sense to do
culling during picking so it might as well stay that way.
https://bugzilla.gnome.org/show_bug.cgi?id=653959
The cursor's on-screen rectangle is defined in terms of the text
length, the current index, and text_x and text_y, which hold the text
offset in overflowing text fields.
When deleting large amounts of text, text_x is set to 0. In some
edge case branch paths, the cursor rectangle could be calculated
after the current index and text length were updated, but before
the text_x offset could be. This left a negative x position, which
consequently blew up Cogl and the widget.
https://bugzilla.gnome.org/show_bug.cgi?id=651079
It was already the intention that the ClutterGLXTexturePixmap API should
be built and made available on any X11 based platforms since there was
nothing specific about the API and it is useful to have for
compatibility. There was a mistake in the Makefile.am though which meant
only the header was getting installed but the code wasn't being built.
Signed-off-by: Emmanuele Bassi <ebassi@linux.intel.com>
Since the implementation of ClutterGLXTexturePixmap has nothing GLX
specific about it (it is simply layered on top of
ClutterX11TexturePixmap) we don't need to include glx.h. Removing this
include also means that the code can be built for compatibility against
GLES drivers.
Signed-off-by: Emmanuele Bassi <ebassi@linux.intel.com>
This removes the is_axis_aligned assertions for the width/height/depth
getters and setters, since for example it is legitimate to query the
width, height or depth of a container's child actors which aren't
necessarily axis aligned.
Signed-off-by: Emmanuele Bassi <ebassi@linux.intel.com>
cogl_renderer_xlib_set_foreign_display was renamed to
cogl_xlib_renderer_set_foriegn_display so this is the corresponding
change to clutter.
Signed-off-by: Emmanuele Bassi <ebassi@linux.intel.com>
The generic cogl_renderer_handle_native_event API was removed from the
Cogl public API in favour of typesafe functions, so this updates the
win32 backend in line with that change.
Signed-off-by: Emmanuele Bassi <ebassi@linux.intel.com>
It is possible, by calling clutter_set_motion_events_enabled() prior to
the creation of any stage, to control the per-actor motion event
delivery flag on each newly created stage. Since we deprecated the
global accessor functions in favour of the per-Stage ones, we need to
remove the call to clutter_get_motion_events_enabled() inside the
ClutterStage instance initialization, and replace it with an internal
function.
This code will go away when we can finally break API and remove the
deprecated functions.
Complete the quest of commit bc548dc862
by making the ClutterStage methods for controlling the per-actor motion
and crossing event delivery public, and deprecating the global ones.
Although this patch doesn't make them public, it documents the
_clutter_actor_get/apply_relative_transform_matrix functions so they
could easily be made public if desired. I think these API could be
useful to have publicly, and I originally documented them because I
thought they would be needed in the MX toolkit.
Previously ClutterActor was using priv->propagated_one_redraw to
determine whether to pass CLUTTER_EFFECT_PAINT_ACTOR_DIRTY to the
paint method of the effect. This isn't a good idea because the
propagated_one_redraw flag is cleared whenever clutter_actor_paint is
called, even if the actor isn't actually painted because of the zero
opacity shortcut. Instead of this, ClutterActor now has a separate
flag called is_dirty that gets set whenever queue_redraw_full is
called or whenever the queue redraw signal is bubbled up from a child
actor. The flag is only cleared in clutter_actor_paint if the effects
are actually run. Therefore it will stay set even if the opacity is
zero or if the parent actor decides not to paint the child.
Previously there were two places set propagated_one_redraw to FALSE -
once if the opacity is zero and once just before we emit the paint
signal. Now that propagated_one_redraw is only used to determine
whether to pass on the queue redraw signal it seems to make sense to
just clear it in one place right at the start of clutter_actor_paint.
https://bugzilla.gnome.org/show_bug.cgi?id=651784
On reviewing the clutter-actor.c code using
_apply_modelview_transform_recursive I noticed various comments stating
that it will never call the stage's ->apply_transform vfunc to transform
into eye coordinates, but actually looking at the implementation that's
not true. The comments probably got out of sync with an earlier
implementation that had that constraint. This removes the miss-leading
comments and also updates various uses of the api where we were manually
applying the stage->apply_transform.
Instead of using the cogl_vertex_buffer API this uses the more concise
cogl_primitive API instead. The aim is to get rid of the
cogl_vertex_buffer API eventually so we should be trying out the
replacement API wherever possible.
When using CLUTTER_PAINT=paint-volumes to visualize the paint-volumes of
actors we were already disabling clipped-redraws because we are drawing
extra geometry that the actors don't know about but we didn't disable
culling. This was resulting in actors disappearing while using this
debug option.
This makes sure we don't try and draw paint-volumes or culling results
during a pick cycle since that results in us reading back invalid ids
from the pick-buffer.
This adds CLUTTER_PAINT=disable-offscreen-redirect to help diagnose
problems with the correct opacity changes. This just makes it so that
it never installs the flatten effect so it will never automatically
redirect an actor offscreen.
This removes the pv->is_xis_aligned assertion in
_clutter_paint_volume_union. We were already considering the case where
the second volume may not be axis aligned and aligning it into a
temporary variable in that case, but we now also consider that the first
pv may also not be aligned.
The removes the pv->is_complete assertion from
_clutter_paint_volume_axis_align() and instead if the volume isn't
complete it calls _clutter_paint_volume_complete().
When calculating the union of a volume with an empty volume we aim to
simply take the contents of the non-empty volume, but we were not
copying the flags across. We now use
_clutter_paint_volume_set_from_volume which copies all the flags except
the is_static flag.
In _clutter_paint_volume_set_from_volume we were using memcpy to simply
copy everything from one volume to another, but that meant we were
trashing the is_static flag which determines if the destination
paint-volume was slice allocated or not.
This removes the constraint that a paint-volume must be axis aligned
before _clutter_paint_volume_complete can be called. NB: A paint volume
is represented by one origin vertex and then three axis vertices to
define the width, height and depth of the volume. It's straightforward
to use the vectors from the origin to the axis vertices to deduce the
other 4 vertices so we can remove the is_axis_aligned assertion.
Since eef9078f the translation of the camera away from the z=zero
plane was hardcoded at 50 which is approximately half way between the
default z_near and z_far values. This ended up with quite a small
distance in user-space coordinates to the far plane with the default
stage size and this was causing test-texture-quality to clip the actor
early.
This patch makes it try to calculate a reasonable value for the
position of the z=0 plane as well as a value for z_far so we maximize
the space in between the z=0 plane and the near plane and we have a
predictable amount of space behind the stage before hitting the far
clipping plane, while considering the trade off of loosing depth
precision by pushing the far plane too far back relative to the near
plane.
With the default fov of 60° it's not possible to use the stage size to
define the gap in-front of the stage plane; only ~87% of the stage size
is possible as an upper limit. We make 85% of the stage_height available
assuming you have a fov of 60°. We consistently provide 10 times the
stage height of space behind the stage regardless of the fov.
It seems worth noting here that we went around in circles a few times
over how to calculate the gaps since there are a number of trade offs to
consider and they also affect the complexity of the solution. In the end
we went for simplicity but commented the issues well enough hopefully so
we can develop a more elaborate solution if we ever have a use-case.
http://bugzilla.clutter-project.org/show_bug.cgi?id=2625
Since eef9078f ClutterStage updates the aspect ratio of the
perspective matrix whenever the size of the stage changes. This meant
that if an application tries to set its own perspective matrix then
part of it would get overridden. It's not really clear what the
use-case of setting the perspective on the stage should be but it
seems like the safest bet is to always try to preserve the
application's request. The documentation for the function has been
tweaked to discourage its use.
http://bugzilla.clutter-project.org/show_bug.cgi?id=2625
Some parts of the StageWindow interface aren't meaningful for all window
systems. This makes stage_window_set_title/fullscreen/cursor_visible
optional instead of requiring those window systems to implement empty
stubs. Notably the empty stubs we had in the Cogl backend (previously
the EGL backend) used g_warning to report the feature as unsupported and
that was causing conformance test failures.
Since GLX and EGL are abstracted by Cogl the two backends are both
implementing everything using the Cogl API and they are almost
identical.
This updates the egl backend to support everything that the glx backend
supports. Now that EGL and GLX are abstracted by Cogl, the plan is that
we will squash the clutter-egl/glx backends into one. Since the EGL
backend in clutter can conditionally not depend on X11 we will use the
EGL backend as the starting point of our common backend.
https://bugzilla.gnome.org/show_bug.cgi?id=649826
We hadn't updated the egl backend inline with a change to the arguments
that cogl_onscreen_x11_set_foreign_window_xid would expect and that was
causing a compilation error.
* 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
Do not just allow animating states connected to signals: add a "warp"
optional key that ends up calling clutter_state_warp_to_state(). This
is useful for debugging.
Currently, defining states for object signals can only be done by
defining a ClutterState inside the ClutterScript definition. We should
allow creating a (named) ClutterState in code, and associating it to a
ClutterScript instance — and have the Script resolve the "state" field
of a signal definition correctly.
One of the uses of a ClutterState state machine along with ClutterScript
is to provide a quick way to transition from state to state in response
to signal emitted on specific instances.
Connecting a real function, in code, to a specific signal does not
improve the ease of use of ClutterScript to define scenes.
By adding a new signal definition to the current one we can have both a
simple way to define application logic in code and in the UI definition
file.
The new syntax is trivial:
{
"name" : <signal name>,
"state" : <state machine script id>,
"target-state" : <target state>
}
The ClutterState instance is identified by its script id, and the target
state is resolved at run-time, so it can be defined both in
ClutterScript or in code. Ideally, we should find a way to associate a
default ClutterState instance to the ClutterScript one that parses the
definition; this way we would be able to remove the "state" member, or
even "style" the behaviour of an object by replacing the ClutterState
instance.
The implementation uses a signal emission hook, to avoid knowing the
signal signature; we check the emitter of the signal against the object
that defined the signal, to avoid erroneous state changes.
cairo.h is intended to be included as <cairo.h> not <cairo/cairo.h> as
is the style for clutter.h. If you have installed cairo to a custom
prefix then using cairo/cairo.h can result in unintentional use of the
system cairo headers, or if they aren't installed then it will result in
a failure to find the header.
