Now that ClutterActor implements the Container contract we can actually
defer the size negotiation to a ClutterLayoutManager directly from the
default implementation of the Actor's virtual functions.
We can provide most of the ClutterContainer implementation directly
within ClutterActor — basically removing the need of having the
Container interface in the first place. For backward compatibility
reasons we can keep the interface, but let Actor implement it directly.
Let's try and move away from the reverse implicit scene graph build API,
which we mutuated from GTK+, towards a more traditional node/child API.
The set_parent()/unparent() API is confusing, unless you know the
history; having a add_child()/remove_child() methods pair makes it more
explicit.
We can easily implement the old set_parent()/unparent() pair in terms of
the newly add_child()/remove_child() one.
Enclose the check inside a #ifdef CLUTTER_ENABLE_DEBUG ... #endif, so
that we can compile it out; also, use g_string_append() instead of the
g_string_append_printf() function, given that we're just concatenating
strings.
Currently, we're emitting the ClutterActor::destroy at the end of the
dispose implementation - right before we chain up to the parent
implementation.
The point of emission makes the ::destroy signal handlers able to just
use the actor pointer - as the actor state will have been mostly cleared
by the time application can run. This (undocumented) behaviour severely
limits the amount of things you can do inside a ::destroy signal
handler, thus making the ::destroy signal just a weird weak reference,
instead of a proper way to break application reference cycles.
Given that this change relaxes some of the conditions, this change
should be safe - obviously, if anything happens, we'll back it out; the
conformance and interactive tests confirm that, for common patterns of
usage, this change does not break existing code.
GLib has a nice, atomic object clearing function that allows us to drop
code looking like:
if (priv->object != NULL)
{
g_object_unref (priv->object);
priv->object = NULL;
}
from the ::dispose implementation.
Add a public version of the clipped queue redraw, using a 2D clip. This
allows implementing actors with trackable 2D clipped regions, like the
ClutterX11TexturePixmap, outside of Clutter itself.
https://bugzilla.gnome.org/show_bug.cgi?id=660997
A lot of the example code in the cookbook and the API reference still
uses the default stage — sometimes as if it were a non-default one,
which once again demonstrates how the default stage was a flawed concept
that just confused people.
These methods are short-hands for accessing the position and size,
which are already shorthands for accessing the various dimensional
and positional attributes. Plus, they use ClutterGeometry, which is a
fairly bad data type for a rectangle.
There are a couple of gotchas in the 'mapped' flag that are not properly
documented, or are documented only in the actor_invariants.txt file; we
should have a proper description in the API reference as well, to avoid
confusion.
Out-of-band transforms are considered to be all actor transforms done
directly with the Cogl API instead of via ClutterActor::apply_transform.
By running with CLUTTER_DEBUG=oob-transform then Clutter will explicitly
try to detect when un-expected transforms have been applied to the
modelview matrix stack.
Out-of-band transforms can lead to awkward bugs in Clutter applications
because Clutter itself doesn't know about them and this can disrupt
Clutter's input handling and calculations of actor paint-volumes
which can lead to visual artifacts.
Reviewed-by: Emmanuele Bassi <ebassi@linux.intel.com>
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.
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>
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.
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>
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'.
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
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.
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.
The G_CONST_RETURN define in GLib is, and has always been, a bit fuzzy.
We always used it to conform to the platform, at least for public-facing
API.
At first I assumed it has something to do with brain-damaged compilers
or with weird platforms where const was not really supported; sadly,
it's something much, much worse: it's a define that can be toggled at
compile-time to remove const from the signature of public API. This is a
truly terrifying feature that I assume was added in the past century,
and whose inception clearly had something to do with massive doses of
absynthe and opium — because any other explanation would make the
existence of such a feature even worse than assuming drugs had anything
to do with it.
Anyway, and pleasing the gods, this dubious feature is being
removed/deprecated in GLib; see bug:
https://bugzilla.gnome.org/show_bug.cgi?id=644611
Before deprecation, though, we should just remove its usage from the
whole API. We should especially remove its usage from Cally's internals,
since there it never made sense in the first place.
If an actor or the stage to which it belongs are being destroyed then
there is no point in queueing a redraw that will not be seen anyway.
Bailing out early also avoids the case in which a redraw is queued
during destruction wil cause redraw entries will be added to the Stage,
which will take references on it and cause the Stage never to be
finalized.
http://bugzilla.clutter-project.org/show_bug.cgi?id=2652
With the instantiatable ClutterShaderEffect, the only reason for
ClutterShader to exist is to make the ClutterActor::paint implementation
miserable.
Yes, ClutterShader doesn't use a FBO, so it's "more efficient" on
ClutterTextures. It's also generally wrong unless you know *exactly* how
the actor's pipeline is set up — something we cannot even guarantee
internally unless we start doing lame type checks.
In _clutter_actor_queue_redraw_with_clip, there was the possibility that
the actor will add itself to the stage's redraw queue without keeping track
of the allocated list member.
In clutter_actor_unparent, the redraw queue entry was being invalidated
before the mapped notify signal was being fired, meaning that queueing a
redraw of an unmapped actor in the mapped notification callback could
cause a crash.
http://bugzilla.clutter-project.org/show_bug.cgi?id=2621
_clutter_stage_queue_actor_redraw returns a pointer to the
ClutterStageQueueRedrawEntry struct which it allocates. The actor is
expected to store a pointer to this so that it doesn't need to search
the list of queued redraws next time a queue redraw is called. However
_clutter_actor_queue_redraw_full wasn't storing this pointer which
meant that it thought every queue redraw was the first queue
redraw. That meant that queueing a redraw with a clip or an effect
would override any previous attempts to queue a redraw instead of
trying to combine them.
I think this happened because the old queue_redraw_with_clip also
didn't store the pointer and queue_redraw_full was based on that.
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.
When calling clutter_actor_clear_constraints the layout of the actor
may change so we need to queue a relayout. Similarly when the effects
are cleared we need to queue a redraw.
This adds a priority property to all ClutterActorMetas. The
ClutterMetaGroup keeps the list sorted so that higher priority metas
remain at the beginning of the list. The priority is a signed integer
with the default as zero. An actor meta can therefore be put before
all default metas with a positive number, or after with a negative
number.
There are constants to set an 'internal' priority. The intention is
that applications wouldn't be allowed to use these values so that we
can keep special internal metas to that are before or after all
application metas.
The property isn't a real GObject property because for now it is
completely internal and only used to implement the 'transparency'
property of ClutterActor. ClutterMetaGroup doesn't currently resort
the list if the property changes so if we wanted to make it public we
should either make it construct-only or make the meta group listen for
changes on the property and resort accordingly.
The methods in ClutterActor that get the list of metas now use a new
function that filters out internal metas from the meta
group. Similarly for clearing the metas, the internal metas are left
in.
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.
The id pool used for the actor's id should be a per-stage field. At some
point, we might have a Stage mapped to multiple framebuffers, or each
Stage mapped to a different framebuffer; also, on backend with low
color precision we don't want to exhaust the size of the available ids
with a global pool. Finally, it's yet another thing we can remove from
the global Clutter context.
Having the id pool allocated per-stage, and the pick id assigned on
Actor:mapped will make the whole pick-id more reliable and future proof.
http://bugzilla.clutter-project.org/show_bug.cgi?id=2633https://bugzilla.gnome.org/show_bug.cgi?id=647876
Do not use the generic GType class name: we have a :name property on
ClutterActor that is generally used for debugging purposes — so we
should use it when creating debugging spew in a consistent way.
This extends visualization for CLUTTER_PAINT=redraws so it now also
draws outlines for actors to show how they are being culled. Actors get
a green outline if they are fully inside the clip region, blue if fully
outside and greeny-blue if only partially inside.
This adds an internal _clutter_stage_get_active_framebuffer function
that can be used to get a pointer to the current CoglFramebuffer pointer
that is in use, in association with a given stage.
The "active" infix in the function name is there because we shouldn't
assume that a stage will always correspond to only a single framebuffer
so we aren't getting a pointer to a sole framebuffer, we are getting
a pointer to the framebuffer that is currently in use/being painted.
This API is now used for culling purposes where we need to check if we
are currently painting an actor to a framebuffer that is offscreen, that
doesn't correspond to the stage.
This renames the two internal functions _cogl_get_draw/read_buffer
as cogl_get_draw_framebuffer and _cogl_get_read_framebuffer. The
former is now also exposed as experimental API.
Previously we were applying the culling optimization to any actor
painted without considering that we may be painting to an offscreen
framebuffer where the stage clip isn't applicable.
For now we simply expose a getter for the current draw framebuffer
and we can assume that a return value of NULL corresponds to the
stage.
Note: This will need to be updated as stages start to be backed by real
CoglFramebuffer objects and so we won't get NULL in those cases.
To give quick visibility to the things going on relating to clipping and
culling this adds some more CLIPPING debug notes to clutter-actor.c and
clutter-stage.c
There's an optimisation in clutter-actor.c to avoid calculating the
last known paint volume whenever culling and clipped redraws are both
disabled. However there was a small thinko in the logic so that it
would also avoid calculating the paint volume whenever only one of the
debug flags is enabled. This fixes it to explicitly check that the two
flags are not both enabled before skipping the paint volume
calculation.
Previously each time we needed to retrieve the model transform for a
given actor we would call the apply_transform vfunc which would build up
a transformation matrix based on the actor's current anchor point, its
scale, its allocation and rotation. The apply_transform implementation
would repeatedly call API like cogl_matrix_rotate, cogl_matrix_translate
and cogl_matrix_scale.
All this micro matrix manipulation APIs were starting to show up in the
profiles of dynamic applications so this adds priv->transform matrix
cache which maintains the combined result of the actors scale, rotation
and anchor point etc. Whenever something like the rotation changes then
then the matrix is marked as dirty, but so long as the matrix isn't
dirty then the apply_transform vfunc now just calls cogl_matrix_multiply
with the cached transform matrix.
This implements a variation of frustum culling whereby we convert screen
space clip rectangles into eye space mini-frustums so that we don't have
to repeatedly transform actor paint-volumes all the way into screen
coordinates to perform culling, we just have to apply the modelview
transform and then determine each points distance from the planes that
make up the clip frustum.
By avoiding the projective transform, perspective divide and viewport
scale for each point culled this makes culling much cheaper.
OpenGL < 4.0 only supports integer based viewports and internally we
have a mixture of code using floats and integers for viewports. This
patch switches all viewports throughout clutter and cogl to be
represented using floats considering that in the future we may want to
take advantage of floating point viewports with modern hardware/drivers.
This is needed if an effect wants to temporarily override the paint
opacity. It needs to be able to restore the old opacity override in
the post_paint handler otherwise it would replace the effect of the
opacity override from any outer effects.
http://bugzilla.clutter-project.org/show_bug.cgi?id=2541
The shader stack held by ClutterMainContext should only be accessed
using functions, and not directly.
Since it's a stack, we can use stack-like operations: push, pop and
peek.
Let's try and start reducing the size of ClutterActorPrivate by moving
some optional, out-of-band data from it to GObject data.
The ShaderData structure is a prime candidate for this migration: it
does not need to be inspected by the actor, and its relationship with an
actor is transient and optional.
By attaching it to the actor's instance through g_object_set_data() we
neatly tie its lifetime to the instance, and we don't have to care
cleaning it up in the finalize()/dispose() implementation of
ClutterActor itself.
In _clutter_actor_queue_redraw_with_clip it has a local variable to
mark when a new paint volume for the clip is created so that it can be
freed when the function returns. However the actual code to free the
paint volume went missing in 3b789490d2 so the variable did
nothing. This patch just adds the free back in.
This time, in Clutter core.
The ObjC standard library provides a type called 'id', which obviously
requires any library to either drop the useful shadowed variable warning
or stop using 'id' as a variable name.
Yes, it's almost unbearably stupid. Well, at least it's not 'index' in
string.h, or 'y2' in math.h.
The 'in_clone_paint' parameter of the private function
_clutter_actor_set_in_clone_paint() shadowed the private function
in_clone_paint(). Rename this parameter to 'is_in_clone_paint' to remove
a compiler warning.
Replace the opacity_parent with an opacity_override variable, to allow
direct overriding of the paint opacity and simplify this mechanism
somewhat.
This also required a new private flag, in_clone_paint, to maintain the
functionality of the public function clutter_actor_is_in_clone_paint()
Don't use ugly "#undef CLUTTER_DISABLE_DEPRECATED" inside source code
using deprecated symbols; we have the handy CLUTTER_COMPILATION define
that we can use as part of the "disable deprecated" conditional.
Use the internal child list for the default map/unmap vfuncs. This removes
the requirement for non-container composite actors to implement their own
map/unmap functions.
Unrealizing an actor is a recursive process that needs to traverse the
children of an actor to ensure they are also unrealized. This maintains
the invariant that if any given actor is marked as unrealized then you
know that all its children have also been unrealized.
The previous implementation would use the container interface's
foreach_with_internals vfunc to explicitly traverse the children of
container actors but this didn't consider composite actors that aren't
containers.
Since clutter-actor now maintains an explicit list of children we can
also handle composite actors that aren't containers using
_clutter_actor_traverse.
This makes it possible to choose the traversal order; either depth first
or breadth first and when visiting actors in a depth first order there
is now a callback called before children are traversed and one called
after. Some tasks such as unrealizing actors need to explicitly control
the traversal order to maintain the invariable that all children of an
actor are unrealized before we actually mark the parent as unrealized.
The callbacks are now passed the relative depth in the graph of the
actor being visited and instead of only being able to return a boolean
to bail out of further traversal it can now do one of: continue,
skip_children or break. To implement something like unrealize it's
desirable to skip children that you find have already been unrealized.
The last_paint_box for an actor represents its "normal" position - we
shouldn't update it or use it to cull drawing if we are painting
a clone of the actor. Tracking whether we are painting a clone is
done by adding _clutter_actor_push/pop_clone_paint() and a global
"clone paint level".
http://bugzilla.clutter-project.org/show_bug.cgi?id=2396
When transforming a paint-volume or transforming allocation vertices we
are transforming more than one point at a time so we can batch those
together with cogl_matrix_transform_points instead of
cogl_matrix_transform_point. Also in both of these cases we don't need
to do a projective transform so using cogl_matrix_transform_points also
lets us reduce the per-vertex computation.
The Behaviour class and its implementations have been replaced by the
new animation framework API and by the constraints for layout-related
animations.
Currently, we need to make tests build, so we undef DISABLE_DEPRECATED
in specific test cases while they get ported.
The paint volume structure is cached in the Actor it references, and
this causes a reference cycle.
The paint volume is going to be used when painting, so the actor must
still be valid - otherwise Clutter will bail out far before than
accessing the actor pointer in ClutterPaintVolume.
Otherwise, we could have used dispose() to check for a valid actor and
remove a reference if the actor field is !NULL; it feels less clean,
though, since we're effectively managing an extra reference on
ourselves.
http://bugzilla.clutter-project.org/show_bug.cgi?id=2431
For internal usage, writing:
clutter_actor_get_name (actor) != NULL
? clutter_actor_get_name (actor)
: G_OBJECT_TYPE_NAME (actor)
is overly verbose and does two type checks. A simple, internal method
for getting the same result without type checks would be much more
appreciated.
Instead of waiting until clutter_actor_paint to check if there are any
handlers connected to the "paint" signal, we now do the check whenever
the paint-volume is requested in _actor_get_paint_volume_mutable().
Previously we checked in clutter_actor_paint(), but at that time we may
already be using a stage clip that could be derived from an invalid
paint-volume. We used to try and handle that by queuing a follow up,
unclipped, redraw but anyway there was an additional problem with the
previous approach because the checking wasn't enough to always catch
invalid volumes involved in culling (considering that containers may
derive their volume from children that haven't yet been painted)
By moving the check to _get_paint_volume time not only do we now
correctly check children in cases where a container derives its volume
from its children's volumes but we no longer need to queue follow up
redraws to cover up artefacts.
Since we now never queue follow up redraws, this in turn means we should
no longer clobber redraws queued with an explicit clip which was
something affecting gnome-shell since it connects a handler to the paint
signal of the stage.
http://bugzilla.clutter-project.org/show_bug.cgi?id=2388
Once an actor had _clutter_stage_queue_redraw_entry_invalidate()
called on it once, then priv->queue_redraw_entry would point to
an entry with entry->actor NULL. _clutter_stage_queue_actor_redraw()
doesn't handle this case and no further redraws would be queued.
To fix this, NULL out priv->queue_redraw_entry() and then make sure
we free the invalidated entry in
_clutter_stage_maybe_finish_queue_redraws() just as we do for
still valid entries.
http://bugzilla.clutter-project.org/show_bug.cgi?id=2389
