The pivot point is a point in normalized coordinates space around which
all transformations revolve.
It supercedes the anchor point and the per-transformation center points
as well as the gravity settings, and tries to sort out the mess that
is the modelview matrix set up in ClutterActor.
https://bugzilla.gnome.org/show_bug.cgi?id=677853
The ClutterActor:depth property has always been a bit of a misnomer:
actors are 2D flat surfaces, so they cannot have "depth"; the property
defines the position on the Z axis.
Another side effect of the :depth property is that it decides the
default paint and allocation order on insertion, and that setting it
will call the ClutterContainer.sort_depth_order() method. This has
proven to be a fairly bad design decision that we strung along from the
0.x days, as it gives a false impression of being able to change the
paint and allocation order simply by changing the position on the Z
axis — something that, in reality, requires depth testing to be enabled
during the paint sequence of an actor's parent.
For 2.0 we need a clean break from the side effects, and a better
defined interface.
ClutterActor:z-position is essentially what ClutterActor:depth is, but
doesn't call into ClutterContainer, and has a more apt name.
https://bugzilla.gnome.org/show_bug.cgi?id=679465
It can be useful to check whether a ClutterActorIter is currently valid,
i.e. if the iterator has been initialized *and* if the actor to which it
refers to hasn't been updated.
We can also use the is_valid() method in the conformance test suite to
check that initialization has been successful, and that changing the
children list through the ClutterActorIter API leaves the iterator in a
valid state.
The implicit animations only apply to properties that are documented as
'animatable'; the explicit animations apply to any property defined
through GObject or ClutterAnimatable.
For 1.x, we still have a duration of 0 msecs, but we have a valid easing
state, so we can change the easing parameters without calling save and
restore.
ClutterContent implementations may allow repeating their contents when
painting; we should provide the repeat policy on the actor, like we do
for scaling filters and content gravity.
Fixed positions are defined to be initialized at 0,0 whenever
enabled, by setting fixed_position_enabled to true, or by setting
just one of x/y. This normally happens in the defaults, but we need
to make sure it also happens if a fixed position was once set but
then disabled. We do this by always resetting it back to 0,0 when
fixed_position_set is unset.
Only for debug builds, the debug name should include a) actor name, b)
type name, and c) pointer address.
For non-debug builds we can live with the actor/type name.
The ::stopped signal is emitted when the timeline has been completely
exhausted or when the timeline has been programmatically stopped by
using clutter_timeline_stop(); the notification at the end of the
timeline run allows to write handlers without having to check whether
the current repeat is the last one, like we are forced to do when using
the ::completed signal.
Based on the patch by: Jasper St. Pierre <jstpierre@mecheye.net>
https://bugzilla.gnome.org/show_bug.cgi?id=676854
Ensure that resizing transitions smoothly when switching between major
axis; the allocation aspect ratio is not important: it's the size of the
allocation that dictates the major axis.
The property uses an array with the following CSS style syntax
[ top, right, bottom, left ] or
[ top, left/right, bottom ] or
[ top/bottom, left/right ] or
[ top/right/bottom/left ]
https://bugzilla.gnome.org/show_bug.cgi?id=676367
When asking for the preferred width and height of an actor, in case
only one of either the minimum or the natural width is set, the margin
offsets should also be applied.
The example code that is meant to be XIncluded into the API reference
should not be part of the interactive test suite: it's code that it is
meant to be used as a reference implementation - whereas the interactive
test suite should be allowed to be lean and test behaviour even in nasty
ways. In short: the test suite should not be the place where we show off
idiomatic code for educational purposes.
The introspection scanner has become slightly more annoying, in the hope
that people start fixing their annotations. As it turns out, it was the
right move.
Calling clutter_actor_allocate() should transition between the current
allocation and the new allocation, by using the defined implementation
of the easing state.
This means that:
clutter_actor_save_easing_state (actor);
clutter_actor_allocate (actor, &new_alloc, flags);
clutter_actor_restore_easing_state (actor);
will cause "actor" to transition between the current allocation and the
desired new allocation.
The trick is to ensure that this happens without invalidating the
entire actor tree, but only the portion of the tree that has the
transitioned actor as the local root. For this reason, we just call the
allocate() implementation from within the transition frame advancement,
without invalidating flags: the actor, after all, *has* a valid
allocation for the duration of the transition.
The :x-expand and :y-expand flags on ClutterActor are used to signal
that an actor should expand horizontally and/or vertically - i.e. that
its parent's layout management policy should try to assign extra space
to the actor when allocating it.
The expand flags are automatic: when set on a leaf node in the actor
tree, they will bubble up through the parent and grandparents up to the
top level actor; during allocation, the actors with children will lazily
compute whether their children needs to expand.
Using a compound type property for position and size has various
advantages: it reduces the amount of checks; it reduces the amount
of notify signals to connect to; it reduces the amount of transitions
generated.
This commit adds a further conditional check for calling
clutter_actor_show() when adding a child to an actor. We cannot
unconditionally change the value of the show-on-set-parent property like
the original solution of commit 81b19a78f5
as that breaks the document invariant that show-on-set-parent will be
changed iff an actor is without a parent.
The new ADD_CHILD_SHOW_ON_SET_PARENT flag is part of the default and
legacy flags, thus retaining the default behaviour when adding a child;
the flag is not passed when reordering the list of children, which means
we ignore the state of the show-on-set-parent property.
The conformance test suite fully passes, including the newly added test
to verify that changing the paint order does not trigger visibility.
https://bugzilla.gnome.org/show_bug.cgi?id=674510
This reverts commit 81b19a78f5.
The commit breaks the conformance test unit for the invariants we
guarantee for the 1.x API:
ERROR:actor-invariants.c:307:actor_show_on_set_parent: assertion failed: (show_on_set_parent)
It's been a year and change, and two stable releases, since we
introduced the paint volume mechanism to allow actors to paint outside
their allocation safely in environments that support clipped redraws.
The time has come to flip the switch, and return a valid paint volume,
matching the actor's allocation, by default - at least for Actor
instances from classes that do not override paint() and
get_paint_volume().
If an actor has a paint signal handler then it's the user responsability
not to paint outside the allocation - and to suffer the consequences of
doing so; in an ideal world, paint() would not be a signal in the first
place anyway. Plus, the idea that painting can happen at any time and
still have a valid surface greatly conflicts with the design goal of
making Clutter's rendering operations fully retained into a render tree.
We can still revert this commit before spinning 1.12, if need be.
When removing the last Action, Constraint, or Effect, we should also be
clearing the corresponding MetaGroup: code inside ClutterActor relies on
NULL checks, and changing them all to check for NULL && n_items == 0
would not be fun.
We need to remove the transition only if the current repeat is equal to
the number of repeats, and if the transition was marked as remove on
complete. Otherwise, the transition has to remain where it is.
The opacity internal setter will do it for us, and it will take into
consideration any eventual flatten effect applied to the actor.
This unbreaks the actor-offscreen-redirect conformance test.
We were using g_list_foreach() prior to the first Apocalypse, and that
function is resilient against changes to the list while iterating it;
since we are not using a GList any more, we need handle this case
ourselves.
When the easing state has a duration of zero milliseconds we can skip
the entire create_transition() call inside set_width() and set_height(),
to avoid what may be a costly call to get_preferred_*.
If we update a transition that is currently playing, we need to check
the current easing state, and look at the eventual duration, in case
the user wants to cancel the transition.
Instead of checking the duration of the current easing state we should
check if there's a transition in progress, and update it
unconditionally.
If there is no easing state, or the easing state has a duration of zero
milliseconds, then create_transition() should bail out early and set the
requested final state.
This allows us to write:
clutter_actor_save_easing_state (actor);
clutter_actor_set_x (actor, 200);
clutter_actor_restore_easing_state (actor);
[...]
clutter_actor_set_x (actor, 100);
and have the second set_x() update the easing in progress, instead of
being ignored.
https://bugzilla.gnome.org/show_bug.cgi?id=672945
Commit 80626e7584 removed an
IN_DESTRUCTION check from within the add_child_internal() method,
outlining an option for bringing it back. It was too late for the 1.10
cycle to do it, and eventually pick up the pieces, but now that we're
at the beginning of the 1.11 cycle we can restore it, and add checks
elsewhere to balance it.
Should not have been there in the first place: the animatable will be
set either using ClutterTransition API, or when adding the transition
to a ClutterActor.
When adding a transition to a ClutterActor, the actor should hold a
reference on it, and release it only when we remove it. This makes
transitions just like other objects held by ClutterActor.
While you can get a per-transition notification of completion, it can be
convenient to also have a way to notify that all the transitions
involving an actor are complete. A simple signal triggered by the
removal of the last transition fits the bill pretty neatly.
If restore_easing_state() is called on the last easing state on the
stack, clean up the stack, so that we don't leave stale pointers
around to later segfault on.
When setting the easing mode, duration, or delay without having ever
called clutter_actor_save_easing_state(). It's confusing, and not
really nice.
In the future, we'll have a default easing state implicitly created by
the actor itself, but for the time being explicitly opting in is
preferrable.
Yes, it's not really the proper GL name for a linear-on-every-axis of a
texture plus linear-between-mipmap-levels minification filter, but it
has three redeeming qualities as a name:
- LINEAR_MIPMAP_LINEAR sucks, as it introduces GL concepts like
mipmaps in the API naming, while we're trying to avoid that;
- people using GL already know what 'trilinear' means in this context
without going all Khronos on their asses;
- we're using 2D textures anyway, so 'linear on two axes and linear
between mipmap levels' can be effectively approximated to
'trilinear'.
I mean, if even the OpenGL official wiki says:
Unfortunately, what most people think of as "trilinear" is not linear
filtering of a 3D texture, but what in OpenGL terms is GL_LINEAR mag
filter and GL_LINEAR_MIPMAP_LINEAR in the min filter in a 2D texture.
That is, it is bilinear filtering of each appropriate mipmap level,
and doing a third linear filter between the adjacent mipmap levels.
Hence the term "trilinear".
-- http://www.opengl.org/wiki/Texture
then the horse has already been flogged to death, and I don't intend to
be accused of necrophilia and sadism by flogging it some more.
Prior art: every single GL tutorial in the history of ever;
CoreAnimation's scaling filter enumerations.
If people want to start using 1D or 3D textures they they are probably
going to be using Cogl API directly, and that has the GL naming scheme
for minification and magnification filters anyway.
It's a bit late in the game for changing the emission of the paint
signal with actors that use paint nodes - mostly because we have both
implicit paint nodes (background color, content) and explicit paint
nodes (the paint_node virtual).
When we branch for 1.12 we can revert this change.
The ::paint signal is the old way to paint an actor; the paint_node()
virtual function is the new way. It's still not possible to traverse the
whole scene graph and build a render tree of PaintNode instances, but
with this change we simultaneously cut out the ::paint signal emission
from the critical path for actors that are using the new PaintNode-based
API, and we retain backward compatibility in the interim period between
1.10 and 2.0.
ClutterContent is an interface for creating delegate objects that handle
what an actor is going to paint.
Since they are a newly added type, they only hook into the new PaintNode
based API.
The position and size of the content is controlled in part by the
content's own preferred size, and by the ClutterContentGravity
enumeration.
The ::paint-node virtual inside ClutterActor is what we want people to
use when painting their actors.
Right now, it's a new code path, that gets called while painting; the
paint_node() implementation should only paint the actor itself, and not
its children — they will get their own paint_node() called when needed.
Internally, ClutterActor will automatically create a dummy PaintNode and
paint the background color; then control will be handed out to the
implementation on the class. This is required to maintain compatibility
with the old ::paint signal emission.
Once we are able to get rid of the paint (and pick) sequences, we'll
switch to a fully retained render tree.
As it turns out, we do end up recursing inside the ::paint signal
emission - especially inside the conformance test suite.
This thoroughly sucks - and we'll only be able to fix it properly
when we bump API for 2.0.
ClutterActor should be able to hold all transitions, even the ones that
have been explicitly created.
This will allow to add new transitions types in the future, like the
keyframe-based one, or the transition group.
It should be possible to set up the delay of a transition, but since
we start the Transition instance before returning control to the caller,
we cannot use clutter_actor_get_transition() to do it without something
extra-awkward, like:
transition = clutter_actor_get_transition (actor, "width");
clutter_timeline_stop (transition);
clutter_timeline_set_delay (transition, 1000);
clutter_timeline_start (transition);
for each property involved. It's much easier to add a delay to the
easing state of an actor.
Clutter is meant to be, and I quote from the README, a toolkit:
for creating fast, compelling, portable, and dynamic graphical
user interfaces
and yet the default mode of operation for setting an actor's state on
the scene graph (position, size, opacity, rotation, scaling, depth,
etc.) is *not* dynamic. We assume a static UI, and then animate it.
This is the wrong way to design an API for a toolkit meant to be used to
create animated user interfaces. The default mode of operation should be
to implicitly animate every state transition, and only allow skipping
the animation if the user consciously decides to do so — i.e. the design
tenet of the API should be to make The Right Thing™ by default, and make
it really hard (or even impossible) to do The Wrong Thing™.
So we should identify "animatable" properties, i.e. those properties
that should be implicitly animated by ClutterActor, and use the
animation framework we provide to tween the transitions between the
current state and the desired state; the implicit animation should
happen when setting these properties using the public accessors, and not
through some added functionality. For instance, the following:
clutter_actor_set_position (actor, newX, newY);
should not make the actor jump to the (newX, newY) point; it should
tween the actor's position between the current point and the desired
point.
Since we have to maintain backward compatibility with existing
applications, we still need to mark the transitions explicitly, but we
can be smart about it, and treat transition states as a stack that can
be pushed and popped, e.g.:
clutter_actor_save_easing_state (actor);
clutter_actor_set_easing_duration (actor, 500);
clutter_actor_set_position (actor, newX, newY);
clutter_actor_set_opacity (actor, newOpacity);
clutter_actor_restore_easing_state (actor);
And we can even start stacking animations, e.g.:
clutter_actor_save_easing_state (actor);
clutter_actor_set_easing_duration (actor, 500);
clutter_actor_set_position (actor, newX, newY);
clutter_actor_save_easing_state (actor);
clutter_actor_set_easing_duration (actor, 500);
clutter_actor_set_easing_mode (actor, CLUTTER_LINEAR);
clutter_actor_set_opacity (actor, newOpacity);
clutter_actor_set_depth (actor, newDepth);
clutter_actor_restore_easing_state (actor);
clutter_actor_restore_easing_state (actor);
And so on, and so forth.
The implementation takes advantage of the newly added Transition API,
which uses only ClutterTimeline sub-classes and ClutterInterval, to cut
down the amount of signal emissions and memory management of object
instances; as well of using the ClutterAnimatable interface for custom
properties and interpolation of values.
The ::paint, ::queue-redraw, and ::queue-relayout signals should be
marked as no-recurse and no-hooks; these signals are emitted *a lot*
during each frame, and since GLib has a bunch of optimizations for
signals with no closures, we should try and squeeze every single CPU
cycle we can.
In theory, handlers connected to the ::allocation-changed signal may be
able to modify the actor's real allocation and allocation flags,
especially now that we use STATIC_SCOPE; let's avoid this, so that we
don't regret it later.
The ActorBox passed to the ::allocation-changed signal should be
annotated as STATIC_SCOPE, given that it's a pointer to a structure
inside ClutterActorPrivate - hence there's no risk of it actually being
freed from a signal handler. This allows the GSignal machinery to avoid
a costly copy/free for each signal emission.
If the redraw entry is not cleared, queueing a redraw from a signal
handler could reinsert the same object in the stage redraw list,
causing the segfault later (as the object is immediately freed)
https://bugzilla.gnome.org/show_bug.cgi?id=671173
We currently check for the IN_DESTRUCTION flag inside the
add_child_internal() function.
This check disallows calling methods that change the stacking order
within the destruction sequence, by triggering a critical warning first,
and leaving the actor in an undefined state, which then ends up being
caught by an assertion.
The reproducible sequence is:
- actor gets destroyed;
- another actor, linked to the first, will try to change the
stacking order of the first actor;
- changing the stacking order is a composite operation composed
by the following steps:
1. ref() the child;
2. remove_child_internal(), which removes the reference;
3. add_child_internal(), which adds a reference;
- the state of the actor is not changed between (2) and (3), as
it could be an expensive recomputation;
- if (3) bails out, then the actor is in an undefined state, but
still alive;
- the destruction sequence terminates, but the actor is unparented
while its state indicates being parented instead.
- assertion failure.
The obvious fix would be to decompose each set_child_*_sibling() method
into proper remove_child()/add_child(), with state validation; this may
cause excessive work, though, and trigger a cascade of other bugs in
code that assumes that a change in the stacking order is an atomic
operation.
Another potential fix is to just remove this check here, and let code
doing stacking order changes inside the destruction sequence of an actor
continue doing the work.
The third fix is to silently bail out early from every
set_child_*_sibling() and set_child_at_index() method, and avoid doing
work.
I have a preference for the second solution, since it involves the least
amount of work, and the least amount of code duplication.
See bug: https://bugzilla.gnome.org/show_bug.cgi?id=670647
Now that ClutterActor has a default paint volume, subclasses may wish
to retrieve it without chaining up to the parent's implementation of
the get_paint_volume() function.
The get_default_paint_volume() returns a ClutterPaintVolume pointer
to the paint volume as computed by the default implementation of the
get_paint_volume() virtual function; it can only be used immediately,
as it's not guaranteed to survive across multiple frames.
The experimental cogl_pipeline_new() api was recently changed so it
explicitly takes a CoglContext. This updates all calls to
cogl_pipeline_new() in clutter accordingly.
If we have N children and the user passes N (or a number beyond N) to
clutter_actor_insert_child_at_index, we should respond by adding the
child at the end, not silently doing nothing.
This should avoid trying to fix the origin of a paint volume set from
the allocation's origin, and thus breaking everything.
A PaintVolume for an actor is defined to be relative to the actor's
modelview unless specifically modified by internal functions; the origin
of an actor's allocation is, on the other hand, parent-relative.
There are times when we don't want to remove all children and count of
the reference count to drop to 0 to ensure destruction; there are cases,
such as managed environments, where it's preferable to ensure that the
children of an actor get actually destroyed.
A bunch of private symbols have escaped into the SO; let's rectify this
situation by using the '_' private prefix, or making them static as they
should have been.
Some of Cogl's experimental apis have changed so that the buffer apis
now need to be passed a context argument and some drawing apis have been
replaced with cogl_framebuffer_ drawing apis that take explicit
framebuffer and pipeline arguments.
These changes were made as part of Cogl moving towards a more stateless
api that doesn't rely on a global context.
This patch updates Clutter to work with the latest Cogl api and bumps
the required Cogl version to 1.9.5.
Reviewed-by: Emmanuele Bassi <ebassi@linux.intel.com>
Reviewed-by: Neil Roberts <neil@linux.intel.com>
Similar to the clutter_actor_iter_remove(), but it'll call destroy()
instead of remove_child().
We can also reimplement the ::destroy default handler using it, and make
it more compact.
There is a typo in the check for a negative index: the index variable
should be index_, not index - unfortunately, the latter can still be
resolved to index(3), so compiler and linker are perfectly happy.
https://bugzilla.gnome.org/show_bug.cgi?id=669730
ClutterActor stopped requiring to override the map and unmap virtual
functions some time ago.
Now that ClutterActor implements the Container interface, overriding map
and unmap to control the MAPPED state of the children is pretty much
going to be a source of bugs and misunderstandings.
Plus, the ordering of the unmap, destroy, dispose, and finalize calls
should be be documented properly.
The documentation should clarify all that.
When calling clutter_actor_destroy(), ClutterActor calls
update_map_state() on itself to unset the REALIZED and MAPPED states,
prior to running the dispose() implementation.
The default dispose() will call remove_child() (either directly or
through the Container implementation), which will check for the MAPPED
state and then run update_map_state() again. We use the previously set
MAPPED state to decide whether or not the parent should queue for a
relayout/redraw when removing a visible children.
If the MAPPED flag was cleared prior to remove_child(), though, it'll
always be unset by the time we get to remove_child(), and this will
cause missing redraws/relayouts; we were ignoring this prior the
post-First Apocalypse changes because we were doing:
if (was_mapped)
clutter_actor_queue_relayout (parent);
clutter_actor_queue_redraw (parent);
which is obviously wrong. Once I removed that glaring brain damage from
the remove_child() implementation, bugs started appearing — bugs that
were probably the reason why we introduced that brain damage in the
first place, instead of checking the source of those bugs.
The obvious fix is to avoid clearing up the actor's state on destroy()
until we remove the actor from its parent. This also reduces the amount
of work we do, and the code paths that can potentially go wrong.
Since the code dealing with ClutterShader is pretty self-contained, now,
we can safely move it outside of the main ClutterActor source file and
into its own. This will allow us to just drop a bunch of files when
branching for 2.0.
Iterating over children and ancestors of an actor is a relatively common
operation. Currently, you only have one option: start a for() loop, get
the first child of the actor, and advance to the next sibling for the
list of children; or start a for() loop and advance to the parent of the
actor.
These operations can be easily done through the ClutterActor API, but
they all require going through the public API, and performing multiple
type checks on the arguments.
Along with the DOM API, it would be nice to have an ancillary, utility
API that uses an iterator structure to hold the state, and can be
advanced in a loop.
https://bugzilla.gnome.org/show_bug.cgi?id=668669
Now that we reinstated Group to its "former glory", we need to ensure
that applications using the deprecated containers with the new DOM API
in ClutterActor can actually work - or, at least, not break horribly.
This actually means making sure that ClutterStage and ClutterGroup can
cope with the DOM, while retaining their old implementations, as well as
their bizarre idiosyncrasies and their utter, utter brokenness.
Making Group just a proxy to Actor broke some behaviour that application
and toolkit code was relying on. Let's keep Group around to fight
another day.
This commit fixes gnome-shell as far as I can test it.
The usual way to implement a container actor is to override the
allocate() virtual function, chain up, and then allocate the actor's
children.
Clutter now has the ability to delegate layout management to
ClutterLayoutManager directly; in the allocation, this is done by
checking whether the actor has children, and then call
clutter_layout_manager_allocate() from within the default implementation
of the ClutterActor::allocate() vfunc. The same vfunc that everyone, has
been chaining up to.
Whoopsie.
Well, we can check if there's a layout manager, and if it's NULL, we
bail out. Except that there's a default layout manager, and it's the
fixed layout manager, so that classes like Group and Stage work by
default.
Double whoopsie.
The fix for this scenario is a bit nasty; we have to check if the actor
class has overridden the allocate() vfunc or not, before actually
looking at the layout manager. This means that classes that override the
allocate() vfunc are expected to do everything that ClutterActor's
default implementation does - which I think it's a fair requirement to
have.
For newly written code, though, it would probably be best if we just
provided a function that does the right thing by default, and that
you're supposed to be calling from within the allocate() vfunc
implementation, if you ever chose to override it. This new function,
clutter_actor_set_allocation(), should come with a warning the size of
Texas, to avoid people thinking it's a way to override the whole "call
allocate() on each child" mechanism. Plus, it should check if we're
inside an allocation sequence, and bail out if not.
If we want to set a default layout manager, we need to do so inside
init(), as it's not guaranteed that people subclassing Actor and
overriding ::constructed will actually chain up as they should.
The default pick() behaviour does not take into consideration the
children of a ClutterActor because the existing containter actors
usually override pick(), chain up, and then paint their children.
With ClutterActor now a concrete class, though, we need a way to pick
its children without requiring a sub-class; we could simply iterate over
the children inside the default pick() implementation, but this would
lead to double painting, which is not acceptable.
A moderately gross hack is to check if the Actor instance did override
the pick() implementation, and if it is not the case, paint the children
in pick mode.
The hide_all() method is pretty much pointless, as hiding an actor will
automatically prevent its children from being painted. The show_all()
method would only be marginally useful, if actors weren't set to be
visible by default when added to another actor - which was the case when
we introduced show_all() and hide_all().
The concept of "internal child" only meant anything when we had a
separate API for containers and actors. Now that we plugged that
particular hole, we can drop all the hacks we used to have in place
to work around its design limitations.
It can be convenient to be able to set, or get, all the components of an
actor's margin at the same time; since we already have a boxed type for
storing a margin, an accessors pair based on it is not a complicated
addition to the API.
Inside the set_child_[above|below]_sibling() and set_child_at_index() we
should be using the internal API for mutating the children list, instead
of the delegate functions. This ensures that we go through a single,
well-defined code path for all operations on the list of children of
an actor.
We have a replacement in ClutterActor, now.
The old ClutterContainer API needs to be deprecated, and the raise() and
lower() virtual functions need a default implementation, so we can check
for implementations overriding them, by using the diagnostic mode like
we do for add(), remove(), and foreach().
The sort_depth_order() virtual function just doesn't do anything, as it
should have been made ages ago.
The Actor wrappers for the Container methods also need to be deprecated.
ClutterActor provides four methods for changing the paint sequence order
of its children:
raise_top()
raise()
lower()
lower_bottom()
The first and last one being just wrappers around raise() and lower(),
respectively. These methods have various issues: they omit the parent,
preferring to retrieve it from the actor passed as the first argument;
this does not match the new style of API introduced to operate on the
list of children of an actor.
Additionally, the raise() and lower() methods of ClutterActor call into
the Container interface, and are not really aptly named (raise() in
particular collides with the completely unrelated 'raise' keyword in
Python, and usually needs to be wrapped in order to be used at all).
Furthermore, we need public methods that Container can call from its
default implementation, as well as methods to port current Container
implementations.
Finally, since we have insert_child_at_index(), we should also have an
equivalent set_child_at_index() as well.
The internal versions of add_child() and remove_child() currently use
boolean arguments to control things like the ChildMeta instances and
the emissions of signals; using more than one boolean argument is an
indication that you need flags to avoid readability issues, as well as
providing a way to add new behaviours without a combinatorial explosion
of arguments, later on.
I don't feel comfortable with this feature, and its implementation
still has too many rough edges. We can safely punt it for now, and
introduce it at a later point, as it doesn't block existing features
or API.
