244 lines
9.7 KiB
C
244 lines
9.7 KiB
C
/*
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* Clutter.
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*
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* An OpenGL based 'interactive canvas' library.
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*
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* Copyright (C) 2010 Intel Corporation.
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*
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* This library is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 2 of the License, or (at your option) any later version.
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*
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* This library is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with this library. If not, see <http://www.gnu.org/licenses/>.
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*
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* Author:
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* Emmanuele Bassi <ebassi@linux.intel.com>
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*/
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/**
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* SECTION:clutter-constraint
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* @Title: ClutterConstraint
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* @Short_Description: Abstract class for constraints on position or size
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* @See_Also: #ClutterAction
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*
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* #ClutterConstraint is a base abstract class for modifiers of a #ClutterActor
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* position or size.
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*
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* A #ClutterConstraint sub-class should contain the logic for modifying
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* the position or size of the #ClutterActor to which it is applied, by
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* updating the actor's allocation. Each #ClutterConstraint can change the
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* allocation of the actor to which they are applied by overriding the
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* #ClutterConstraintClass.update_allocation() virtual function.
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*
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* #ClutterConstraint is available since Clutter 1.4
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*
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* ## Using Constraints
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*
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* Constraints can be used with fixed layout managers, like
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* #ClutterFixedLayout, or with actors implicitly using a fixed layout
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* manager, like #ClutterGroup and #ClutterStage.
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*
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* Constraints provide a way to build user interfaces by using
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* relations between #ClutterActors, without explicit fixed
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* positioning and sizing, similarly to how fluid layout managers like
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* #ClutterBoxLayout and #ClutterTableLayout lay out their children.
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*
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* Constraints are attached to a #ClutterActor, and are available
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* for inspection using clutter_actor_get_constraints().
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*
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* Clutter provides different implementation of the #ClutterConstraint
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* abstract class, for instance:
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*
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* - #ClutterAlignConstraint, a constraint that can be used to align
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* an actor to another one on either the horizontal or the vertical
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* axis, using a normalized value between 0 and 1.
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* - #ClutterBindConstraint, a constraint binds the X, Y, width or height
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* of an actor to the corresponding position or size of a source actor,
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* with or without an offset.
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* - #ClutterSnapConstraint, a constraint that "snaps" together the edges
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* of two #ClutterActors; if an actor uses two constraints on both its
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* horizontal or vertical edges then it can also expand to fit the empty
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* space.
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*
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* The [constraints example](https://git.gnome.org/browse/clutter/tree/examples/constraints.c?h=clutter-1.18)
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* uses various types of #ClutterConstraints to lay out three actors on a
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* resizable stage. Only the central actor has an explicit size, and no
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* actor has an explicit position.
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*
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* - The #ClutterActor with #ClutterActor:name `layerA` is explicitly
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* sized to 100 pixels by 25 pixels, and it's added to the #ClutterStage
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* - two #ClutterAlignConstraints are used to anchor `layerA` to the
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* center of the stage, by using 0.5 as the alignment #ClutterAlignConstraint:factor on
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* both the X and Y axis
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* - the #ClutterActor with #ClutterActor:name `layerB` is added to the
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* #ClutterStage with no explicit size
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* - the #ClutterActor:x and #ClutterActor:width of `layerB` are bound
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* to the same properties of `layerA` using two #ClutterBindConstraint
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* objects, thus keeping `layerB` aligned to `layerA`
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* - the top edge of `layerB` is snapped together with the bottom edge
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* of `layerA`; the bottom edge of `layerB` is also snapped together with
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* the bottom edge of the #ClutterStage; an offset is given to the two
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* #ClutterSnapConstraintss to allow for some padding; since `layerB` is
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* snapped between two different #ClutterActors, its height is stretched
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* to match the gap
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* - the #ClutterActor with #ClutterActor:name `layerC` mirrors `layerB`,
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* snapping the top edge of the #ClutterStage to the top edge of `layerC`
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* and the top edge of `layerA` to the bottom edge of `layerC`
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*
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* You can try resizing interactively the #ClutterStage and verify
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* that the three #ClutterActors maintain the same position and
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* size relative to each other, and to the #ClutterStage.
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*
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* It is important to note that Clutter does not avoid loops or
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* competing constraints; if two or more #ClutterConstraints
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* are operating on the same positional or dimensional attributes of an
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* actor, or if the constraints on two different actors depend on each
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* other, then the behavior is undefined.
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*
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* ## Implementing a ClutterConstraint
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*
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* Creating a sub-class of #ClutterConstraint requires the
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* implementation of the #ClutterConstraintClass.update_allocation()
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* virtual function.
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*
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* The `update_allocation()` virtual function is called during the
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* allocation sequence of a #ClutterActor, and allows any #ClutterConstraint
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* attached to that actor to modify the allocation before it is passed to
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* the actor's #ClutterActorClass.allocate() implementation.
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*
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* The #ClutterActorBox passed to the `update_allocation()` implementation
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* contains the original allocation of the #ClutterActor, plus the eventual
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* modifications applied by the other #ClutterConstraints, in the same order
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* the constraints have been applied to the actor.
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*
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* It is not necessary for a #ClutterConstraint sub-class to chain
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* up to the parent's implementation.
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*
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* If a #ClutterConstraint is parametrized - i.e. if it contains
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* properties that affect the way the constraint is implemented - it should
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* call clutter_actor_queue_relayout() on the actor to which it is attached
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* to whenever any parameter is changed. The actor to which it is attached
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* can be recovered at any point using clutter_actor_meta_get_actor().
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*/
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#ifdef HAVE_CONFIG_H
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#include "config.h"
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#endif
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#include <string.h>
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#include "clutter-constraint-private.h"
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#include "clutter-actor.h"
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#include "clutter-actor-meta-private.h"
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#include "clutter-private.h"
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G_DEFINE_ABSTRACT_TYPE (ClutterConstraint,
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clutter_constraint,
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CLUTTER_TYPE_ACTOR_META);
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static void
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constraint_update_allocation (ClutterConstraint *constraint,
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ClutterActor *actor,
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ClutterActorBox *allocation)
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{
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}
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static void
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constraint_update_preferred_size (ClutterConstraint *constraint,
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ClutterActor *actor,
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ClutterOrientation direction,
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float for_size,
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float *minimum_size,
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float *natural_size)
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{
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}
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static void
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clutter_constraint_notify (GObject *gobject,
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GParamSpec *pspec)
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{
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if (strcmp (pspec->name, "enabled") == 0)
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{
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ClutterActorMeta *meta = CLUTTER_ACTOR_META (gobject);
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ClutterActor *actor = clutter_actor_meta_get_actor (meta);
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if (actor != NULL)
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clutter_actor_queue_relayout (actor);
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}
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if (G_OBJECT_CLASS (clutter_constraint_parent_class)->notify != NULL)
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G_OBJECT_CLASS (clutter_constraint_parent_class)->notify (gobject, pspec);
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}
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static void
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clutter_constraint_class_init (ClutterConstraintClass *klass)
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{
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GObjectClass *gobject_class = G_OBJECT_CLASS (klass);
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gobject_class->notify = clutter_constraint_notify;
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klass->update_allocation = constraint_update_allocation;
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klass->update_preferred_size = constraint_update_preferred_size;
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}
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static void
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clutter_constraint_init (ClutterConstraint *self)
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{
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}
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/*< private >
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* clutter_constraint_update_allocation:
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* @constraint: a #ClutterConstraint
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* @actor: a #ClutterActor
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* @allocation: (inout): the allocation to modify
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*
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* Asks the @constraint to update the @allocation of a #ClutterActor.
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*
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* Returns: %TRUE if the allocation was updated
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*/
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gboolean
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clutter_constraint_update_allocation (ClutterConstraint *constraint,
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ClutterActor *actor,
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ClutterActorBox *allocation)
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{
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ClutterActorBox old_alloc;
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g_return_val_if_fail (CLUTTER_IS_CONSTRAINT (constraint), FALSE);
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g_return_val_if_fail (CLUTTER_IS_ACTOR (actor), FALSE);
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g_return_val_if_fail (allocation != NULL, FALSE);
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old_alloc = *allocation;
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CLUTTER_CONSTRAINT_GET_CLASS (constraint)->update_allocation (constraint,
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actor,
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allocation);
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return !clutter_actor_box_equal (allocation, &old_alloc);
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}
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void
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clutter_constraint_update_preferred_size (ClutterConstraint *constraint,
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ClutterActor *actor,
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ClutterOrientation direction,
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float for_size,
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float *minimum_size,
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float *natural_size)
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{
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g_return_if_fail (CLUTTER_IS_CONSTRAINT (constraint));
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g_return_if_fail (CLUTTER_IS_ACTOR (actor));
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CLUTTER_CONSTRAINT_GET_CLASS (constraint)->update_preferred_size (constraint, actor,
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direction,
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for_size,
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minimum_size,
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natural_size);
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}
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