/**
* SECTION:clutter-constraint
* @Title: ClutterConstraint
* @Short_Description: Abstract class for constraints on position or size
* @See_Also: #ClutterAction
*
* #ClutterConstraint is a base abstract class for modifiers of a #ClutterActor
* position or size.
*
* A #ClutterConstraint sub-class should contain the logic for modifying
* the position or size of the #ClutterActor to which it is applied, by
* updating the actor's allocation. Each #ClutterConstraint can change the
* allocation of the actor to which they are applied by overriding the
* #ClutterConstraintClass.update_allocation() virtual function.
*
* #ClutterConstraint is available since Clutter 1.4
*
* ## Using Constraints
*
* Constraints can be used with fixed layout managers, like
* #ClutterFixedLayout, or with actors implicitly using a fixed layout
* manager, like #ClutterGroup and #ClutterStage.
*
* Constraints provide a way to build user interfaces by using
* relations between #ClutterActors, without explicit fixed
* positioning and sizing, similarly to how fluid layout managers like
* #ClutterBoxLayout and #ClutterTableLayout lay out their children.
*
* Constraints are attached to a #ClutterActor, and are available
* for inspection using clutter_actor_get_constraints().
*
* Clutter provides different implementation of the #ClutterConstraint
* abstract class, for instance:
*
* - #ClutterAlignConstraint, a constraint that can be used to align
* an actor to another one on either the horizontal or the vertical
* axis, using a normalized value between 0 and 1.
* - #ClutterBindConstraint, a constraint binds the X, Y, width or height
* of an actor to the corresponding position or size of a source actor,
* with or without an offset.
* - #ClutterSnapConstraint, a constraint that "snaps" together the edges
* of two #ClutterActors; if an actor uses two constraints on both its
* horizontal or vertical edges then it can also expand to fit the empty
* space.
*
* The [constraints example](https://git.gnome.org/browse/clutter/tree/examples/constraints.c?h=clutter-1.18)
* uses various types of #ClutterConstraints to lay out three actors on a
* resizable stage. Only the central actor has an explicit size, and no
* actor has an explicit position.
*
* - The #ClutterActor with #ClutterActor:name `layerA` is explicitly
* sized to 100 pixels by 25 pixels, and it's added to the #ClutterStage
* - two #ClutterAlignConstraints are used to anchor `layerA` to the
* center of the stage, by using 0.5 as the alignment #ClutterAlignConstraint:factor on
* both the X and Y axis
* - the #ClutterActor with #ClutterActor:name `layerB` is added to the
* #ClutterStage with no explicit size
* - the #ClutterActor:x and #ClutterActor:width of `layerB` are bound
* to the same properties of `layerA` using two #ClutterBindConstraint
* objects, thus keeping `layerB` aligned to `layerA`
* - the top edge of `layerB` is snapped together with the bottom edge
* of `layerA`; the bottom edge of `layerB` is also snapped together with
* the bottom edge of the #ClutterStage; an offset is given to the two
* #ClutterSnapConstraintss to allow for some padding; since `layerB` is
* snapped between two different #ClutterActors, its height is stretched
* to match the gap
* - the #ClutterActor with #ClutterActor:name `layerC` mirrors `layerB`,
* snapping the top edge of the #ClutterStage to the top edge of `layerC`
* and the top edge of `layerA` to the bottom edge of `layerC`
*
* You can try resizing interactively the #ClutterStage and verify
* that the three #ClutterActors maintain the same position and
* size relative to each other, and to the #ClutterStage.
*
* It is important to note that Clutter does not avoid loops or
* competing constraints; if two or more #ClutterConstraints
* are operating on the same positional or dimensional attributes of an
* actor, or if the constraints on two different actors depend on each
* other, then the behavior is undefined.
*
* ## Implementing a ClutterConstraint
*
* Creating a sub-class of #ClutterConstraint requires the
* implementation of the #ClutterConstraintClass.update_allocation()
* virtual function.
*
* The `update_allocation()` virtual function is called during the
* allocation sequence of a #ClutterActor, and allows any #ClutterConstraint
* attached to that actor to modify the allocation before it is passed to
* the actor's #ClutterActorClass.allocate() implementation.
*
* The #ClutterActorBox passed to the `update_allocation()` implementation
* contains the original allocation of the #ClutterActor, plus the eventual
* modifications applied by the other #ClutterConstraints, in the same order
* the constraints have been applied to the actor.
*
* It is not necessary for a #ClutterConstraint sub-class to chain
* up to the parent's implementation.
*
* If a #ClutterConstraint is parametrized - i.e. if it contains
* properties that affect the way the constraint is implemented - it should
* call clutter_actor_queue_relayout() on the actor to which it is attached
* to whenever any parameter is changed. The actor to which it is attached
* can be recovered at any point using clutter_actor_meta_get_actor().
*/
#ifdef HAVE_CONFIG_H
#include "config.h"
#endif
#include <string.h>
#include "clutter-constraint.h"
#include "clutter-actor.h"
#include "clutter-actor-meta-private.h"
#include "clutter-private.h"
G_DEFINE_ABSTRACT_TYPE (ClutterConstraint,
clutter_constraint,
CLUTTER_TYPE_ACTOR_META);
static void
constraint_update_allocation (ClutterConstraint *constraint,
ClutterActor *actor,
ClutterActorBox *allocation)
{
}
static void
clutter_constraint_notify (GObject *gobject,
GParamSpec *pspec)
{
if (strcmp (pspec->name, "enabled") == 0)
{
ClutterActorMeta *meta = CLUTTER_ACTOR_META (gobject);
ClutterActor *actor = clutter_actor_meta_get_actor (meta);
if (actor != NULL)
clutter_actor_queue_relayout (actor);
}
if (G_OBJECT_CLASS (clutter_constraint_parent_class)->notify != NULL)
G_OBJECT_CLASS (clutter_constraint_parent_class)->notify (gobject, pspec);
}
static void
clutter_constraint_class_init (ClutterConstraintClass *klass)
{
GObjectClass *gobject_class = G_OBJECT_CLASS (klass);
gobject_class->notify = clutter_constraint_notify;
klass->update_allocation = constraint_update_allocation;
}
static void
clutter_constraint_init (ClutterConstraint *self)
{
}
void
_clutter_constraint_update_allocation (ClutterConstraint *constraint,
ClutterActor *actor,
ClutterActorBox *allocation)
{
g_return_if_fail (CLUTTER_IS_CONSTRAINT (constraint));
g_return_if_fail (CLUTTER_IS_ACTOR (actor));
g_return_if_fail (allocation != NULL);
CLUTTER_CONSTRAINT_GET_CLASS (constraint)->update_allocation (constraint,
actor,
allocation);
}