Class

ClutterConstraint

Description [src]

abstract class Clutter.Constraint : Clutter.ActorMeta
{
  /* No available fields */
}

Abstract class for constraints on position or size

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 Clutter.ConstraintClass.update_allocation virtual function.

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 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.

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 Clutter.ConstraintClass.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().

Hierarchy

Ancestors

Descendants

Instance methods

clutter_constraint_update_preferred_size

Asks the constraint to update the size request of a ClutterActor.

Methods inherited from GObject (43)

Please see GObject for a full list of methods.

Properties

Signals

Signals inherited from GObject (1)

GObject::notify

The notify signal is emitted on an object when one of its properties has its value set through g_object_set_property(), g_object_set(), et al.

Class structure

struct ClutterConstraintClass {
  void (* update_allocation) (
    ClutterConstraint* constraint,
    ClutterActor* actor,
    ClutterActorBox* allocation
  );
  void (* update_preferred_size) (
    ClutterConstraint* constraint,
    ClutterActor* actor,
    ClutterOrientation direction,
    float for_size,
    float* minimum_size,
    float* natural_size
  );
  
}

The ClutterConstraintClass structure contains only private data.

Class members

update_allocation: void (* update_allocation) ( ClutterConstraint* constraint, ClutterActor* actor, ClutterActorBox* allocation ): Virtual function used to update the allocation of the ClutterActor using the ClutterConstraint.
update_preferred_size: void (* update_preferred_size) ( ClutterConstraint* constraint, ClutterActor* actor, ClutterOrientation direction, float for_size, float* minimum_size, float* natural_size ): Virtual function used to update the preferred size of the ClutterActor using the ClutterConstraint; optional, since 1.22.

Virtual methods

Clutter.ConstraintClass.update_allocation

Virtual function used to update the allocation of the ClutterActor using the ClutterConstraint.

Clutter.ConstraintClass.update_preferred_size

Asks the constraint to update the size request of a ClutterActor.

Class

ClutterConstraint

Description [src]

Using Constraints

Implementing a ClutterConstraint

Hierarchy

Ancestors

Descendants

Instance methods

clutter_constraint_update_preferred_size

Methods inherited from ClutterActorMeta (5)

clutter_actor_meta_get_actor

clutter_actor_meta_get_enabled

clutter_actor_meta_get_name

clutter_actor_meta_set_enabled

clutter_actor_meta_set_name