### Class

# Clutter Effect

#### Description [src]

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

Base class for actor effects

The `ClutterEffect` class provides a default type and API for creating effects for generic actors.

Effects are a `ClutterActorMeta` sub-class that modify the way an actor is painted in a way that is not part of the actor’s implementation.

Effects should be the preferred way to affect the paint sequence of an actor without sub-classing the actor itself and overriding the `Clutter.ActorClass.paint` virtual function.

## Implementing a ClutterEffect

Creating a sub-class of `ClutterEffect` requires overriding the `Clutter.EffectClass.paint` method. The implementation of the function should look something like this:

    void effect_paint (ClutterEffect *effect, ClutterEffectPaintFlags flags)
    {
      // Set up initialisation of the paint such as binding a
      // CoglOffscreen or other operations

      // Chain to the next item in the paint sequence. This will either call
      // ‘paint’ on the next effect or just paint the actor if this is
      // the last effect.
      ClutterActor *actor =
        clutter_actor_meta_get_actor (CLUTTER_ACTOR_META (effect));

      clutter_actor_continue_paint (actor);

      // perform any cleanup of state, such as popping the CoglOffscreen
    }

The effect can optionally avoid calling `clutter_actor_continue_paint()` to skip any further stages of the paint sequence. This is useful for example if the effect contains a cached image of the actor. In that case it can optimise painting by avoiding the actor paint and instead painting the cached image.

The `CLUTTER_EFFECT_PAINT_ACTOR_DIRTY` flag is useful in this case. Clutter will set this flag when a redraw has been queued on the actor since it was last painted. The effect can use this information to decide if the cached image is still valid.

## A simple ClutterEffect implementation

The example below creates two rectangles: one will be painted “behind” the actor, while another will be painted “on top” of the actor.

The `ClutterActorMetaClass`.set_actor() implementation will create the two pipelines used for the two different rectangles; the `ClutterEffectClass`.paint() implementation will paint the first pipeline using cogl_rectangle(), before continuing and then it will paint paint the second pipeline after.

     typedef struct {
       ClutterEffect parent_instance;

       CoglPipeline *rect_1;
       CoglPipeline *rect_2;
     } MyEffect;

     typedef struct _ClutterEffectClass MyEffectClass;

     G_DEFINE_TYPE (MyEffect, my_effect, CLUTTER_TYPE_EFFECT);

     static void
     my_effect_set_actor (ClutterActorMeta *meta,
                          ClutterActor     *actor)
     {
       MyEffect *self = MY_EFFECT (meta);
       CoglColor color;

       // Clear the previous state //
       if (self->rect_1)
         {
           g_object_unref (self->rect_1);
           self->rect_1 = NULL;
         }

       if (self->rect_2)
         {
           g_object_unref (self->rect_2);
           self->rect_2 = NULL;
         }

       // Maintain a pointer to the actor
       self->actor = actor;

       // If we've been detached by the actor then we should just bail out here
       if (self->actor == NULL)
         return;

       // Create a red pipeline
       self->rect_1 = cogl_pipeline_new ();
       cogl_color_init_from_4f (&color, 1.0, 1.0, 1.0, 1.0);
       cogl_pipeline_set_color (self->rect_1, &color);

       // Create a green pipeline
       self->rect_2 = cogl_pipeline_new ();
       cogl_color_init_from_4f (&color, 0.0, 1.0, 0.0, 1.0);
       cogl_pipeline_set_color (self->rect_2, &color);
     }

     static gboolean
     my_effect_paint (ClutterEffect *effect)
     {
       MyEffect *self = MY_EFFECT (effect);
       gfloat width, height;

       clutter_actor_get_size (self->actor, &width, &height);

       // Paint the first rectangle in the upper left quadrant
       cogl_set_source (self->rect_1);
       cogl_rectangle (0, 0, width / 2, height / 2);

       // Continue to the rest of the paint sequence
       clutter_actor_continue_paint (self->actor);

       // Paint the second rectangle in the lower right quadrant
       cogl_set_source (self->rect_2);
       cogl_rectangle (width / 2, height / 2, width, height);
     }

     static void
     my_effect_class_init (MyEffectClass *klass)
     {
       ClutterActorMetaClass *meta_class = CLUTTER_ACTOR_META_CLASS (klass);

       meta_class->set_actor = my_effect_set_actor;

       klass->paint = my_effect_paint;
     }

#### Ancestors

- ClutterActorMeta
- GInitiallyUnowned
- GObject

#### Descendants

- ClutterOffscreenEffect

#### Instance methods

###### clutter_effect_queue_repaint

Queues a repaint of the effect. The effect can detect when the ‘paint’ method is called as a result of this function because it will not have the `CLUTTER_EFFECT_PAINT_ACTOR_DIRTY` flag set. In that case the effect is free to assume that the actor has not changed its appearance since the last time it was painted so it doesn’t need to call `clutter_actor_continue_paint()` if it can draw a cached image. This is mostly intended for effects that are using a %CoglOffscreen to redirect the actor (such as %ClutterOffscreenEffect). In that case the effect can save a bit of rendering time by painting the cached texture without causing the entire actor to be painted.

##### Methods inherited from ClutterActorMeta (5)

###### clutter_actor_meta_get_actor

Retrieves a pointer to the `ClutterActor` that owns `meta`.

###### clutter_actor_meta_get_enabled

Retrieves whether `meta` is enabled.

###### clutter_actor_meta_get_name

Retrieves the name set using `clutter_actor_meta_set_name()`.

###### clutter_actor_meta_set_enabled

Sets whether `meta` should be enabled or not.

###### clutter_actor_meta_set_name

Sets the name of `meta`.

##### Methods inherited from GObject (43)

Please see GObject for a full list of methods.

#### Properties

##### Properties inherited from ClutterActorMeta (3)

###### Clutter.ActorMeta:actor

The `ClutterActor` attached to the `ClutterActorMeta` instance.

###### Clutter.ActorMeta:enabled

Whether or not the `ClutterActorMeta` is enabled.

###### Clutter.ActorMeta:name

The unique name to access the `ClutterActorMeta`.

#### 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 ClutterEffectClass {
      gboolean (* pre_paint) (
        ClutterEffect* effect,
        ClutterPaintNode* node,
        ClutterPaintContext* paint_context
      );
      void (* post_paint) (
        ClutterEffect* effect,
        ClutterPaintNode* node,
        ClutterPaintContext* paint_context
      );
      gboolean (* modify_paint_volume) (
        ClutterEffect* effect,
        ClutterPaintVolume* volume
      );
      void (* paint) (
        ClutterEffect* effect,
        ClutterPaintNode* node,
        ClutterPaintContext* paint_context,
        ClutterEffectPaintFlags flags
      );
      void (* paint_node) (
        ClutterEffect* effect,
        ClutterPaintNode* node,
        ClutterPaintContext* paint_context,
        ClutterEffectPaintFlags flags
      );
      void (* pick) (
        ClutterEffect* effect,
        ClutterPickContext* pick_context
      );

    }

The `ClutterEffectClass` structure contains only private data.

###### Class members

`pre_paint: gboolean (* pre_paint) ( ClutterEffect* effect, ClutterPaintNode* node, ClutterPaintContext* paint_context )`

  Virtual function.

`post_paint: void (* post_paint) ( ClutterEffect* effect, ClutterPaintNode* node, ClutterPaintContext* paint_context )`

  Virtual function.

`modify_paint_volume: gboolean (* modify_paint_volume) ( ClutterEffect* effect, ClutterPaintVolume* volume )`

  Virtual function.

`paint: void (* paint) ( ClutterEffect* effect, ClutterPaintNode* node, ClutterPaintContext* paint_context, ClutterEffectPaintFlags flags )`

  Virtual function.

`paint_node: void (* paint_node) ( ClutterEffect* effect, ClutterPaintNode* node, ClutterPaintContext* paint_context, ClutterEffectPaintFlags flags )`

  No description available.

`pick: void (* pick) ( ClutterEffect* effect, ClutterPickContext* pick_context )`

  Virtual function.

#### Virtual methods

###### Clutter.EffectClass.modify_paint_volume

Virtual function.

###### Clutter.EffectClass.paint

Virtual function.

###### Clutter.EffectClass.paint_node

No description available.

###### Clutter.EffectClass.pick

Virtual function.

###### Clutter.EffectClass.post_paint

Virtual function.

###### Clutter.EffectClass.pre_paint

Virtual function.