ClutterEffect

ClutterEffect — Base class for actor effects

Synopsis

                    ClutterEffect;
struct              ClutterEffectClass;
void                clutter_effect_queue_rerun          (ClutterEffect *effect);

Object Hierarchy

  GObject
   +----GInitiallyUnowned
         +----ClutterActorMeta
               +----ClutterEffect
                     +----ClutterOffscreenEffect

Description

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 "paint" virtual function.

Implementing a ClutterEffect

Creating a sub-class of ClutterEffect requires overriding the ‘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_RUN_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.

The ‘paint’ virtual was added in Clutter 1.8. Prior to that there were two separate functions as follows.

  • pre_paint(), which is called before painting the ClutterActor.
  • post_paint(), which is called after painting the ClutterActor.

The pre_paint() function was used to set up the ClutterEffect right before the ClutterActor's paint sequence. This function can fail, and return FALSE; in that case, no post_paint() invocation will follow.

The post_paint() function was called after the ClutterActor's paint sequence.

With these two functions it is not possible to skip the rest of the paint sequence. The default implementation of the ‘paint’ virtual calls pre_paint(), clutter_actor_continue_paint() and then post_paint() so that existing actors that aren't using the paint virtual will continue to work. New actors using the paint virtual do not need to implement pre or post paint.

Example 4. 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 set_actor() implementation will create the two materials used for the two different rectangles; the paint() function will paint the first material using cogl_rectangle(), before continuing and then it will paint paint the second material after.

 typedef struct {
   ClutterEffect parent_instance;

   CoglHandle rect_1;
   CoglHandle 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);

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

   if (self->rect_2)
     {
       cogl_handle_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 material */
   self->rect_1 = cogl_material_new ();
   cogl_material_set_color4f (self->rect_1, 1.0, 0.0, 0.0, 1.0);

   /* Create a green material */
   self->rect_2 = cogl_material_new ();
   cogl_material_set_color4f (self->rect_2, 0.0, 1.0, 0.0, 1.0);
 }

 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)
 {
   ClutterActorMetaClas *meta_class = CLUTTER_ACTOR_META_CLASS (klass);

   meta_class->set_actor = my_effect_set_actor;

   klass->paint = my_effect_paint;
 }
    

ClutterEffect is available since Clutter 1.4

Details

ClutterEffect

typedef struct _ClutterEffect ClutterEffect;

The ClutterEffect structure contains only private data and should be accessed using the provided API

Since 1.4


struct ClutterEffectClass

struct ClutterEffectClass {
  gboolean (* pre_paint)        (ClutterEffect           *effect);
  void     (* post_paint)       (ClutterEffect           *effect);

  gboolean (* get_paint_volume) (ClutterEffect           *effect,
                                 ClutterPaintVolume      *volume);

  void     (* paint)            (ClutterEffect           *effect,
                                 ClutterEffectPaintFlags  flags);
  void     (* pick)             (ClutterEffect           *effect,
                                 ClutterEffectPaintFlags  flags);
};

The ClutterEffectClass structure contains only private data

pre_paint ()

virtual function

post_paint ()

virtual function

get_paint_volume ()

virtual function

paint ()

virtual function

pick ()

Since 1.4


clutter_effect_queue_rerun ()

void                clutter_effect_queue_rerun          (ClutterEffect *effect);