2. Changing an actor's paint sequence using ClutterEffect
Prev | Chapter 9. Effects | Next

## 2. Changing an actor's paint sequence using ClutterEffect

### 2.1. Problem

You want to paint on top of or under an actor in a generic way, without editing the actor's `paint()` implementation. Example use cases are:

- Adding a border on top of an actor.

- Drawing a background for an actor.

A quick way to achieve the same thing (though not readily portable between actors) is to connect a callback before or after an actor's paint signal. See this recipe for more details. However, using a ClutterEffect implementation, as explained in this recipe, is the preferred approach.

### 2.2. Solution

Create a subclass of the ClutterEffect abstract class; then implement the `pre_paint()` and/or `post_paint()` virtual functions. When the effect is applied to an actor, these functions will paint before and after the actor's own `paint()` implementation.

### Note

For this solution, we implement a simple CbBackgroundEffect which draws a gray rectangle under an actor. The full source is in this section. To keep it simple, the effect has no properties and isn't configurable (the background is always gray); see the border effect for a more detailed implementation with GObject trimmings.

First, create a ClutterEffect subclass. This requires the trappings of a GObject class; in particular, it needs a private struct to hold the effect's state. This should include any CoglMaterials, CoglColors or other private member variables you intend to use to draw the effect.

In the case of the background effect, we have a background CoglMaterial and a CoglColor for that material:

    struct _CbBackgroundEffectPrivate
    {
      CoglMaterial *background;
      CoglColor    *color;
    };

In the `init()` function for objects of your class, create any Cogl resources which you need to draw the effect. In the case of the background effect, we need to create the CoglMaterial and CoglColor for the private struct:

    static void
    cb_background_effect_init (CbBackgroundEffect *self)
    {
      /* get the private struct for the object
      CbBackgroundEffectPrivate *priv;
      priv = self->priv = CB_BACKGROUND_EFFECT_GET_PRIVATE (self);

      /* create the background material */
      priv->background = cogl_material_new ();

      /* gray color for filling the background material */
      priv->color = cogl_color_new ();
      cogl_color_init_from_4ub (priv->color, 122, 122, 122, 255);

      /* set the color on the material; NB this isn't configurable
       * for this effect, and is always gray
       */
      cogl_material_set_color (priv->background, priv->color);
    }

Optionally, you can create GObject properties for the class, if you want a configurable effect: see this section for details.

The `dispose()` function for your effect should clean up any Cogl resources:

    static void
    cb_background_effect_dispose (GObject *gobject)
    {
      CbBackgroundEffectPrivate *priv = CB_BACKGROUND_EFFECT (gobject)->priv;

      if (priv->background != COGL_INVALID_HANDLE)
        {
          cogl_handle_unref (priv->background);
          priv->background = COGL_INVALID_HANDLE;
        }

      if (priv->color != NULL)
        {
          cogl_color_free (priv->color);
          priv->color = NULL;
        }

      G_OBJECT_CLASS (cb_background_effect_parent_class)->dispose (gobject);
    }

Now, the important part: implement `pre_paint()` and/or `post_paint()`, using Cogl to draw on the material(s) set up for the effect.

For the background effect, we implement `pre_paint()`, to draw a gray rectangle under the actor:

    /* note that if pre_paint() returns FALSE
     * any post_paint() defined for the effect will not be called
     */
    static gboolean
    cb_background_effect_pre_paint (ClutterEffect *self)
    {
      ClutterActor *actor;
      gfloat width;
      gfloat height;
      CbBackgroundEffectPrivate *priv;

      priv = CB_BACKGROUND_EFFECT (self)->priv;

      /* get the associated actor's dimensions */
      actor = clutter_actor_meta_get_actor (CLUTTER_ACTOR_META (self));
      clutter_actor_get_size (actor, &width, &height);

      /* draw a Cogl rectangle in the background using the default color */
      cogl_set_source (priv->background);

      /* the rectangle has the same dimensions as the actor */
      cogl_rectangle (0, 0, width, height);

      return TRUE;
    }

Now, in the `init()` function for the effect class, assign your implementations to the virtual methods of the ClutterEffect abstract class:

    static void
    cb_background_effect_class_init (CbBackgroundEffectClass *klass)
    {
      ClutterEffectClass *effect_class = CLUTTER_EFFECT_CLASS (klass);
      GObjectClass *gobject_class = G_OBJECT_CLASS (klass);

      effect_class->pre_paint = cb_background_effect_pre_paint;
      gobject_class->dispose = cb_background_effect_dispose;

      g_type_class_add_private (klass, sizeof (CbBackgroundEffectPrivate));
    }

If you intend to make your effect reusable, provide a public constructor (as is done for the example effects in this recipe):

    ClutterEffect *
    cb_background_effect_new ()
    {
      return g_object_new (CB_TYPE_BACKGROUND_EFFECT,
                           NULL);
    }

The effect is now ready to be used. The application code for applying your effect to an actor is the same as for any other effect:

    ClutterActor *texture;
    ClutterEffect *background_effect;

    /* ...initialize texture, load image file etc... */

    /* create a gray background effect */
    background_effect = cb_background_effect_new ();

    /* apply the effect to the actor */
    clutter_actor_add_effect (texture, background_effect);

Below is an example of applying this effect to a texture loaded with an image; the image has a transparent background, so the background is visible through it. The screenshot is from the example application:

### 2.3. Discussion

A basic ClutterEffect is particularly useful for amending the appearance of an actor on the fly: for example, to highlight an actor in response to a button presses. This could be done by creating a custom widget whose appearance could be toggled. But what if you wanted to make an arbitrary actor's appearance "togglable"? A generic effect in the style of the border effect in this recipe can be applied to any actor, and easily toggled by enabling/disabling the effect.

ClutterEffect works best where you want to overlay or underlay the actor with Cogl paths or primitives, without changing the actor's geometry. If you want to do complicated geometry transformations, or other subtle manipulations of an actor's appearance, it is better to use a ClutterEffect subclass like ClutterOffscreenEffect, ClutterDeformEffect, or ClutterShaderEffect.

In a similar vein, when a ClutterEffect is applied to an actor, the effect shouldn't paint outside the actor's allocation. However, if the effect provides a `get_paint_volume()` implementation which returns a volume larger than the actor's allocation, the effect can paint anywhere within that volume. Though in most cases, creating a custom paint volume is only going to be useful for offscreen effects, where you are changing the actor's geometry.

#### 2.3.1. Effect properties

If your effect has GObject properties, you should ensure that an actor associated with the effect is queued for a redraw when those properties change. (You only need to do this for properties which change the effect's appearance; but this is likely to include most of an effect's properties.)

In most cases, you're likely define standard GObject properties for the class; for example, CbBorderEffect defines a `width` property like this:

    static void
    cb_border_effect_class_init (CbBorderEffectClass *klass)
    {
      GObjectClass *gobject_class = G_OBJECT_CLASS (klass);
      GParamSpec *pspec;

      /* ...more class initialization code here... */

      pspec = g_param_spec_float ("width",
                                  "Width",
                                  "The width of the border (in pixels)",
                                  1.0, 100.0,
                                  10.0,
                                  G_PARAM_READWRITE);
      obj_props[PROP_WIDTH] = pspec;
      g_object_class_install_property (gobject_class, PROP_WIDTH, pspec);

      /* ...more property definitions...*/
    }

It also defines a standard GObject `set_property()` function for `width`:

    static void
    cb_border_effect_set_property (GObject      *gobject,
                                   guint         prop_id,
                                   const GValue *value,
                                   GParamSpec   *pspec)
    {
      CbBorderEffect *effect = CB_BORDER_EFFECT (gobject);

      switch (prop_id)
        {
        /* ...other cases here ... */

        case PROP_WIDTH:
          cb_border_effect_set_width (effect, g_value_get_float (value));
          break;

        /* ...default case ... */
        }
    }

Note that this calls `cb_border_effect_set_width()`, which is also exposed in the public API. This is where the `width` member variable is actually set in the private struct; and also where the redraw for the actor associated with the effect should be queued:

    /* queues a redraw of the actor associated with the effect, if there is one */
    static void
    cb_border_effect_update (CbBorderEffect *self)
    {
      ClutterActor *actor = clutter_actor_meta_get_actor (CLUTTER_ACTOR_META (self));

      /* this guard is necessary as an effect's properties can be manipulated
       * before it has an actor associated with it
       */
      if (actor != NULL)
        clutter_actor_queue_redraw (actor);
    }

    /* public setter for the width property, which calls the update function */
    void
    cb_border_effect_set_width (CbBorderEffect *self,
                                gfloat          width)
    {
      CbBorderEffectPrivate *priv;

      g_return_if_fail (CB_IS_BORDER_EFFECT (self));

      priv = CB_BORDER_EFFECT_GET_PRIVATE (self);

      priv->width = width;

      /* the property has been updated, so queue a redraw of the actor (if set) */
      cb_border_effect_update (self);
    }

Any other property setters which affect the associated actor's appearance (i.e. color in the case of CbBorderEffect) should also call the update function after setting the property.

### Tip

If your effect exposes GObject properties in this way, it can also be animated with the Clutter animation API as usual. For example, you could animate the border effect in this recipe so that the border gradually becomes thinner or thicker.

### 2.4. Full example

The example application applies two effects to a group of ClutterTextures:

- A CbBackgroundEffect which draws a gray background under each actor. The effect is implemented in a header file and a C code file.

- A CbBorderEffect which draws a red border on top of an actor; this is toggled by clicking on the actor. The effect is implemented in a header file and a C code file.

The application creates textures from the file paths specified on the command line then applies both of these effects to each texture. In the case of the CbBorderEffect, a 5 pixel red border is applied; this is also disabled by default, and enabled when a texture is clicked.

Here is an example of the output when the application is loaded with four images:

#### 2.4.1. CbBackgroundEffect

Example 9.2. `cb-background-effect.h` (header file)

    #ifndef __CB_BACKGROUND_EFFECT_H__
    #define __CB_BACKGROUND_EFFECT_H__

    #include <clutter/clutter.h>

    GType cb_background_effect_get_type (void);

    #define CB_TYPE_BACKGROUND_EFFECT (cb_background_effect_get_type ())
    #define CB_BACKGROUND_EFFECT(obj) (G_TYPE_CHECK_INSTANCE_CAST ((obj), \
                                                                   CB_TYPE_BACKGROUND_EFFECT, \
                                                                   CbBackgroundEffect))
    #define CB_IS_BACKGROUND_EFFECT(obj)         (G_TYPE_CHECK_INSTANCE_TYPE ((obj), \
                                                                              CB_TYPE_BACKGROUND_EFFECT))
    #define CB_BACKGROUND_EFFECT_CLASS(klass)    (G_TYPE_CHECK_CLASS_CAST ((klass), \
                                                                           CB_TYPE_BACKGROUND_EFFECT, \
                                                                           CbBackgroundEffectClass))
    #define CB_IS_BACKGROUND_EFFECT_CLASS(klass) (G_TYPE_CHECK_CLASS_TYPE ((klass), \
                                                                           CB_TYPE_BACKGROUND_EFFECT))
    #define CB_BACKGROUND_EFFECT_GET_CLASS(obj)  (G_TYPE_INSTANCE_GET_CLASS ((obj), \
                                                                             CB_TYPE_BACKGROUND_EFFECT, \
                                                                             CbBackgroundEffectClass))

    typedef struct _CbBackgroundEffectPrivate CbBackgroundEffectPrivate;
    typedef struct _CbBackgroundEffect        CbBackgroundEffect;
    typedef struct _CbBackgroundEffectClass   CbBackgroundEffectClass;

    /* object */
    struct _CbBackgroundEffect
    {
      ClutterEffect              parent_instance;
      CbBackgroundEffectPrivate *priv;
    };

    /* class */
    struct _CbBackgroundEffectClass
    {
      ClutterEffectClass parent_class;
    };

    ClutterEffect *cb_background_effect_new ();

    #endif /* __CB_BACKGROUND_EFFECT_H__ */

Example 9.3. `cb-background-effect.c` (code file)

    #include "cb-background-effect.h"

    G_DEFINE_TYPE (CbBackgroundEffect, cb_background_effect, CLUTTER_TYPE_EFFECT);

    #define CB_BACKGROUND_EFFECT_GET_PRIVATE(obj) (G_TYPE_INSTANCE_GET_PRIVATE ((obj), \
                                                                                CB_TYPE_BACKGROUND_EFFECT, \
                                                                                CbBackgroundEffectPrivate))

    struct _CbBackgroundEffectPrivate
    {
      CoglMaterial *background;
      CoglColor    *color;
    };

    /* ClutterEffect implementation */

    /* note that if pre_paint() returns FALSE
     * any post_paint() defined for the effect will not be called
     */
    static gboolean
    cb_background_effect_pre_paint (ClutterEffect *self)
    {
      ClutterActor *actor;
      gfloat width;
      gfloat height;
      CbBackgroundEffectPrivate *priv;

      priv = CB_BACKGROUND_EFFECT (self)->priv;

      /* get the associated actor's dimensions */
      actor = clutter_actor_meta_get_actor (CLUTTER_ACTOR_META (self));
      clutter_actor_get_size (actor, &width, &height);

      /* draw a grey Cogl rectangle in the background */
      cogl_set_source (priv->background);

      cogl_rectangle (0, 0, width, height);

      return TRUE;
    }

    /* GObject implementation */
    static void
    cb_background_effect_dispose (GObject *gobject)
    {
      CbBackgroundEffectPrivate *priv = CB_BACKGROUND_EFFECT (gobject)->priv;

      if (priv->background != COGL_INVALID_HANDLE)
        {
          cogl_handle_unref (priv->background);
          priv->background = COGL_INVALID_HANDLE;
        }

      if (priv->color != NULL)
        {
          cogl_color_free (priv->color);
          priv->color = NULL;
        }

      G_OBJECT_CLASS (cb_background_effect_parent_class)->dispose (gobject);
    }

    static void
    cb_background_effect_class_init (CbBackgroundEffectClass *klass)
    {
      ClutterEffectClass *effect_class = CLUTTER_EFFECT_CLASS (klass);
      GObjectClass *gobject_class = G_OBJECT_CLASS (klass);

      effect_class->pre_paint = cb_background_effect_pre_paint;
      gobject_class->dispose = cb_background_effect_dispose;

      g_type_class_add_private (klass, sizeof (CbBackgroundEffectPrivate));
    }

    static void
    cb_background_effect_init (CbBackgroundEffect *self)
    {
      CbBackgroundEffectPrivate *priv;

      priv = self->priv = CB_BACKGROUND_EFFECT_GET_PRIVATE (self);

      priv->background = cogl_material_new ();

      /* grey color for filling the background material */
      priv->color = cogl_color_new ();
      cogl_color_init_from_4ub (priv->color, 122, 122, 122, 255);

      cogl_material_set_color (priv->background, priv->color);
    }

    /* public API */

    /**
     * cb_background_effect_new:
     *
     * Creates a new #ClutterEffect which adds a grey background
     * when applied to a rectangular actor.
     */
    ClutterEffect *
    cb_background_effect_new ()
    {
      return g_object_new (CB_TYPE_BACKGROUND_EFFECT,
                           NULL);
    }

#### 2.4.2. CbBorderEffect

This is a more sophisticated effect with configurable border color and width.

Example 9.4. `cb-border-effect.h` (header file)

    #ifndef __CB_BORDER_EFFECT_H__
    #define __CB_BORDER_EFFECT_H__

    #include <clutter/clutter.h>

    GType cb_border_effect_get_type (void);

    #define CB_TYPE_BORDER_EFFECT (cb_border_effect_get_type ())
    #define CB_BORDER_EFFECT(obj) (G_TYPE_CHECK_INSTANCE_CAST ((obj), \
                                                               CB_TYPE_BORDER_EFFECT, \
                                                               CbBorderEffect))
    #define CB_IS_BORDER_EFFECT(obj)         (G_TYPE_CHECK_INSTANCE_TYPE ((obj), \
                                                                          CB_TYPE_BORDER_EFFECT))
    #define CB_BORDER_EFFECT_CLASS(klass)    (G_TYPE_CHECK_CLASS_CAST ((klass), \
                                                                       CB_TYPE_BORDER_EFFECT, \
                                                                       CbBorderEffectClass))
    #define CB_IS_BORDER_EFFECT_CLASS(klass) (G_TYPE_CHECK_CLASS_TYPE ((klass), \
                                                                       CB_TYPE_BORDER_EFFECT))
    #define CB_BORDER_EFFECT_GET_CLASS(obj)  (G_TYPE_INSTANCE_GET_CLASS ((obj), \
                                                                         CB_TYPE_BORDER_EFFECT, \
                                                                         CbBorderEffectClass))

    typedef struct _CbBorderEffectPrivate CbBorderEffectPrivate;
    typedef struct _CbBorderEffect        CbBorderEffect;
    typedef struct _CbBorderEffectClass   CbBorderEffectClass;

    /* object */
    struct _CbBorderEffect
    {
      ClutterEffect          parent_instance;
      CbBorderEffectPrivate *priv;
    };

    /* class */
    struct _CbBorderEffectClass
    {
      ClutterEffectClass parent_class;
    };

    ClutterEffect *cb_border_effect_new (gfloat              width,
                                         const ClutterColor *color);

    void cb_border_effect_set_color (CbBorderEffect     *self,
                                     const ClutterColor *color);

    void cb_border_effect_get_color (CbBorderEffect *self,
                                     ClutterColor   *color);

    void cb_border_effect_set_width (CbBorderEffect *self,
                                     gfloat          width);

    gfloat cb_border_effect_get_width (CbBorderEffect *self);

    #endif /* __CB_BORDER_EFFECT_H__ */

Example 9.5. `cb-border-effect.c` (code file)

    #include "cb-border-effect.h"

    G_DEFINE_TYPE (CbBorderEffect, cb_border_effect, CLUTTER_TYPE_EFFECT);

    #define CB_BORDER_EFFECT_GET_PRIVATE(obj) (G_TYPE_INSTANCE_GET_PRIVATE ((obj), \
                                                                            CB_TYPE_BORDER_EFFECT, \
                                                                            CbBorderEffectPrivate))

    static const ClutterColor grey = { 0xaa, 0xaa, 0xaa, 0xff };

    struct _CbBorderEffectPrivate
    {
      CoglMaterial *border;
      ClutterColor  color;
      gfloat        width;
    };

    enum {
      PROP_0,

      PROP_COLOR,
      PROP_WIDTH,

      PROP_LAST
    };

    static GParamSpec *obj_props[PROP_LAST];

    /* ClutterEffect implementation */
    static void
    cb_border_effect_post_paint (ClutterEffect *self)
    {
      ClutterActor *actor;
      gfloat width;
      gfloat height;
      CbBorderEffectPrivate *priv;

      priv = CB_BORDER_EFFECT (self)->priv;

      /* get the associated actor's dimensions */
      actor = clutter_actor_meta_get_actor (CLUTTER_ACTOR_META (self));
      clutter_actor_get_size (actor, &width, &height);

      /* draw Cogl rectangles on top */
      cogl_set_source (priv->border);
      cogl_path_new ();

      /* left rectangle */
      cogl_path_rectangle (0, 0, priv->width, height);

      /* top rectangle */
      cogl_path_rectangle (priv->width, 0, width, priv->width);

      /* right rectangle */
      cogl_path_rectangle (width - priv->width, priv->width, width, height);

      /* bottom rectangle */
      cogl_path_rectangle (priv->width,
                           height - priv->width,
                           width - priv->width,
                           height);

      cogl_path_fill ();
    }

    /* GObject implementation */
    static void
    cb_border_effect_dispose (GObject *gobject)
    {
      CbBorderEffectPrivate *priv = CB_BORDER_EFFECT (gobject)->priv;

      if (priv->border != COGL_INVALID_HANDLE)
        {
          cogl_handle_unref (priv->border);
          priv->border = COGL_INVALID_HANDLE;
        }

      G_OBJECT_CLASS (cb_border_effect_parent_class)->dispose (gobject);
    }

    static void
    cb_border_effect_set_property (GObject      *gobject,
                                   guint         prop_id,
                                   const GValue *value,
                                   GParamSpec   *pspec)
    {
      CbBorderEffect *effect = CB_BORDER_EFFECT (gobject);

      switch (prop_id)
        {
        case PROP_COLOR:
          cb_border_effect_set_color (effect, clutter_value_get_color (value));
          break;

        case PROP_WIDTH:
          cb_border_effect_set_width (effect, g_value_get_float (value));
          break;

        default:
          G_OBJECT_WARN_INVALID_PROPERTY_ID (gobject, prop_id, pspec);
          break;
        }
    }

    static void
    cb_border_effect_get_property (GObject    *gobject,
                                   guint       prop_id,
                                   GValue     *value,
                                   GParamSpec *pspec)
    {
      CbBorderEffectPrivate *priv = CB_BORDER_EFFECT (gobject)->priv;

      switch (prop_id)
        {
        case PROP_COLOR:
          g_value_set_object (value, &(priv->color));
          break;

        case PROP_WIDTH:
          g_value_set_float (value, priv->width);
          break;

        default:
          G_OBJECT_WARN_INVALID_PROPERTY_ID (gobject, prop_id, pspec);
          break;
        }
    }

    /* GObject class and instance init */
    static void
    cb_border_effect_class_init (CbBorderEffectClass *klass)
    {
      ClutterEffectClass *effect_class = CLUTTER_EFFECT_CLASS (klass);
      GObjectClass *gobject_class = G_OBJECT_CLASS (klass);
      GParamSpec *pspec;

      effect_class->post_paint = cb_border_effect_post_paint;

      gobject_class->set_property = cb_border_effect_set_property;
      gobject_class->get_property = cb_border_effect_get_property;
      gobject_class->dispose = cb_border_effect_dispose;

      g_type_class_add_private (klass, sizeof (CbBorderEffectPrivate));

      /**
       * CbBorderEffect:width:
       *
       * The width of the border
       */
      pspec = g_param_spec_float ("width",
                                  "Width",
                                  "The width of the border (in pixels)",
                                  1.0, 100.0,
                                  10.0,
                                  G_PARAM_READWRITE);
      obj_props[PROP_WIDTH] = pspec;
      g_object_class_install_property (gobject_class, PROP_WIDTH, pspec);

      /**
       * CbBorderEffect:color:
       *
       * The color of the border
       */
      pspec = clutter_param_spec_color ("color",
                                        "Color",
                                        "The border color",
                                        &grey,
                                        G_PARAM_READWRITE);
      obj_props[PROP_COLOR] = pspec;
      g_object_class_install_property (gobject_class, PROP_COLOR, pspec);
    }

    static void
    cb_border_effect_init (CbBorderEffect *self)
    {
      CbBorderEffectPrivate *priv;

      priv = self->priv = CB_BORDER_EFFECT_GET_PRIVATE (self);

      priv->border = cogl_material_new ();

      priv->color = grey;
    }

    /* called each time a property is set on the effect */
    static void
    cb_border_effect_update (CbBorderEffect *self)
    {
      ClutterActor *actor = clutter_actor_meta_get_actor (CLUTTER_ACTOR_META (self));

      if (actor != NULL)
        clutter_actor_queue_redraw (actor);
    }

    /* public API */

    /**
     * cb_border_effect_new:
     * @width: width of the border applied by the effect
     * @color: a #ClutterColor
     *
     * Creates a new #ClutterEffect with the given @width
     * and of the given @color.
     */
    ClutterEffect *
    cb_border_effect_new (gfloat              width,
                          const ClutterColor *color)
    {
      return g_object_new (CB_TYPE_BORDER_EFFECT,
                           "width", width,
                           "color", color,
                           NULL);
    }

    /**
     * cb_border_effect_set_color:
     * @self: a #CbBorderEffect
     * @color: a #ClutterColor
     *
     * Sets the color of the border provided by the effect @self.
     */
    void
    cb_border_effect_set_color (CbBorderEffect     *self,
                                const ClutterColor *color)
    {
      CbBorderEffectPrivate *priv;

      g_return_if_fail (CB_IS_BORDER_EFFECT (self));
      g_return_if_fail (color != NULL);

      priv = CB_BORDER_EFFECT_GET_PRIVATE (self);

      priv->color.red = color->red;
      priv->color.green = color->green;
      priv->color.blue = color->blue;
      priv->color.alpha = color->alpha;

      cogl_material_set_color4ub (priv->border,
                                  color->red,
                                  color->green,
                                  color->blue,
                                  color->alpha);

      cb_border_effect_update (self);
    }

    /**
     * cb_border_effect_get_color:
     * @self: a #CbBorderEffect
     * @color: return location for a #ClutterColor
     *
     * Retrieves the color of the border applied by the effect @self.
     */
    void
    cb_border_effect_get_color (CbBorderEffect *self,
                                ClutterColor   *color)
    {
      CbBorderEffectPrivate *priv;

      g_return_if_fail (CB_IS_BORDER_EFFECT (self));

      priv = CB_BORDER_EFFECT_GET_PRIVATE (self);

      color->red = priv->color.red;
      color->green = priv->color.green;
      color->blue = priv->color.blue;
      color->alpha = priv->color.alpha;
    }

    /**
     * cb_border_effect_set_width:
     * @self: a #CbBorderEffect
     * @width: the width of the border
     *
     * Sets the width (in pixels) of the border applied by the effect @self.
     */
    void
    cb_border_effect_set_width (CbBorderEffect *self,
                                gfloat          width)
    {
      CbBorderEffectPrivate *priv;

      g_return_if_fail (CB_IS_BORDER_EFFECT (self));

      priv = CB_BORDER_EFFECT_GET_PRIVATE (self);

      priv->width = width;

      cb_border_effect_update (self);
    }

    /**
     * cb_border_effect_get_width:
     * @self: a #CbBorderEffect
     *
     * Gets the width (in pixels) of the border applied by the effect @self.
     *
     * Return value: the border's width, or 0.0 if @self is not
     * a #CbBorderEffect
     */
    gfloat
    cb_border_effect_get_width (CbBorderEffect *self)
    {
      CbBorderEffectPrivate *priv;

      g_return_val_if_fail (CB_IS_BORDER_EFFECT (self), 0.0);

      priv = CB_BORDER_EFFECT_GET_PRIVATE (self);

      return priv->width;
    }

#### 2.4.3. Application

Example 9.6. Application which applies CbBorderEffect and CbBackgroundEffect to a group of ClutterTextures.

    #include <stdlib.h>
    #include <clutter/clutter.h>

    #include "cb-border-effect.h"
    #include "cb-background-effect.h"

    static const ClutterColor stage_color = { 0x33, 0x33, 0x55, 0xff };
    static ClutterColor red_color = { 0xff, 0x00, 0x00, 0xff };

    static gboolean
    toggle_highlight (ClutterActor *actor,
                      ClutterEvent *event,
                      gpointer      user_data)
    {
      ClutterActorMeta *meta = CLUTTER_ACTOR_META (user_data);

      gboolean effect_enabled = clutter_actor_meta_get_enabled (meta);

      clutter_actor_meta_set_enabled (meta, !effect_enabled);

      return CLUTTER_EVENT_STOP;
    }

    int
    main (int   argc,
          char *argv[])
    {
      ClutterActor *stage;
      ClutterActor *box;
      ClutterLayoutManager *layout_manager;
      ClutterActor *texture;
      ClutterEffect *background_effect;
      ClutterEffect *border_effect;
      ClutterConstraint *width_constraint;
      gchar *filename;
      guint i;
      GError *error = NULL;

      if (argc < 2)
        {
          g_print ("Usage: %s <image files>\n", argv[0]);
          return EXIT_FAILURE;
        }

      if (clutter_init (&argc, &argv) != CLUTTER_INIT_SUCCESS)
        return EXIT_FAILURE;

      stage = clutter_stage_new ();
      clutter_stage_set_color (CLUTTER_STAGE (stage), &stage_color);
      clutter_stage_set_user_resizable (CLUTTER_STAGE (stage), TRUE);
      clutter_actor_set_size (stage, 600, 400);
      g_signal_connect (stage, "destroy", G_CALLBACK (clutter_main_quit), NULL);

      layout_manager = clutter_flow_layout_new (CLUTTER_FLOW_HORIZONTAL);
      clutter_flow_layout_set_column_spacing (CLUTTER_FLOW_LAYOUT (layout_manager),
                                              10);
      clutter_flow_layout_set_row_spacing (CLUTTER_FLOW_LAYOUT (layout_manager),
                                           10);

      box = clutter_actor_new ();
      clutter_actor_set_layout_manager (box, layout_manager);
      width_constraint = clutter_bind_constraint_new (stage,
                                                      CLUTTER_BIND_WIDTH,
                                                      0.0);
      clutter_actor_add_constraint (box, width_constraint);

      /* loop through the files specified on the command line, adding
       * each one into the box
       */
      for (i = 1; i < argc; i++)
        {
          filename = argv[i];

          texture = clutter_texture_new ();
          clutter_texture_set_keep_aspect_ratio (CLUTTER_TEXTURE (texture), TRUE);
          clutter_actor_set_width (texture, 150);
          clutter_actor_set_reactive (texture, TRUE);

          clutter_texture_set_from_file (CLUTTER_TEXTURE (texture),
                                         filename,
                                         &error);

          if (error != NULL)
            g_warning ("Error loading file %s:\n%s",
                       filename,
                       error->message);

          /* create a grey background effect */
          background_effect = cb_background_effect_new ();

          /* apply the effect to the actor */
          clutter_actor_add_effect (texture, background_effect);

          /* create a 5 pixel red border effect */
          border_effect = cb_border_effect_new (5.0, &red_color);

          /* apply the effect to the actor, but disabled */
          clutter_actor_add_effect (texture, border_effect);
          clutter_actor_meta_set_enabled (CLUTTER_ACTOR_META (border_effect),
                                          FALSE);

          /* on mouse click, toggle the "enabled" property of the border effect */
          g_signal_connect (texture,
                            "button-press-event",
                            G_CALLBACK (toggle_highlight),
                            border_effect);

          clutter_container_add_actor (CLUTTER_CONTAINER (box), texture);
        }

      clutter_container_add_actor (CLUTTER_CONTAINER (stage), box);

      clutter_actor_show (stage);

      clutter_main ();

      return EXIT_SUCCESS;
    }

Prev | Up | Next
Chapter 9. Effects | Home | 3. Creating and animating a custom ClutterDeformEffect