4. Arranging actors in a single row or column
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## 4. Arranging actors in a single row or column

### 4.1. Problem

You want to layout several actors in a single row or column.

Example use cases:

- Creating an application menu.

- Showing message subject lines as a list in an email client.

### 4.2. Solution

Create a ClutterActor with a ClutterBoxLayout as its layout manager.

A ClutterBoxLayout can hold a single row or column of ClutterActors, and has configurable spacing, actor alignments, and expand and fill options.

The code fragment below is excerpted from the full example. It demonstrates how to lay out three rectangles in a vertical column. A different approach is used to set the `x-fill` property on each rectangle, so each fills the horizontal space in the layout (each rectangle is 100 pixels wide, while the box they are inside is 200 pixels wide).

    /* create a ClutterBoxLayout */
    box_layout = clutter_box_layout_new ();

    /* configure it to lay out actors vertically */
    clutter_box_layout_set_vertical (CLUTTER_BOX_LAYOUT (box_layout), TRUE);

    /* put 5px of spacing between actors */
    clutter_box_layout_set_spacing (CLUTTER_BOX_LAYOUT (box_layout), 5);

    /* actors are packed into this box; we set its width, but
     * allow its height to be determined by the children it contains
     */
    box = clutter_actor_new ();
    clutter_actor_set_layout_manager (box, box_layout);
    clutter_actor_set_background_color (box, &box_color);
    clutter_actor_set_position (box, 100, 50);
    clutter_actor_set_width (box, 200);

    /* pack an actor into the layout and set all layout properties on it
     * at the same time
     */
    yellow = clutter_rectangle_new_with_color (&yellow_color);
    clutter_actor_set_size (yellow, 100, 100);

    clutter_box_layout_pack (CLUTTER_BOX_LAYOUT (box_layout),
                             yellow,
                             FALSE,                         /* expand */
                             TRUE,                          /* x-fill */
                             FALSE,                         /* y-fill */
                             CLUTTER_BOX_ALIGNMENT_START,   /* x-align */
                             CLUTTER_BOX_ALIGNMENT_START);  /* y-align */

    /* add an actor to the box as a container and set layout properties
     * afterwards; the latter is useful if you want to change properties on
     * actors already inside a layout, but note that you have to
     * pass the function both the layout AND the container
     */
    red = clutter_rectangle_new_with_color (&red_color);
    clutter_actor_set_size (red, 100, 100);

    clutter_actor_add_child (box, blue);

    clutter_layout_manager_child_set (box_layout,
                                      CLUTTER_CONTAINER (box),
                                      blue,
                                      "x-fill", TRUE,
                                      NULL);

    blue = clutter_rectangle_new_with_color (&blue_color);
    clutter_actor_set_size (blue, 100, 100);

    clutter_actor_add_child (box, blue);

    clutter_layout_manager_child_set (box_layout,
                                      CLUTTER_CONTAINER (box),
                                      blue,
                                      "x-fill", TRUE,
                                      NULL);

    /* put the box on the stage */
    clutter_actor_add_child (stage, box);

The result looks like this:

### 4.3. Discussion

ClutterBoxLayout is not a reflowing layout: that is, if the layout's container changes size, the actors inside aren't automatically repositioned to occupy or find new positions in its available area. If you want that behaviour, use ClutterFlowLayout instead.

If you want the container to be resizable, but find that resizing the container obscures its child actors, you could put the container inside a scrollable area. Then the container's actors can be scrolled to if they go out of sight. This recipe explains how to make a container scrollable.

#### 4.3.1. Layout properties

ClutterBoxLayout is very flexible, with several properties which influence the appearance of the layout and its children. As with other layouts, these properties are either applicable to the layout itself, or to individual children of the layout.

As most of these properties are documented in the API reference, they aren't covered in much detail here. However, below is a brief overview of the properties available, as well as details of properties particular to ClutterBoxLayout.

The main issue you may face when applying these properties is understanding how they interact. As this is harder to describe than to show, you can run the example below to toggle and tweak various properties and see how they affect the layout's appearance.

### Note

The "toggle and tweak" example sets child properties (fill, alignment, expand) on all children of the layout when those properties are changed. If you want to see the effect of setting these to different values for each child, you will have to experiment yourself.

##### 4.3.1.1. ClutterBoxLayout properties

ClutterBoxLayout has the following properties which affect the appearance of all children inside the container.

### Note

Animation properties are covered separately later.

- `vertical`; set with `clutter_box_layout_set_vertical()`. Set to `TRUE` to lay out child actors in a column; if `FALSE` (the default), actors are laid out horizontally.

- `homogeneous`; set with `clutter_box_layout_set_homogeneous()`. Set to `TRUE` to allocate all child actors the same amount of space in the row or column (depending on the setting for `vertical`). This overrides per-actor `expand` settings and preferred sizes for child actors. The default value for this property is `FALSE`.

- `spacing`; set with `clutter_box_layout_set_spacing()`. Sets the number of pixels to place between actors in the layout.

  Note that if you increase spacing too much, actors may go outside the edges of the layout's container (if the container has a fixed size).

- `pack-start`; set with `clutter_box_layout_set_pack_start()`. Set `pack-start` to `TRUE` to configure the layout to prepend actors to the row or column; the default is `FALSE`, meaning that actors are appended to the row or column when added.

  Changing this property on a layout which already has actors in it will reverse the order of those actors, as well as changing how new actors are added to the layout.

##### 4.3.1.2. Child properties

These properties apply to individual children within the layout's container. Each child can have different values for each of these properties.

To set properties, you can use `clutter_box_layout_pack()` or `clutter_box_pack()` (if using a ClutterBox) while packing actors into the layout. You can also set properties later using `clutter_layout_manager_child_set()` etc. See the layouts introduction for more details.

- `x-fill` and `y-fill` set whether an actor will fill its allocated horizontal or vertical space (respectively) within the layout. Setting these properties only has an effect where an actor is smaller (on the appropriate fill axes) than the layout's container.

  Note that the actor's actual size is not changed if it is set to fill: the reported width and height are unaffected.

- `expand` sets whether an actor will be expanded inside the layout. If `expand` is `TRUE` and `fill` is `TRUE` for the orientation axis, the actor is resized to fill its whole allocation on that axis; if `expand` is `TRUE` but `fill` is `FALSE`, extra padding is added around the actor to fill the allocation.

- `x-align` and `y-align` set how an actor is aligned within its allocation, in cases where it doesn't fill that allocation. In practical terms, these properties come into effect if a child is set to expand but `fill` is set to `FALSE` on the align axis.

  For example, if `expand` is `TRUE` but `x-fill` is `FALSE`, some padding is added around the actor to fill its allocation. In this case, the `x-align` property can be set to align the actor to the left, center or right of the allocation; any whitespace would be redistributed around the actor's new position after alignment.

These properties are only useful where you have actors of non-uniform sizes and/or a container which is either wider or taller (or both) than one or more of the child actors it contains.

#### 4.3.2. Animating layout changes

If actors are added to a layout, or if the layout's properties or its children's properties are changed, the appearance of the layout may also change. The `use-animations` property (set with `clutter_box_layout_set_use_animations()`) determines whether such changes to the layout are animated: if set to `TRUE`, any changes to actor allocations resulting from the changes (movements, resizings) are animated.

If this property is `FALSE` (the default) changes to other properties or addition of new actors will cause actors to be laid out instantaneously. For example, if a new actor is prepended with animations on, the new actor is added to the layout and the other actors shifted to make room for it; if animations are off, child actors jump to their new positions at the same instant as the new actor is added.

To change the appearance of the animations, you can use `clutter_box_layout_set_easing_mode()` and `clutter_box_layout_set_duration()` (see the animations introduction for more about easing and duration properties).

The "toggle and tweak" example uses animation for layout changes, and can give you some idea of what to expect in your own animated layouts.

### 4.4. Full examples

Example 7.6. Different approaches to setting child layout properties in a ClutterBoxLayout

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

    static const ClutterColor stage_color = { 0x33, 0x33, 0x55, 0xff };
    static const ClutterColor box_color = { 0xff, 0xff, 0xff, 0xff };
    static const ClutterColor yellow_color = { 0xaa, 0xaa, 0x00, 0xff };
    static const ClutterColor red_color = { 0xff, 0x00, 0x00, 0xff };
    static const ClutterColor blue_color = { 0x00, 0x00, 0xff, 0xff };

    int
    main (int   argc,
          char *argv[])
    {
      ClutterActor *stage;
      ClutterLayoutManager *box_layout;
      ClutterActor *box;
      ClutterActor *yellow;
      ClutterActor *red;
      ClutterActor *blue;

      if (clutter_init (&argc, &argv) != CLUTTER_INIT_SUCCESS)
        return 1;

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

      /* create a ClutterBoxLayout */
      box_layout = clutter_box_layout_new ();

      /* configure it to lay out actors vertically */
      clutter_box_layout_set_vertical (CLUTTER_BOX_LAYOUT (box_layout), TRUE);

      /* put 5px of spacing between actors */
      clutter_box_layout_set_spacing (CLUTTER_BOX_LAYOUT (box_layout), 5);

      /* actors are packed into this actor; we set its width, but
       * allow its height to be determined by the children it contains
       */
      box = clutter_actor_new ();
      clutter_actor_set_layout_manager (box, box_layout);
      clutter_actor_set_background_color (box, CLUTTER_COLOR_White);
      clutter_actor_set_position (box, 100, 50);
      clutter_actor_set_width (box, 200);

      /* pack an actor into the layout and set all layout properties on it
       * at the same time
       */
      yellow = clutter_actor_new ();
      clutter_actor_set_background_color (yellow, CLUTTER_COLOR_Yellow);
      clutter_actor_set_size (yellow, 100, 100);

      clutter_box_layout_pack (CLUTTER_BOX_LAYOUT (box_layout),
                               yellow,
                               FALSE,                         /* expand */
                               TRUE,                          /* x-fill */
                               FALSE,                         /* y-fill */
                               CLUTTER_BOX_ALIGNMENT_START,   /* x-align */
                               CLUTTER_BOX_ALIGNMENT_START);  /* y-align */

      /* add an actor to the box as a container and set layout properties
       * afterwards; the latter is useful if you want to change properties on
       * actors already inside a layout, but note that you have to
       * pass the function both the layout AND the container
       */
      red = clutter_actor_new ();
      clutter_actor_set_background_color (red, CLUTTER_COLOR_Red);
      clutter_actor_set_size (red, 100, 100);

      clutter_actor_add_child (box, red);
      clutter_layout_manager_child_set (box_layout,
                                        CLUTTER_CONTAINER (box),
                                        red,
                                        "x-fill", TRUE,
                                        NULL);

      blue = clutter_actor_new ();
      clutter_actor_set_background_color (blue, CLUTTER_COLOR_Blue);
      clutter_actor_set_size (blue, 100, 100);

      clutter_actor_add_child (box, blue);
      clutter_layout_manager_child_set (box_layout,
                                        CLUTTER_CONTAINER (box),
                                        blue,
                                        "x-fill", TRUE,
                                        NULL);

      /* put the box on the stage */
      clutter_actor_add_child (stage, box);

      clutter_actor_show (stage);

      clutter_main ();

      return EXIT_SUCCESS;
    }

Example 7.7. A simple ClutterBoxLayout menu

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

    #define FONT "Sans 20px"

    static const ClutterColor stage_color = { 0x33, 0x33, 0x55, 0xff };
    static const ClutterColor yellow_color = { 0xaa, 0xaa, 0x00, 0xff };
    static const ClutterColor black_color = { 0x00, 0x00, 0x00, 0xff };

    static void
    menu_run_option (ClutterActor *actor,
                     ClutterEvent *event,
                     gpointer      user_data)
    {
      g_debug ("%s pressed", (gchar *) user_data);
    }

    static void
    menu_add_option (ClutterBox *menu,
                     gchar      *text,
                     gchar      *shortcut)
    {
      ClutterActor *entry;

      entry = clutter_box_new (clutter_bin_layout_new (CLUTTER_BIN_ALIGNMENT_CENTER,
                                                       CLUTTER_BIN_ALIGNMENT_CENTER));
      clutter_box_set_color (CLUTTER_BOX (entry), &black_color);
      clutter_actor_set_width (entry, 250);
      clutter_actor_set_reactive (entry, TRUE);

      clutter_box_pack (CLUTTER_BOX (entry),
                        clutter_text_new_full (FONT, text, &yellow_color),
                        "x-align", CLUTTER_BIN_ALIGNMENT_START,
                        NULL);

      clutter_box_pack (CLUTTER_BOX (entry),
                        clutter_text_new_full (FONT, shortcut, &yellow_color),
                        "x-align", CLUTTER_BIN_ALIGNMENT_END,
                        NULL);

      clutter_container_add_actor (CLUTTER_CONTAINER (menu), entry);

      g_signal_connect (entry,
                        "button-press-event",
                        G_CALLBACK (menu_run_option),
                        text);
    }

    static void
    menu_toggle (ClutterActor *actor,
                 ClutterEvent *event,
                 gpointer      user_data)
    {
      ClutterAnimation *animation;
      ClutterActor *menu = CLUTTER_ACTOR (user_data);

      if (clutter_actor_get_animation (menu))
        return;

      if (clutter_actor_get_opacity (menu) > 0)
        {
          animation = clutter_actor_animate (menu, CLUTTER_EASE_OUT_CUBIC, 200,
                                             "opacity", 0,
                                             NULL);

          /* hide the menu once it is fully transparent */
          g_signal_connect_swapped (animation,
                                    "completed",
                                    G_CALLBACK (clutter_actor_hide),
                                    menu);
        }
      else
        {
          clutter_actor_show (menu);

          clutter_actor_animate (menu, CLUTTER_EASE_OUT_CUBIC, 200,
                                 "opacity", 255,
                                 NULL);
        }
    }

    int
    main (int   argc,
          char *argv[])
    {
      ClutterActor *stage;
      ClutterActor *button;
      ClutterLayoutManager *menu_layout;
      ClutterActor *menu;

      if (clutter_init (&argc, &argv) != CLUTTER_INIT_SUCCESS)
        return 1;

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

      /* button */
      button = clutter_box_new (clutter_bin_layout_new (CLUTTER_BIN_ALIGNMENT_CENTER,
                                                        CLUTTER_BIN_ALIGNMENT_CENTER));
      clutter_actor_set_width (button, 100);
      clutter_actor_set_position (button, 50, 50);
      clutter_actor_set_reactive (button, TRUE);
      clutter_box_set_color (CLUTTER_BOX (button), &black_color);
      clutter_box_pack (CLUTTER_BOX (button),
                        clutter_text_new_full (FONT, "Edit", &yellow_color),
                        "x-align", CLUTTER_BIN_ALIGNMENT_FILL,
                        "y-align", CLUTTER_BIN_ALIGNMENT_FILL,
                        NULL);

      /* menu */
      menu_layout = clutter_box_layout_new ();
      clutter_box_layout_set_homogeneous (CLUTTER_BOX_LAYOUT (menu_layout), TRUE);
      clutter_box_layout_set_vertical (CLUTTER_BOX_LAYOUT (menu_layout), TRUE);
      clutter_box_layout_set_spacing (CLUTTER_BOX_LAYOUT (menu_layout), 2);

      menu = clutter_box_new (menu_layout);
      clutter_box_set_color (CLUTTER_BOX (menu), &yellow_color);
      menu_add_option (CLUTTER_BOX (menu), "Undo", "Ctrl-z");
      menu_add_option (CLUTTER_BOX (menu), "Redo", "Ctrl-Shift-z");
      menu_add_option (CLUTTER_BOX (menu), "Cut", "Ctrl-x");
      menu_add_option (CLUTTER_BOX (menu), "Copy", "Ctrl-c");
      menu_add_option (CLUTTER_BOX (menu), "Paste", "Ctrl-v");

      /* align left-hand side of menu with left-hand side of button */
      clutter_actor_add_constraint (menu, clutter_align_constraint_new (button,
                                                                        CLUTTER_ALIGN_X_AXIS,
                                                                        0.0));

      /* align top of menu with the bottom of the button */
      clutter_actor_add_constraint (menu, clutter_bind_constraint_new (button,
                                                                       CLUTTER_BIND_Y,
                                                                       clutter_actor_get_height (button)));

      /* hide the menu until we're ready to animate it in */
      clutter_actor_set_opacity (menu, 0);
      clutter_actor_hide (menu);

      /* clicking on the button toggles the menu */
      g_signal_connect (button, "button-press-event", G_CALLBACK (menu_toggle), menu);

      clutter_container_add_actor (CLUTTER_CONTAINER (stage), menu);

      clutter_container_add_actor (CLUTTER_CONTAINER (stage), button);

      clutter_actor_show (stage);

      clutter_main ();

      return EXIT_SUCCESS;
    }

Example 7.8. A demonstrator for "toggling and tweaking" a ClutterBoxLayout's properties

    /*
     * Experiment with permutations of layout properties for a ClutterBoxLayout
     *
     * See the text (in brackets) at the bottom of the application
     * window for available key presses
     */
    #include <stdlib.h>
    #include <clutter/clutter.h>

    #define STAGE_SIDE 510
    #define BOX_SIDE STAGE_SIDE * 0.75
    #define RED_SIDE STAGE_SIDE / 4
    #define GREEN_SIDE STAGE_SIDE / 8
    #define BLUE_SIDE STAGE_SIDE / 16

    typedef struct
    {
      ClutterLayoutManager *box_layout;
      ClutterActor         *box;
      ClutterActor         *status_display;
      gboolean              x_fill;
      gboolean              y_fill;
      gboolean              expand;
      ClutterBoxAlignment   x_align;
      ClutterBoxAlignment   y_align;
    } State;

    static const ClutterColor stage_color = { 0x33, 0x33, 0x55, 0xff };
    static const ClutterColor box_color = { 0x66, 0x66, 0x00, 0xff };
    static const ClutterColor red_color = { 0xff, 0x00, 0x00, 0xff };
    static const ClutterColor green_color = { 0x00, 0xff, 0x00, 0xff };
    static const ClutterColor blue_color = { 0x00, 0x00, 0xff, 0xff };
    static const ClutterColor white_color = { 0xff, 0xff, 0xff, 0xff };

    static GValue
    gboolean_to_gvalue (gboolean value)
    {
      GValue gval = {0};

      g_value_init (&gval, G_TYPE_BOOLEAN);
      g_value_set_boolean (&gval, value);

      return gval;
    }

    static GValue
    alignment_to_gvalue (ClutterBoxAlignment value)
    {
      GValue gval = {0};

      g_value_init (&gval, G_TYPE_INT);
      g_value_set_int (&gval, value);

      return gval;
    }

    static gchar*
    alignment_as_string (ClutterBoxAlignment value)
    {
      gchar *align_string = "start ";

      switch (value)
        {
        case CLUTTER_BOX_ALIGNMENT_CENTER:
          align_string = "center";
          break;

        case CLUTTER_BOX_ALIGNMENT_END:
          align_string = "end   ";
          break;

        case CLUTTER_BOX_ALIGNMENT_START:
          align_string = "start ";
          break;
        }

      return align_string;
    }

    static ClutterBoxAlignment
    get_next_alignment (ClutterBoxAlignment alignment)
    {
      alignment++;

      if (alignment > CLUTTER_BOX_ALIGNMENT_CENTER)
        alignment = CLUTTER_BOX_ALIGNMENT_START;

      return alignment;
    }

    static void
    show_status (State *state)
    {
      ClutterText *text = CLUTTER_TEXT (state->status_display);
      ClutterBoxLayout *box_layout = CLUTTER_BOX_LAYOUT (state->box_layout);

      gboolean homogeneous = clutter_box_layout_get_homogeneous (box_layout);
      gboolean vertical = clutter_box_layout_get_vertical (box_layout);

      gchar *message = g_strdup_printf ("x_fill (x): %s\t\t\t"
                                        "y_fill (y): %s\n"
                                        "expand (e): %s\t\t"
                                        "homogeneous (h): %s\n"
                                        "spacing (+/-): %dpx\t\t"
                                        "vertical (v): %s\n"
                                        "x_align (right): %s\t"
                                        "y_align (up): %s",
                                        (state->x_fill ? "true" : "false"),
                                        (state->y_fill ? "true" : "false"),
                                        (state->expand ? "true" : "false"),
                                        (homogeneous ? "true" : "false"),
                                        clutter_box_layout_get_spacing (box_layout),
                                        (vertical ? "true" : "false"),
                                        alignment_as_string (state->x_align),
                                        alignment_as_string (state->y_align));

      clutter_text_set_text (text, message);

      g_free (message);
    }

    static void
    set_property_on_layout_children (State       *state,
                                     const gchar *property,
                                     GValue       value)
    {
      ClutterActor *actor;
      ClutterContainer *container = CLUTTER_CONTAINER (state->box);
      ClutterLayoutManager *manager = CLUTTER_LAYOUT_MANAGER (state->box_layout);
      GList *actors = clutter_container_get_children (container);

      for (; actors; actors = actors->next)
        {
          actor = CLUTTER_ACTOR (actors->data);

          clutter_layout_manager_child_set_property (manager,
                                                     container,
                                                     actor,
                                                     property,
                                                     &value);
        }

      g_list_free (actors);
    }

    static void
    toggle_x_fill (GObject            *instance,
                   const gchar        *action_name,
                   guint               key_val,
                   ClutterModifierType modifiers,
                   gpointer            user_data)
    {
      State *state = (State *) user_data;

      state->x_fill = !state->x_fill;

      set_property_on_layout_children (state,
                                       "x-fill",
                                       gboolean_to_gvalue (state->x_fill));
    }

    static void
    toggle_y_fill (GObject            *instance,
                   const gchar        *action_name,
                   guint               key_val,
                   ClutterModifierType modifiers,
                   gpointer            user_data)
    {
      State *state = (State *) user_data;

      state->y_fill = !state->y_fill;

      set_property_on_layout_children (state,
                                       "y-fill",
                                       gboolean_to_gvalue (state->y_fill));
    }

    static void
    toggle_expand (GObject            *instance,
                   const gchar        *action_name,
                   guint               key_val,
                   ClutterModifierType modifiers,
                   gpointer            user_data)
    {
      State *state = (State *) user_data;

      state->expand = !state->expand;

      set_property_on_layout_children (state,
                                       "expand",
                                       gboolean_to_gvalue (state->expand));
    }

    static void
    rotate_x_alignment (GObject            *instance,
                        const gchar        *action_name,
                        guint               key_val,
                        ClutterModifierType modifiers,
                        gpointer            user_data)
    {
      State *state = (State *) user_data;

      state->x_align = get_next_alignment (state->x_align);

      set_property_on_layout_children (state,
                                       "x-align",
                                       alignment_to_gvalue (state->x_align));
    }

    static void
    rotate_y_alignment (GObject            *instance,
                        const gchar        *action_name,
                        guint               key_val,
                        ClutterModifierType modifiers,
                        gpointer            user_data)
    {
      State *state = (State *) user_data;

      state->y_align = get_next_alignment (state->y_align);

      set_property_on_layout_children (state,
                                       "y-align",
                                       alignment_to_gvalue (state->y_align));
    }

    static void
    toggle_vertical (GObject            *instance,
                     const gchar        *action_name,
                     guint               key_val,
                     ClutterModifierType modifiers,
                     gpointer            user_data)
    {
      State *state = (State *) user_data;
      ClutterBoxLayout *box_layout = CLUTTER_BOX_LAYOUT (state->box_layout);
      gboolean vertical = clutter_box_layout_get_vertical (box_layout);

      clutter_box_layout_set_vertical (box_layout, !vertical);
    }

    static void
    toggle_homogeneous (GObject            *instance,
                        const gchar        *action_name,
                        guint               key_val,
                        ClutterModifierType modifiers,
                        gpointer            user_data)
    {
      State *state = (State *) user_data;
      ClutterBoxLayout *box_layout = CLUTTER_BOX_LAYOUT (state->box_layout);
      gboolean homogeneous = clutter_box_layout_get_homogeneous (box_layout);

      clutter_box_layout_set_homogeneous (box_layout, !homogeneous);
    }

    static void
    increase_spacing (GObject            *instance,
                      const gchar        *action_name,
                      guint               key_val,
                      ClutterModifierType modifiers,
                      gpointer            user_data)
    {
      State *state = (State *) user_data;
      ClutterBoxLayout *box_layout = CLUTTER_BOX_LAYOUT (state->box_layout);
      guint spacing = clutter_box_layout_get_spacing (box_layout) + 5;

      clutter_box_layout_set_spacing (box_layout, spacing);
    }

    static void
    decrease_spacing (GObject            *instance,
                      const gchar        *action_name,
                      guint               key_val,
                      ClutterModifierType modifiers,
                      gpointer            user_data)
    {
      State *state = (State *) user_data;
      ClutterBoxLayout *box_layout = CLUTTER_BOX_LAYOUT (state->box_layout);
      guint spacing = clutter_box_layout_get_spacing (box_layout);

      if (spacing >= 5)
        clutter_box_layout_set_spacing (box_layout, spacing - 5);
    }

    static gboolean
    key_pressed_cb (ClutterActor *actor,
                    ClutterEvent *event,
                    gpointer      user_data)
    {
      State *state = (State *) user_data;
      ClutterBindingPool *pool;
      gboolean return_value;

      pool = clutter_binding_pool_find (G_OBJECT_TYPE_NAME (actor));

      return_value = clutter_binding_pool_activate (pool,
                                                    clutter_event_get_key_symbol (event),
                                                    clutter_event_get_state (event),
                                                    G_OBJECT (actor));

      show_status (state);

      return return_value;
    }

    int
    main (int   argc,
          char *argv[])
    {
      ClutterActor *stage;
      GObjectClass *stage_class;
      ClutterBindingPool *binding_pool;
      ClutterActor *red;
      ClutterActor *green;
      ClutterActor *blue;

      State *state = g_new0 (State, 1);

      if (clutter_init (&argc, &argv) != CLUTTER_INIT_SUCCESS)
        return 1;

      state->x_fill = FALSE;
      state->y_fill = FALSE;
      state->expand = FALSE;
      state->x_align = CLUTTER_BOX_ALIGNMENT_START;

      stage = clutter_stage_new ();
      clutter_actor_set_size (stage, STAGE_SIDE, STAGE_SIDE);
      clutter_stage_set_color (CLUTTER_STAGE (stage), &stage_color);
      g_signal_connect (stage, "destroy", G_CALLBACK (clutter_main_quit), NULL);

      /* for key bindings */
      stage_class = G_OBJECT_GET_CLASS (stage);
      binding_pool = clutter_binding_pool_get_for_class (stage_class);

      clutter_binding_pool_install_action (binding_pool,
                                           "toggle-expand",
                                           CLUTTER_KEY_e,
                                           0,
                                           G_CALLBACK (toggle_expand),
                                           state,
                                           NULL);

      clutter_binding_pool_install_action (binding_pool,
                                           "toggle-x-fill",
                                           CLUTTER_KEY_x,
                                           0,
                                           G_CALLBACK (toggle_x_fill),
                                           state,
                                           NULL);

      clutter_binding_pool_install_action (binding_pool,
                                           "toggle-y-fill",
                                           CLUTTER_KEY_y,
                                           0,
                                           G_CALLBACK (toggle_y_fill),
                                           state,
                                           NULL);

      clutter_binding_pool_install_action (binding_pool,
                                           "toggle-vertical",
                                           CLUTTER_KEY_v,
                                           0,
                                           G_CALLBACK (toggle_vertical),
                                           state,
                                           NULL);

      clutter_binding_pool_install_action (binding_pool,
                                           "toggle-homogeneous",
                                           CLUTTER_KEY_h,
                                           0,
                                           G_CALLBACK (toggle_homogeneous),
                                           state,
                                           NULL);

      clutter_binding_pool_install_action (binding_pool,
                                           "rotate-x-alignment",
                                           CLUTTER_KEY_Right,
                                           0,
                                           G_CALLBACK (rotate_x_alignment),
                                           state,
                                           NULL);

      clutter_binding_pool_install_action (binding_pool,
                                           "rotate-y-alignment",
                                           CLUTTER_KEY_Up,
                                           0,
                                           G_CALLBACK (rotate_y_alignment),
                                           state,
                                           NULL);

      clutter_binding_pool_install_action (binding_pool,
                                           "increase-spacing",
                                           CLUTTER_KEY_plus,
                                           CLUTTER_SHIFT_MASK,
                                           G_CALLBACK (increase_spacing),
                                           state,
                                           NULL);

      clutter_binding_pool_install_action (binding_pool,
                                           "decrease-spacing",
                                           CLUTTER_KEY_minus,
                                           0,
                                           G_CALLBACK (decrease_spacing),
                                           state,
                                           NULL);

      /* rectangles inside the layout */
      red = clutter_rectangle_new_with_color (&red_color);
      clutter_actor_set_size (red, RED_SIDE, RED_SIDE);

      green = clutter_rectangle_new_with_color (&green_color);
      clutter_actor_set_size (green, GREEN_SIDE, GREEN_SIDE);

      blue = clutter_rectangle_new_with_color (&blue_color);
      clutter_actor_set_size (blue, BLUE_SIDE, BLUE_SIDE);

      /* the layout */
      state->box_layout = clutter_box_layout_new ();
      clutter_box_layout_set_use_animations (CLUTTER_BOX_LAYOUT (state->box_layout),
                                             TRUE);

      state->box = clutter_box_new (state->box_layout);
      clutter_box_set_color (CLUTTER_BOX (state->box), &box_color);
      clutter_actor_set_size (state->box, BOX_SIDE, BOX_SIDE);
      clutter_actor_add_constraint (state->box,
                                    clutter_align_constraint_new (stage, CLUTTER_ALIGN_X_AXIS, 0.5));
      clutter_actor_add_constraint (state->box,
                                    clutter_align_constraint_new (stage, CLUTTER_ALIGN_Y_AXIS, 0.1));

      /* text to show status */
      state->status_display = clutter_text_new ();
      clutter_text_set_color (CLUTTER_TEXT (state->status_display), &white_color);
      clutter_actor_set_size (state->status_display,
                              STAGE_SIDE,
                              STAGE_SIDE * 0.2);
      clutter_actor_set_position (state->status_display,
                                  (STAGE_SIDE - BOX_SIDE) / 2,
                                  STAGE_SIDE * 0.8);

      /* set text for initial state */
      show_status (state);

      /* connect key presses to a callback on the binding pool */
      g_signal_connect (stage,
                        "key-press-event",
                        G_CALLBACK (key_pressed_cb),
                        state);

      /* pack UI */
      clutter_container_add (CLUTTER_CONTAINER (state->box), red, green, blue, NULL);

      clutter_container_add (CLUTTER_CONTAINER (stage),
                             state->box,
                             state->status_display,
                             NULL);

      /* show stage */
      clutter_actor_show (stage);

      clutter_main ();

      /* clean up */
      g_object_unref (binding_pool);
      g_free (state);

      return EXIT_SUCCESS;
    }

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