"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">

         xmlns:xi="http://www.w3.org/2003/XInclude">

  <title>Layout management</title>

  <epigraph>

    <attribution>Abigail Adams, wife of John Adams, in a letter to John

    Thaxter (1778-09-29)</attribution>

    <para>If we do not lay out ourselves in the service of mankind,

    whom should we serve?</para>

  </epigraph>

  <section id="layouts-introduction">

    <title>Introduction</title>

    <para>Layout management in Clutter controls how an actor and

    children "inside" that actor are sized and positioned. More

    specifically, layouts are managed by associating a parent with a

    <type>ClutterLayoutManager</type>; the parent is usually either a

    composite <type>ClutterActor</type> (composed of several

    <type>ClutterActors</type>) or a <type>ClutterContainer</type>

    (containing child <type>ClutterActors</type>). The

    <type>ClutterLayoutManager</type> then manages:</para>

    <orderedlist>

      <listitem>

        <para>The <emphasis>size requisition</emphasis>

        (determination of the desired height and width) of the

        parent.</para>

      </listitem>

      <listitem>

        <para>The <emphasis>allocation</emphasis> (size and position)

        assigned to each composed or child ClutterActor.</para>

      </listitem>

    </orderedlist>

    <note>

      <para>To make this more concrete, imagine you have a sheet of

      paper and some coloured squares to place on it. Someone stands

      next to you telling you how big the piece of paper should be,

      how big the squares should be, and where to put each square on the

      piece of paper.</para>

      <para>The sheet of paper is analogous to the container or

      composite actor; the squares are analogous to the child

      <type>ClutterActors</type>; and the person giving you instructions

      is analogous to the layout manager.</para>

    </note>

    <para>The following sections give an overview of how layout

    management works in Clutter.</para>

    <section>

      <title>Using layouts</title>

      <para>Although Clutter provides plenty of flexibility in how you

      can use layout management, the simplest way to get started is to

      use the built-in <type>ClutterActor</type> class with one of the

      provided <type>ClutterLayoutManager</type> implementations.</para>

      <para>The pattern for doing this is:</para>

      <itemizedlist>

        <listitem>

          <para>Create an instance of one of the

          <type>ClutterLayoutManager</type> implementations (see

          <link linkend="layouts-introduction-manager-types">the

          following section</link>).</para>

        </listitem>

        <listitem>

          <para>Configure the layout manager's default policies

          (e.g. how actors are aligned by default, whether to pack

          actors horizontally or vertically, spacing between actors

          in the layout).</para>

        </listitem>

        <listitem>

          <para>Create a <type>ClutterActor</type>, setting its layout

          manager to the one you just created.</para>

        </listitem>

        <listitem>

          <para>Pack actors into the <type>ClutterActor</type>,

          setting layout properties (if required) as each is added.</para>

        </listitem>

        <listitem>

          <para>Modify layout properties of child actors using

          <function>clutter_layout_manager_child_set()</function>

          (if required).</para>

        </listitem>

      </itemizedlist>

      <para>Individual recipes in this section give more examples of

      how to make use of the different layout manager

      implementations.</para>

    </section>

    <section id="layouts-introduction-manager-types">

      <title>Types of layout manager</title>

      <para>Clutter provides a range of layout managers suitable

      for different use cases:</para>

      <itemizedlist>

        <listitem>

          <para><type>ClutterFixedLayout</type> arranges actors

          at fixed positions on the stage. No alignment options are

          available, so you have to manually compute and manage the

          coordinates (or use <type>ClutterConstraints</type>) which

          will align actors how you want them.</para>

        </listitem>

        <listitem>

          <para><type>ClutterBinLayout</type> arranges actors in a

          depth-ordered stack on top of each other, aligned to the container.

          This is useful for arranging actors inside composites (e.g.

          creating a button widget from a <type>ClutterTexture</type>

          with a <type>ClutterText</type> on top of it).</para>

        </listitem>

        <listitem>

          <para><type>ClutterBoxLayout</type> arranges actors in a

          single horizontal row or vertical column. This type of layout is

          common in UI elements like toolbars and menus.</para>

        </listitem>

        <listitem>

          <para><type>ClutterFlowLayout</type> arranges actors

          in reflowing columns and rows. If the container's allocation

          changes, the child actors are rearranged to fit inside its

          new allocation. This can be useful for arranging actors

          where you're not sure how many there might be; or where

          new ones are going to be added into the UI, perhaps displacing

          others. An example might be a photo viewer or an

          RSS feed display.</para>

        </listitem>

      </itemizedlist>

    </section>

    <section id="layouts-introduction-layout-properties">

      <title>Layout properties</title>

      <para>How actors are sized and positioned inside a container

      associated with a layout manager depends on two things:</para>

      <orderedlist>

        <listitem>

          <formalpara>

            <title>Properties which apply to all actors added to the layout</title>

            <para>There will be one setting at the layout level which can't

            be overridden per actor. This includes properties like spacing

            between rows and columns, whether the layout is homogenous

            (each actor gets the same allocation), etc.</para>

          </formalpara>

        </listitem>

        <listitem>

          <formalpara>

            <title>Properties for each actor added to the layout</title>

            <para>These are properties of the relationship between the

            layout, the container associated with the layout, and the

            children of the container. Each layout/container/actor

            combination can have different settings for each of these

            properties.</para>

          </formalpara>

        </listitem>

      </orderedlist>

      <para>Each layout manager implementation supports a subset of the

      following layout properties; different managers may have different

      names or functions for setting them, but the functionality remains

      the same. Individual recipes give more details about which

      properties can be set for each layout manager implementation.</para>

      <itemizedlist>

        <listitem>

          <formalpara>

            <title>Alignment</title>

            <para>How an actor aligns to the container's axes, e.g.

            aligned to the container's left, right, or center. For some

            layouts (like <type>ClutterBinLayout</type>) alignment

            is also used to set expand and fill properties.</para>

          </formalpara>

        </listitem>

        <listitem>

          <formalpara>

            <title>Horizontal/vertical orientation</title>

            <para>Whether actors are arranged in a horizontal row or

            vertical column.</para>

          </formalpara>

        </listitem>

        <listitem>

          <formalpara>

            <title>Homogenous rows and columns</title>

            <para>Grid-like layouts (e.g. <type>ClutterFlowLayout</type>)

            can be configured to have uniform rows and/or columns,

            expanding to fit the largest actor they contain.</para>

          </formalpara>

        </listitem>

        <listitem>

          <formalpara>

            <title>Row height and column width</title>

            <para>Grid-like layouts arranged in rows and columns

            can be configured with maximum and minimum row height and

            column width.</para>

          </formalpara>

        </listitem>

        <listitem>

          <formalpara>

            <title>Row and column spacing</title>

            <para>Grid-like layouts enable you to define a space (in pixels)

            between rows and columns.</para>

          </formalpara>

        </listitem>

        <listitem>

          <formalpara>

            <title>Expand</title>

            <para>Some layouts can be configured to minimize their size request

            to fit the actors they contain (<emphasis>expand is FALSE</emphasis>);

            or to increase the allocation of actors they contain so

            that all available space in the layout is used

            (<emphasis>expand is TRUE</emphasis>). In the latter case, you'd

            also need to set a size for the container associated with

            the layout, otherwise the container will just fit itself to the

            actors inside it.</para>

          </formalpara>

        </listitem>

        <listitem>

          <formalpara>

            <title>Fill</title>

            <para>This property only has an effect when

            <emphasis>expand</emphasis> is on. The <emphasis>fill</emphasis>

            setting controls whether actors are resized to fill their

            allocation (<emphasis>fill is TRUE</emphasis>); or if the

            space around the actor is increased (<emphasis>fill is

            FALSE</emphasis>).</para>

          </formalpara>

        </listitem>

        <listitem>

          <formalpara>

            <title>Pack at start/end</title>

            <para>This controls whether actors at prepended or appended

            to the layout.</para>

            <itemizedlist>

              <listitem>

                <para>If the orientation is vertical, prepended

                actors are added to the top of the layout and appended

                actors to the bottom.</para>

              </listitem>

              <listitem>

                <para>If the orientation is horizontal, prepended

                actors are added at the left of the layout and appended actors

                on the right.</para>

              </listitem>

            </itemizedlist>

          </formalpara>

        </listitem>

      </itemizedlist>

      <section>

        <title>Setting layout properties</title>

        <para>Layout properties can be set in one or more of the following ways

        (depending on the type of property and the layout manager):</para>

        <orderedlist>

          <listitem>

            <para>By setting a default value for the property on the

            layout manager (e.g. using

            <function>clutter_bin_layout_set_alignment()</function>,

            <function>clutter_box_layout_set_expand()</function>). Any

            actor added to the layout gets this value for the property,

            unless it is overridden for that actor.</para>

          </listitem>

          <listitem>

            <para>When adding an actor to a <type>ClutterBox</type> container

            using <function>clutter_box_pack()</function>, you can set

            properties on the actor which you're adding.</para>

          </listitem>

          <listitem>

            <para>When adding an actor to a layout you can use a function

            which enables setting properties simultaneously (e.g.

            <function>clutter_box_layout_pack()</function>,

            <function>clutter_bin_layout_add()</function>).</para>

          </listitem>

          <listitem>

            <para>By using

            <function>clutter_layout_manager_child_set()</function> on

            the child of a layout.</para>

          </listitem>

        </orderedlist>

      </section>

    </section>

    <section id="layouts-introduction-not-using-layout-managers">

      <title>Not using layout managers</title>

      <para>It is perfectly possible to arrange <type>ClutterActors</type>

      without using layout managers; however, you may have to do

      more of your own calculations about actor sizes and positions.</para>

      <para>There are two (not mutually-exclusive) approaches you can

      take to do this, described below.</para>

      <section>

        <title>Manual positioning and alignment</title>

        <para>This basically means using the <type>ClutterActor</type>

        bounding box mechanism (see the <type>ClutterActor</type>

        documentation for details) to set actor sizes and positions.

        This is the approach you will see in a lot of older Clutter

        code (written before layout managers were available).</para>

        <para>This approach is simplest where the UI is relatively static

        and is composed of a few known actors. It will work in larger,

        more complex scenarios, but in those sorts of cases it is better

        to make use of layout managers and constraints (see below) instead.</para>

      </section>

      <section>

        <title>Using <type>ClutterConstraint</type></title>

        <para>Constraints provide mechanisms for:</para>

        <itemizedlist>

          <listitem>

            <para>Aligning actors with each other

            (<type>ClutterAlignConstraint</type>). For example, you

            can align the top, bottom or center of one actor with the

            top, bottom or center of another (on the y

            axis). Similarly, you can align one actor to another

            on the x axis.</para>

          </listitem>

          <listitem>

            <para>Binding properties of one actor to those of

            another. For example, you could ensure that two actors

            always remain the same width; or you could specify

            that two actors always have the same x

            coordinate. In both these cases and others, you can

            specify that the properties should be the same, or the same

            +/- some offset.</para>

          </listitem>

        </itemizedlist>

        <note>

          <para><type>ClutterConstraints</type> can be used in combination

          with some layout managers, but you need to be careful that

          constraints don't fight with the layout manager policies.

          Unpredictable results could ensue.</para>

        </note>

      </section>

    </section>

  </section>

  <section id="layouts-stacking">

    <title>Stacking actors on top of each other</title>

    <section>

      <title>Problem</title>

      <para>You want to lay out several actors so that they are in

      layers on top of each other (e.g. to create a button widget

      composed from a rectangle with text on top of it).</para>

    </section>

    <section id="layouts-stacking-solution">

      <title>Solution</title>

      <para>The most flexible approach is to use a <type>ClutterBinLayout</type>

      associated with a <type>ClutterActor</type>:</para>

      <informalexample>

        <programlisting>

/* define some colors */

const ClutterColor background_color = { 0xaa, 0x99, 0x00, 0xff };

const ClutterColor text_color = { 0xff, 0xff, 0xff, 0xff };

ClutterLayoutManager *layout;

ClutterActor *box;

ClutterActor *background;

ClutterActor *text;

/*

 * create a layout, setting the default x and y alignment;

 * actors fill the whole allocation of the layout's container

 * by default

 */

layout = clutter_bin_layout_new (CLUTTER_BIN_ALIGNMENT_FILL,

                                 CLUTTER_BIN_ALIGNMENT_FILL);

/* create the box whose children the layout will manage */

box = clutter_box_new (layout);

/*

 * fill doesn't have much effect here

 * unless the container has height and/or width

 */

clutter_actor_set_size (box, 100, 30);

/*

 * background for the button; could equally be a texture

 * with an image loaded into it or any other ClutterActor

 */

background = clutter_rectangle_new_with_color (&background_color);

/*

 * add the background to the container;

 * as it should use the default alignment, it can be added

 * direct to the container, rather than via the layout

 */

clutter_actor_add_child (box, background);

/* text for the button */

text = clutter_text_new_full ("Sans 15px", "Click me", &text_color);

/*

 * the text requires a different alignment from the background

 * (centered on the box)

 * so we add it via the layout so the default

 * alignment can be overridden

 */

clutter_bin_layout_add (CLUTTER_BIN_LAYOUT (layout),

                        text,

                        CLUTTER_BIN_ALIGNMENT_CENTER,

                        CLUTTER_BIN_ALIGNMENT_CENTER);

/*

 * ensure the actors are arranged in the correct depth order;

 * in this case, the text is on top

 * (NB this is not strictly necesary here as text is added after

 * background)

 */

clutter_actor_raise_top (text);

]]>

        </programlisting>

      </informalexample>

    </section>

    <section>

      <title>Discussion</title>

      <para>This section covers some other aspects of using a

      <type>ClutterBinLayout</type>.</para>

      <section>

        <title>Setting and changing alignment</title>

        <para>Alignment is the only

        <link linkend="layouts-introduction-layout-properties">layout

        property</link> available for <type>ClutterBinLayout</type>. Each

        actor can have a different setting for its alignment in one or both

        of the x or y axes. However, as shown in the

        solution above, alignment can also be used to expand an actor to

        fill the container (<constant>CLUTTER_BIN_ALIGNMENT_FILL</constant>)

        in one or both axes.</para>

        <para>Setting alignment does not have any effect if the container

        is the same size as all of the actors inside it: in this case,

        every alignment produces the same layout. But if the container

        associated with the layout is larger than the actor being aligned,

        alignment will have an effect; see

        <link linkend="layouts-stacking-size-requisitioning">this

        section</link> for more details.</para>

        <para>Changing an actor's alignment after it has been added

        to a <type>ClutterBinLayout</type> may make the actor "jump"

        (without animation) to a new position and/or change its size.

        The exception is changing from some other alignment to

        <constant>CLUTTER_BIN_ALIGNMENT_FIXED</constant>:

        in this case, the actor will retain the position and size it

        had before its alignment was fixed.</para>

      </section>

      <section id="layouts-stacking-size-requisitioning">

        <title>Size requisitioning</title>

        <para>A container with a <type>ClutterBinLayout</type> will by

        default request the width of the widest actor in it, and the

        height of the tallest. If you add actors smaller than those

        dimensions, they will be aligned inside the container according

        to the layout's policies. Here's an example where a

        <type>ClutterBinLayout</type> requests a size to encompass the

        tallest (light grey rectangle) and widest (dark grey rectangle)

        actors inside it, with other actors aligned within

        those bounds:</para>

        <screenshot>

          <mediaobject>

            <imageobject>

                         fileref="images/layouts-stacking-diff-actor-sizes.png" />

            </imageobject>

            <alt>

              <para>Size requisition in a <type>ClutterBinLayout</type></para>

            </alt>

          </mediaobject>

        </screenshot>

        <note>

          <para>The screenshot also shows the 9 possible combinations

          of start, center and end alignments on the x and

          y axes. See

          <link linkend="layouts-stacking-example-1">the sample

          code</link> for more details.</para>

        </note>

        <para>The white space is the stage visible behind the

        <type>ClutterActor</type> holding the coloured rectangles.

        Notice that the layout is the width of the widest actor

        within it and the height of the tallest.</para>

        <para>You can also manually set a size on the container associated

        with a layout to override the automatically-computed size

        requisition.</para>

      </section>

      <section>

        <title>Depth ordering</title>

        <para>Another important consideration is the

        <emphasis>depth ordering</emphasis> of actors inside a

        <type>ClutterBinLayout</type>. By default, the depth ordering

        mirrors the order in which actors are added to the layout: the

        earlier an actor is added, the lower down in the depth order it

        is. If this isn't what you want, you can fix the depth ordering using

        <function>clutter_actor_set_child_above_sibling()</function>,

        <function>clutter_actor_set_child_below_sibling()</function> and

        their relatives.</para>

      </section>

      <section>

        <title>Other ways to stack actors</title>

        <para><type>ClutterBinLayout</type> makes it simple to lay out

        large numbers of actors in a stack and align them to the

        container; see <link linkend="layouts-stacking-example-2">the

        example below</link> which shows layering of many actors on

        top of each other.</para>

        <para>However, if you have a small number of actors and you

        need some simple alignment, an alternative is to use

        manual positioning inside a <type>ClutterFixedLayout</type>, possibly

        combined with <type>ClutterConstraints</type> to align actors with

        each other and bind their widths and heights together. See

        <link linkend="layouts-introduction-not-using-layout-managers">this

        section</link> for more details.</para>

        <note><para>By default, <type>ClutterActor</type> uses a

        <type>ClutterFixedLayout</type> as its layout manager.</para></note>

      </section>

    </section>

    <section>

      <title>Full examples</title>

      <example id="layouts-stacking-example-1">

        <title><type>ClutterBinLayout</type>, with actors in 9

        combinations of start, center and end alignment combinations</title>

        <programlisting>

<xi:include href="examples/layouts-stacking-diff-sized-actors.c" parse="text">

  <xi:fallback>a code sample should be here... but isn't</xi:fallback>

</xi:include>

        </programlisting>

      </example>

      <example id="layouts-stacking-example-2">

        <title>Layering multiple textures on top of each other

        inside a <type>ClutterBinLayout</type></title>

        <programlisting>

<xi:include href="examples/layouts-stacking.c" parse="text">

  <xi:fallback>a code sample should be here... but isn't</xi:fallback>

</xi:include>

        </programlisting>

      </example>

    </section>

  </section>

  <section id="layouts-bind-constraint">

    <title>Binding the size of one actor to the size of another</title>

    <section>

      <title>Problem</title>

      <para>You want one actor (the "target") to automatically change

      its width or height (or both) when the size of another

      actor (the "source") changes.</para>

      <para>Example use cases:</para>

      <itemizedlist>

        <listitem>

          <para>Making an actor adjust itself to the size of the stage

          (particularly when the stage is resizable).</para>

        </listitem>

        <listitem>

          <para>Putting one actor on top of another and keeping their

          sizes in sync.</para>

        </listitem>

      </itemizedlist>

    </section>

    <section>

      <title>Solution</title>

      <para>Create a <type>ClutterBindConstraint</type> bound to the

      width and/or height of one actor (the "source"). Add that constraint

      to an actor (the "target") whose size should follow the

      size of the source.</para>

      <para>This short example shows how to create and add a constraint;

      <varname>source</varname> and <varname>target</varname> can

      be any two <type>ClutterActors</type>:</para>

      <informalexample>

        <programlisting>

<emphasis>ClutterConstraint *width_constraint;</emphasis>

/* create a constraint which binds a target actor's width to 100px less than

 * the width of the source actor (use CLUTTER_BIND_HEIGHT to create a

 * constraint based on an actor's height)

 *

 * the third argument is a positive or negative offset from the actor's

 * dimension, in pixels; this is added to the height or width of the source

 * actor before the constraint is applied to the target actor

 */

<emphasis>width_constraint = clutter_bind_constraint_new (source, CLUTTER_BIND_WIDTH, -100);</emphasis>

/* add the constraint to an actor */

<emphasis>clutter_actor_add_constraint (target, width_constraint);</emphasis>

        </programlisting>

      </informalexample>

      <para>Below is a full example, showing how to incorporate a

      constraint into a Clutter application.</para>

      <example id="layouts-bind-constraint-example-1">

        <title>Constraining the size of a texture to

        the size of the stage using <type>ClutterBindConstraint</type></title>

        <programlisting>

<xi:include href="examples/layouts-bind-constraint-stage.c" parse="text">

  <xi:fallback>a code sample should be here... but isn't</xi:fallback>

</xi:include>

        </programlisting>

      </example>

      <para>The texture in this example is 100px smaller than the stage,

      leaving a border of visible stage around the texture; and the texture

      has a tiled image on it. The tiling changes as the texture changes

      size. Also note that two <type>ClutterAlignConstraints</type> are

      added to center the actor on the stage.</para>

      <para>The result looks like this:</para>

      <screenshot>

          <mediaobject>

            <imageobject>

                         fileref="images/layouts-bind-constraint-stage.png" />

            </imageobject>

            <alt>

              <para>A texture bound to the height and width of the

              stage using <type>ClutterBindConstraint</type></para>

            </alt>

          </mediaobject>

        </screenshot>

    </section>

    <section>

      <title>Discussion</title>

      <para>Sizing constraints are a good solution in these cases:</para>

      <itemizedlist>

        <listitem>

          <para>Where you can't use a layout manager. For

          example, you can't apply a layout manager to the stage

          directly; so if you want to control the size of an actor

          based on the size of the stage (as in

          <link linkend="layouts-bind-constraint-example-1">the example

          above</link>), constraints are a good substitute for a layout

          manager .</para>

        </listitem>

        <listitem>

          <para>Where the layout of a UI is fairly simple (perhaps

          up to half a dozen actors) and fairly static. An example

          might be something like a text editor, where the arrangement

          of the UI (menu bar, toolbar, editing panel, footer) changes

          infrequently. Of course, it is possible to arrange top-level

          components using constraints, but still use layout

          managers inside individual components (e.g. a flow layout

          manager to manage buttons in the toolbar).</para>

        </listitem>

        <listitem>

          <para>Where you have an actor whose size can change erratically,

          but you still want to be able to track its size to control

          another actor's size. An example might be an application like

          a drawing program, where a user can create their own actors:

          you might want the user to be able to describe loose, custom

          constraints between actors like "keep these actors at the

          same width", then allow those actors to be moved around and

          resized in a free-form way as a group. In this situation, a

          layout manager is too rigid and not appropriate;

          but adding <type>ClutterConstraints</type> to actors

          in response to user actions could work well.</para>

          <para>The <link linkend="layouts-bind-constraint-example-2">sample

          code in the appendix</link> is the kind of thing you might include

          in a drawing program: you can resize a texture with a key press

          (+ to increase size, - to decrease), and

          click on the actor to select/deselect it (a semi-transparent overlay is

          toggled on the texture). The size of the overlay is bound and

          aligned to the texture, so that it covers and slightly overlaps the

          texture regardless of its size.</para>

        </listitem>

      </itemizedlist>

      <note>

        <para>You can bind an actor to a single dimension (just height or

        depth) of another actor: you don't have to bind both height

        and width. Also, you don't have to bind both dimensions of the

        target to the same source: for example, you could bind the target's

        height to one source (actor A) and its width to another source

        (actor B).</para>

        <para>A <type>ClutterBindConstraint</type> can also be used to

        constrain a target actor's position on the x and

        y axes to the position of a source actor. This is

        covered in another recipe.</para>

      </note>

      <section>

        <title>Another way to bind actors' sizes together</title>

        <para>There is another way to control the size of a target

        actor, based on the size of a source: you can create a handler

        for the allocation-changed signal

        of the source, emitted when its size and/or position

        changes. This signal includes all the data

        about the source's new allocation (height, width, x and y

        coordindates), which the handler function can then use to

        resize the target.</para>

        <para>Alternatively, if you're only interested in

        a change to width or height, you can create a handler

        for the notify::width or

        notify::height signal (respectively), and modify

        the target's width/height in the handler.</para>

        <para>This approach may be useful if you need a type of

        control over alignment and size which is not possible using

        constraints alone (e.g. one actor's size should be

        a proportion of another's). See

        <link linkend="layouts-bind-constraint-example-3">the code in

        this section</link> for an example where the size

        of one actor is dynamically set to 10% more than the

        size of another.</para>

        <note>

          <para><link linkend="actors-allocation-notify">This recipe</link>

          explains more about monitoring changes to an actor's size.</para>

        </note>

      </section>

    </section>

    <section>

      <title>Full examples</title>

      <example id="layouts-bind-constraint-example-2">

        <title>Creating an automatically-resizing overlay for a

        texture using <type>ClutterBindConstraint</type></title>

        <programlisting>

<xi:include href="examples/layouts-bind-constraint-overlay.c" parse="text">

  <xi:fallback>a code sample should be here... but isn't</xi:fallback>

</xi:include>

        </programlisting>

      </example>

      <example id="layouts-bind-constraint-example-3">

        <title>Using the allocation-changed

        signal of one actor to trigger proportional size changes in

        another</title>

        <programlisting>

<xi:include href="examples/layouts-bind-constraint-allocation.c" parse="text">

  <xi:fallback>a code sample should be here... but isn't</xi:fallback>

</xi:include>

        </programlisting>

      </example>

    </section>

  </section>

  <section id="layouts-box">

    <title>Arranging actors in a single row or column</title>

    <section>

      <title>Problem</title>

      <para>You want to layout several actors in a single row

      or column.</para>

      <para>Example use cases:</para>

      <itemizedlist>

        <listitem>

          <para>Creating an application menu.</para>

        </listitem>

        <listitem>

          <para>Showing message subject lines as a list in an

          email client.</para>

        </listitem>

      </itemizedlist>

    </section>

    <section>

      <title>Solution</title>

      <para>Create a <type>ClutterActor</type> with a

      <type>ClutterBoxLayout</type> as its layout manager.</para>

      <para>A <type>ClutterBoxLayout</type> can hold a single row or

      column of <type>ClutterActors</type>, and has configurable spacing,

      actor alignments, and expand and fill options.</para>

      <para>The code fragment below is excerpted from the

      <link linkend="layouts-box-example-1">full example</link>. It

      demonstrates how to lay out three rectangles in a vertical

      column. A different approach is used to set the <varname>x-fill</varname>

      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).</para>

      <informalexample>

        <programlisting>

/* 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 */