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cookbook: Added layouts section and introduction

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doc/cookbook/clutter-cookbook.xml.in
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<xi:include href="textures.xml" />
<xi:include href="animations.xml" />
<xi:include href="text.xml" />
<xi:include href="layouts.xml" />
<appendix id="contributing">
<title>Contributing to this document</title>

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<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<chapter id="layouts"
xmlns:xi="http://www.w3.org/2003/XInclude">
<title>Layout management</title>
<epigraph>
<attribution>who</attribution>
<para>what they said</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>ClutterActor</type>s) or a <type>ClutterContainer</type>
(containing child <type>ClutterActor</type>s). 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>
<para>The following sections give a brief 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>ClutterBox</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>ClutterBox</type>, setting its layout
manager to the one you just created.</para>
</listitem>
<listitem>
<para>Pack actors into the <type>ClutterBox</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>ClutterConstraint</type>s) 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>
<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.</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>
</chapter>