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layout-manager: Document the animation support

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Add a section inside the LayoutManager class API reference documenting,
with examples, how to implement animation support inside a layout
manager sub-class.
This commit is contained in:
Emmanuele Bassi 2009-12-23 10:35:16 +00:00
parent 713c295241
commit 934eee17ae
1 changed files with 190 additions and 23 deletions
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187
clutter/clutter-layout-manager.c
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@ -36,10 +36,10 @@
* a generic container using #ClutterLayoutManager called #ClutterBox.
*
* Clutter provides some simple #ClutterLayoutManager sub-classes, like
* #ClutterFixedLayout and #ClutterBinLayout.
* #ClutterFlowLayout and #ClutterBinLayout.
*
* <refsect2 id="ClutterLayoutManager-use-in-Actor">
* <title>Using ClutterLayoutManager inside an Actor</title>
* <title>Using a Layout Manager inside an Actor</title>
* <para>In order to use a #ClutterLayoutManager inside a #ClutterActor
* sub-class you should invoke clutter_layout_manager_get_preferred_width()
* inside the <structname>ClutterActor</structname>::get_preferred_width()
@ -70,18 +70,20 @@
* #ClutterActor, so you should read the relative documentation
* <link linkend="clutter-subclassing-ClutterActor">for subclassing
* ClutterActor</link>.</para>
* <para>The layout manager implementation can hold a back reference
* to the #ClutterContainer by implementing the set_container()
* virtual function. The layout manager should not hold a reference
* on the container actor, to avoid reference cycles.</para>
* <para>The layout manager implementation can hold a back pointer
* to the #ClutterContainer by implementing the
* <function>set_container()</function> virtual function. The layout manager
* should not hold a real reference (i.e. call g_object_ref()) on the
* container actor, to avoid reference cycles.</para>
* <para>If the layout manager has properties affecting the layout
* policies then it should emit the #ClutterLayoutManager::layout-changed
* signal on itself by using the clutter_layout_manager_layout_changed()
* function.</para>
* function whenever one of these properties changes.</para>
* <para>If the layout manager has layout properties, that is properties that
* should exist only as the result of the presence of a specific (layout
* manager, container actor, child actor) combination, then it should
* override the <structname>ClutterLayoutManager</structname>::get_child_meta_type()
* manager, container actor, child actor) combination, and it wishes to store
* those properties inside a #ClutterLayoutMeta then it should override the
* <structname>ClutterLayoutManager</structname>::get_child_meta_type()
* virtual function to return the #GType of the #ClutterLayoutMeta sub-class
* used to store the layout properties; optionally, the #ClutterLayoutManager
* sub-class might also override the
@ -109,7 +111,172 @@
*
* <refsect2 id="ClutterLayoutManager-animation">
* <title>Animating a ClutterLayoutManager</title>
* <para>...</para>
* <para>A layout manager is used to let a #ClutterContainer take complete
* ownership over the layout (that is: the position and sizing) of its
* children; this means that using the Clutter animation API, like
* clutter_actor_animate(), to animate the position and sizing of a child of
* a layout manager it is not going to work properly, as the animation will
* automatically override any setting done by the layout manager
* itself.</para>
* <para>It is possible for a #ClutterLayoutManager sub-class to animate its
* children layout by using the base class animation support. The
* #ClutterLayoutManager animation support consists of three virtual
* functions: <function>begin_animation()</function>,
* <function>get_animation_progress()</function> and
* <function>end_animation()</function>.</para>
* <variablelist>
* <varlistentry>
* <term><function>begin_animation (duration, easing)</function></term>
* <listitem><para>This virtual function is invoked when the layout
* manager should begin an animation. The implementation should set up
* the state for the animation and create the ancillary objects for
* animating the layout. The default implementation creates a
* #ClutterTimeline for the given duration and a #ClutterAlpha binding
* the timeline to the given easing mode. This function returns a
* #ClutterAlpha which should be used to control the animation from
* the caller perspective.</para></listitem>
* </varlistentry>
* <varlistentry>
* <term><function>get_animation_progress()</function></term>
* <listitem><para>This virtual function should be invoked when animating
* a layout manager. It returns the progress of the animation, using the
* same semantics as the #ClutterAlpha:alpha value.</para></listitem>
* </varlistentry>
* <varlistentry>
* <term><function>end_animation()</function></term>
* <listitem><para>This virtual function is invoked when the animation of
* a layout manager ends, and it is meant to be used for bookkeeping the
* objects created in the <function>begin_animation()</function>
* function. The default implementation will call it implicitly when the
* timeline is complete.</para></listitem>
* </varlistentry>
* </variablelist>
* <para>The simplest way to animate a layout is to create a #ClutterTimeline
* inside the <function>begin_animation()</function> virtual function, along
* with a #ClutterAlpha, and for each #ClutterTimeline::new-frame signal
* emission call clutter_layout_manager_layout_changed(), which will cause a
* relayout. The #ClutterTimeline::completed signal emission should cause
* clutter_layout_manager_end_animation() to be called. The default
* implementation provided internally by #ClutterLayoutManager does exactly
* this, so most sub-classes should either not override any animation-related
* virtual function or simply override <function>begin_animation()</function>
* and <function>end_animation()</function> to set up ad hoc state, and then
* chain up to the parent's implementation.</para>
* <example id="example-ClutterLayoutManager-animation">
* <title>Animation of a Layout Manager</title>
* <para>The code below shows how a #ClutterLayoutManager sub-class should
* provide animating the allocation of its children from within the
* <function>allocate()</function> virtual function implementation. The
* animation is computed between the last stable allocation performed
* before the animation started and the desired final allocation.</para>
* <para>The <varname>is_animating</varname> variable is stored inside the
* #ClutterLayoutManager sub-class and it is updated by overriding the
* <function>begin_animation()</function> and
* <function>end_animation()</function> virtual functions and chaining up
* to the base class implementation.</para>
* <para>The last stable allocation is stored within a #ClutterLayoutMeta
* sub-class used by the implementation.</para>
* <programlisting>
* static void
* my_layout_manager_allocate (ClutterLayoutManager *manager,
* ClutterContainer *container,
* const ClutterActorBox *allocation,
* ClutterAllocationFlags flags)
* {
* MyLayoutManager *self = MY_LAYOUT_MANAGER (manager);
* GList *children, *l;
*
* children = clutter_container_get_children (container);
*
* for (l = children; l != NULL; l = l-&gt;next)
* {
* ClutterActor *child = l->data;
* ClutterLayoutMeta *meta;
* MyLayoutMeta *my_meta;
*
* /&ast; retrieve the layout meta-object &ast;/
* meta = clutter_layout_manager_get_child_meta (manager,
* container,
* child);
* my_meta = MY_LAYOUT_META (meta);
*
* /&ast; compute the desired allocation for the child &ast;/
* compute_allocation (self, my_meta, child,
* allocation, flags,
* &amp;child_box);
*
* /&ast; this is the additional code that deals with the animation
* &ast; of the layout manager
* &ast;/
* if (!self-&gt;is_animating)
* {
* /&ast; store the last stable allocation for later use &ast;/
* my_meta-&gt;last_alloc = clutter_actor_box_copy (&amp;child_box);
* }
* else
* {
* ClutterActorBox end = { 0, };
* gdouble p;
*
* /&ast; get the progress of the animation &ast;/
* p = clutter_layout_manager_get_animation_progress (manager);
*
* if (my_meta-&gt;last_alloc != NULL)
* {
* /&ast; copy the desired allocation as the final state &ast;/
* end = child_box;
*
* /&ast; then interpolate the initial and final state
* &ast; depending on the progress of the animation,
* &ast; and put the result inside the box we will use
* &ast; to allocate the child
* &ast;/
* clutter_actor_box_interpolate (my_meta-&gt;last_alloc,
* &amp;end,
* p,
* &amp;child_box);
* }
* else
* {
* /&ast; if there is no stable allocation then the child was
* &ast; added while animating; one possible course of action
* &ast; is to just bail out and fall through to the allocation
* &ast; to position the child directly at its final state
* &ast;/
* my_meta-&gt;last_alloc =
* clutter_actor_box_copy (&amp;child_box);
* }
* }
*
* /&ast; allocate the child &ast;/
* clutter_actor_allocate (child, &child_box, flags);
* }
*
* g_list_free (children);
* }
* </programlisting>
* </example>
* <para>Sub-classes of #ClutterLayoutManager that support animations of the
* layout changes should call clutter_layout_manager_begin_animation()
* whenever a layout property changes value, e.g.:</para>
* <informalexample>
* <programlisting>
* if (self->orientation != new_orientation)
* {
* ClutterLayoutManager *manager;
*
* self->orientation = new_orientation;
*
* manager = CLUTTER_LAYOUT_MANAGER (self);
* clutter_layout_manager_layout_changed (manager);
* clutter_layout_manager_begin_animation (manager, 500, CLUTTER_LINEAR);
*
* g_object_notify (G_OBJECT (self), "orientation");
* }
* </programlisting>
* </informalexample>
* <para>The code above will animate a change in the
* <varname>orientation</varname> layout property of a layout manager.</para>
* </refsect2>
*
* #ClutterLayoutManager is available since Clutter 1.2