cookbook: Add recipe for animated scaling of an actor
Recipe explains how to animate scaling a single actor. Also covers scaling vs. resizing, scale center, and scaling within layouts and containers. The first example shows how animations around each scale gravity look, as well as tracking the transformed position and size of the actor and displaying those. The second example is a simple image viewer with zoom in/out using scaling.
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Elliot Smith
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@ -2709,7 +2709,20 @@ timeline_completed_cb (ClutterTimeline *timeline,
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<section>
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<section>
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<title>Problem</title>
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<title>Problem</title>
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<para>You want to animate scaling of an actor.</para>
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<para>You want to animate scaling of an actor. Example use
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cases:</para>
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<itemizedlist>
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<listitem>
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<para>To animate zooming in/out of a texture in an
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image viewer application.</para>
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</listitem>
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<listitem>
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<para>To add an animated "bounce" effect (quick scale up
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followed by scale down) to a UI element
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to indicate it has received focus.</para>
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</listitem>
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</itemizedlist>
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</section>
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</section>
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<section>
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<section>
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@ -2717,18 +2730,19 @@ timeline_completed_cb (ClutterTimeline *timeline,
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<para>Animate the actor's <varname>scale-x</varname> and
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<para>Animate the actor's <varname>scale-x</varname> and
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<varname>scale-y</varname> properties to change the scaling on
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<varname>scale-y</varname> properties to change the scaling on
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the x and y axes respectively.</para>
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the <varname>x</varname> and <varname>y</varname> axes
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respectively.</para>
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<para>For example, to animate an actor to twice its initial scale
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<para>For example, to animate an actor to twice its current scale
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with implicit animations:</para>
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with implicit animations:</para>
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<informalexample>
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<informalexample>
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<programlisting>
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<programlisting>
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<![CDATA[
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<![CDATA[
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/* get the actor's current scale */
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gdouble scale_x;
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gdouble scale_x;
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gdouble scale_y;
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gdouble scale_y;
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/* get the actor's current scale */
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clutter_actor_get_scale (actor, &scale_x, &scale_y);
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clutter_actor_get_scale (actor, &scale_x, &scale_y);
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/* animate to twice current scale on both axes */
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/* animate to twice current scale on both axes */
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@ -2742,79 +2756,263 @@ clutter_actor_animate (actor, CLUTTER_LINEAR, 1000,
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<para>Alternatively, <type>ClutterAnimator</type> or
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<para>Alternatively, <type>ClutterAnimator</type> or
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<type>ClutterState</type> can be used to animate an actor's scale
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<type>ClutterState</type> can be used to animate an actor's scale
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properties. See <link linkend="animations-scaling-example-1">this
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properties. See <link linkend="animations-scaling-example-1">this
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example</link> for details.</para>
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example</link> which uses <type>ClutterState</type> to animate
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scaling.</para>
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</section>
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</section>
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<section>
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<section>
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<title>Discussion</title>
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<title>Discussion</title>
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<!--
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<para>Scaling an actor is done through its <varname>scale-x</varname>
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<para>The scale value is a double. Values less than 1.0 will reduce the apparent size of the actor; values greater than 1.0 will increase the apparent size.</para>
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and <varname>scale-y</varname> properties, each of which takes
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a <code>double</code> value. A value of less than
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<code>1.0</code> for an axis scales an actor down on that axis,
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reducing its apparent size; values greater than <code>1.0</code>
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scale an actor up, increasing its apparent size.</para>
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When you scale an actor, you aren't changing the actor's real size: you are applying a transform which changes its <emphasis>apparent</emphasis> size. Changing the scale will also transform the actor's position (i.e. it will appear to be at a different position within its container, although it will actually report its original position if you call clutter_actor_get_position(), clutter_actor_get_x() or clutter_actor_get_y()).
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<para>Why "apparent" size? Because scaling applies a transform
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to an actor which changes how it appears on the
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stage, without changing its "real" size. Similarly, scaling an
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actor may transform its position: it could appear to move to a
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different position within its container,
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although it is "really" at its original position. Run
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<link linkend="animations-scaling-example-1">the
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example</link> to see how size and position are
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transformed by scaling.</para>
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<para>It can be useful to know an actor's
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<emphasis>transformed</emphasis> position and size after scaling:
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for example, if you were implementing a reflowing layout manager
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which used scaling as part of its allocation algorithm.
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Here's an example of how to get these properties for an
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actor:</para>
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You can get the transformed (apparent) position and size for an actor with <function>clutter_actor_get_transformed_position()</function> and <function>clutter_actor_get_transformed_size()</function> respectively.
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<informalexample>
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<programlisting>
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<![CDATA[
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gfloat transformed_x;
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gfloat transformed_y;
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Because an actor is at a different apparent size when scaled, mouse clicks need translating into actor coordinates before you can use them.
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gfloat transformed_width;
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gfloat transformed_height;
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clutter_actor_get_transformed_position (actor, &transformed_x, &transformed_y);
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clutter_actor_get_transformed_size (actor, &transformed_width, &transformed_height);
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]]>
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</programlisting>
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</informalexample>
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<para>Note that you can scale an actor on both axes by the same
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amount (uniform scaling), or by a different amount on each axis
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(differential scaling).</para>
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You can scale on both axes by the same amount (uniform scaling), or by a different amount on each axis (differential scaling).
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<para>Use <function>clutter_actor_is_scaled()</function> to determine
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whether scaling has been applied to an actor: this function returns
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<code>FALSE</code> if both <varname>scale-x</varname> and
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<varname>scale-y</varname> are <code>1.0</code>; otherwise, it
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returns <code>TRUE</code>.</para>
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clutter_actor_is_scaled() tells you whether scaling has been applied to the actor: it returns FALSE if both scale-x and scale-y are 1.0.
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<section>
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<title>Scaling vs. resizing</title>
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<para>Scaling changes the <emphasis>apparent</emphasis> size
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of an actor, while leaving its real size unchanged. By contrast,
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resizing changes the <emphasis>real</emphasis> size of the actor,
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by modifying its <varname>width</varname> and
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<varname>height</varname> properties.</para>
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<para>Resizing and scaling produce the same visual
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effect, as both make an actor appear to be larger or
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smaller. Therefore, for most purposes, they are interchangeable
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if you just want to change an actor's apparent size.</para>
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<para>So why would you scale an actor rather than resize it?</para>
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Scaling a container scales all actors inside the container.
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<itemizedlist>
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<listitem>
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<para>If you've scaled an actor, you can easily reset it
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to its original size, by setting its
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scale back to <code>1.0</code> on both axes. By contrast,
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to reset a resized actor to its original size,
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you would have to track the original size manually: the
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actor doesn't make its original size accessible.</para>
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</listitem>
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-->
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<listitem>
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<para>Scaling can easily change the apparent size
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of multiple actors inside a container. For example, say you
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wanted to shrink multiple actors inside a container
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to half their original size. There are two ways you
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could do this:</para>
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<orderedlist>
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<listitem>
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<para>The hard way would be to resize
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each actor individually. You couldn't just resize the container,
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as resizing a container doesn't resize its children: usually
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they will be clipped so that they are either partially or
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wholly hidden.</para>
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</listitem>
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<listitem>
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<para>The easy way would be to set the container's scale
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to half its initial value: the actors
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in the container would retain their original sizes, but would
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appear at half size.</para>
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</listitem>
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</orderedlist>
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</listitem>
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</itemizedlist>
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</section>
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<section>
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<title>Scaling, layouts and containers</title>
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<para>It is possible to scale actors inside containers. For
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example, if you were using a <type>ClutterBox</type>
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which has a <type>ClutterBoxLayout</type> layout manager,
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you could scale the children of that layout.</para>
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<para>However, you should remain aware that layout managers
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don't take account of the scale of their children, only their
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size. So if you scale up an actor inside a layout manager,
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it may overlap other actors in the layout: the size allocated
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by the layout manager doesn't increase as an actor's scale
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increases.</para>
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<para>Similarly, scaling an actor down doesn't reduce the space
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it will be allocated by a layout.</para>
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</section>
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<section>
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<section>
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<title>Setting the scale center</title>
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<title>Setting the scale center</title>
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<!--
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<para>An actor's scale center is the point around which
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You can change the center of the scaling, using either gravity or actor-relative coordinates. Note that setting the scale gravity on an actor sets the scale-center-x and scale-center-y values behind the scenes.
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scaling occurs: when you scale the actor, it will "shrink"
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into (if scale < 1.0) or "expand" out of (if scale > 1.0)
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its scale center.</para>
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<para>You can change an actor's scale center using
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either gravity (a named position on the actor; for example, the
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middle of the top edge of the actor is
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<constant>CLUTTER_GRAVITY_NORTH</constant>); or
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x,y coordinates relative to the actor's anchor point (by default,
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the anchor point for an actor is at <code>0,0</code>).</para>
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<para>Setting scale gravity has the same consequences as
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setting both the <varname>scale-center-x</varname> and
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<varname>scale-center-y</varname> properties for an actor.
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For example, <constant>CLUTTER_GRAVITY_NORTH_EAST</constant>
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sets the scale center to <code><width of the actor>, 0</code>,
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relative to the actor's anchor point (defaults to the top-right
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corner of the actor). However, the advantage of scale
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gravities is that they change with the actor: so if the
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actor is resized, you don't have to manually reset the scale
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center. This means that <constant>CLUTTER_GRAVITY_NORTH_EAST</constant>
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will always represent the top-right corner of the actor,
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regardless of how it is scaled or resized. The same is true
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of each of the other scale gravities.</para>
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<para>If you're animating an actor's scale but want a different
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scale center, set it before the animation begins. One way to
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do this is to leave the actor's scale unchanged, but with
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a different scale center:</para>
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When you scale the actor, it will "shrink" into (if scale < 1.0) or "expand" out of (if scale > 1.0) the center.
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<informalexample>
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<programlisting>
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<![CDATA[
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gdouble scale_x;
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gdouble scale_y;
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You can't really change the scaling center as part of the animation: you should do it before scaling an actor with an animation.
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/* get the actor's current scale */
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clutter_actor_get_scale (actor, &scale_x, &scale_y);
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Once you've scaled an actor, it's not a great idea to change the scale center: if you do, it probably won't do what you expect.
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/* set scale center using x,y coordinates, leaving scale unchanged;
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* the actor's size here is assumed to be 200x200
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*/
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clutter_actor_set_scale_full (actor,
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scale_x,
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scale_y,
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100.0, /* center x */
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100.0 /* center y */);
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/* set scale center using gravity, leaving scale unchanged */
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clutter_actor_set_scale_with_gravity (actor,
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scale_x,
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scale_y,
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CLUTTER_GRAVITY_CENTER);
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]]>
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</programlisting>
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</informalexample>
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<para>Another approach is to set scale center properties
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via GObject, which doesn't require you to figure out the
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actor's scale first:</para>
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animations-scaling.c shows all the scale gravities
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<informalexample>
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<programlisting>
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<![CDATA[
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/* set scale center using x,y coordinates */
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g_object_set (actor,
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"scale-center-x", 100.0, /* center x */
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"scale-center-y", 100.0, /* center y */
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NULL);
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/* set scale center using gravity */
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g_object_set (actor,
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"scale-gravity", CLUTTER_GRAVITY_CENTER,
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NULL);
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]]>
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</programlisting>
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</informalexample>
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<para>Once the scale center is set, you can animate the
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scaling as per usual.</para>
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<para>It is even possible to animate the
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<varname>scale-center-*</varname> properties, which can
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produce interesting, though slightly
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unpredictable, effects. It's usually better to change the
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scale center before the animation starts.</para>
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What if you set scale centers and scale gravity? which gets precedence - I think scale center
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<para><link linkend="animations-scaling-example-1">The
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example</link> cycles through the available scale gravities,
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showing the effect on the animation of each of the scale
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centers.</para>
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<para>The <link linkend="animations-scaling-example-2">second
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example</link> shows how to combine scaling in and out on a
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texture, in response to mouse button presses. In this case,
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the scale gravity remains at <constant>CLUTTER_GRAVITY_NORTH_WEST</constant>
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(i.e. at the anchor point of the actor). However, the anchor
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point is moved to the coordinates of each double click on button 1
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(usually the left mouse button) or button 3 (usually the right
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mouse button); which in turn automatically moves the scale center
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before the texture is scaled. As a result, the texture
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"expands" or "contracts" around the clicked point,
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while the point remains still.</para>
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<warning>
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<para>One final caveat about scale centers: if an actor is
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already scaled, the scale center coordinates are relative to
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the <emphasis>real size</emphasis> of the actor, rather than
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its <emphasis>transformed</emphasis> size. This can result in
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a "jumping" effect if you change the scale center on
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a scaled actor.</para>
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<para>For example, you might set the scale gravity of an actor
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to <constant>CLUTTER_GRAVITY_WEST</constant>, then
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scale the actor to <code>0.5</code> on both axes. Later, you
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change the actor's scale gravity to
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<constant>CLUTTER_GRAVITY_EAST</constant>. The effect of this
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is to "jump" the actor to the right, so its right-hand edge
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is aligned with where it was at scale <code>1.0</code>.</para>
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For example, you have a square actor size 200x200 at x=100, y=100.
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<para>If this isn't desirable, you can just retain the scale
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center on a scaled actor, and only change it when the actor
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You scale it to half scale, setting the scale center to x=100, y=0 (middle of the top of the square)
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is unscaled.</para>
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(the scale center is relative to the actor)
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</warning>
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The center of the top of the square stays where it is
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The part of the line either side of the center "shrinks" in towards the center of the line
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The top of the square stays still; the rest of the square "shrinks" up towards the top
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The square now appears at half its original size, and with an _transformed_ position of x=150, y=0
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Note that the scale center is relative to the actor's actual size, not its transformed size.
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-->
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</section>
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</section>
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</section>
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</section>
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@ -2828,6 +3026,17 @@ Note that the scale center is relative to the actor's actual size, not its trans
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<programlisting>
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<programlisting>
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<xi:include href="examples/animations-scaling.c" parse="text">
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<xi:include href="examples/animations-scaling.c" parse="text">
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<xi:fallback>a code sample should be here... but isn't</xi:fallback>
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<xi:fallback>a code sample should be here... but isn't</xi:fallback>
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</xi:include>
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</programlisting>
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</example>
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<example id="animations-scaling-example-2">
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<title>Animated scaling (up and down) of a texture in response
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to button presses. Call with the path to an image as the
|
||||||
|
first argument.</title>
|
||||||
|
<programlisting>
|
||||||
|
<xi:include href="examples/animations-scaling-zoom.c" parse="text">
|
||||||
|
<xi:fallback>a code sample should be here... but isn't</xi:fallback>
|
||||||
</xi:include>
|
</xi:include>
|
||||||
</programlisting>
|
</programlisting>
|
||||||
</example>
|
</example>
|
||||||
|
|||||||
Loading…
Reference in New Issue
Block a user