<html><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8"><title>9. Animated scaling</title><link rel="stylesheet" type="text/css" href="style.css"><meta name="generator" content="DocBook XSL Stylesheets Vsnapshot"><link rel="home" href="index.html" title="The Clutter Cookbook"><link rel="up" href="animations.html" title="Chapter 5. Animations"><link rel="prev" href="animations-looping.html" title="8. Looping an animation"><link rel="next" href="animations-path.html" title="10. Animating an actor along a curved path"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">9. Animated scaling</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="animations-looping.html">Prev</a> </td><th width="60%" align="center">Chapter 5. Animations</th><td width="20%" align="right"> <a accesskey="n" href="animations-path.html">Next</a></td></tr></table><hr></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="animations-scaling"></a>9. Animated scaling</h2></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="idm140200507193808"></a>9.1. Problem</h3></div></div></div><p>You want to animate scaling of an actor. Example use
cases:</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p>To animate zooming in/out of a texture in an
image viewer application.</p></li><li class="listitem"><p>To add an animated "bounce" effect (quick scale up
followed by scale down) to a UI element
to indicate it has received focus.</p></li></ul></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="idm140200507190400"></a>9.2. Solution</h3></div></div></div><p>Animate the actor's <code class="varname">scale-x</code> and
<code class="varname">scale-y</code> properties to change the scaling on
the <code class="varname">x</code> and <code class="varname">y</code> axes
respectively.</p><p>For example, to animate an actor to twice its current scale
with implicit animations:</p><div class="informalexample"><pre class="programlisting">gdouble scale_x;
gdouble scale_y;
/* get the actor's current scale */
clutter_actor_get_scale (actor, &scale_x, &scale_y);
/* animate to twice current scale on both axes */
clutter_actor_animate (actor, CLUTTER_LINEAR, 1000,
"scale-x", scale_x * 2,
"scale-y", scale_y * 2);</pre></div><p>Alternatively, <span class="type">ClutterAnimator</span> or
<span class="type">ClutterState</span> can be used to animate an actor's scale
properties. See <a class="link" href="animations-scaling.html#animations-scaling-example-1" title="Example 5.14. Animated scaling of an actor using each of the scale gravities. Press any key to start the animation.">this
example</a> which uses <span class="type">ClutterState</span> to animate
scaling.</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="idm140200507183616"></a>9.3. Discussion</h3></div></div></div><p>Scaling an actor is done through its <code class="varname">scale-x</code>
and <code class="varname">scale-y</code> properties, each of which takes
a <code class="code">double</code> value. A value of less than
<code class="code">1.0</code> for an axis scales an actor down on that axis,
reducing its apparent size; values greater than <code class="code">1.0</code>
scale an actor up, increasing its apparent size.</p><p>Why "apparent" size? Because scaling applies a transform
to an actor which changes how it appears on the
stage, without changing its "real" size. Similarly, scaling an
actor may transform its position: it could appear to move to a
different position within its container,
although it is "really" at its original position. Run
<a class="link" href="animations-scaling.html#animations-scaling-example-1" title="Example 5.14. Animated scaling of an actor using each of the scale gravities. Press any key to start the animation.">the
example</a> to see how size and position are
transformed by scaling.</p><p>It can be useful to know an actor's
<span class="emphasis"><em>transformed</em></span> position and size after scaling:
for example, if you were implementing a reflowing layout manager
which used scaling as part of its allocation algorithm.
Here's an example of how to get these properties for an
actor:</p><div class="informalexample"><pre class="programlisting">gfloat transformed_x;
gfloat transformed_y;
gfloat transformed_width;
gfloat transformed_height;
clutter_actor_get_transformed_position (actor, &transformed_x, &transformed_y);
clutter_actor_get_transformed_size (actor, &transformed_width, &transformed_height);</pre></div><p>Note that you can scale an actor on both axes by the same
amount (uniform scaling), or by a different amount on each axis
(differential scaling).</p><p>Use <code class="function">clutter_actor_is_scaled()</code> to determine
whether scaling has been applied to an actor: this function returns
<code class="code">FALSE</code> if both <code class="varname">scale-x</code> and
<code class="varname">scale-y</code> are <code class="code">1.0</code>; otherwise, it
returns <code class="code">TRUE</code>.</p><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="idm140200507173168"></a>9.3.1. Scaling vs. resizing</h4></div></div></div><p>Scaling changes the <span class="emphasis"><em>apparent</em></span> size
of an actor, while leaving its real size unchanged. By contrast,
resizing changes the <span class="emphasis"><em>real</em></span> size of the actor,
by modifying its <code class="varname">width</code> and
<code class="varname">height</code> properties.</p><p>Resizing and scaling produce the same visual
effect, as both make an actor appear to be larger or
smaller. Therefore, for most purposes, they are interchangeable
if you just want to change an actor's apparent size.</p><p>So why would you scale an actor rather than resize it?</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p>If you've scaled an actor, you can easily reset it
to its original size, by setting its
scale back to <code class="code">1.0</code> on both axes. By contrast,
to reset a resized actor to its original size,
you would have to track the original size manually: the
actor doesn't make its original size accessible.</p></li><li class="listitem"><p>Scaling can easily change the apparent size
of multiple actors inside a container. For example, say you
wanted to shrink multiple actors inside a container
to half their original size. There are two ways you
could do this:</p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><p>The hard way would be to resize
each actor individually. You couldn't just resize the container,
as resizing a container doesn't resize its children: usually
they will be clipped so that they are either partially or
wholly hidden.</p></li><li class="listitem"><p>The easy way would be to set the container's scale
to half its initial value: the actors
in the container would retain their original sizes, but would
appear at half size.</p></li></ol></div></li></ul></div></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="idm140200507163424"></a>9.3.2. Scaling, layouts and containers</h4></div></div></div><p>It is possible to scale actors inside containers. For
example, if you were using a <span class="type">ClutterBox</span>
which has a <span class="type">ClutterBoxLayout</span> layout manager,
you could scale the children of that layout.</p><p>However, you should remain aware that layout managers
don't take account of the scale of their children, only their
size. So if you scale up an actor inside a layout manager,
it may overlap other actors in the layout: the size allocated
by the layout manager doesn't increase as an actor's scale
increases.</p><p>Similarly, scaling an actor down doesn't reduce the space
it will be allocated by a layout.</p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="idm140200507160064"></a>9.3.3. Setting the scale center</h4></div></div></div><p>An actor's scale center is the point around which
scaling occurs: when you scale the actor, it will "shrink"
into (if scale < 1.0) or "expand" out of (if scale > 1.0)
its scale center.</p><p>You can change an actor's scale center using
either gravity (a named position on the actor; for example, the
middle of the top edge of the actor is
<code class="constant">CLUTTER_GRAVITY_NORTH</code>); or
x,y coordinates relative to the actor's anchor point (by default,
the anchor point for an actor is at <code class="code">0,0</code>).</p><p>Setting scale gravity has the same consequences as
setting both the <code class="varname">scale-center-x</code> and
<code class="varname">scale-center-y</code> properties for an actor.
For example, <code class="constant">CLUTTER_GRAVITY_NORTH_EAST</code>
sets the scale center to <code class="code"><width of the actor>, 0</code>,
relative to the actor's anchor point (defaults to the top-right
corner of the actor). However, the advantage of scale
gravities is that they change with the actor: so if the
actor is resized, you don't have to manually reset the scale
center. This means that <code class="constant">CLUTTER_GRAVITY_NORTH_EAST</code>
will always represent the top-right corner of the actor,
regardless of how it is scaled or resized. The same is true
of each of the other scale gravities.</p><p>If you're animating an actor's scale but want a different
scale center, set it before the animation begins. One way to
do this is to leave the actor's scale unchanged, but with
a different scale center:</p><div class="informalexample"><pre class="programlisting">gdouble scale_x;
gdouble scale_y;
/* get the actor's current scale */
clutter_actor_get_scale (actor, &scale_x, &scale_y);
/* set scale center using x,y coordinates, leaving scale unchanged;
* the actor's size here is assumed to be 200x200
*/
clutter_actor_set_scale_full (actor,
scale_x,
scale_y,
100.0, /* center x */
100.0 /* center y */);
/* set scale center using gravity, leaving scale unchanged */
clutter_actor_set_scale_with_gravity (actor,
scale_x,
scale_y,
CLUTTER_GRAVITY_CENTER);</pre></div><p>Another approach is to set scale center properties
via GObject, which doesn't require you to figure out the
actor's scale first:</p><div class="informalexample"><pre class="programlisting">/* set scale center using x,y coordinates */
g_object_set (actor,
"scale-center-x", 100.0, /* center x */
"scale-center-y", 100.0, /* center y */
NULL);
/* set scale center using gravity */
g_object_set (actor,
"scale-gravity", CLUTTER_GRAVITY_CENTER,
NULL);</pre></div><p>Once the scale center is set, you can animate the
scaling as per usual.</p><p>It is even possible to animate the
<code class="varname">scale-center-*</code> properties, which can
produce interesting, though slightly
unpredictable, effects. It's usually better to change the
scale center before the animation starts.</p><p><a class="link" href="animations-scaling.html#animations-scaling-example-1" title="Example 5.14. Animated scaling of an actor using each of the scale gravities. Press any key to start the animation.">The
example</a> cycles through the available scale gravities,
showing the effect on the animation of each of the scale
centers.</p><p>The <a class="link" href="animations-scaling.html#animations-scaling-example-2" title="Example 5.15. Animated scaling (up and down) of a texture in response to button presses. Call with the path to an image as the first argument.">second
example</a> shows how to combine scaling in and out on a
texture, in response to mouse button presses. In this case,
the scale gravity remains at <code class="constant">CLUTTER_GRAVITY_NORTH_WEST</code>
(i.e. at the anchor point of the actor). However, the anchor
point is moved to the coordinates of each double click on button 1
(usually the left mouse button) or button 3 (usually the right
mouse button); which in turn automatically moves the scale center
before the texture is scaled. As a result, the texture
"expands" or "contracts" around the clicked point,
while the point remains still.</p><div class="warning" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Warning</h3><p>One final caveat about scale centers: if an actor is
already scaled, the scale center coordinates are relative to
the <span class="emphasis"><em>real size</em></span> of the actor, rather than
its <span class="emphasis"><em>transformed</em></span> size. This can result in
a "jumping" effect if you change the scale center on
a scaled actor.</p><p>For example, you might set the scale gravity of an actor
to <code class="constant">CLUTTER_GRAVITY_WEST</code>, then
scale the actor to <code class="code">0.5</code> on both axes. Later, you
change the actor's scale gravity to
<code class="constant">CLUTTER_GRAVITY_EAST</code>. The effect of this
is to "jump" the actor to the right, so its right-hand edge
is aligned with where it was at scale <code class="code">1.0</code>.</p><p>If this isn't desirable, you can just retain the scale
center on a scaled actor, and only change it when the actor
is unscaled.</p></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="animations-scaling-examples"></a>9.4. Full examples</h3></div></div></div><div class="example"><a name="animations-scaling-example-1"></a><p class="title"><b>Example 5.14. Animated scaling of an actor using each of the
scale gravities. Press any key to start the animation.</b></p><div class="example-contents"><pre class="programlisting">#include <stdlib.h>
#include <clutter/clutter.h>
typedef struct
{
ClutterState *transitions;
ClutterActor *actor;
ClutterActor *props_display;
guint scale_gravity;
gboolean transitions_running;
} State;
static const ClutterColor stage_color = { 0x33, 0x33, 0x55, 0xff };
static const ClutterColor red_color = { 0xff, 0x00, 0x00, 0xff };
static const ClutterColor yellow_color = { 0xff, 0xff, 0x00, 0xff };
static void
show_scale_properties_cb (ClutterActor *actor,
gpointer user_data)
{
State *state = (State *) user_data;
gfloat transformed_x, transformed_y;
gfloat transformed_width, transformed_height;
gfloat scale_center_x, scale_center_y;
gchar *message;
clutter_actor_get_transformed_position (state->actor,
&transformed_x,
&transformed_y);
clutter_actor_get_transformed_size (state->actor,
&transformed_width,
&transformed_height);
g_object_get (G_OBJECT (actor),
"scale-center-x", &scale_center_x,
"scale-center-y", &scale_center_y,
NULL);
/* draw cross on the scale center */
cogl_set_source_color4ub (255, 255, 0, 255);
cogl_path_move_to (scale_center_x, scale_center_y);
cogl_path_rel_line_to (10, 10);
cogl_path_rel_line_to (-20, -20);
cogl_path_move_to (scale_center_x, scale_center_y);
cogl_path_rel_line_to (10, -10);
cogl_path_rel_line_to (-20, 20);
cogl_path_stroke ();
/* show actor properties */
message = g_strdup_printf ("Scale center: %.0f, %.0f\n"
"Transformed position: %.2f, %.2f\n"
"Transformed size: %.2f, %.2f",
scale_center_x, scale_center_y,
transformed_x, transformed_y,
transformed_width, transformed_height);
clutter_text_set_text (CLUTTER_TEXT (state->props_display), message);
g_free (message);
}
static void
next_transition_cb (ClutterState *transitions,
gpointer user_data)
{
State *state = (State *) user_data;
if (clutter_actor_is_scaled (state->actor))
clutter_state_set_state (state->transitions, "not-scaled");
else if (state->scale_gravity > 9)
{
/* gravity is at center, so reset ready for next key press */
state->scale_gravity = CLUTTER_GRAVITY_NORTH;
state->transitions_running = FALSE;
}
else
{
g_object_set (G_OBJECT (state->actor),
"scale-gravity", state->scale_gravity,
NULL);
state->scale_gravity++;
clutter_state_set_state (state->transitions, "scaled-down");
}
}
static gboolean
key_pressed_cb (ClutterActor *actor,
ClutterEvent *event,
gpointer user_data)
{
State *state = (State *) user_data;
if (!state->transitions_running)
{
state->transitions_running = TRUE;
next_transition_cb (NULL, state);
}
return TRUE;
}
int
main (int argc,
char *argv[])
{
State *state = g_new0 (State, 1);
ClutterActor *stage;
if (clutter_init (&argc, &argv) != CLUTTER_INIT_SUCCESS)
return 1;
stage = clutter_stage_new ();
clutter_actor_set_size (stage, 350, 350);
clutter_stage_set_color (CLUTTER_STAGE (stage), &stage_color);
g_signal_connect (stage, "destroy", G_CALLBACK (clutter_main_quit), NULL);
state->scale_gravity = CLUTTER_GRAVITY_NORTH;
state->transitions_running = FALSE;
state->props_display = clutter_text_new ();
clutter_actor_set_size (state->props_display, 340, 80);
clutter_actor_set_position (state->props_display, 5, 280);
clutter_text_set_color (CLUTTER_TEXT (state->props_display), &yellow_color);
state->actor = clutter_rectangle_new_with_color (&red_color);
clutter_actor_set_size (state->actor, 200, 200);
clutter_actor_set_position (state->actor, 75, 50);
g_object_set (G_OBJECT (state->actor),
"scale-gravity", state->scale_gravity,
NULL);
state->transitions = clutter_state_new ();
clutter_state_set_duration (state->transitions, NULL, NULL, 400);
clutter_state_set (state->transitions, NULL, "not-scaled",
state->actor, "scale-x", CLUTTER_LINEAR, 1.0,
state->actor, "scale-y", CLUTTER_LINEAR, 1.0,
NULL);
clutter_state_set (state->transitions, NULL, "scaled-down",
state->actor, "scale-x", CLUTTER_LINEAR, 0.25,
state->actor, "scale-y", CLUTTER_LINEAR, 0.25,
NULL);
clutter_state_warp_to_state (state->transitions, "not-scaled");
g_signal_connect (stage,
"key-press-event",
G_CALLBACK (key_pressed_cb),
state);
g_signal_connect (state->transitions,
"completed",
G_CALLBACK (next_transition_cb),
state);
g_signal_connect_after (state->actor,
"paint",
G_CALLBACK (show_scale_properties_cb),
state);
clutter_container_add (CLUTTER_CONTAINER (stage),
state->actor,
state->props_display,
NULL);
clutter_actor_show (stage);
clutter_main ();
g_object_unref (state->transitions);
g_free (state);
return EXIT_SUCCESS;
}
</pre></div></div><br class="example-break"><div class="example"><a name="animations-scaling-example-2"></a><p class="title"><b>Example 5.15. Animated scaling (up and down) of a texture in response
to button presses. Call with the path to an image as the
first argument.</b></p><div class="example-contents"><pre class="programlisting">/*
* Load an image into a texture, which can then be zoomed in/out
* (double click on button 1, double click on button 3 respectively);
* also resets the texture to the stage center when a key is pressed
* (better would be to prevent drags taking the actor off-stage,
* but the implementation is much more complicated)
*/
#include <stdlib.h>
#include <clutter/clutter.h>
#define STAGE_SIDE 400.0
static const ClutterColor stage_color = { 0x33, 0x33, 0x55, 0xff };
/* on key press, center the actor on the stage;
* useful if you drag it off-stage accidentally
*/
static gboolean
key_press_cb (ClutterActor *actor,
ClutterEvent *event,
gpointer user_data)
{
gfloat width, height;
clutter_actor_get_size (actor, &width, &height);
clutter_actor_set_anchor_point (actor, width / 2, height / 2);
clutter_actor_set_position (actor,
STAGE_SIDE / 2,
STAGE_SIDE / 2);
return TRUE;
}
/* on double click, zoom in on the clicked point;
* also keeps scale in the range 0.1 to 20
*/
static gboolean
clicked_cb (ClutterActor *actor,
ClutterEvent *event,
gpointer user_data)
{
gdouble scale;
gfloat click_x, click_y;
gfloat click_target_x, click_target_y;
guint32 button;
/* don't do anything unless there was a double click */
if (clutter_event_get_click_count (event) < 2)
return TRUE;
/* work out new scale */
button = clutter_event_get_button (event);
clutter_actor_get_scale (actor, &scale, NULL);
if (button == CLUTTER_BUTTON_PRIMARY)
scale *= 1.2;
else if (button == CLUTTER_BUTTON_SECONDARY)
scale /= 1.2;
/* don't do anything if scale is outside bounds */
if (scale < 0.1 || scale > 20.0)
return TRUE;
/* get the location of the click on the scaled actor */
clutter_event_get_coords (event, &click_x, &click_y);
clutter_actor_transform_stage_point (actor,
click_x, click_y,
&click_target_x, &click_target_y);
/* anchor the actor on the clicked point on its surface */
clutter_actor_set_anchor_point (actor, click_target_x, click_target_y);
/* set the actor's position to the click coords: it won't move,
* because the anchor point is already there; but
* the scale will now be centered on these coords (as the
* scale center defaults to the anchor point); so the anchor point
* on the actor won't move from under the pointer
*/
clutter_actor_set_position (actor, click_x, click_y);
clutter_actor_animate (actor, CLUTTER_LINEAR, 500,
"scale-x", scale,
"scale-y", scale,
NULL);
return TRUE;
}
int
main (int argc,
char *argv[])
{
ClutterActor *stage;
ClutterActor *texture;
gchar *image_path;
GError *error = NULL;
if (argc < 2)
{
g_print ("Usage: %s <path to image file>\n", argv[0]);
exit (EXIT_FAILURE);
}
image_path = argv[1];
if (clutter_init (&argc, &argv) != CLUTTER_INIT_SUCCESS)
return 1;
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);
texture = clutter_texture_new ();
clutter_actor_set_reactive (texture, TRUE);
clutter_actor_set_width (texture, STAGE_SIDE);
clutter_texture_set_keep_aspect_ratio (CLUTTER_TEXTURE (texture), TRUE);
clutter_actor_add_action (texture, clutter_drag_action_new ());
g_object_set (G_OBJECT (texture),
"scale-gravity", CLUTTER_GRAVITY_NORTH_WEST,
NULL);
clutter_texture_set_from_file (CLUTTER_TEXTURE (texture), image_path, &error);
if (error != NULL)
{
g_warning ("Error loading %s\n%s", image_path, error->message);
g_error_free (error);
exit (EXIT_FAILURE);
}
clutter_actor_set_y (texture, (STAGE_SIDE - clutter_actor_get_height (texture)) * 0.5);
g_signal_connect (texture,
"button-release-event",
G_CALLBACK (clicked_cb),
NULL);
g_signal_connect_swapped (stage,
"key-press-event",
G_CALLBACK (key_press_cb),
texture);
clutter_container_add_actor (CLUTTER_CONTAINER (stage), texture);
clutter_actor_show (stage);
clutter_main ();
return EXIT_SUCCESS;
}
</pre></div></div><br class="example-break"></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="animations-looping.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="animations.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="animations-path.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">8. Looping an animation </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> 10. Animating an actor along a curved path</td></tr></table></div></body></html>