<html><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8"><title>3. Binding the size of one actor to the size of another</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="layouts.html" title="Chapter 7. Layout management"><link rel="prev" href="layouts-stacking.html" title="2. Stacking actors on top of each other"><link rel="next" href="layouts-box.html" title="4. Arranging actors in a single row or column"></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">3. Binding the size of one actor to the size of another</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="layouts-stacking.html">Prev</a> </td><th width="60%" align="center">Chapter 7. Layout management</th><td width="20%" align="right"> <a accesskey="n" href="layouts-box.html">Next</a></td></tr></table><hr></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="layouts-bind-constraint"></a>3. Binding the size of one actor to the size of another</h2></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="idm140200506982304"></a>3.1. Problem</h3></div></div></div><p>You want one actor (the "target") to automatically change
its width or height (or both) when the size of another
actor (the "source") changes.</p><p>Example use cases:</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p>Making an actor adjust itself to the size of the stage
(particularly when the stage is resizable).</p></li><li class="listitem"><p>Putting one actor on top of another and keeping their
sizes in sync.</p></li></ul></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="idm140200506978064"></a>3.2. Solution</h3></div></div></div><p>Create a <span class="type">ClutterBindConstraint</span> 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.</p><p>This short example shows how to create and add a constraint;
<code class="varname">source</code> and <code class="varname">target</code> can
be any two <span class="type">ClutterActors</span>:</p><div class="informalexample"><pre class="programlisting"><span class="emphasis"><em>ClutterConstraint *width_constraint;</em></span>
/* 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
*/
<span class="emphasis"><em>width_constraint = clutter_bind_constraint_new (source, CLUTTER_BIND_WIDTH, -100);</em></span>
/* add the constraint to an actor */
<span class="emphasis"><em>clutter_actor_add_constraint (target, width_constraint);</em></span></pre></div><p>Below is a full example, showing how to incorporate a
constraint into a Clutter application.</p><div class="example"><a name="layouts-bind-constraint-example-1"></a><p class="title"><b>Example 7.3. Constraining the size of a texture to
the size of the stage using <span class="type">ClutterBindConstraint</span></b></p><div class="example-contents"><pre class="programlisting">#include <stdlib.h>
#include <clutter/clutter.h>
static const ClutterColor stage_color = { 0x33, 0x33, 0x55, 0xff };
static const ClutterColor rectangle_color = { 0xaa, 0x99, 0x00, 0xff };
int
main (int argc, char *argv[])
{
/* the stage is the "source" for constraints on the texture */
ClutterActor *stage;
/* the "target" actor which will be bound by the constraints */
ClutterActor *texture;
ClutterConstraint *width_binding;
ClutterConstraint *height_binding;
if (clutter_init (&argc, &argv) != CLUTTER_INIT_SUCCESS)
return 1;
stage = clutter_stage_new ();
clutter_actor_set_size (stage, 400, 400);
clutter_stage_set_color (CLUTTER_STAGE (stage), &stage_color);
g_signal_connect (stage, "destroy", G_CALLBACK (clutter_main_quit), NULL);
/* make the stage resizable */
clutter_stage_set_user_resizable (CLUTTER_STAGE (stage), TRUE);
texture = clutter_texture_new ();
clutter_actor_set_opacity (texture, 50);
clutter_texture_set_repeat (CLUTTER_TEXTURE (texture), TRUE, TRUE);
clutter_texture_set_from_file (CLUTTER_TEXTURE (texture), "smiley.png", NULL);
/* the texture's width will be 100px less than the stage's */
width_binding = clutter_bind_constraint_new (stage, CLUTTER_BIND_WIDTH, -100);
/* the texture's height will be 100px less than the stage's */
height_binding = clutter_bind_constraint_new (stage, CLUTTER_BIND_HEIGHT, -100);
/* add the constraints to the texture */
clutter_actor_add_constraint (texture, width_binding);
clutter_actor_add_constraint (texture, height_binding);
/* add some alignment constraints */
clutter_actor_add_constraint (texture, clutter_align_constraint_new (stage, CLUTTER_ALIGN_X_AXIS, 0.5));
clutter_actor_add_constraint (texture, clutter_align_constraint_new (stage, CLUTTER_ALIGN_Y_AXIS, 0.5));
clutter_container_add_actor (CLUTTER_CONTAINER (stage), texture);
clutter_actor_show (stage);
clutter_main ();
return EXIT_SUCCESS;
}
</pre></div></div><br class="example-break"><p>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 <span class="type">ClutterAlignConstraints</span> are
added to center the actor on the stage.</p><p>The result looks like this:</p><div class="screenshot"><div class="mediaobject"><img src="images/layouts-bind-constraint-stage.png" alt="A texture bound to the height and width of the stage using ClutterBindConstraint"></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="idm140200506960848"></a>3.3. Discussion</h3></div></div></div><p>Sizing constraints are a good solution in these cases:</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p>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
<a class="link" href="layouts-bind-constraint.html#layouts-bind-constraint-example-1" title="Example 7.3. Constraining the size of a texture to the size of the stage using ClutterBindConstraint">the example
above</a>), constraints are a good substitute for a layout
manager .</p></li><li class="listitem"><p>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).</p></li><li class="listitem"><p>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 <span class="type">ClutterConstraints</span> to actors
in response to user actions could work well.</p><p>The <a class="link" href="layouts-bind-constraint.html#layouts-bind-constraint-example-2" title="Example 7.4. Creating an automatically-resizing overlay for a texture using ClutterBindConstraint">sample
code in the appendix</a> is the kind of thing you might include
in a drawing program: you can resize a texture with a key press
(<code class="code">+</code> to increase size, <code class="code">-</code> 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.</p></li></ul></div><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>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).</p><p>A <span class="type">ClutterBindConstraint</span> can also be used to
constrain a target actor's position on the <code class="code">x</code> and
<code class="code">y</code> axes to the position of a source actor. This is
covered in another recipe.</p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="idm140200506948640"></a>3.3.1. Another way to bind actors' sizes together</h4></div></div></div><p>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 <code class="code">allocation-changed</code> 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.</p><p>Alternatively, if you're only interested in
a change to width or height, you can create a handler
for the <code class="code">notify::width</code> or
<code class="code">notify::height</code> signal (respectively), and modify
the target's width/height in the handler.</p><p>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
<a class="link" href="layouts-bind-constraint.html#layouts-bind-constraint-example-3" title="Example 7.5. Using the allocation-changed signal of one actor to trigger proportional size changes in another">the code in
this section</a> for an example where the size
of one actor is dynamically set to 10% more than the
size of another.</p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p><a class="link" href="actors-allocation-notify.html" title="3. Knowing when an actor's position or size changes">This recipe</a>
explains more about monitoring changes to an actor's size.</p></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="idm140200506941968"></a>3.4. Full examples</h3></div></div></div><div class="example"><a name="layouts-bind-constraint-example-2"></a><p class="title"><b>Example 7.4. Creating an automatically-resizing overlay for a
texture using <span class="type">ClutterBindConstraint</span></b></p><div class="example-contents"><pre class="programlisting">#include <stdlib.h>
#include <clutter/clutter.h>
#define STAGE_SIDE 400
#define RECTANGLE_SIDE STAGE_SIDE * 0.5
#define TEXTURE_SIZE_MAX STAGE_SIDE * 0.9
#define TEXTURE_SIZE_MIN STAGE_SIDE * 0.1
#define TEXTURE_SIZE_STEP 0.2
#define OVERLAY_OPACITY_OFF 0
#define OVERLAY_OPACITY_ON 100
static const ClutterColor stage_color = { 0x33, 0x33, 0x55, 0xff };
static const ClutterColor overlay_color = { 0xaa, 0x99, 0x00, 0xff };
/* change the texture size with +/- */
static gboolean
key_press_cb (ClutterActor *actor,
ClutterEvent *event,
gpointer user_data)
{
ClutterActor *texture;
gfloat texture_width, texture_height;
guint key_pressed;
texture = CLUTTER_ACTOR (user_data);
clutter_actor_get_size (texture, &texture_width, &texture_height);
key_pressed = clutter_event_get_key_symbol (event);
if (key_pressed == CLUTTER_KEY_plus)
{
texture_width *= 1.0 + TEXTURE_SIZE_STEP;
texture_height *= 1.0 + TEXTURE_SIZE_STEP;
}
else if (key_pressed == CLUTTER_KEY_minus)
{
texture_width *= 1.0 - TEXTURE_SIZE_STEP;
texture_height *= 1.0 - TEXTURE_SIZE_STEP;
}
if (texture_width <= TEXTURE_SIZE_MAX && texture_width >= TEXTURE_SIZE_MIN)
clutter_actor_animate (texture, CLUTTER_EASE_OUT_CUBIC, 500,
"width", texture_width,
"height", texture_height,
NULL);
return TRUE;
}
/* turn overlay opacity on/off */
static void
click_cb (ClutterClickAction *action,
ClutterActor *actor,
gpointer user_data)
{
ClutterActor *overlay = CLUTTER_ACTOR (user_data);
guint8 opacity = clutter_actor_get_opacity (overlay);
if (opacity < OVERLAY_OPACITY_ON)
opacity = OVERLAY_OPACITY_ON;
else
opacity = OVERLAY_OPACITY_OFF;
clutter_actor_set_opacity (overlay, opacity);
}
int
main (int argc, char *argv[])
{
ClutterActor *stage;
ClutterActor *texture;
ClutterActor *overlay;
ClutterAction *click;
GError *error = NULL;
const gchar *filename = "redhand.png";
if (argc > 1)
filename = 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_texture_set_keep_aspect_ratio (CLUTTER_TEXTURE (texture), TRUE);
clutter_actor_set_reactive (texture, TRUE);
clutter_actor_set_size (texture, RECTANGLE_SIDE, RECTANGLE_SIDE);
clutter_actor_add_constraint (texture, clutter_align_constraint_new (stage, CLUTTER_ALIGN_X_AXIS, 0.5));
clutter_actor_add_constraint (texture, clutter_align_constraint_new (stage, CLUTTER_ALIGN_Y_AXIS, 0.5));
clutter_texture_set_from_file (CLUTTER_TEXTURE (texture),
filename,
&error);
if (error != NULL)
{
g_warning ("Error loading %s\n%s", filename, error->message);
g_error_free (error);
exit (EXIT_FAILURE);
}
/* overlay is 10px wider and taller than the texture, and centered on it;
* initially, it is transparent; but it is made semi-opaque when the
* texture is clicked
*/
overlay = clutter_rectangle_new_with_color (&overlay_color);
clutter_actor_set_opacity (overlay, OVERLAY_OPACITY_OFF);
clutter_actor_add_constraint (overlay, clutter_bind_constraint_new (texture, CLUTTER_BIND_WIDTH, 10));
clutter_actor_add_constraint (overlay, clutter_bind_constraint_new (texture, CLUTTER_BIND_HEIGHT, 10));
clutter_actor_add_constraint (overlay, clutter_align_constraint_new (texture, CLUTTER_ALIGN_X_AXIS, 0.5));
clutter_actor_add_constraint (overlay, clutter_align_constraint_new (texture, CLUTTER_ALIGN_Y_AXIS, 0.5));
click = clutter_click_action_new ();
clutter_actor_add_action (texture, click);
clutter_container_add (CLUTTER_CONTAINER (stage), texture, overlay, NULL);
clutter_actor_raise_top (overlay);
g_signal_connect (click, "clicked", G_CALLBACK (click_cb), overlay);
g_signal_connect (stage,
"key-press-event",
G_CALLBACK (key_press_cb),
texture);
clutter_actor_show (stage);
clutter_main ();
return EXIT_SUCCESS;
}
</pre></div></div><br class="example-break"><div class="example"><a name="layouts-bind-constraint-example-3"></a><p class="title"><b>Example 7.5. Using the <code class="code">allocation-changed</code>
signal of one actor to trigger proportional size changes in
another</b></p><div class="example-contents"><pre class="programlisting">#include <stdlib.h>
#include <clutter/clutter.h>
#define OVERLAY_FACTOR 1.1
static const ClutterColor stage_color = { 0x33, 0x33, 0x55, 0xff };
void
allocation_changed_cb (ClutterActor *actor,
const ClutterActorBox *allocation,
ClutterAllocationFlags flags,
gpointer user_data)
{
ClutterActor *overlay = CLUTTER_ACTOR (user_data);
gfloat width, height, x, y;
clutter_actor_box_get_size (allocation, &width, &height);
clutter_actor_box_get_origin (allocation, &x, &y);
clutter_actor_set_size (overlay,
width * OVERLAY_FACTOR,
height * OVERLAY_FACTOR);
clutter_actor_set_position (overlay,
x - ((OVERLAY_FACTOR - 1) * width * 0.5),
y - ((OVERLAY_FACTOR - 1) * width * 0.5));
}
int
main (int argc, char *argv[])
{
ClutterActor *stage;
ClutterActor *actor;
ClutterActor *overlay;
if (clutter_init (&argc, &argv) != CLUTTER_INIT_SUCCESS)
return 1;
stage = clutter_stage_new ();
clutter_actor_set_size (stage, 400, 400);
clutter_stage_set_color (CLUTTER_STAGE (stage), &stage_color);
g_signal_connect (stage, "destroy", G_CALLBACK (clutter_main_quit), NULL);
actor = clutter_actor_new ();
clutter_actor_set_background_color (actor, CLUTTER_COLOR_Red);
clutter_actor_set_size (actor, 100, 100);
clutter_actor_set_position (actor, 150, 150);
clutter_actor_add_child (stage, actor);
overlay = clutter_actor_new ();
clutter_actor_set_background_color (overlay, CLUTTER_COLOR_Blue);
clutter_actor_set_opacity (overlay, 128);
g_signal_connect (actor,
"allocation-changed",
G_CALLBACK (allocation_changed_cb),
overlay);
clutter_actor_add_child (stage, overlay);
clutter_actor_animate (actor, CLUTTER_LINEAR, 2000,
"width", 300.0,
"height", 300.0,
"x", 50.0,
"y", 50.0,
NULL);
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="layouts-stacking.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="layouts.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="layouts-box.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">2. Stacking actors on top of each other </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> 4. Arranging actors in a single row or column</td></tr></table></div></body></html>