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<refentry id="multihead" revision="1 May 2002">
  <refmeta>
    <refentrytitle>Multi-head Support Overview</refentrytitle>
    <manvolnum>3</manvolnum>
    <refmiscinfo>GDK Library</refmiscinfo>
  </refmeta>

  <refnamediv>
    <refname>Multi-head Support Overview</refname>
    <refpurpose>Overview of GdkDisplay and GdkScreen</refpurpose>
  </refnamediv>

  <refsect1>
    <title>Overview</title>
      <para>
	Multihead support is based around two main object types:
	<itemizedlist>
	  <listitem><para>GdkDisplay</para></listitem>
	  <listitem><para>GdkScreen</para></listitem>
	</itemizedlist>
      </para>
      
      <para>
	<link linkend="gdk-GdkDisplay">GdkDisplay</link> objects are the GDK
	representation of the X Display which can be described as <emphasis>a
	workstation consisting of a keyboard a pointing device (such as a
	  mouse) and one or more screens</emphasis>. 
	It is used to open and keep track of various <link
	  linkend="gdk-GdkScreen">GdkScreen</link> objects currently 
	instanciated by the application. It is also used to grab and release
	the keyboard and the mouse pointer.
      </para>
      <para>
	<link linkend="gdk-GdkScreen">GdkScreen</link> objects are the GDK
	representation of a physical screen. It is used throughout GDK and GTK+
	to specify which screen the top level windows are to be displayed on. 
	It is also used to query the screen specification and default settings such as 
	the default colormap (<link linkend="gdk-screen-get-default-colormap">gdk_screen_get_default_colormap</link>()),
	the screen width (<link linkend="gdk-screen-get-width">gdk_screen_get_width</link>()), etc.
      </para>
      <para> 
	The following code samples demonstrate common usage of the objects described above.
      </para>
      
      <example>
	<title>Testing the number of screen on the current display</title>
	<programlisting><!--
-->gint num_screen = 0;
gchar *displayname = NULL;
GdkScreen **screen_list;
GdkDisplay *display;

gtk_init (&amp;argc, &amp;argv);

display = gdk_display_get_default ();
num_screen = gdk_display_get_n_screens (display);
displayname = gdk_display_get_name (display);
if (num_screen &lt;= 1)
  {
    printf ("This Xserver (%s) manages only one screen. exiting...\n",
            displayname);
    exit (1);
  }
else
  {
    printf ("This Xserver (%s) manages %d screens.\n", displayname,
            num_screen);
  }<!--

-->     </programlisting>
      </example>
      <example>
	<title>Opening a second display</title>
	<programlisting><!--
-->gchar *second_screen_name;
GdkDisplay *second_display;
GdkScreen *second_screen;
GtkWidget *window;

gtk_init (&amp;argc, &amp;argv);

/* screen2_name needs to be initialized before calling 
/* gdk_display_new() */
second_display = gdk_display_new (&amp;argc, &amp;argv, second_screen_name);
if (second_display)
    second_screen = gdk_display_get_default_screen (second_display);
else 
  {
	g_print ("Can't open display :\n\t%s\n\n",
		  second_screen_name);
    exit (1);	
  }
/* now GdkScreen can be assigned to GtkWindows */

window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
gtk_window_set_screen (window, second_screen);<!--
     --></programlisting>
      </example>
    </refsect1>
    <refsect1>
      <title>See Also</title>
      <para>
	<variablelist>
	  <varlistentry>
	    <term><link linkend="GdkDisplay">GdkDisplay</link></term>
	    <listitem><para>the GDK Object used to represent and manipulate display
		related data</para></listitem>
	  </varlistentry>
	  <varlistentry>
	    <term><link linkend="GdkScreen">GdkScreen</link></term>
	    <listitem><para>the GDK Object used to represent and query screen related
		data</para></listitem>
	  </varlistentry>
	</variablelist>
      </para>
    </refsect1>
  </refentry>
  
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