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<refentry id="gtk-x11">
<refmeta>
<refentrytitle>Using GTK+ on the X Window System</refentrytitle>
<manvolnum>3</manvolnum>
<refmiscinfo>GTK Library</refmiscinfo>
</refmeta>

<refnamediv>
<refname>Using GTK+ on the X Window System</refname>
<refpurpose>
X11-specific aspects of using GTK+
</refpurpose>
</refnamediv>

<refsect1>
<title>GTK+ for the X Window System</title>

<para>
On UNIX, the X backend is the default build for GTK+.
So you don't need to do anything special when compiling it,
and everything should "just work."
</para>

<para>
To mix low-level Xlib routines into a GTK program,
see <link linkend="gdk-X-Window-System-Interaction">GDK X Window
System interaction</link> in the GDK manual.
</para>

<para>
GTK+ includes an cross-process embedding facility in the form of
the #GtkSocket and #GtkPlug widgets. These are X11-specific, and
you have to include the <filename>gtk/gtkx.h</filename> header
to use them.
</para>

<refsect2 id="x11-cmdline">
<title>X11-specific commandline options</title>

<para>
The X backend understands some additional command line arguments.
</para>

<formalpara>
<title><systemitem>--display <replaceable>display</replaceable></systemitem></title>

<para>
The name of the X display to open instead of the one specified
in the <envar>DISPLAY</envar> environment variable.
</para>
</formalpara>

</refsect2>

<refsect2 id="x11-envar">
<title>X11-specific environment variables</title>

<para>
The X11 GDK backend can be influenced with some additional environment variables.
</para>

<formalpara>
  <title><envar>GDK_SYNCHRONIZE</envar></title>

  <para>
    If set, GDK makes all X requests synchronously. This is a useful
    option for debugging, but it will slow down the performance considerably.
  </para>
</formalpara>

<formalpara>
  <title><envar>GDK_CORE_DEVICE_EVENTS</envar></title>

  <para>
    If set, GDK makes does not use the XInput extension, and only reacts
    to core X input events.
  </para>
</formalpara>

<formalpara>
  <title><envar>GDK_SCALE</envar></title>

  <para>
    Must be set to an integer, typically 2. If set, GDK will scale all
    windows by the specified factor. Scaled output is meant to be used on
    high-dpi displays. Normally, GDK will pick up a suitable scale factor
    for each monitor from the display system. This environment variable
    allows to override that.
  </para>
</formalpara>

<formalpara>
  <title><envar>GDK_DPI_SCALE</envar></title>

  <para>
    This can be useful when using scale-aware GTK+ applications together
    with scale-unaware applications on a high-dpi display. In that case,
    the font resolution can be doubled to make scale-unaware applications
    readable, and <envar>GDK_DPI_SCALE=0.5</envar> can be set to compensate
    for that in GTK+ applications which are already scaled by setting
    <envar>GDK_SCALE=2</envar>.
  </para>
</formalpara>

</refsect2>

</refsect1>

<refsect1 id="gtk-X11-arch">
<title>Understanding the X11 architecture</title>

<para>
People coming from a Windows or MacOS background often find certain
aspects of the X Window System surprising. This section introduces
some basic X concepts at a high level. For more details, the book most
people use is called the <citetitle pubwork="book">Xlib Programming
Manual</citetitle> by Adrian Nye; this book is volume one in the
O'Reilly X Window System series.
</para>
<para>
Standards are another important resource if you're poking in low-level
X11 details, in particular the ICCCM and the Extended Window Manager
Hints specifications. <ulink
url="http://www.freedesktop.org/standards/">freedesktop.org</ulink>
has links to many relevant specifications.
</para>
<para>
The GDK manual covers <link
linkend="gdk-X-Window-System-Interaction">using Xlib in a GTK
program</link>.
</para>

<refsect2>
<title>Server, client, window manager</title>

<para>
Other window systems typically put all their functionality in the
application itself. With X, each application involves three different
programs: the <firstterm>X server</firstterm>, the application (called
a <firstterm>client</firstterm> because it's a client of the X
server), and a special client called the <firstterm>window
manager</firstterm>.
</para>

<para>
The X server is in charge of managing resources, processing drawing
requests, and dispatching events such as keyboard and mouse events to
interested applications. So client applications can ask the X server
to create a window, draw a circle, or move windows around.
</para>

<para>
The window manager is in charge of rendering the frame or borders
around windows; it also has final say on the size of each window,
and window states such as minimized, maximized, and so forth.
On Windows and MacOS the application handles most of this.
On X11, if you wish to modify the window's state, or 
change its frame, you must ask the window manager to do so on your
behalf, using an established  <ulink
url="http://www.freedesktop.org/standards/">convention</ulink>.
</para>

<para>
GTK+ has functions for asking the window manager to do various things;
see for example <link
linkend="gtk-window-iconify">gtk_window_iconify()</link> or <link
linkend="gtk-window-maximize">gtk_window_maximize()</link> or <link
linkend="gtk-window-set-decorated">gtk_window_set_decorated()</link>.
Keep in mind that <link
linkend="gtk-window-move">gtk_window_move()</link> and window sizing
are ultimately controlled by the window manager as well and most
window managers <emphasis>will</emphasis> ignore certain requests from
time to time, in the interests of good user interface.
</para>

<!--
May also want to explain DESKTOP_STARTUP_ID here. 
http://www.freedesktop.org/Standards/startup-notification-spec
-->

</refsect2>

</refsect1>

</refentry>
