<chapter xmlns="http://docbook.org/ns/docbook"
         xmlns:xlink="http://www.w3.org/1999/xlink"
         xmlns:xi="http://www.w3.org/2001/XInclude"
         version="5.0"
         xml:id="sec-x11">
 <title>X Window System</title>
 <para>
  The X Window System (X11) provides the basis of NixOS’ graphical user
  interface. It can be enabled as follows:
<programlisting>
<xref linkend="opt-services.xserver.enable"/> = true;
</programlisting>
  The X server will automatically detect and use the appropriate video driver
  from a set of X.org drivers (such as <literal>vesa</literal> and
  <literal>intel</literal>). You can also specify a driver manually, e.g.
<programlisting>
<xref linkend="opt-services.xserver.videoDrivers"/> = [ "r128" ];
</programlisting>
  to enable X.org’s <literal>xf86-video-r128</literal> driver.
 </para>
 <para>
  You also need to enable at least one desktop or window manager. Otherwise,
  you can only log into a plain undecorated <command>xterm</command> window.
  Thus you should pick one or more of the following lines:
<programlisting>
<xref linkend="opt-services.xserver.desktopManager.plasma5.enable"/> = true;
<xref linkend="opt-services.xserver.desktopManager.xfce.enable"/> = true;
<xref linkend="opt-services.xserver.desktopManager.gnome.enable"/> = true;
<xref linkend="opt-services.xserver.desktopManager.mate.enable"/> = true;
<xref linkend="opt-services.xserver.windowManager.xmonad.enable"/> = true;
<xref linkend="opt-services.xserver.windowManager.twm.enable"/> = true;
<xref linkend="opt-services.xserver.windowManager.icewm.enable"/> = true;
<xref linkend="opt-services.xserver.windowManager.i3.enable"/> = true;
<xref linkend="opt-services.xserver.windowManager.herbstluftwm.enable"/> = true;
</programlisting>
 </para>
 <para>
  NixOS’s default <emphasis>display manager</emphasis> (the program that
  provides a graphical login prompt and manages the X server) is LightDM. You
  can select an alternative one by picking one of the following lines:
<programlisting>
<xref linkend="opt-services.xserver.displayManager.sddm.enable"/> = true;
<xref linkend="opt-services.xserver.displayManager.gdm.enable"/> = true;
</programlisting>
 </para>
 <para>
  You can set the keyboard layout (and optionally the layout variant):
<programlisting>
<xref linkend="opt-services.xserver.layout"/> = "de";
<xref linkend="opt-services.xserver.xkbVariant"/> = "neo";
</programlisting>
 </para>
 <para>
  The X server is started automatically at boot time. If you don’t want this
  to happen, you can set:
<programlisting>
<xref linkend="opt-services.xserver.autorun"/> = false;
</programlisting>
  The X server can then be started manually:
<screen>
<prompt># </prompt>systemctl start display-manager.service
</screen>
 </para>
 <para>
  On 64-bit systems, if you want OpenGL for 32-bit programs such as in Wine,
  you should also set the following:
<programlisting>
<xref linkend="opt-hardware.opengl.driSupport32Bit"/> = true;
</programlisting>
 </para>
 <simplesect xml:id="sec-x11-auto-login">
  <title>Auto-login</title>
  <para>
  The x11 login screen can be skipped entirely, automatically logging you into
  your window manager and desktop environment when you boot your computer.
  </para>
  <para>
  This is especially helpful if you have disk encryption enabled. Since you
  already have to provide a password to decrypt your disk, entering a second
  password to login can be redundant.
  </para>
  <para>
  To enable auto-login, you need to define your default window manager and
  desktop environment. If you wanted no desktop environment and i3 as your your
  window manager, you'd define:
<programlisting>
<xref linkend="opt-services.xserver.displayManager.defaultSession"/> = "none+i3";
</programlisting>
  Every display manager in NixOS supports auto-login, here is an example
  using lightdm for a user <literal>alice</literal>:
<programlisting>
<xref linkend="opt-services.xserver.displayManager.lightdm.enable"/> = true;
<xref linkend="opt-services.xserver.displayManager.autoLogin.enable"/> = true;
<xref linkend="opt-services.xserver.displayManager.autoLogin.user"/> = "alice";
</programlisting>
  </para>
 </simplesect>
 <simplesect xml:id="sec-x11--graphics-cards-intel">
  <title>Intel Graphics drivers</title>
  <para>
   There are two choices for Intel Graphics drivers in X.org:
   <literal>modesetting</literal> (included in the <package>xorg-server</package> itself)
   and <literal>intel</literal> (provided by the package <package>xf86-video-intel</package>).
  </para>
  <para>
   The default and recommended is <literal>modesetting</literal>.
   It is a generic driver which uses the kernel
   <link xlink:href="https://en.wikipedia.org/wiki/Mode_setting">mode setting</link>
   (KMS) mechanism. It supports Glamor (2D graphics acceleration via OpenGL)
   and is actively maintained but may perform worse in some cases (like in old chipsets).
  </para>
  <para>
   The second driver, <literal>intel</literal>, is specific to Intel GPUs,
   but not recommended by most distributions: it lacks several modern features
   (for example, it doesn't support Glamor) and the package hasn't been officially
   updated since 2015.
  </para>
  <para>
   The results vary depending on the hardware, so you may have to try both drivers.
   Use the option <xref linkend="opt-services.xserver.videoDrivers"/> to set one.
   The recommended configuration for modern systems is:
<programlisting>
  <xref linkend="opt-services.xserver.videoDrivers"/> = [ "modesetting" ];
  <xref linkend="opt-services.xserver.useGlamor"/> = true;
</programlisting>
   If you experience screen tearing no matter what, this configuration was
   reported to resolve the issue:
<programlisting>
  <xref linkend="opt-services.xserver.videoDrivers"/> = [ "intel" ];
  <xref linkend="opt-services.xserver.deviceSection"/> = ''
    Option "DRI" "2"
    Option "TearFree" "true"
  '';
</programlisting>
   Note that this will likely downgrade the performance compared to
  <literal>modesetting</literal> or <literal>intel</literal> with DRI 3 (default).
  </para>
 </simplesect>
 <simplesect xml:id="sec-x11-graphics-cards-nvidia">
  <title>Proprietary NVIDIA drivers</title>
  <para>
   NVIDIA provides a proprietary driver for its graphics cards that has better
   3D performance than the X.org drivers. It is not enabled by default because
   it’s not free software. You can enable it as follows:
<programlisting>
<xref linkend="opt-services.xserver.videoDrivers"/> = [ "nvidia" ];
</programlisting>
   Or if you have an older card, you may have to use one of the legacy drivers:
<programlisting>
<xref linkend="opt-services.xserver.videoDrivers"/> = [ "nvidiaLegacy390" ];
<xref linkend="opt-services.xserver.videoDrivers"/> = [ "nvidiaLegacy340" ];
<xref linkend="opt-services.xserver.videoDrivers"/> = [ "nvidiaLegacy304" ];
</programlisting>
   You may need to reboot after enabling this driver to prevent a clash with
   other kernel modules.
  </para>
 </simplesect>
 <simplesect xml:id="sec-x11--graphics-cards-amd">
  <title>Proprietary AMD drivers</title>
  <para>
   AMD provides a proprietary driver for its graphics cards that is not
   enabled by default because it’s not Free Software, is often broken
   in nixpkgs and as of this writing doesn't offer more features or
   performance. If you still want to use it anyway, you need to explicitly set:
<programlisting>
<xref linkend="opt-services.xserver.videoDrivers"/> = [ "amdgpu-pro" ];
</programlisting>
   You will need to reboot after enabling this driver to prevent a clash with
   other kernel modules.
  </para>
 </simplesect>
 <simplesect xml:id="sec-x11-touchpads">
  <title>Touchpads</title>
  <para>
   Support for Synaptics touchpads (found in many laptops such as the Dell
   Latitude series) can be enabled as follows:
<programlisting>
<xref linkend="opt-services.xserver.libinput.enable"/> = true;
</programlisting>
   The driver has many options (see <xref linkend="ch-options"/>). For
   instance, the following disables tap-to-click behavior:
<programlisting>
<xref linkend="opt-services.xserver.libinput.touchpad.tapping"/> = false;
</programlisting>
   Note: the use of <literal>services.xserver.synaptics</literal> is deprecated
   since NixOS 17.09.
  </para>
 </simplesect>
 <simplesect xml:id="sec-x11-gtk-and-qt-themes">
  <title>GTK/Qt themes</title>
  <para>
   GTK themes can be installed either to user profile or system-wide (via
   <literal>environment.systemPackages</literal>). To make Qt 5 applications
   look similar to GTK2 ones, you can install <literal>qt5.qtbase.gtk</literal>
   package into your system environment. It should work for all Qt 5 library
   versions.
  </para>
 </simplesect>
 <simplesect xml:id="custom-xkb-layouts">
  <title>Custom XKB layouts</title>
  <para>
   It is possible to install custom
   <link xlink:href="https://en.wikipedia.org/wiki/X_keyboard_extension">
    XKB
   </link>
   keyboard layouts using the option
   <option><link linkend="opt-services.xserver.extraLayouts">
     services.xserver.extraLayouts</link></option>.
  </para>
  <para>
   As a first example, we are going to create a layout based on the basic US
   layout, with an additional layer to type some greek symbols by pressing the
   right-alt key.
  </para>
  <para>
   Create a file called <literal>us-greek</literal> with the following
   content (under a directory called <literal>symbols</literal>; it's
   an XKB peculiarity that will help with testing):
  </para>
<programlisting>
xkb_symbols &quot;us-greek&quot;
{
  include &quot;us(basic)&quot;            // includes the base US keys
  include &quot;level3(ralt_switch)&quot;  // configures right alt as a third level switch

  key &lt;LatA&gt; { [ a, A, Greek_alpha ] };
  key &lt;LatB&gt; { [ b, B, Greek_beta  ] };
  key &lt;LatG&gt; { [ g, G, Greek_gamma ] };
  key &lt;LatD&gt; { [ d, D, Greek_delta ] };
  key &lt;LatZ&gt; { [ z, Z, Greek_zeta  ] };
};
</programlisting>
  <para>
   A minimal layout specification must include the following:
  </para>
<programlisting>
<xref linkend="opt-services.xserver.extraLayouts"/>.us-greek = {
  description = "US layout with alt-gr greek";
  languages   = [ "eng" ];
  symbolsFile = /yourpath/symbols/us-greek;
}
</programlisting>
  <note>
  <para>
   The name should match the one given to the
   <literal>xkb_symbols</literal> block.
  </para>
  </note>
  <para>
   Applying this customization requires rebuilding several packages,
   and a broken XKB file can lead to the X session crashing at login.
   Therefore, you're strongly advised to <emphasis role="strong">test
   your layout before applying it</emphasis>:
<screen>
<prompt>$ </prompt>nix-shell -p xorg.xkbcomp
<prompt>$ </prompt>setxkbmap -I/yourpath us-greek -print | xkbcomp -I/yourpath - $DISPLAY
</screen>
  </para>
  <para>
   You can inspect the predefined XKB files for examples:
<screen>
<prompt>$ </prompt>echo "$(nix-build --no-out-link '&lt;nixpkgs&gt;' -A xorg.xkeyboardconfig)/etc/X11/xkb/"
</screen>
  </para>
  <para>
   Once the configuration is applied, and you did a logout/login
   cycle, the layout should be ready to use. You can try it by e.g.
   running <literal>setxkbmap us-greek</literal> and then type
   <literal>&lt;alt&gt;+a</literal> (it may not get applied in your
   terminal straight away). To change the default, the usual
   <option>
    <link linkend="opt-services.xserver.layout">
     services.xserver.layout
    </link>
   </option>
   option can still be used.
  </para>
  <para>
   A layout can have several other components besides
   <literal>xkb_symbols</literal>, for example we will define new
   keycodes for some multimedia key and bind these to some symbol.
  </para>
  <para>
   Use the <emphasis>xev</emphasis> utility from
   <literal>pkgs.xorg.xev</literal> to find the codes of the keys of
   interest, then create a <literal>media-key</literal> file to hold
   the keycodes definitions
  </para>
<programlisting>
xkb_keycodes &quot;media&quot;
{
 &lt;volUp&gt;   = 123;
 &lt;volDown&gt; = 456;
}
</programlisting>
  <para>
    Now use the newly define keycodes in <literal>media-sym</literal>:
  </para>
<programlisting>
xkb_symbols &quot;media&quot;
{
 key.type = &quot;ONE_LEVEL&quot;;
 key &lt;volUp&gt;   { [ XF86AudioLowerVolume ] };
 key &lt;volDown&gt; { [ XF86AudioRaiseVolume ] };
}
</programlisting>
  <para>
    As before, to install the layout do
  </para>
<programlisting>
<xref linkend="opt-services.xserver.extraLayouts"/>.media = {
  description  = "Multimedia keys remapping";
  languages    = [ "eng" ];
  symbolsFile  = /path/to/media-key;
  keycodesFile = /path/to/media-sym;
};
</programlisting>
  <note>
  <para>
   The function <literal>pkgs.writeText &lt;filename&gt; &lt;content&gt;
   </literal> can be useful if you prefer to keep the layout definitions
   inside the NixOS configuration.
  </para>
  </note>
  <para>
    Unfortunately, the Xorg server does not (currently) support setting a
    keymap directly but relies instead on XKB rules to select the matching
    components (keycodes, types, ...) of a layout. This means that components
    other than symbols won't be loaded by default. As a workaround, you
    can set the keymap using <literal>setxkbmap</literal> at the start of the
    session with:
  </para>
<programlisting>
<xref linkend="opt-services.xserver.displayManager.sessionCommands"/> = "setxkbmap -keycodes media";
</programlisting>
  <para>
    If you are manually starting the X server, you should set the argument
    <literal>-xkbdir /etc/X11/xkb</literal>, otherwise X won't find your layout files.
    For example with <command>xinit</command> run
    <screen><prompt>$ </prompt>xinit -- -xkbdir /etc/X11/xkb</screen>
  </para>
  <para>
   To learn how to write layouts take a look at the XKB
  <link xlink:href="https://www.x.org/releases/current/doc/xorg-docs/input/XKB-Enhancing.html#Defining_New_Layouts">
   documentation
  </link>. More example layouts can also be found
  <link xlink:href="https://wiki.archlinux.org/index.php/X_KeyBoard_extension#Basic_examples">
   here
  </link>.
  </para>
</simplesect>
</chapter>
