path: root/specs/CH2.xml

<chapter><title>Using Widgets</title>
<sect1 id='Using_Widgets'>
<title>Using Widgets</title>
<para>
Widgets serve as the primary tools for building a user interface or
application environment.  The Athena widget set consists of primitive
widgets that contain no children (for example, a command button) and
composite widgets which may contain one or more widget children (for
example, a Box widget).
</para>
<para>
The remaining chapters explain the widgets that are provided
by the Athena widget set.
These user-interface components serve as an interface for
application programmers who do not want to implement their own widgets.
In addition, they serve as a starting point
for those widget programmers who, using the Intrinsics mechanisms,
want to implement alternative application programming interfaces.
</para>
<para>
This chapter is a brief introduction to widget programming.  The
examples provided use the Athena widgets, though most of the concepts
will apply to all widget sets.  Although there are several programming
interfaces to the X Toolkit, only one is described here.  A full
description of the programming interface is provided in the document
<olink targetdoc='intrinsics' targetptr='intrinsics'
><citetitle>X Toolkit Intrinsics - C Language Interface</citetitle></olink>.
</para>
<sect2 id="Setting_the_Locale">
<title>Setting the Locale</title>
<para>
<!-- .LP -->
<!-- .XS -->
<!-- 	Setting the Locale -->
<!-- .XE -->
If it is desirable that the application take advantage of
internationalization (i18n), you must establish locale with
<function>XtSetLanguageProc</function>
prior to calling
<xref linkend='XtOpenApplication' xrefstyle='select: title'/>,
<function>XtOpenDisplay</function>,
<function>XtDisplayInitialize</function>,
or
<function>XtAppInitialize</function>.
For full details, please refer to the document
<olink targetdoc='intrinsics' targetptr='Establishing_the_Locale'
><citetitle>X Toolkit Intrinsics - C Language Interface</citetitle>,
section 2.2</olink>. However, the following simplest-case
call is sufficient in many or most applications.
</para>
<para>
<!-- .LP -->
<indexterm><primary>internationalization</primary></indexterm>
<indexterm significance="preferred"><primary>XtSetLanguageProc</primary></indexterm>
<indexterm><primary>locale</primary></indexterm>
<literallayout class="monospaced">
<!-- .TA .5i 2i -->
<!-- .ta .5i 2i -->
	XtSetLanguageProc(NULL, NULL, NULL);
</literallayout>
</para>
<para>
<!-- .LP -->
Most notably, this will affect the Standard C locale, determine which
resource files will be loaded, and what fonts will be required of FontSet
specifications.  In many cases, the addition of this line is the only source change
required to internationalize Xaw programs, and will not disturb the function
of programs in the default "C" locale.
</para>
</sect2>
<sect2 id="Initializing_the_Toolkit">
<title>Initializing the Toolkit</title>
<para>
<!-- .LP -->
<!-- .XS -->
<!-- 	Initializing the Toolkit -->
<!-- .XE -->
You must call a toolkit initialization function before invoking any
other toolkit routines (besides locale setting, above).
<xref linkend='XtOpenApplication' xrefstyle='select: title'/>,
opens the X server connection, parses the command line,
and creates an initial widget that will serve as the root of
a tree of widgets created by this application.
<indexterm significance="preferred"><primary>initialization</primary></indexterm>
<indexterm significance="preferred"><primary>toolkit initialization</primary></indexterm>
<indexterm significance="preferred"><primary>XtOpenApplication</primary></indexterm>
<indexterm significance="preferred"><primary>fallback resources</primary></indexterm>
<funcsynopsis id='XtOpenApplication'>
<funcprototype>
<funcdef>Widget <function>XtOpenApplication</function></funcdef>
  <paramdef>XtAppContext *<parameter>app_context_return</parameter></paramdef>
  <paramdef>String <parameter>application_class</parameter></paramdef>
  <paramdef>XrmOptionDescList <parameter>options</parameter></paramdef>
  <paramdef>Cardinal <parameter>num_options</parameter></paramdef>
  <paramdef>int *<parameter>argc_in_out</parameter></paramdef>
  <paramdef>String *<parameter>argv_in_out</parameter></paramdef>
  <paramdef>String *<parameter>fallback_resources</parameter></paramdef>
  <paramdef>WidgetClass <parameter>widget_class</parameter></paramdef>
  <paramdef>ArgList <parameter>args</parameter></paramdef>
  <paramdef>Cardinal <parameter>num_args</parameter></paramdef>
</funcprototype>
</funcsynopsis>
<!-- .FN -->
<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>app_context_return</emphasis>
    </term>
    <listitem>
      <para>
Returns the application context of this application, if non-NULL.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>application_class</emphasis>
    </term>
    <listitem>
      <para>
Specifies the class name of this application,
which is usually the generic name for all instances of this application.
A useful convention is to form the class name by capitalizing the
first letter of the application name. For example, the application named
<quote>xman</quote> has a class name of <quote>Xman</quote>.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>options</emphasis>
    </term>
    <listitem>
      <para>
Specifies how to parse the command line for any application-specific
resources.
The options argument is passed as a parameter to
<olink targetdoc='libX11' targetptr='XrmParseCommand'><function>XrmParseCommand</function></olink>.
For further information,
see <olink targetdoc='libX11' targetptr='XrmParseCommand'
><citetitle>Xlib - C Language Interface</citetitle></olink>.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>num_options</emphasis>
    </term>
    <listitem>
      <para>
Specifies the number of entries in the options list.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>argc_in_out</emphasis>
    </term>
    <listitem>
      <para>
Specifies a pointer to the number of command line parameters.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>argv_in_out</emphasis>
    </term>
    <listitem>
      <para>
Specifies the command line parameters.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>fallback_resources</emphasis>
    </term>
    <listitem>
      <para>
Specifies resource values to be used if the site-wide application class
defaults file cannot be opened, or NULL.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>widget_class</emphasis>
    </term>
    <listitem>
      <para>
Specifies the class of the widget to be created.  Must be shellWidgetClass
or a subclass.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>args</emphasis>
    </term>
    <listitem>
      <para>
Specifies the argument list to use when creating the Application shell.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>num_args</emphasis>
    </term>
    <listitem>
      <para>
Specifies the number of arguments in <emphasis remap='I'>args</emphasis>.
    </para>
  </listitem>
  </varlistentry>
</variablelist>
</para>
<para>
<!-- .LP -->
This function will remove the command line arguments that the toolkit
reads from <emphasis remap='I'>argc_in_out</emphasis>, and <emphasis remap='I'>argv_in_out</emphasis>.  It will then
attempt to open the display.  If the display cannot be opened, an error
message is issued and XtAppInitialize terminates the application.  Once
the display is opened, all resources are read from the locations
specified by the Intrinsics.  This function returns an ApplicationShell
widget to be used as the root of the application's widget tree.
</para>
</sect2>
<sect2 id="Creating_a_Widget">
<title>Creating a Widget</title>
<para>
<!-- .LP -->
<!-- .XS -->
<!-- 	Creating a Widget -->
<!-- .XE -->
<indexterm significance="preferred"><primary>widget creation</primary></indexterm>
<indexterm significance="preferred"><primary>creating widgets</primary></indexterm>
<indexterm><primary>XtRealizeWidget</primary></indexterm>
Creating a widget is a three-step process.  First, the widget instance
is allocated, and various instance-specific attributes are set by
using <function>XtCreateWidget</function>.  Second, the widget's parent is informed
of the new child by using <function>XtManageChild</function>.  Finally, X windows are
created for the parent and all its children by using <xref linkend='XtRealizeWidget' xrefstyle='select: title'/>
and specifying the top-most widget. The first two steps can be
combined by using <xref linkend='XtCreateManagedWidget' xrefstyle='select: title'/>.  In addition,
<xref linkend='XtRealizeWidget' xrefstyle='select: title'/> is automatically called when the child becomes
managed if the parent is already realized.
</para>
<para>
<!-- .LP -->
To allocate, initialize, and manage a widget, use
<function>XtCreateManagedWidget</function>.
<indexterm significance="preferred"><primary>XtCreateManagedWidget</primary></indexterm>
<funcsynopsis id='XtCreateManagedWidget'>
<funcprototype>
  <funcdef>Widget<function> XtCreateManagedWidget</function></funcdef>
  <paramdef>String<parameter> name</parameter></paramdef>
  <paramdef>WidgetClass<parameter> widget_class</parameter></paramdef>
  <paramdef>Widget<parameter> parent</parameter></paramdef>
  <paramdef>ArgList<parameter> args</parameter></paramdef>
  <paramdef>Cardinal<parameter> num_args</parameter></paramdef>
</funcprototype>
</funcsynopsis>
<!-- .FN -->
<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>name</emphasis>
    </term>
    <listitem>
      <para>
Specifies the instance name for the created widget that is used for retrieving
widget resources.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>widget_class</emphasis>
    </term>
    <listitem>
      <para>
Specifies the widget class pointer for the created widget.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>parent</emphasis>
    </term>
    <listitem>
      <para>
Specifies the parent widget ID.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>args</emphasis>
    </term>
    <listitem>
      <para>
Specifies the argument list.  The argument list is a variable-length
list composed of name and value pairs that contain information
pertaining to the specific widget instance being created.  For further
information, see Section 2.7.2. <!-- xref> -->
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>num_args</emphasis>
    </term>
    <listitem>
      <para>
Specifies the number of arguments in the argument list.
If the num_args is zero, the argument list is never referenced.
    </para>
  </listitem>
  </varlistentry>
</variablelist>
</para>
<para>
<!-- .LP -->
When a widget instance is successfully created, the widget identifier
is returned to the application.  If an error is encountered, the
<function>XtError</function>
routine is invoked to inform the user of the error.
<indexterm><primary>XtError</primary></indexterm>
</para>
<para>
<!-- .LP -->
For further information, see
<olink targetdoc='intrinsics' targetptr='Creating_Widgets'
><citetitle>X Toolkit Intrinsics - C Language Interface</citetitle></olink>.
</para>
</sect2>
<sect2 id="Common_Resources">
<title>Common Resources</title>
<!-- .XS -->
<!-- 	Common Resources -->
<!-- .XE -->
<indexterm><primary>resource</primary></indexterm>
<para>
<!-- .LP -->
Although a widget can have unique arguments that it understands, all
widgets have common arguments that provide some regularity of operation.
The common arguments allow arbitrary widgets to be managed by
higher-level components without regard for the individual widget type.
Widgets will ignore any argument that they do not understand.
</para>
<para>
<!-- .LP -->
The following resources are retrieved from the argument list
or from the resource database by all of the Athena widgets:
<informaltable>
  <tgroup cols='4' align='center'>
  <colspec colname='c1'/>
  <colspec colname='c2'/>
  <colspec colname='c3'/>
  <colspec colname='c4'/>
  <thead>
    <row>
      <entry>Name</entry>
      <entry>Class</entry>
      <entry>Type</entry>
      <entry>Default Value</entry>
    </row>
  </thead>
  <tbody>
    <row>
      <entry>accelerators</entry>
      <entry>Accelerators</entry>
      <entry>AcceleratorTable</entry>
      <entry>NULL</entry>
    </row>
    <row>
      <entry>ancestorSensitive</entry>
      <entry>AncestorSensitive</entry>
      <entry>Boolean</entry>
      <entry>True</entry>
    </row>
    <row>
      <entry>background</entry>
      <entry>Background</entry>
      <entry>Pixel</entry>
      <entry>XtDefaultBackground</entry>
    </row>
    <row>
      <entry>backgroundPixmap</entry>
      <entry>Pixmap</entry>
      <entry>Pixmap</entry>
      <entry>XtUnspecifiedPixmap</entry>
    </row>
    <row>
      <entry>borderColor</entry>
      <entry>BorderColor</entry>
      <entry>Pixel</entry>
      <entry>XtDefaultForeground</entry>
    </row>
    <row>
      <entry>borderPixmap</entry>
      <entry>Pixmap</entry>
      <entry>Pixmap</entry>
      <entry>XtUnspecifiedPixmap</entry>
    </row>
    <row>
      <entry>borderWidth</entry>
      <entry>BorderWidth</entry>
      <entry>Dimension</entry>
      <entry>1</entry>
    </row>
    <row>
      <entry>colormap</entry>
      <entry>Colormap</entry>
      <entry>Colormap</entry>
      <entry>Parent's Colormap</entry>
    </row>
    <row>
      <entry>depth</entry>
      <entry>Depth</entry>
      <entry>int</entry>
      <entry>Parent's Depth</entry>
    </row>
    <row>
      <entry>destroyCallback</entry>
      <entry>Callback</entry>
      <entry>XtCallbackList</entry>
      <entry>NULL</entry>
    </row>
    <row>
      <entry>height</entry>
      <entry>Height</entry>
      <entry>Dimension</entry>
      <entry><emphasis remap='I'>widget dependent</emphasis></entry>
    </row>
    <row>
      <entry>mappedWhenManaged</entry>
      <entry>MappedWhenManaged</entry>
      <entry>Boolean</entry>
      <entry>True</entry>
    </row>
    <row>
      <entry>screen</entry>
      <entry>Screen</entry>
      <entry>Screen</entry>
      <entry>Parent's Screen</entry>
    </row>
    <row>
      <entry>sensitive</entry>
      <entry>Sensitive</entry>
      <entry>Boolean</entry>
      <entry>True</entry>
    </row>
    <row>
      <entry>translations</entry>
      <entry>Translations</entry>
      <entry>TranslationTable</entry>
      <entry><emphasis remap='I'>widget dependent</emphasis></entry>
    </row>
    <row>
      <entry>width</entry>
      <entry>Width</entry>
      <entry>Dimension</entry>
      <entry><emphasis remap='I'>widget dependent</emphasis></entry>
    </row>
    <row>
      <entry>x</entry>
      <entry>Position</entry>
      <entry>Position</entry>
      <entry>0</entry>
    </row>
    <row>
      <entry>y</entry>
      <entry>Position</entry>
      <entry>Position</entry>
      <entry>0</entry>
    </row>
  </tbody>
  </tgroup>
</informaltable>
<indexterm><primary>XtDefaultForeground</primary></indexterm>
<indexterm><primary>XtDefaultBackground</primary></indexterm>
</para>
<para>
<!-- .LP -->
The following additional resources are retrieved from the argument list
or from the resource database by many of the Athena widgets:
<informaltable>
  <tgroup cols='4' align='center'>
  <colspec colname='c1'/>
  <colspec colname='c2'/>
  <colspec colname='c3'/>
  <colspec colname='c4'/>
  <thead>
    <row>
      <entry>Name</entry>
      <entry>Class</entry>
      <entry>Type</entry>
      <entry>Default Value</entry>
    </row>
  </thead>
  <tbody>
    <row>
      <entry>callback</entry>
      <entry>Callback</entry>
      <entry>XtCallbackList</entry>
      <entry>NULL</entry>
    </row>
    <row>
      <entry>cursor</entry>
      <entry>Cursor</entry>
      <entry>Cursor</entry>
      <entry><emphasis remap='I'>widget dependent</emphasis></entry>
    </row>
    <row>
      <entry>foreground</entry>
      <entry>Foreground</entry>
      <entry>Pixel</entry>
      <entry>XtDefaultForeground</entry>
    </row>
    <row>
      <entry>insensitiveBorder</entry>
      <entry>Insensitive</entry>
      <entry>Pixmap</entry>
      <entry>GreyPixmap</entry>
    </row>
  </tbody>
  </tgroup>
</informaltable>
<indexterm><primary>XtDefaultForeground</primary></indexterm>
</para>
</sect2>
<sect2 id="Resource_Conversions">
<title>Resource Conversions</title>
<!-- .XS -->
<!-- 	Resource Conversions -->
<!-- .XE -->
<indexterm significance="preferred"><primary>conversions</primary></indexterm>
<indexterm significance="preferred"><primary>string conversions</primary></indexterm>
<indexterm significance="preferred"><primary>type conversions</primary></indexterm>
<para>
<!-- .LP -->
Most resources in the Athena widget set have a converter registered that
will translate the string in a resource file to the correct internal
representation.  While some are obvious (string to integer, for example),
others need specific mention of the allowable values.  Three general
converters are described here:
</para>
<itemizedlist>
  <listitem>
    <para>
Cursor
    </para>
  </listitem>
  <listitem>
    <para>
Pixel
    </para>
  </listitem>
  <listitem>
    <para>
Bitmap
    </para>
  </listitem>
</itemizedlist>
<para>
<!-- .LP -->
Many widgets have defined special converters that apply only to that
widget.  When these occur, the documentation section for that widget
will describe the converter.
</para>
<sect3 id="Cursor_Conversion">
<title>Cursor Conversion</title>
<indexterm significance="preferred"><primary>conversions</primary><secondary>ColorCursor</secondary></indexterm>
<indexterm significance="preferred"><primary>conversions</primary><secondary>Cursor</secondary></indexterm>
<indexterm><primary>cursor</primary></indexterm>
<para>
<!-- .LP -->
The value for the <function>cursorName</function> resource is specified in the resource
database as a string, and is of the following forms:
</para>
<itemizedlist>
  <listitem>
    <para>
A standard X cursor name from <function>&lt; X11/cursorfont.h &gt;</function>.
The names in <function>cursorfont.h</function> each describe a specific cursor.  The
resource names for these cursors are exactly like the names in this file
except the <function>XC_</function> is not used.  The cursor definition <function>XC_gumby</function>
has a resource name of <function>gumby</function>.
    </para>
  </listitem>
  <listitem>
    <para>
Glyphs, as in <emphasis remap='I'>FONT font-name glyph-index [[ font-name ] glyph-index ]</emphasis>.
The first font and glyph specify the cursor source pixmap.
The second font and glyph specify the cursor mask pixmap.
The mask font defaults to the source font,
and the mask glyph index defaults to the source glyph index.
    </para>
  </listitem>
  <listitem>
    <para>
A relative or absolute file name.
If a relative or absolute file name is specified, that file is used to
create the source pixmap.  Then the string "Mask" is appended to
locate the cursor mask pixmap.  If the "Mask" file does not exist, the
suffix "msk" is tried.  If "msk" fails, no cursor mask will be used.
If the filename does not start with '/' or './' the the bitmap
file path is used (see section 2.4.3). <!-- xref -->
    </para>
  </listitem>
</itemizedlist>
</sect3>
<sect3 id="Pixel_Conversion">
<title>Pixel Conversion</title>
<para>
<!-- .LP -->
<indexterm significance="preferred"><primary>conversions</primary><secondary>Pixel</secondary></indexterm>
<indexterm><primary>pixel</primary></indexterm>
<indexterm><primary>rgb.txt</primary></indexterm>
<indexterm><primary>XtDefaultForeground</primary></indexterm>
<indexterm><primary>XtDefaultBackground</primary></indexterm>
The string-to-pixel converter takes any name that is acceptable to
XParseColor (see <olink targetdoc='libX11' targetptr='Color_Strings'
><citetitle>Xlib - C Language Interface</citetitle></olink>).  In addition this routine understands
the special toolkit symbols `XtDefaultForeground' and
`XtDefaultBackground', described in
<olink targetdoc='intrinsics' targetptr='Predefined_Resource_Converters'
><citetitle>X Toolkit Intrinsics - C Language Interface</citetitle></olink>.  In short the acceptable
pixel names are:
</para>
<itemizedlist>
  <listitem>
    <para>
Any color name for the rgb.txt file (typically in the directory
/usr/lib/X11 on POSIX systems).
    </para>
  </listitem>
  <listitem>
    <para>
A numeric specification of the form #&lt;red&gt;&lt;green&gt;&lt;blue&gt; where these
numeric values are hexadecimal digits (both upper and lower case).
    </para>
  </listitem>
  <listitem>
    <para>
The special strings `XtDefaultForeground' and `XtDefaultBackground'
    </para>
  </listitem>
</itemizedlist>
</sect3>
<sect3 id="Bitmap_Conversion">
<title>Bitmap Conversion</title>
<indexterm significance="preferred"><primary>bitmap conversions</primary></indexterm>
<indexterm significance="preferred"><primary>conversions</primary><secondary>Bitmap</secondary></indexterm>
<indexterm significance="preferred"><primary>bitmapFilePath</primary></indexterm>
<indexterm significance="preferred"><primary>BitmapFilePath</primary></indexterm>
<indexterm><primary>/usr/include/X11/bitmaps</primary></indexterm>
<para>
<!-- .LP -->
The string-to-bitmap converter attempts to locate a file containing
bitmap data whose name is specified by the input string.  If the file
name is relative (i.e. does not begin with / or ./), the directories to
be searched are specified in the <function>bitmapFilePath</function> resource--class
<function>BitmapFilePath</function>.  This resource specifies a colon (:) separated
list of directories that will be searched for the named bitmap or
cursor glyph (see section 2.4.1).  The <function>bitmapFilePath</function> resource is
global to the application, and may <function>not</function> be specified differently
for each widget that wishes to convert a cursor to bitmap.  In addition
to the directories specified in the <function>bitmapFilePath</function> resource a
default directory is searched.  When using POSIX the default
directory is
<function>/usr/include/X11/bitmaps</function>.
</para>
</sect3>
</sect2>
<sect2 id="Realizing_a_Widget">
<title>Realizing a Widget</title>
<para>
<!-- .LP -->
<!-- .XS -->
<!-- 	Realizing a Widget -->
<!-- .XE -->
<indexterm significance="preferred"><primary>realizing widgets</primary></indexterm>
The
<xref linkend='XtRealizeWidget' xrefstyle='select: title'/>
function performs two tasks:
</para>
<itemizedlist>
  <listitem>
    <para>
Calculates the geometry constraints of all managed descendants
of this widget.  The actual calculation is put off until realize time
for performance reasons.
    </para>
  </listitem>
  <listitem>
    <para>
Creates an X window for the widget and, if it is a composite widget,
realizes each of its managed children.
<indexterm significance="preferred"><primary>XtRealizeWidget</primary></indexterm>
<funcsynopsis id='XtRealizeWidget'>
<funcprototype>
  <funcdef>void<function> XtRealizeWidget</function></funcdef>
  <paramdef>Widget<parameter> w</parameter></paramdef>
</funcprototype>
</funcsynopsis>
<!-- .FN -->
    </para>
  </listitem>
  <listitem>
    <para>
Specifies the widget.
    </para>
  </listitem>
</itemizedlist>
<para>
<!-- .LP -->
For further information about this function,
see the <olink targetdoc='intrinsics' targetptr='XtRealizeWidget'
><citetitle>X Toolkit Intrinsics - C Language Interface</citetitle></olink>.
</para>
</sect2>
<sect2 id="Processing_Events">
<title>Processing Events</title>
<para>
<!-- .LP -->
<!-- .XS -->
<!-- 	Processing Events -->
<!-- .XE -->
<indexterm><primary>events</primary></indexterm>
<indexterm><primary>XtAppInitialize</primary></indexterm>
Now that the application has created, managed and realized its
widgets, it is ready to process the events that will be delivered by the
X Server to this client.  A function call that will process the
events is <xref linkend='XtAppMainLoop' xrefstyle='select: title'/>.
<indexterm significance="preferred"><primary>XtAppMainLoop</primary></indexterm>
<funcsynopsis id='XtAppMainLoop'>
<funcprototype>
  <funcdef>void<function> XtAppMainLoop</function></funcdef>
  <paramdef>XtAppContext<parameter> app_context</parameter></paramdef>
</funcprototype>
</funcsynopsis>
<!-- .FN -->
<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>app_context</emphasis>
    </term>
    <listitem>
      <para>
Specifies the application context of this application.  The value is
normally returned by <xref linkend='XtOpenApplication' xrefstyle='select: title'/>.
    </para>
  </listitem>
  </varlistentry>
</variablelist>
</para>
<para>
<!-- .LP -->
This function never returns: it is an infinite loop that processes the
X events.  User input can be handled through callback procedures and
application defined action routines.  More details are provided in
<olink targetdoc='intrinsics' targetptr='Event_Management'
><citetitle>X Toolkit Intrinsics - C Language Interface</citetitle></olink>.
</para>
</sect2>
<sect2 id="Standard_Widget_Manipulation_Functions">
<title>Standard Widget Manipulation Functions</title>
<!-- .XS -->
<!-- 	Standard Widget Manipulation Functions -->
<!-- .XE -->
<para>
<!-- .LP -->
After a widget has been created, a client can interact with that
widget by calling one of the standard widget manipulation routines
provided by the Intrinsics, or a widget class-specific manipulation routine.
</para>
<para>
<!-- .LP -->
The Intrinsics provide generic routines to give the application programmer
access to a set of standard widget functions.  The common widget
routines let an application or composite widget perform the following
operations on widgets without requiring explicit knowledge of the widget
type.
</para>
<itemizedlist>
  <listitem>
    <para>
Control the mapping of widget windows
    </para>
  </listitem>
  <listitem>
    <para>
Destroy a widget instance
    </para>
  </listitem>
  <listitem>
    <para>
Obtain an argument value
    </para>
  </listitem>
  <listitem>
    <para>
Set an argument value
    </para>
  </listitem>
</itemizedlist>
<sect3 id="Mapping_Widgets">
<title>Mapping Widgets</title>
<para>
<!-- .LP -->
By default,
widget windows are mapped (made viewable) automatically by
<xref linkend='XtRealizeWidget' xrefstyle='select: title'/>.  This behavior can be disabled by using
<xref linkend='XtSetMappedWhenManaged' xrefstyle='select: title'/>, making the client responsible for calling
<xref linkend='XtMapWidget' xrefstyle='select: title'/> to make the widget viewable.
<indexterm significance="preferred"><primary>XtSetMappedWhenManaged</primary></indexterm>
<indexterm><primary>XtMapWidget</primary></indexterm>
<indexterm><primary>XtRealizeWidget</primary></indexterm>
<funcsynopsis id='XtSetMappedWhenManaged'>
<funcprototype>
  <funcdef>void<function> XtSetMappedWhenManaged</function></funcdef>
  <paramdef>Widget<parameter> w</parameter></paramdef>
  <paramdef>Boolean<parameter> map_when_managed</parameter></paramdef>
</funcprototype>
</funcsynopsis>
<!-- .FN -->
<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>w</emphasis>
    </term>
    <listitem>
      <para>
Specifies the widget.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>map_when_managed</emphasis>
    </term>
    <listitem>
      <para>
Specifies the new value.
If map_when_managed is <function>True</function>, the widget is mapped automatically
when it is realized.  If map_when_managed is <function>False</function>, the client
must call
<xref linkend='XtMapWidget' xrefstyle='select: title'/>
or make a second call to
<xref linkend='XtSetMappedWhenManaged' xrefstyle='select: title'/>
to cause the child window to be mapped.
    </para>
  </listitem>
  </varlistentry>
</variablelist>
</para>
<para>
<!-- .LP -->
<!-- .sp -->
The definition for
<xref linkend='XtMapWidget' xrefstyle='select: title'/>
is:
<indexterm significance="preferred"><primary>XtMapWidget</primary></indexterm>
<funcsynopsis id='XtMapWidget'>
<funcprototype>
  <funcdef>void<function> XtMapWidget</function></funcdef>
  <paramdef>Widget<parameter> w</parameter></paramdef>
</funcprototype>
</funcsynopsis>
<!-- .FN -->
<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>w</emphasis>
    </term>
    <listitem>
      <para>
Specifies the widget.
    </para>
  </listitem>
  </varlistentry>
</variablelist>
</para>
<para>
<!-- .LP -->
When you are creating several children in sequence for a previously
realized common parent it is generally more efficient to construct a
list of children as they are created (using <function>XtCreateWidget</function>) and
then use <xref linkend='XtManageChildren' xrefstyle='select: title'/> to request that their parent managed
them all at once.  By managing a list of children at one time, the
parent can avoid wasteful duplication of geometry processing and the
associated <quote>screen flash</quote>.
<indexterm significance="preferred"><primary>XtManageChildren</primary></indexterm>
<indexterm><primary>XtCreateWidget</primary></indexterm>
<funcsynopsis id='XtManageChildren'>
<funcprototype>
  <funcdef>void<function> XtManageChildren</function></funcdef>
  <paramdef>WidgetList<parameter> children</parameter></paramdef>
  <paramdef>Cardinal<parameter> num_children</parameter></paramdef>
</funcprototype>
</funcsynopsis>
<!-- .FN -->
<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>children</emphasis>
    </term>
    <listitem>
      <para>
Specifies a list of children to add.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>num_children</emphasis>
    </term>
    <listitem>
      <para>
Specifies the number of children to add.
    </para>
  </listitem>
  </varlistentry>
</variablelist>
</para>
<para>
<!-- .LP -->
If the parent is already visible on the screen, it is especially
important to batch updates so that the minimum amount of visible window
reconfiguration is performed.
</para>
<para>
<!-- .LP -->
For further information about these functions,
see the <olink targetdoc='intrinsics' targetptr='intrinsics'
><citetitle>X Toolkit Intrinsics - C Language Interface</citetitle></olink>.
</para>
</sect3>
<sect3 id="Destroying_Widgets">
<title>Destroying Widgets</title>
<para>
<!-- .LP -->
To destroy a widget instance of any type, use
<xref linkend='XtDestroyWidget' xrefstyle='select: title'/>
<indexterm significance="preferred"><primary>XtDestroyWidget</primary></indexterm>
<funcsynopsis id='XtDestroyWidget'>
<funcprototype>
  <funcdef>void<function> XtDestroyWidget</function></funcdef>
  <paramdef>Widget<parameter> w</parameter></paramdef>
</funcprototype>
</funcsynopsis>
<!-- .FN -->
<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>w</emphasis>
    </term>
    <listitem>
      <para>
Specifies the widget.
    </para>
  </listitem>
  </varlistentry>
</variablelist>
</para>
<para>
<!-- .LP -->
<xref linkend='XtDestroyWidget' xrefstyle='select: title'/>
destroys the widget and recursively destroys any children that it may have,
including the windows created by its children.
After calling
<function>XtDestroyWidget</function>,
no further references should be made to the widget or any children
that the destroyed widget may have had.
</para>
</sect3>
<sect3 id="Retrieving_Widget_Resource_Values">
<title>Retrieving Widget Resource Values</title>
<para>
<!-- .LP -->
To retrieve the current value of a resource attribute associated
with a widget instance, use
<function>XtGetValues</function>.
<indexterm significance="preferred"><primary>XtGetValues</primary></indexterm>
<funcsynopsis id='XtGetValues'>
<funcprototype>
  <funcdef>void<function> XtGetValues</function></funcdef>
  <paramdef>Widget<parameter> w</parameter></paramdef>
  <paramdef>ArgList<parameter> args</parameter></paramdef>
  <paramdef>Cardinal<parameter> num_args</parameter></paramdef>
</funcprototype>
</funcsynopsis>
<!-- .FN -->
<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>w</emphasis>
    </term>
    <listitem>
      <para>
Specifies the widget.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>args</emphasis>
    </term>
    <listitem>
      <para>
Specifies a variable-length argument list of name and <function>address</function>
pairs that contain the resource name and the address into which the
resource value is stored.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>num_args</emphasis>
    </term>
    <listitem>
      <para>
Specifies the number of arguments in the argument list.
    </para>
  </listitem>
  </varlistentry>
</variablelist>
</para>
<para>
<!-- .LP -->
The arguments and values passed in the argument list are dependent on
the widget. Note that the caller is responsible for providing space
into which the returned resource value is copied; the <function>ArgList</function>
contains a pointer to this storage (e.g. x and y must be
allocated as Position).  For further information, see the
<olink targetdoc='intrinsics' targetptr='Reading_and_Writing_Widget_State'
><citetitle>X Toolkit Intrinsics - C Language Interface</citetitle></olink>.
</para>
</sect3>
<sect3 id="Modifying_Widget_Resource_Values">
<title>Modifying Widget Resource Values</title>
<para>
<!-- .LP -->
To modify the current value of a resource attribute associated with a
widget instance, use
<function>XtSetValues</function>.
<indexterm significance="preferred"><primary>XtSetValues</primary></indexterm>
<funcsynopsis id='XtSetValues'>
<funcprototype>
  <funcdef>void<function> XtSetValues</function></funcdef>
  <paramdef>Widget<parameter> w</parameter></paramdef>
  <paramdef>ArgList<parameter> args</parameter></paramdef>
  <paramdef>Cardinal<parameter> num_args</parameter></paramdef>
</funcprototype>
</funcsynopsis>
<!-- .FN -->
<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>w</emphasis>
    </term>
    <listitem>
      <para>
Specifies the widget.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>args</emphasis>
    </term>
    <listitem>
      <para>
Specifies an array of name and <function>value</function> pairs that contain the
arguments to be modified and their new values.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>num_args</emphasis>
    </term>
    <listitem>
      <para>
Specifies the number of arguments in the argument list.
    </para>
  </listitem>
  </varlistentry>
</variablelist>
</para>
<para>
<!-- .LP -->
The arguments and values that are passed will depend on the widget
being modified.  Some widgets may not allow certain resources to be
modified after the widget instance has been created or realized.
No notification is given if any part of a <xref linkend='XtSetValues' xrefstyle='select: title'/> request is
ignored.
</para>
<para>
<!-- .LP -->
For further information about these functions, see the
<olink targetdoc='intrinsics' targetptr='Reading_and_Writing_Widget_State'
><citetitle>X Toolkit Intrinsics - C Language Interface</citetitle></olink>.
<indexterm><primary>XtGetValues</primary></indexterm>
<indexterm><primary>XtSetValues</primary></indexterm>
<!-- .NT -->
The argument list entry for
<xref linkend='XtGetValues' xrefstyle='select: title'/>
specifies the address to which the caller wants the value copied.  The
argument list entry for
<function>XtSetValues</function>,
however, contains the new value itself, if the size of value is less than
sizeof(XtArgVal) (architecture dependent, but at least sizeof(long));
otherwise, it is a pointer to the value.  String resources are always
passed as pointers, regardless of the length of the string.
<!-- .NE -->
</para>
</sect3>
</sect2>
<sect2 id="Using_the_Client_Callback_Interface">
<title>Using the Client Callback Interface</title>
<para>
<!-- .LP -->
<!-- .XS -->
<!-- 	Using the Client Callback Interface -->
<!-- .XE -->
<indexterm><primary>callbacks</primary></indexterm>
Widgets can communicate changes in their state to their clients
by means of a callback facility.
The format for a client's callback handler is:
<indexterm significance="preferred"><primary>CallbackProc</primary></indexterm>
<funcsynopsis id='CallbackProc'>
<funcprototype>
  <funcdef>void<function> CallbackProc</function></funcdef>
  <paramdef>Widget<parameter> w</parameter></paramdef>
  <paramdef>XtPointer<parameter> client_data</parameter></paramdef>
  <paramdef>XtPointer<parameter> call_data</parameter></paramdef>
</funcprototype>
</funcsynopsis>
<!-- .FN -->
<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>w</emphasis>
    </term>
    <listitem>
      <para>
Specifies widget for which the callback is registered.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>client_data</emphasis>
    </term>
    <listitem>
      <para>
Specifies arbitrary client-supplied data that the widget should pass
back to the client when the widget executes the client's callback
procedure.  This is a way for the client registering the callback to
also register client-specific data: a pointer to additional information
about the widget, a reason for invoking the callback, and so on. If no
additional information is necessary, NULL may be passed as this argument.
This field is also frequently known as the <emphasis remap='I'>closure</emphasis>.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>call_data</emphasis>
    </term>
    <listitem>
      <para>
Specifies any callback-specific data the widget wants to pass to the client.
For example, when Scrollbar executes its <function>jumpProc</function> callback list,
it passes the current position of the thumb in <emphasis remap='I'>call_data</emphasis>.
    </para>
  </listitem>
  </varlistentry>
</variablelist>
</para>
<para>
<!-- .LP -->
Callbacks can be registered either by creating an argument containing
the callback list described below or by using the special convenience
routines <xref linkend='XtAddCallback' xrefstyle='select: title'/> and <function>XtAddCallbacks</function>.  When the widget
is created, a pointer to a list of callback procedure and data pairs can
be passed in the argument list to
<function>XtCreateWidget</function>.
The list is of type
<function>XtCallbackList :</function>
<indexterm><primary>XtCallbackProc</primary></indexterm>
<indexterm><primary>XtAddCallbacks</primary></indexterm>
<indexterm><primary>XtAddCallback</primary></indexterm>
<indexterm significance="preferred"><primary>XtCallbackList</primary></indexterm>
<indexterm significance="preferred"><primary>XtCallbackRec</primary></indexterm>
</para>
<para>
<!-- .LP -->
<literallayout class="monospaced">
<!-- .TA .5i 3i -->
<!-- .ta .5i 3i -->
typedef struct {
	XtCallbackProc callback;
	XtPointer closure;
} XtCallbackRec, *XtCallbackList;
</literallayout>
</para>
<para>
<!-- .LP -->
The callback list must be allocated and initialized before calling
<function>XtCreateWidget</function>.
<indexterm><primary>XtCreateWidget</primary></indexterm>
The end of the list is identified by an entry containing NULL in
callback and closure.  Once the widget is created, the client can change
or de-allocate this list; the widget itself makes no further reference
to it.  The closure field contains the client_data passed to the
callback when the callback list is executed.
</para>
<para>
<!-- .LP -->
The second method for registering callbacks is to use
<xref linkend='XtAddCallback' xrefstyle='select: title'/>
after the widget has been created.
<indexterm significance="preferred"><primary>XtAddCallback</primary></indexterm>
<funcsynopsis id='XtAddCallback'>
<funcprototype>
  <funcdef>void<function> XtAddCallback</function></funcdef>
  <paramdef>Widget<parameter> w</parameter></paramdef>
  <paramdef>String<parameter> callback_name</parameter></paramdef>
  <paramdef>XtCallbackProc<parameter> callback</parameter></paramdef>
  <paramdef>XtPointer<parameter> client_data</parameter></paramdef>
</funcprototype>
</funcsynopsis>
<!-- .FN -->
<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>w</emphasis>
    </term>
    <listitem>
      <para>
Specifies the widget to add the callback to.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>callback_name</emphasis>
    </term>
    <listitem>
      <para>
Specifies the callback list within the widget to append to.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>callback</emphasis>
    </term>
    <listitem>
      <para>
Specifies the callback procedure to add.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>client_data</emphasis>
    </term>
    <listitem>
      <para>
Specifies the data to be passed to the callback when it is invoked.
    </para>
  </listitem>
  </varlistentry>
</variablelist>
</para>
<para>
<!-- .LP -->
<xref linkend='XtAddCallback' xrefstyle='select: title'/>
adds the specified callback to the list for the named widget.
</para>
<para>
<!-- .LP -->
All widgets provide a callback list named
<function>destroyCallback</function>
<indexterm significance="preferred"><primary>destroyCallback</primary></indexterm>
where clients can register procedures that are to be executed when the
widget is destroyed.  The destroy callbacks are executed when the widget
or an ancestor is destroyed.  The <emphasis remap='I'>call_data</emphasis> argument is unused for
destroy callbacks.
</para>
</sect2>
<sect2 id="Programming_Considerations">
<title>Programming Considerations</title>
<para>
<!-- .LP -->
<!-- .XS -->
<!-- 	Programming Considerations -->
<!-- .XE -->
This section provides some guidelines on how to set up an application
program that uses the X Toolkit.
</para>
<sect3 id="Writing_Applications">
<title>Writing Applications</title>
<para>
<!-- .LP -->
<indexterm><primary>writing applications</primary></indexterm>
<indexterm><primary>StringDefs.h</primary></indexterm>
<indexterm><primary>Intrinsic.h</primary></indexterm>
When writing an application that uses the X Toolkit,
you should make sure that your application performs the following:
</para>
<orderedlist>
  <listitem>
    <para>
Include
<function>&lt; X11/Intrinsic.h &gt;</function>
in your application programs.
This header file automatically includes
<function>&lt; X11/Xlib.h &gt;</function>,
so all Xlib functions also are defined.
It may also be necessary to include <function>&lt; X11/StringDefs.h &gt;</function> when setting
up argument lists, as many of the XtN<emphasis remap='I'>something</emphasis> definitions are
only defined in this file.
    </para>
  </listitem>
  <listitem>
    <para>
Include the widget-specific header files for each widget type
that you need to use.
For example,
<function>&lt; X11/Xaw/Label.h &gt;</function>
and
<function>&lt; X11/Xaw/Command.h &gt;</function>.
    </para>
  </listitem>
  <listitem>
    <para>
Call the
<xref linkend='XtOpenApplication' xrefstyle='select: title'/>
<indexterm><primary>XtOpenApplication</primary></indexterm>
function before invoking any other toolkit or Xlib functions.
For further information,
see Section 2.1 and the
<olink targetdoc='intrinsics' targetptr='Widget_Instantiation'
><citetitle>X Toolkit Intrinsics - C Language Interface</citetitle></olink>.
    </para>
  </listitem>
  <listitem>
    <para>
To pass attributes to the widget creation routines that will override
any site or user customizations, set up argument lists.  In this
document, a list of valid argument names is provided in the discussion
of each widget.  The names each have a global symbol defined that begins
with <function>XtN</function> to help catch spelling errors.  For example,
<function>XtNlabel</function> is defined for the <function>label</function> resource of many widgets.
<indexterm significance="preferred"><primary>XtN</primary></indexterm>
    </para>
    <para>
For further information, see Section 2.9.2.2.  <!-- xref -->
    </para>
  </listitem>
  <listitem>
    <para>
When the argument list is set up, create the widget with the
<xref linkend='XtCreateManagedWidget' xrefstyle='select: title'/> function.  For further information, see
Section 2.2 and the
<olink targetdoc='intrinsics' targetptr='XtCreateManagedWidget'
><citetitle>X Toolkit Intrinsics - C Language Interface</citetitle></olink>.
<indexterm><primary>XtCreateManagedWidget</primary></indexterm>
    </para>
  </listitem>
  <listitem>
    <para>
If the widget has any callback routines, set by the
<function>XtNcallback</function>
argument or the
<xref linkend='XtAddCallback' xrefstyle='select: title'/>
function, declare these routines within the application.
<indexterm><primary>XtAddCallback</primary></indexterm>
    </para>
  </listitem>
  <listitem>
    <para>
After creating the initial widget hierarchy, windows must be created
for each widget by calling
<xref linkend='XtRealizeWidget' xrefstyle='select: title'/>
on the top level widget.
<indexterm><primary>XtRealizeWidget</primary></indexterm>
    </para>
  </listitem>
  <listitem>
    <para>
Most applications now sit in a loop processing events using
<function>XtAppMainLoop</function>,
for example:
<indexterm><primary>XtAppMainLoop</primary></indexterm>
<literallayout class="monospaced">
XtCreateManagedWidget(<emphasis remap='I'>name</emphasis>, <emphasis remap='I'>class</emphasis>, <emphasis remap='I'>parent</emphasis>, <emphasis remap='I'>args</emphasis>, <emphasis remap='I'>num_args</emphasis>);
XtRealizeWidget(<emphasis remap='I'>shell</emphasis>);
XtAppMainLoop(<emphasis remap='I'>app_context</emphasis>);
</literallayout>
    </para>
  </listitem>
  <listitem>
    <para>
For information about this function, see the
<olink targetdoc='intrinsics' targetptr='Event_Management'
><citetitle>X Toolkit Intrinsics - C Language Interface</citetitle></olink>.
    </para>
  </listitem>
  <listitem>
    <para>
Link your application with
<function>libXaw</function>
(the Athena widgets),
<function>libXmu</function>
(miscellaneous utilities),
<function>libXt</function>
(the X Toolkit Intrinsics),
<function>libSM</function>
(Session Management),
<function>libICE</function>
(Inter-Client Exchange),
<function>libXext</function>
(the extension library needed for the shape extension code which allows
rounded Command buttons), and
<function>libX11</function>
(the core X library).
The following provides a sample command line:
<indexterm><primary>libXaw</primary></indexterm>
<indexterm><primary>libXmu</primary></indexterm>
<indexterm><primary>libXt</primary></indexterm>
<indexterm><primary>libSM</primary></indexterm>
<indexterm><primary>libICE</primary></indexterm>
<indexterm><primary>libXext</primary></indexterm>
<indexterm><primary>libX11</primary></indexterm>
<indexterm><primary>linking applications</primary></indexterm>
<indexterm><primary>compiling applications</primary></indexterm>
    </para>
  </listitem>
  <listitem>
    <para>
<literallayout class="monospaced">
cc -o <emphasis remap='I'>application</emphasis> <emphasis remap='I'>application</emphasis>.c -lXaw -lXmu -lXt -lSM -lICE -lXext -lX11
</literallayout>
    </para>
  </listitem>
</orderedlist>
</sect3>
<sect3 id="Changing_Resource_Values">
<title>Changing Resource Values</title>
<indexterm><primary>resource</primary></indexterm>
<para>
<!-- .LP -->
The Intrinsics support two methods of changing the default resource
values; the resource manager, and an argument list passed into
XtCreateWidget.  While resources values will get updated no matter
which method you use, the two methods provide slightly different
functionality.
<variablelist>
  <varlistentry>
    <term>Resource Manager</term>
    <listitem>
      <para>
This method picks up resource definitions described in
<olink targetdoc='libX11' targetptr='Resource_Manager_Functions'
><citetitle>Xlib - C Language Interface</citetitle></olink> from
many different locations at run time.  The locations most important to
the application programmer are the <emphasis remap='I'>fallback resources</emphasis> and the
<emphasis remap='I'>app-defaults</emphasis> file, (see
<olink targetdoc='intrinsics' targetptr='Loading_the_Resource_Database'
><citetitle>X Toolkit Intrinsics - C Language Interface</citetitle></olink>
for the complete list).
Since these resource are loaded at run time, they can be overridden by
the user, allowing an application to be customized to fit the
particular needs of each individual user.  These values can also be
modified without the need to rebuild the application, allowing rapid
prototyping of user interfaces.  Application programmers should use
resources in preference to hard-coded values whenever possible.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>Argument Lists</term>
    <listitem>
      <para>
The values passed into the widget at creation time via an argument list
cannot be modified by the user, and allow no opportunity for
customization.  It is used to set resources that cannot be specified as
strings (e.g. callback lists) or resources that should not be
overridden (e.g. window depth) by the user.
    </para>
  </listitem>
  </varlistentry>
</variablelist>
</para>
<sect4 id="Specifying_Resources">
<title>Specifying Resources</title>
<para>
<!-- .LP -->
It is important for all X Toolkit application programmers to
understand how to use the X Resource Manager to specify resources for
widgets in an X application.  This section will describe the most common
methods used to specify these resources, and how to use the X Resource
manager.
<indexterm><primary>xrdb</primary></indexterm>
<variablelist>
  <varlistentry>
    <term>
      <function>Xrdb</function>
    </term>
    <listitem>
      <para>
The <function>xrdb</function> utility may be used to load a file containing
resources into the X server.   Once the resources are loaded, the
resources will affect any new applications started on the display that
they were loaded onto.
<indexterm><primary>application defaults</primary></indexterm>
<indexterm><primary>app-defaults</primary></indexterm>
<indexterm><primary>/usr/lib/X11/app-defaults</primary></indexterm>
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>Application Defaults</term>
    <listitem>
      <para>
The application defaults (app-defaults) file (normally in
/usr/lib/X11/app-defaults/<emphasis remap='I'>classname</emphasis>) for an application is loaded
whenever the application is started.
    </para>
  </listitem>
  </varlistentry>
</variablelist>
</para>
<para>
<!-- .LP -->
The resource specification has two colon-separated parts, a name, and
a value.  The <emphasis remap='I'>value</emphasis> is a string whose format is dependent on the
resource specified by <emphasis remap='I'>name</emphasis>.  <emphasis remap='I'>Name</emphasis> is constructed by
appending a resource name to a full widget name.
</para>
<para>
<!-- .LP -->
The full widget name is a list of the name of every ancestor of the
desired widget separated by periods (.).  Each widget also has a class
associated with it.  A class is a type of widget (e.g. Label or
Scrollbar or Box).  Notice that class names, by convention, begin with
capital letters and instance names begin with lower case letters.  The
class of any widget may be used in place of its name in a resource
specification.  Here are a few examples:
<variablelist>
  <varlistentry>
    <term>
      xman.form.button1
    </term>
    <listitem>
      <para>
This is a fully specified resource name, and will affect only widgets
called button1 that are children of widgets called form that are
children of
applications named xman.  (Note that while typically two widgets that
are siblings will have different names, it is not prohibited.)

      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      Xman.Form.Command
    </term>
    <listitem>
      <para>
This will match any Command widget that is a child of a Form widget
that is itself a child of an application of class <emphasis remap='I'>Xman</emphasis>.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      Xman.Form.button1
    </term>
    <listitem>
      <para>
This is a mixed resource name with both widget names and classes specified.
    </para>
  </listitem>
  </varlistentry>
</variablelist>
</para>
<para>
<!-- .LP -->
This syntax allows an application programmer to specify any widget
in the widget tree.  To match more than one widget (for example a user
may want to make all Command buttons blue), use an asterisk (*)
instead of a period.  When an asterisk is used, any number of widgets
(including zero) may exist between the two widget names. For example:
<variablelist>
  <varlistentry>
    <term>
      Xman*Command
    </term>
    <listitem>
      <para>
This matches all Command widgets in the Xman application.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      Foo*button1
    </term>
    <listitem>
      <para>
This matches any widget in the Foo application that is named <emphasis remap='I'>button1</emphasis>.
    </para>
  </listitem>
  </varlistentry>
</variablelist>
</para>
<para>
<!-- .LP -->
The root of all application widget trees is the widget returned by
<xref linkend='XtOpenApplication' xrefstyle='select: title'/>.  Even though this is actually an
ApplicationShell widget, the toolkit replaces its widget class with the
class name of the application.  The name of this widget is either
the name used to invoke the application (<function>argv[0]</function>) or the name of
the application specified using the standard <emphasis remap='I'>-name</emphasis> command line
option supported by the Intrinsics.
</para>
<para>
<!-- .LP -->
The last step in constructing the resource name is to append the name of
the resource with either a period or asterisk to the full or partial
widget name already constructed.
<variablelist>
  <varlistentry>
    <term>
      *foreground:Blue
    </term>
    <listitem>
      <para>
Specifies that all widgets in all applications will have a foreground
color of blue.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      Xman*borderWidth:10
    </term>
    <listitem>
      <para>
Specifies that all widgets in an application whose class is Xman will
have a border width of 10 (pixels).
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      xman.form.button1.label:Testing
    </term>
    <listitem>
      <para>
Specifies that a particular widget in the xman application will have a
label named <emphasis remap='I'>Testing</emphasis>.
    </para>
  </listitem>
  </varlistentry>
</variablelist>
</para>
<para>
<!-- .LP -->
An exclamation point (!) in the first column of a line indicates
that the rest of the line should be treated as a comment.
</para>
<para>
<!-- .LP -->
<function>Final Words</function>
</para>
<para>
<!-- .LP -->
The Resource manager is a powerful tool that can be used very
effectively to customize X Toolkit applications at run time by either the
application programmer or the user.  Some final points to note:
</para>
<itemizedlist>
  <listitem>
    <para>
An application programmer may add new resources to their
application.  These resources are associated with the global
application, and not any particular widget.  The X Toolkit function used for
adding the application resources is <function>XtGetApplicationResources</function>.
<indexterm><primary>XtGetApplicationResources</primary></indexterm>
    </para>
  </listitem>
  <listitem>
    <para>
Be careful when creating resource files.  Since widgets will
ignore resources that they do not understand, any spelling
errors will cause a resource to have no effect.
    </para>
  </listitem>
  <listitem>
    <para>
Only one resource line will match any given resource.  There is a set
of precedence rules, which take the following general stance.
<!-- .ta 10n -->
    </para>
  </listitem>
  <listitem>
    <itemizedlist>
      <listitem>
        <para>
More specific overrides less specific, thus period always overrides asterisk.
        </para>
      </listitem>
      <listitem>
        <para>
Names on the left are more specific and override names on the right.
        </para>
      </listitem>
      <listitem>
        <para>
When resource specifications are exactly the same, user defaults
will override program defaults.
        </para>
      </listitem>
    </itemizedlist>
  </listitem>
</itemizedlist>
<para>
<!-- .LP -->
For a complete explanation of the rules of precedence, and
other specific topics see
<olink targetdoc='intrinsics' targetptr='Loading_the_Resource_Database'
><citetitle>X Toolkit Intrinsics - C Language Interface</citetitle></olink> and <olink targetdoc='libX11' targetptr='Resource_Manager_Functions'
><citetitle>Xlib - C Language Interface</citetitle></olink>.
</para>
</sect4>
<sect4 id="Creating_Argument_Lists">
<title>Creating Argument Lists</title>
<indexterm significance="preferred"><primary>argument lists</primary></indexterm>
<para>
<!-- .LP -->
To set up an argument list for the inline specification of widget attributes,
you may use any of the four approaches discussed in this section.
Each resource name has a global symbol associated with it.  This
global symbol has the form XtN<emphasis remap='I'>resource name</emphasis>.  For example, the
symbol for <quote>foreground</quote> is <function>XtNforeground</function>. For further information,
see the <olink targetdoc='intrinsics' targetptr='intrinsics'
><citetitle>X Toolkit Intrinsics - C Language Interface</citetitle></olink>.
</para>
<para>
<!-- .LP -->
Argument are specified by using the following structure:
<indexterm significance="preferred"><primary>ArgList</primary></indexterm>
<indexterm significance="preferred"><primary>Arg</primary></indexterm>
</para>
<para>
<!-- .LP -->
<literallayout class="monospaced">
<!-- .TA .5i 1.5i -->
<!-- .ta .5i 1.5i -->
typedef struct {
	String name;
	XtArgVal value;
} Arg, *ArgList;
</literallayout>
</para>
<para>
<!-- .LP -->
The first approach is to statically initialize the argument list.
For example:
</para>
<para>
<!-- .LP -->
<literallayout class="monospaced">
<!-- .TA .5i -->
<!-- .ta .5i -->
static Arg arglist[] = {
	{XtNwidth, (XtArgVal) 400},
	{XtNheight, (XtArgVal) 300},
};
</literallayout>
</para>
<para>
<!-- .LP -->
This approach is convenient for lists that do not need to be computed
at runtime and makes adding or deleting new elements easy.
The
<indexterm><primary>XtNumber</primary></indexterm>
<function>XtNumber</function>
macro is used to compute the number of elements in the argument list,
preventing simple programming errors:
</para>
<para>
<!-- .LP -->
<literallayout class="monospaced">
XtCreateWidget(<emphasis remap='I'>name</emphasis>, <emphasis remap='I'>class</emphasis>, <emphasis remap='I'>parent</emphasis>, <emphasis remap='I'>arglist</emphasis>, XtNumber(<emphasis remap='I'>arglist</emphasis>));
</literallayout>
<indexterm significance="preferred"><primary>XtSetArg</primary></indexterm>
</para>
<para>
<!-- .LP -->
The second approach is to use the
<function>XtSetArg</function>
macro.
For example:
</para>
<para>
<!-- .LP -->
<literallayout class="monospaced">
<!-- .TA .5i -->
<!-- .ta .5i -->
Arg arglist[10];
XtSetArg(arglist[1], XtNwidth, 400);
XtSetArg(arglist[2], XtNheight, 300);
</literallayout>
</para>
<para>
<!-- .LP -->
To make it easier to insert and delete entries,
you also can use a variable index:
</para>
<para>
<!-- .LP -->
<literallayout class="monospaced">
<!-- .TA .5i -->
<!-- .ta .5i -->
Arg arglist[10];
Cardinal i=0;
XtSetArg(arglist[i], XtNwidth,  400);       i++;
XtSetArg(arglist[i], XtNheight, 300);       i++;
</literallayout>
</para>
<para>
<!-- .LP -->
The i variable can then be used as the argument list count in the widget
create function.
In this example,
<indexterm><primary>XtNumber</primary></indexterm>
<function>XtNumber</function>
would return 10, not 2, and therefore is not useful.
<!-- .NT -->
You should not use auto-increment or auto-decrement
within the first argument to
<function>XtSetArg</function>.
As it is currently implemented,
<function>XtSetArg</function>
is a macro that dereferences the first argument twice.
<!-- .NE -->
</para>
<para>
<!-- .LP -->
The third approach is to individually set the elements of the
argument list array:
</para>
<para>
<!-- .LP -->
<literallayout class="monospaced">
<!-- .TA .5i -->
<!-- .ta .5i -->
Arg arglist[10];
arglist[0].name  = XtNwidth;
arglist[0].value = (XtArgVal) 400;
arglist[1].name  = XtNheight;
arglist[1].value = (XtArgVal) 300;
</literallayout>
</para>
<para>
<!-- .LP -->
Note that in this example, as in the previous example,
<indexterm><primary>XtNumber</primary></indexterm>
<function>XtNumber</function>
would return 10, not 2, and therefore would not be useful.
</para>
<para>
<!-- .LP -->
The fourth approach is to use a mixture of the first and third approaches:
you can statically define the argument list but modify some entries at runtime.
For example:
</para>
<para>
<!-- .LP -->
<literallayout class="monospaced">
<!-- .TA .5i -->
<!-- .ta .5i -->
static Arg arglist[] = {
	{XtNwidth, (XtArgVal) 400},
	{XtNheight, (XtArgVal) NULL},
};
arglist[1].value = (XtArgVal) 300;
</literallayout>
</para>
<para>
<!-- .LP -->
In this example,
<indexterm><primary>XtNumber</primary></indexterm>
<function>XtNumber</function>
can be used, as in the first approach, for easier code maintenance.
</para>
</sect4>
</sect3>
</sect2>
<sect2 id="Example_Programs">
<title>Example Programs</title>
<!-- .XS -->
<!-- 	Example Programs -->
<!-- .XE -->
<indexterm><primary>examples</primary></indexterm>
<para>
<!-- .LP -->
The best way to understand how to use any programming library is by
trying some simple examples.  A collection of example programs that
introduces each of the widgets in that Athena widget set, as well as many
important toolkit programming concepts, is available in the X11R5 contrib
release as distributed by the X Consortium.  It can be found in the
directory <filename>contrib/examples/Xaw</filename> in the archive
at <ulink url="http://www.x.org/releases/X11R5/contrib-1.tar.Z" />
See the <filename>README</filename> file from that directory for a guide
to the examples.
</para>
</sect2>
</sect1>
</chapter>