xref: /xsrc/external/mit/libXaw/dist/specs/Scrollbar.xml

<sect1 id="Scrollbar_Widget">
<title>Scrollbar Widget</title>

<literallayout class="monospaced">
Application header file     &lt;X11/Xaw/Scrollbar.h&gt;
Class header file           &lt;X11/Xaw/ScrollbarP.h&gt;
Class                       scrollbarWidgetClass
Class Name                  Scrollbar
Superclass                  Simple
</literallayout>

<para>
A Scrollbar widget is a rectangle, called the <quote>canvas,</quote> on
which another rectangle, the <quote>thumb,</quote> moves in one
dimension, either vertically or horizontally.  A Scrollbar
can be used alone, as a value generator, or it can be used
within a composite widget (for example, a Viewport).  When a
Scrollbar is used to move, or <quote>scroll,</quote> the contents of
another widget, the size and the position of the thumb usually give
feedback as to what portion of the other widget's contents
are visible.
</para>

<para>
Each pointer button invokes a specific action.  Pointer
buttons 1 and 3 do not move the thumb automatically.
Instead, they return the pixel position of the cursor on the
scroll region.  When pointer button 2 is clicked, the thumb
moves to the current pointer position.  When pointer button
2 is held down and the pointer is moved, the thumb follows
the pointer.
</para>

<para>
The pointer cursor in the scroll region changes depending on the current
action.  When no pointer button is pressed, the cursor appears as a
double-headed arrow that points in the direction that scrolling can
occur.  When pointer button 1 or 3 is pressed, the cursor appears as a
single-headed arrow that points in the logical direction that the thumb
will move.  When pointer button 2 is pressed, the cursor
appears as an arrow that points to the top or the left of the thumb.
</para>

<para>
When the user scrolls, the application receives notification
through callback procedures.  For both discrete scrolling actions, the
callback returns the Scrollbar widget, the client_data, and the pixel
position of the pointer when the button was released.  For continuous
scrolling, the callback routine returns the scroll bar widget, the
client data, and the current relative position of the thumb.  When the
thumb is moved using pointer button 2, the callback procedure is invoked
continuously.  When either button 1 or 3 is pressed, the callback
procedure is invoked only when the button is released and the client
callback procedure is responsible for moving the thumb.
</para>

<sect2 id='Scrollbar::Resources'>
<title>Resources</title>

<para>
When creating a Scrollbar widget instance, the following resources are
retrieved from the argument list or from the resource database:
</para>

<informaltable>
  <tgroup cols='5' align='center'>
  <colspec colname='c1'/>
  <colspec colname='c2'/>
  <colspec colname='c3'/>
  <colspec colname='c4'/>
  <colspec colname='c5'/>
  <thead>
    <row>
      <entry>Name</entry>
      <entry>Class</entry>
      <entry>Type</entry>
      <entry>Notes</entry>
      <entry>Default Value</entry>
    </row>
  </thead>
  <tbody>
    <row>
      <entry>accelerators</entry>
      <entry>Accelerators</entry>
      <entry>AcceleratorTable</entry>
      <entry></entry>
      <entry>NULL</entry>
    </row>
    <row>
      <entry>ancestorSensitive</entry>
      <entry>AncestorSensitive</entry>
      <entry>Boolean</entry>
      <entry>D</entry>
      <entry>True</entry>
    </row>
    <row>
      <entry>background</entry>
      <entry>Background</entry>
      <entry>Pixel</entry>
      <entry></entry>
      <entry>XtDefaultBackground</entry>
    </row>
    <row>
      <entry>backgroundPixmap</entry>
      <entry>Pixmap</entry>
      <entry>Pixmap</entry>
      <entry></entry>
      <entry>XtUnspecifiedPixmap</entry>
    </row>
    <row>
      <entry>borderColor</entry>
      <entry>BorderColor</entry>
      <entry>Pixel</entry>
      <entry></entry>
      <entry>XtDefaultForeground</entry>
    </row>
    <row>
      <entry>borderPixmap</entry>
      <entry>Pixmap</entry>
      <entry>Pixmap</entry>
      <entry></entry>
      <entry>XtUnspecifiedPixmap</entry>
    </row>
    <row>
      <entry>borderWidth</entry>
      <entry>BorderWidth</entry>
      <entry>Dimension</entry>
      <entry></entry>
      <entry>1</entry>
    </row>
    <row>
      <entry>colormap</entry>
      <entry>Colormap</entry>
      <entry>Colormap</entry>
      <entry></entry>
      <entry>parent's Colormap</entry>
    </row>
    <row>
      <entry>cursor</entry>
      <entry>Cursor</entry>
      <entry>Cursor</entry>
      <entry></entry>
      <entry>None</entry>
    </row>
    <row>
      <entry>cursorName</entry>
      <entry>Cursor</entry>
      <entry>String</entry>
      <entry></entry>
      <entry>NULL</entry>
    </row>
    <row>
      <entry>depth</entry>
      <entry>Depth</entry>
      <entry>int</entry>
      <entry>C</entry>
      <entry>parent's Depth</entry>
    </row>
    <row>
      <entry>destroyCallback</entry>
      <entry>Callback</entry>
      <entry>XtCallbackList</entry>
      <entry></entry>
      <entry>NULL</entry>
    </row>
    <row>
      <entry>foreground</entry>
      <entry>Foreground</entry>
      <entry>Pixel</entry>
      <entry></entry>
      <entry>XtDefaultForeground</entry>
    </row>
    <row>
      <entry>height</entry>
      <entry>Height</entry>
      <entry>Dimension</entry>
      <entry>A</entry>
      <entry>depends on orientation</entry>
    </row>
    <row>
      <entry>insensitiveBorder</entry>
      <entry>Insensitive</entry>
      <entry>Pixmap</entry>
      <entry></entry>
      <entry>GreyPixmap</entry>
    </row>
    <row>
      <entry>international</entry>
      <entry>International</entry>
      <entry>Boolean</entry>
      <entry>C</entry>
      <entry>False</entry>
    </row>
    <row>
      <entry>jumpProc</entry>
      <entry>Callback</entry>
      <entry>XtCallbackList</entry>
      <entry></entry>
      <entry>NULL</entry>
    </row>
    <row>
      <entry>length</entry>
      <entry>Length</entry>
      <entry>Dimension</entry>
      <entry></entry>
      <entry>1</entry>
    </row>
    <row>
      <entry>mappedWhenManaged</entry>
      <entry>MappedWhenManaged</entry>
      <entry>Boolean</entry>
      <entry></entry>
      <entry>True</entry>
    </row>
    <row>
      <entry>minimumThumb</entry>
      <entry>MinimumThumb</entry>
      <entry>Dimension</entry>
      <entry></entry>
      <entry>7</entry>
    </row>
    <row>
      <entry>orientation</entry>
      <entry>Orientation</entry>
      <entry>Orientation</entry>
      <entry></entry>
      <entry>XtorientVertical (vertical)</entry>
    </row>
    <row>
      <entry>pointerColor</entry>
      <entry>Foreground</entry>
      <entry>Pixel</entry>
      <entry></entry>
      <entry>XtDefaultForeground</entry>
    </row>
    <row>
      <entry>pointerColorBackground</entry>
      <entry>Background</entry>
      <entry>Pixel</entry>
      <entry></entry>
      <entry>XtDefaultBackground</entry>
    </row>
    <row>
      <entry>screen</entry>
      <entry>Screen</entry>
      <entry>Screen</entry>
      <entry>R</entry>
      <entry>parent's Screen</entry>
    </row>
    <row>
      <entry>scrollDCursor</entry>
      <entry>Cursor</entry>
      <entry>Cursor</entry>
      <entry></entry>
      <entry>XC_sb_down_arrow</entry>
    </row>
    <row>
      <entry>scrollHCursor</entry>
      <entry>Cursor</entry>
      <entry>Cursor</entry>
      <entry></entry>
      <entry>XC_sb_h_double_arrow</entry>
    </row>
    <row>
      <entry>scrollLCursor</entry>
      <entry>Cursor</entry>
      <entry>Cursor</entry>
      <entry></entry>
      <entry>XC_sb_left_arrow</entry>
    </row>
    <row>
      <entry>scrollProc</entry>
      <entry>Callback</entry>
      <entry>XtCallbackList</entry>
      <entry></entry>
      <entry>NULL</entry>
    </row>
    <row>
      <entry>scrollRCursor</entry>
      <entry>Cursor</entry>
      <entry>Cursor</entry>
      <entry></entry>
      <entry>XC_sb_right_arrow</entry>
    </row>
    <row>
      <entry>scrollUCursor</entry>
      <entry>Cursor</entry>
      <entry>Cursor</entry>
      <entry></entry>
      <entry>XC_sb_up_arrow</entry>
    </row>
    <row>
      <entry>scrollVCursor</entry>
      <entry>Cursor</entry>
      <entry>Cursor</entry>
      <entry></entry>
      <entry>XC_sb_v_arrow</entry>
    </row>
    <row>
      <entry>sensitive</entry>
      <entry>Sensitive</entry>
      <entry>Boolean</entry>
      <entry></entry>
      <entry>True</entry>
    </row>
    <row>
      <entry>shown</entry>
      <entry>Shown</entry>
      <entry>Float</entry>
      <entry></entry>
      <entry>0.0</entry>
    </row>
    <row>
      <entry>thickness</entry>
      <entry>Thickness</entry>
      <entry>Dimension</entry>
      <entry></entry>
      <entry>14</entry>
    </row>
    <row>
      <entry>thumb</entry>
      <entry>Thumb</entry>
      <entry>Bitmap</entry>
      <entry></entry>
      <entry>GreyPixmap</entry>
    </row>
    <row>
      <entry>thumbProc</entry>
      <entry>Callback</entry>
      <entry>XtCallbackList</entry>
      <entry></entry>
      <entry>NULL</entry>
    </row>
    <row>
      <entry>topOfThumb</entry>
      <entry>TopOfThumb</entry>
      <entry>Float</entry>
      <entry></entry>
      <entry>0.0</entry>
    </row>
    <row>
      <entry>translations</entry>
      <entry>Translations</entry>
      <entry>TranslationTable</entry>
      <entry></entry>
      <entry>See below</entry>
    </row>
    <row>
      <entry>width</entry>
      <entry>Width</entry>
      <entry>Dimension</entry>
      <entry>A</entry>
      <entry>depends on orientation</entry>
    </row>
    <row>
      <entry>x</entry>
      <entry>Position</entry>
      <entry>Position</entry>
      <entry></entry>
      <entry>0</entry>
    </row>
    <row>
      <entry>y</entry>
      <entry>Position</entry>
      <entry>Position</entry>
      <entry></entry>
      <entry>0</entry>
    </row>
  </tbody>
  </tgroup>
</informaltable>

<variablelist>
  <varlistentry>
    <term>
      <function>foreground</function>
    </term>
    <listitem>
      <para>
A pixel value which indexes the widget's colormap to derive the color
used to draw the thumb.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <function>jumpProc</function>
    </term>
    <listitem>
      <para>
All functions on this callback list are called when the
<function>NotifyThumb</function> action is invoked.  See
<xref linkend="Scrollbar_Actions" /> for details.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <function>length</function>
    </term>
    <listitem>
      <para>
The height of a vertical scrollbar or the width of a horizontal scrollbar.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <function>minimumThumb</function>
    </term>
    <listitem>
      <para>
The smallest size, in pixels, to which the thumb can shrink.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <function>orientation</function>
    </term>
    <listitem>
      <para>
The orientation is the direction that the thumb will be allowed to move.
This value can be either <function>XtorientVertical</function> or
<function>XtorientHorizontal</function>.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <function>scrollDCursor</function>
    </term>
    <listitem>
      <para>
This cursor is used when scrolling backward in a vertical scrollbar.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <function>scrollHCursor</function>
    </term>
    <listitem>
      <para>
This cursor is used when a horizontal scrollbar is inactive.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <function>scrollLCursor</function>
    </term>
    <listitem>
      <para>
This cursor is used when scrolling forward in a horizontal scrollbar.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <function>scrollProc</function>
    </term>
    <listitem>
      <para>
All functions on this callback list may be called when the
<function>NotifyScroll</function> action is invoked.  See
<xref linkend="Scrollbar_Actions" /> for details.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <function>scrollRCursor</function>
    </term>
    <listitem>
      <para>
This cursor is used when scrolling backward in a horizontal scrollbar,
or when thumbing a vertical scrollbar.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <function>scrollUCursor</function>
    </term>
    <listitem>
      <para>
This cursor is used when scrolling forward in a vertical scrollbar, or when
thumbing a horizontal scrollbar.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <function>scrollVCursor</function>
    </term>
    <listitem>
      <para>
This cursor is used when a vertical scrollbar is inactive.
<!-- .Se -->
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <function>shown</function>
    </term>
    <listitem>
      <para>
This is the size of the thumb, expressed as a percentage (0.0 - 1.0)
of the length of the scrollbar.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <function>thickness</function>
    </term>
    <listitem>
      <para>
The width of a vertical scrollbar or the height of a horizontal scrollbar.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <function>thumb</function>
    </term>
    <listitem>
      <para>
This pixmap is used to tile (or stipple) the thumb of the scrollbar.  If
no tiling is desired, then set this resource to <function>None</function>.  This
resource will accept either a bitmap or a pixmap that is the same depth
as the window.  The resource converter for this resource constructs
bitmaps from the contents of files.  (See <function>Converting Bitmaps</function> for
details.)
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <function>topOfThumb</function>
    </term>
    <listitem>
      <para>
The location of the top of the thumb, as a percentage (0.0 - 1.0)
of the length of the scrollbar.  This resource was called <function>top</function> in
previous versions of the Athena widget set.  The name collided with the
a Form widget constraint resource, and had to be changed.
    </para>
  </listitem>
  </varlistentry>
</variablelist>

</sect2>

<sect2 id="Scrollbar_Actions">
<title>Scrollbar Actions</title>
<para>
<!-- .LP -->
The actions supported by the Scrollbar widget are:
</para>
<variablelist>
  <varlistentry>
    <term>
      <function>StartScroll</function>(<emphasis remap='I'>value</emphasis>)
    </term>
    <listitem>
      <para>
The possible <emphasis remap='I'>values</emphasis> are Forward, Backward, or Continuous.
This must be the first action to begin a new movement.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <function>NotifyScroll</function>(<emphasis remap='I'>value</emphasis>)
    </term>
    <listitem>
      <para>
The possible <emphasis remap='I'>values</emphasis> are Proportional or FullLength.  If the
argument to StartScroll was Forward or Backward, NotifyScroll executes
the <function>scrollProc</function> callbacks and passes either; the position of the
pointer, if <emphasis remap='I'>value</emphasis> is Proportional, or the full length of the
scroll bar, if <emphasis remap='I'>value</emphasis> is FullLength.  If the argument to
StartScroll was Continuous, NotifyScroll returns without executing any
callbacks.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <function>EndScroll</function>(&#x200A;)
    </term>
    <listitem>
      <para>
This must be the last action after a movement is complete.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <function>MoveThumb</function>(&#x200A;)
    </term>
    <listitem>
      <para>
Repositions the Scrollbar's thumb to the current pointer location.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <function>NotifyThumb</function>(&#x200A;)\
    </term>
    <listitem>
      <para>
Calls the
<!-- .PN jumpProc -->
callbacks and passes the relative position of the
pointer as a percentage of the scroll bar length.
    </para>
  </listitem>
  </varlistentry>
</variablelist>
<para>
The default bindings for Scrollbar are:
<indexterm><primary>Scrollbar widget</primary><secondary>default translation table</secondary></indexterm>
</para>

<literallayout class="monospaced">
     &lt;Btn1Down&gt;:     StartScroll(Forward)
     &lt;Btn2Down&gt;:     StartScroll(Continuous) MoveThumb(&#x2006;) NotifyThumb(&#x2006;)
     &lt;Btn3Down&gt;:     StartScroll(Backward)
     &lt;Btn2Motion&gt;:     MoveThumb(&#x2006;) NotifyThumb(&#x2006;)
     &lt;BtnUp&gt;:     NotifyScroll(Proportional) EndScroll(&#x2006;)
</literallayout>

<para>
Examples of additional bindings a user might wish to specify in a
resource file are:
</para>

<literallayout class="monospaced">
*Scrollbar.Translations: \\
     ~Meta&lt;Key&gt;space:     StartScroll(Forward) NotifyScroll(FullLength) \\n\\
      Meta&lt;Key&gt;space:     StartScroll(Backward) NotifyScroll(FullLength) \\n\\
          EndScroll(&#x2006;)
</literallayout>

</sect2>

<sect2 id="Scrollbar_Callbacks">
<title>Scrollbar Callbacks</title>
<indexterm><primary>Scrollbar widget</primary><secondary>callbacks</secondary></indexterm>
<para>
<!-- .LP -->
There are two callback lists provided by the Scrollbar widget.
The procedural interface for these functions is described here.
</para>

<para>
<!-- .LP -->
The calling interface to the <function>scrollProc</function> callback procedure is:
<indexterm significance="preferred"><primary>ScrollProc</primary></indexterm>
</para>
<funcsynopsis id='ScrollProc'>
<funcprototype>
  <funcdef>void<function> ScrollProc</function></funcdef>
  <paramdef>Widget<parameter> scrollbar</parameter></paramdef>
  <paramdef>XtPointer<parameter> client_data</parameter></paramdef>
  <paramdef>XtPointer<parameter> position</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>scrollbar</emphasis>
    </term>
    <listitem>
      <para>
Specifies the Scrollbar widget.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>client_data</emphasis>
    </term>
    <listitem>
      <para>
Specifies the client data.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>position</emphasis>
    </term>
    <listitem>
      <para>
Specifies a pixel position in integer form.
    </para>
  </listitem>
  </varlistentry>
</variablelist>

<para>
The <function>scrollProc</function> callback is used for incremental scrolling
and is called by the <function>NotifyScroll</function> action.
The position argument is a signed quantity and should be cast to an int
when used. Using the default button bindings, button 1 returns a
positive value, and button 3 returns a negative value. In both cases,
the magnitude of the value is the distance of the pointer in
pixels from the top (or left) of the Scrollbar. The value will never
be greater than the length of the Scrollbar.
</para>

<para>
The calling interface to the <function>jumpProc</function> callback procedure is:
</para>
<indexterm significance="preferred"><primary>jumpProc</primary></indexterm>
<funcsynopsis id='JumpProc'>
<funcprototype>
  <funcdef>void<function> JumpProc</function></funcdef>
  <paramdef>Widget<parameter> scrollbar</parameter></paramdef>
  <paramdef>XtPointer<parameter> client_data</parameter></paramdef>
  <paramdef>XtPointer<parameter> percent_ptr</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<!-- .FN -->
<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>scrollbar</emphasis>
    </term>
    <listitem>
      <para>
Specifies the ID of the scroll bar widget.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>client_data</emphasis>
    </term>
    <listitem>
      <para>
Specifies the client data.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>percent_ptr</emphasis>
    </term>
    <listitem>
      <para>
Specifies the floating point position of the thumb (0.0 &#x2013; 1.0).
    </para>
  </listitem>
  </varlistentry>
</variablelist>

<para>
The <function>jumpProc</function> callback is used to implement smooth scrolling and
is called by the <function>NotifyThumb</function> action.  Percent_ptr must be cast
to a pointer to float before use; i.e.
</para>

<literallayout class="monospaced">
     float percent = *(float*)percent_ptr;
</literallayout>

<para>
With the default button bindings, button 2 moves the thumb interactively,
and the <function>jumpProc</function> is called on each new position of the pointer,
while the pointer button remains down.  The value specified by
<emphasis remap='I'>percent_ptr</emphasis> is the current location of the thumb (from the top or
left of the Scrollbar) expressed as a percentage of the length of the
Scrollbar.
</para>

</sect2>

<sect2 id="Convenience_Routines">
<title>Convenience Routines</title>
<para>
<indexterm><primary>Scrollbar widget</primary><secondary>setting thumb values</secondary></indexterm>
To set the position and length of a Scrollbar thumb, use
<!-- .PN XawScrollbarSetThumb . -->
<indexterm significance="preferred"><primary>XawScrollbarSetThumb</primary></indexterm>
</para>
<funcsynopsis id='XawScrollbarSetThumb'>
<funcprototype>
  <funcdef>void<function> XawScrollbarSetThumb</function></funcdef>
  <paramdef>Widget<parameter> w</parameter></paramdef>
  <paramdef>float<parameter> top</parameter></paramdef>
  <paramdef>float<parameter> shown</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>w</emphasis>
    </term>
    <listitem>
      <para>
Specifies the Scrollbar widget.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>top</emphasis>
    </term>
    <listitem>
      <para>
Specifies the position of the top of the thumb as a fraction of the
length of the Scrollbar.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>shown</emphasis>
    </term>
    <listitem>
      <para>
Specifies the length of the thumb as a fraction of the total length
of the Scrollbar.
    </para>
  </listitem>
  </varlistentry>
</variablelist>

<para>
<function>XawScrollbarThumb</function>
moves the visible thumb to a new position (0.0 &#x2013; 1.0) and length (0.0 &#x2013; 1.0).
Either the top or shown arguments can be specified as -1.0,
in which case the current value is left unchanged.
Values greater than 1.0 are truncated to 1.0.
</para>

<para>
If called from <function>jumpProc</function>, <xref linkend='XawScrollbarSetThumb' xrefstyle='select: title'/> has no effect.
</para>

</sect2>

<sect2 id="Setting_Float_Resources">
<title>Setting Float Resources</title>
<indexterm><primary>float resources</primary><secondary>setting</secondary></indexterm>
<para>
The <function>shown</function> and <function>topOfThumb</function> resources are of type
<emphasis remap='I'>float</emphasis>.  These resources can be difficult to get into an
argument list.  The reason is that C performs an automatic cast of
the float value to an integer value, usually truncating the important
information.  The following code fragment is one portable method of
getting a float into an argument list.
</para>
<literallayout class="monospaced">
     top = 0.5;
     if (sizeof(float) &gt; sizeof(XtArgVal)) {
     /*
      * If a float is larger than an XtArgVal then pass this
      * resource value by reference.
      */
          XtSetArg(args[0], XtNshown, &amp;top);
     }
     else {
     /*
      * Convince C not to perform an automatic conversion, which
      * would truncate 0.5 to 0.
      */
          XtArgVal * l_top = (XtArgVal *) &amp;top;
          XtSetArg(args[0], XtNshown, *l_top);
     }
</literallayout>

</sect2>
</sect1>