path: root/specs/CH06.xml

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<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.3//EN" "http://www.oasis-open.org/docbook/xml/4.3/docbookx.dtd">

<chapter id='Geometry_Management'>
<title>Geometry Management</title>

<para>
A widget does not directly control its size and location;
rather, its parent is responsible for controlling them.
Although the position of children is usually left up to their parent,
the widgets themselves often have the best idea of their optimal sizes
and, possibly, preferred locations.
</para>

<para>
To resolve physical layout conflicts between sibling widgets and between
a widget and its parent, the Intrinsics provide the geometry management mechanism.
Almost all
composite
widgets have a geometry manager specified in the <emphasis remap='I'>geometry_manager</emphasis> field
in the widget class record that is responsible for the size, position, and
stacking order of the widget's children.
The only exception is fixed boxes,
which create their children themselves and can ensure that
their children will never make a geometry request.
</para>

<sect1 id="Initiating_Geometry_Changes">
<title>Initiating Geometry Changes</title>

<para>
Parents, children, and clients each initiate geometry changes differently.
Because a parent has absolute control of its children's geometry,
it changes the geometry directly by calling
<function>XtMoveWidget</function>,
<xref linkend='XtResizeWidget' xrefstyle='select: title'/>,
or
<xref linkend='XtConfigureWidget' xrefstyle='select: title'/>.
A child must ask its parent for a geometry change by calling
<xref linkend='XtMakeGeometryRequest' xrefstyle='select: title'/>
or
<xref linkend='XtMakeResizeRequest' xrefstyle='select: title'/>.
An application or other client code initiates a geometry change by calling
<xref linkend='XtSetValues' xrefstyle='select: title'/>
on the appropriate geometry fields,
thereby giving the widget the opportunity to modify or reject the client
request before it gets propagated to the parent and the opportunity
to respond appropriately to the parent's reply.
</para>

<para>
When a widget that needs to change its size, position, border width,
or stacking depth asks its parent's geometry manager to make the desired
changes,
the geometry manager can allow the request, disallow the request, or
suggest a compromise.
</para>

<para>
When the geometry manager is asked to change the geometry of a child,
the geometry manager may also rearrange and resize any or all
of the other children that it controls.
The geometry manager can move children around freely using
<xref linkend='XtMoveWidget' xrefstyle='select: title'/>.
When it resizes a child (that is, changes the width, height, or
border width) other than the one making the request,
it should do so by calling
<xref linkend='XtResizeWidget' xrefstyle='select: title'/>.
The requesting child may be given special treatment; see
<xref linkend='Child_Geometry_Management_The_geometry_manager_Procedure' />.
It can simultaneously move and resize a child with a single call to
<xref linkend='XtConfigureWidget' xrefstyle='select: title'/>.
</para>

<para>
Often, geometry managers find that they can satisfy a request only if
they can reconfigure a widget that they are not in control of; in particular,
the
composite
widget may want to change its own size.
In this case,
the geometry manager makes a request to its parent's geometry manager.
Geometry requests can cascade this way to arbitrary depth.
</para>

<para>
Because such cascaded arbitration of widget geometry can involve extended
negotiation,
windows are not actually allocated to widgets at application
startup until all widgets are satisfied with their geometry;
see <xref linkend='Creating_Widgets' /> and
<xref linkend='Realizing_Widgets' />.
</para>

<note>
<orderedlist>
  <listitem>
    <para>
The Intrinsics treatment of stacking requests is deficient in several areas.
Stacking requests for unrealized widgets are granted but will have no effect.
In addition, there is no way to do an
<xref linkend='XtSetValues' xrefstyle='select: title'/>
that will generate a stacking geometry request.
    </para>
  </listitem>
  <listitem>
    <para>
After a successful geometry request (one that returned
<function>XtGeometryYes</function>),
a widget does not know whether its resize procedure has been called.
Widgets should have resize procedures that can be called more than once
without ill effects.
    </para>
  </listitem>
</orderedlist>
</note>
</sect1>

<sect1 id="General_Geometry_Manager_Requests">
<title>General Geometry Manager Requests</title>
<para>
When making a geometry request, the child specifies an
<function>XtWidgetGeometry</function>
structure.
</para>

<programlisting>
typedef unsigned long XtGeometryMask;
typedef struct {
        XtGeometryMask  request_mode;
        Position        x, y;
        Dimension       width, height;
        Dimension       border_width;
        Widget          sibling;
        int             stack_mode;
} XtWidgetGeometry;
</programlisting>

<para>
To make a general geometry manager request from a widget, use
<xref linkend='XtMakeGeometryRequest' xrefstyle='select: title'/>.
</para>

<funcsynopsis id='XtMakeGeometryRequest'>
<funcprototype>
<funcdef>XtGeometryResult <function>XtMakeGeometryRequest</function></funcdef>
   <paramdef>Widget <parameter>w</parameter></paramdef>
   <paramdef>XtWidgetGeometry *<parameter>request</parameter></paramdef>
   <paramdef>XtWidgetGeometry *<parameter>reply_return</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>w</emphasis>
    </term>
    <listitem>
      <para>
Specifies the widget making the request.  Must be of class RectObj or any subclass thereof.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>request</emphasis>
    </term>
    <listitem>
      <para>
Specifies the desired widget geometry (size, position, border width,
and stacking order).
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>reply_return</emphasis>
    </term>
    <listitem>
      <para>
Returns the allowed widget size, or may be NULL
if the requesting widget is not interested in handling
<function>XtGeometryAlmost</function>.
    </para>
  </listitem>
  </varlistentry>
</variablelist>


<para>
Depending on the condition,
<xref linkend='XtMakeGeometryRequest' xrefstyle='select: title'/>
performs the following:
</para>

<itemizedlist spacing='compact'>
  <listitem>
    <para>
If the widget is unmanaged or the widget's parent is not realized,
it makes the changes and returns
<function>XtGeometryYes</function>.
    </para>
  </listitem>
  <listitem>
    <para>
If the parent's class is not a subclass of
<function>compositeWidgetClass</function>
or the parent's <emphasis remap='I'>geometry_manager</emphasis> field is NULL,
it issues an error.
    </para>
  </listitem>
  <listitem>
    <para>
If the widget's <emphasis remap='I'>being_destroyed</emphasis> field is
<function>True</function>,
it returns
<function>XtGeometryNo</function>.
    </para>
  </listitem>
  <listitem>
    <para>
If the widget <emphasis remap='I'>x</emphasis>, <emphasis remap='I'>y</emphasis>, <emphasis remap='I'>width</emphasis>, <emphasis remap='I'>height</emphasis>, and
<emphasis remap='I'>border_width</emphasis> fields are
all equal to the requested values,
it returns
<function>XtGeometryYes</function>;
otherwise, it calls the parent's geometry_manager procedure
with the given parameters.
    </para>
  </listitem>
  <listitem>
    <para>
If the parent's geometry manager returns
<function>XtGeometryYes</function>
and if
<function>XtCWQueryOnly</function>
is not set in <emphasis remap='I'>request-&gt;request_mode</emphasis>
and if the widget is realized,
<xref linkend='XtMakeGeometryRequest' xrefstyle='select: title'/>
calls the
<function>XConfigureWindow</function>
Xlib function to reconfigure the widget's window (set its size, location,
and stacking order as appropriate).
    </para>
  </listitem>
  <listitem>
    <para>
If the geometry manager returns
<function>XtGeometryDone</function>,
the change has been approved and actually has been done.
In this case,
<xref linkend='XtMakeGeometryRequest' xrefstyle='select: title'/>
does no configuring and returns
<function>XtGeometryYes</function>.
<xref linkend='XtMakeGeometryRequest' xrefstyle='select: title'/>
never returns
<function>XtGeometryDone</function>.
    </para>
  </listitem>
  <listitem>
    <para>
Otherwise,
<xref linkend='XtMakeGeometryRequest' xrefstyle='select: title'/>
just returns the resulting value from the parent's geometry manager.
    </para>
  </listitem>
</itemizedlist>

<para>
Children of primitive widgets are always unmanaged; therefore,
<xref linkend='XtMakeGeometryRequest' xrefstyle='select: title'/>
always returns
<function>XtGeometryYes</function>
when called by a child of a primitive widget.
</para>

<para>
The return codes from geometry managers are
</para>

<programlisting>
typedef enum {
        XtGeometryYes,
        XtGeometryNo,
        XtGeometryAlmost,
        XtGeometryDone
} XtGeometryResult;
</programlisting>

<para>
The <emphasis remap='I'>request_mode</emphasis> definitions are from
<filename class="headerfile">&lt;X11/X.h&gt;</filename>.
</para>

<informaltable frame='none'>
  <?dbfo keep-together="always" ?>
  <tgroup cols='3' align='left' colsep='0' rowsep='0'>
  <colspec colwidth='1.0*' colname='c1'/>
  <colspec colwidth='1.0*' colname='c2'/>
  <colspec colwidth='1.0*' colname='c3'/>
  <tbody>
    <row>
      <entry>#define</entry>
      <entry><function>CWX</function></entry>
      <entry>(1&lt;&lt;0)</entry>
    </row>
    <row>
      <entry>#define</entry>
      <entry><function>CWY</function></entry>
      <entry>(1&lt;&lt;1)</entry>
    </row>
    <row>
      <entry>#define</entry>
      <entry><function>CWWidth</function></entry>
      <entry>(1&lt;&lt;2)</entry>
    </row>
    <row>
      <entry>#define</entry>
      <entry><function>CWHeight</function></entry>
      <entry>(1&lt;&lt;3)</entry>
    </row>
    <row>
      <entry>#define</entry>
      <entry><function>CWBorderWidth</function></entry>
      <entry>(1&lt;&lt;4)</entry>
    </row>
    <row>
      <entry>#define</entry>
      <entry><function>CWSibling</function></entry>
      <entry>(1&lt;&lt;5)</entry>
    </row>
    <row>
      <entry>#define</entry>
      <entry><function>CWStackMode</function></entry>
      <entry>(1&lt;&lt;6)</entry>
    </row>
  </tbody>
  </tgroup>
</informaltable>

<para>
The Intrinsics also support the following value.
</para>

<informaltable frame='none'>
  <?dbfo keep-together="always" ?>
  <tgroup cols='3' align='left' colsep='0' rowsep='0'>
  <colspec colwidth='1.0*' colname='c1'/>
  <colspec colwidth='1.0*' colname='c2'/>
  <colspec colwidth='1.0*' colname='c3'/>
  <tbody>
    <row>
      <entry>#define</entry>
      <entry><function>XtCWQueryOnly</function></entry>
      <entry>(1&lt;&lt;7)</entry>
    </row>
  </tbody>
  </tgroup>
</informaltable>

<para>
<function>XtCWQueryOnly</function>
indicates that the corresponding geometry request is only a query
as to what would happen if this geometry request were made
and that no widgets should actually be changed.
</para>

<para>
<xref linkend='XtMakeGeometryRequest' xrefstyle='select: title'/>,
like the
<function>XConfigureWindow</function>
Xlib function, uses <emphasis remap='I'>request_mode</emphasis> to determine which fields in the
<function>XtWidgetGeometry</function>
structure the caller wants to specify.
</para>

<para>
The <emphasis remap='I'>stack_mode</emphasis> definitions are from
<filename class="headerfile">&lt;X11/X.h&gt;</filename>:
</para>

<informaltable frame='none'>
  <?dbfo keep-together="always" ?>
  <tgroup cols='3' align='left' colsep='0' rowsep='0'>
  <colspec colwidth='1.0*' colname='c1'/>
  <colspec colwidth='1.0*' colname='c2'/>
  <colspec colwidth='1.0*' colname='c3'/>
  <tbody>
    <row>
      <entry>#define</entry>
      <entry><function>Above</function></entry>
      <entry>0</entry>
    </row>
    <row>
      <entry>#define</entry>
      <entry><function>Below</function></entry>
      <entry>1</entry>
    </row>
    <row>
      <entry>#define</entry>
      <entry><function>TopIf</function></entry>
      <entry>2</entry>
    </row>
    <row>
      <entry>#define</entry>
      <entry><function>BottomIf</function></entry>
      <entry>3</entry>
    </row>
    <row>
      <entry>#define</entry>
      <entry><function>Opposite</function></entry>
      <entry>4</entry>
    </row>
  </tbody>
  </tgroup>
</informaltable>

<para>
The Intrinsics also support the following value.
</para>

<informaltable frame='none'>
  <?dbfo keep-together="always" ?>
  <tgroup cols='3' align='left' colsep='0' rowsep='0'>
  <colspec colwidth='1.0*' colname='c1'/>
  <colspec colwidth='1.0*' colname='c2'/>
  <colspec colwidth='1.0*' colname='c3'/>
  <tbody>
    <row>
      <entry>#define</entry>
      <entry><function>XtSMDontChange</function></entry>
      <entry>5</entry>
    </row>
  </tbody>
  </tgroup>
</informaltable>

<para>
For definition and behavior of
<function>Above</function>,
<function>Below</function>,
<function>TopIf</function>,
<function>BottomIf</function>,
and
<function>Opposite</function>,
<olink targetdoc='libX11' targetptr='Configuring_Windows' >BLAH</olink>
in <olink targetptr='libX11' targetdoc='libX11'>Xlib &mdash; C Language X Interface</olink>.
<function>XtSMDontChange</function>
indicates that the widget wants its current stacking order preserved.
</para>
</sect1>

<sect1 id="Resize_Requests">
<title>Resize Requests</title>
<para>
To make a simple resize request from a widget, you can use
<xref linkend='XtMakeResizeRequest' xrefstyle='select: title'/>
as an alternative to
<xref linkend='XtMakeGeometryRequest' xrefstyle='select: title'/>.
</para>

<funcsynopsis id='XtMakeResizeRequest'>
<funcprototype>
<funcdef>typedef XtGeometryResult <function>XtMakeResizeRequest</function></funcdef>
   <paramdef>Widget <parameter>w</parameter></paramdef>
   <paramdef>Dimension <parameter>width</parameter></paramdef>
   <paramdef>Dimension *<parameter>width_return</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>w</emphasis>
    </term>
    <listitem>
      <para>
Specifies the widget making the request.  Must be of class RectObj or any subclass thereof.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>width</emphasis>
    </term>
    <listitem>
      <para>
Specify the desired widget width and height.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>height</emphasis>
    </term>
    <listitem>
      <para></para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>width_return</emphasis>
    </term>
    <listitem>
      <para>
Return the allowed widget width and height.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>height_return</emphasis>
    </term>
    <listitem>
     <para></para>
  </listitem>
  </varlistentry>
</variablelist>


<para>
The
<xref linkend='XtMakeResizeRequest' xrefstyle='select: title'/>
function, a simple interface to
<xref linkend='XtMakeGeometryRequest' xrefstyle='select: title'/>,
creates an
<function>XtWidgetGeometry</function>
structure and specifies that width and height should change
by setting <emphasis remap='I'>request_mode</emphasis> to
<function>CWWidth</function>
<function>|</function>
<function>CWHeight</function>.
The geometry manager is free to modify any of the other window attributes
(position or stacking order) to satisfy the resize request.
If the return value is
<function>XtGeometryAlmost</function>,
<emphasis remap='I'>width_return</emphasis> and <emphasis remap='I'>height_return</emphasis> contain a compromise width and height.
If these are acceptable,
the widget should immediately call
<xref linkend='XtMakeResizeRequest' xrefstyle='select: title'/>
again and request that the compromise width and height be applied.
If the widget is not interested in
<function>XtGeometryAlmost</function>
replies,
it can pass NULL for <emphasis remap='I'>width_return</emphasis> and <emphasis remap='I'>height_return</emphasis>.
</para>
</sect1>

<sect1 id="Potential_Geometry_Changes">
<title>Potential Geometry Changes</title>
<para>
Sometimes a geometry manager cannot respond to
a geometry request from a child without first making a geometry request
to the widget's own parent (the original requestor's grandparent).
If the request to the grandparent would allow the parent to satisfy the
original request,
the geometry manager can make the intermediate geometry request
as if it were the originator.
On the other hand,
if the geometry manager already has determined that the original request
cannot be completely satisfied (for example, if it always denies
position changes),
it needs to tell the grandparent to respond to the intermediate request
without actually changing the geometry
because it does not know if the child will accept the compromise.
To accomplish this, the geometry manager uses
<function>XtCWQueryOnly</function>
in the intermediate request.
</para>

<para>
When
<function>XtCWQueryOnly</function>
is used, the geometry manager needs to cache
enough information to exactly reconstruct the intermediate request.
If the grandparent's response to the intermediate query was
<function>XtGeometryAlmost</function>,
the geometry manager needs to cache the entire
reply geometry in the event the child accepts the parent's compromise.
</para>

<para>
If the grandparent's response was
<function>XtGeometryAlmost</function>,
it may also be necessary to cache the entire reply geometry from
the grandparent when
<function>XtCWQueryOnly</function>
is not used.
If the geometry manager is still able to satisfy the original request,
it may immediately accept the grandparent's compromise
and then act on the child's request.
If the grandparent's compromise geometry is insufficient to allow
the child's request and if the geometry manager is willing to offer
a different compromise to the child,
the grandparent's compromise should not be accepted until the child
has accepted the new compromise.
</para>

<para>
Note that a compromise geometry returned with
<function>XtGeometryAlmost</function>
is guaranteed only for the next call to the same widget;
therefore, a cache of size 1 is sufficient.
</para>
</sect1>

<sect1 id="Child_Geometry_Management_The_geometry_manager_Procedure">
<title>Child Geometry Management: The geometry_manager Procedure</title>
<para>
The geometry_manager procedure pointer in a composite widget class is of type
<xref linkend='XtGeometryHandler' xrefstyle='select: title'/>.
</para>

<funcsynopsis id='XtGeometryHandler'>
<funcprototype>
<funcdef>typedef XtGeometryResult *<function>XtGeometryHandler</function></funcdef>
   <paramdef>Widget <parameter>w</parameter></paramdef>
   <paramdef>XtWidgetGeometry *<parameter>request</parameter></paramdef>
   <paramdef>XtWidgetGeometry *<parameter>geometry_return</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>w</emphasis>
    </term>
    <listitem>
      <para>
Passes the widget making the request.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>request</emphasis>
    </term>
    <listitem>
      <para>
Passes the new geometry the child desires.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>geometry_return</emphasis>
    </term>
    <listitem>
      <para>
Passes a geometry structure in which the geometry manager may store a
compromise.
    </para>
  </listitem>
  </varlistentry>
</variablelist>

<para>
A class can inherit its superclass's geometry manager during class
initialization.
</para>

<para>
A bit set to zero in the request's <emphasis remap='I'>request_mode</emphasis>
field means that the child widget
does not care about the value of the corresponding field,
so the geometry manager can change this field as it wishes.
A bit set to 1 means that the child wants that geometry element set
to the value in the corresponding field.
</para>

<para>
If the geometry manager can satisfy all changes requested
and if
<function>XtCWQueryOnly</function>
is not specified,
it updates the widget's <emphasis remap='I'>x</emphasis>, <emphasis remap='I'>y</emphasis>, <emphasis remap='I'>width</emphasis>, <emphasis remap='I'>height</emphasis>,
and <emphasis remap='I'>border_width</emphasis> fields
appropriately.
Then, it returns
<function>XtGeometryYes</function>,
and the values pointed to by the <emphasis remap='I'>geometry_return</emphasis> argument are undefined.
The widget's window is moved and resized automatically by
<xref linkend='XtMakeGeometryRequest' xrefstyle='select: title'/>.
</para>

<para>
Homogeneous composite widgets often find it convenient to treat the widget
making the request the same as any other widget, including reconfiguring
it using
<xref linkend='XtConfigureWidget' xrefstyle='select: title'/>
or
<xref linkend='XtResizeWidget' xrefstyle='select: title'/>
as part of its layout process, unless
<function>XtCWQueryOnly</function>
is specified.
If it does this,
it should return
<function>XtGeometryDone</function>
to inform
<xref linkend='XtMakeGeometryRequest' xrefstyle='select: title'/>
that it does not need to do the configuration itself.
</para>

<note>
<para>
To remain
compatible with layout techniques used in older widgets (before
<function>XtGeometryDone</function>
was added to the Intrinsics), a geometry manager should avoid using
<xref linkend='XtResizeWidget' xrefstyle='select: title'/>
or
<xref linkend='XtConfigureWidget' xrefstyle='select: title'/>
on the child making
the request because the layout process of the child may be in an
intermediate state in which it is not prepared to handle a call to its
resize procedure.  A self-contained widget set may choose this
alternative geometry management scheme, however, provided that it
clearly warns widget developers of the compatibility consequences.
</para>
</note>

<para>
Although
<xref linkend='XtMakeGeometryRequest' xrefstyle='select: title'/>
resizes the widget's window
(if the geometry
manager returns
<function>XtGeometryYes</function>),
it does not call the widget class's resize procedure.
The requesting widget must perform whatever
resizing calculations are needed explicitly.
</para>

<para>
If the geometry manager disallows the request,
the widget cannot change its geometry.
The values pointed to by <emphasis remap='I'>geometry_return</emphasis> are undefined,
and the geometry manager returns
<function>XtGeometryNo</function>.
</para>

<para>
Sometimes the geometry manager cannot satisfy the request exactly
but may be able to satisfy a similar request.
That is,
it could satisfy only a subset of the requests (for example,
size but not position) or a lesser request
(for example, it cannot make the child as big as the
request but it can make the child bigger than its current size).
In such cases,
the geometry manager fills in the structure pointed to by
<emphasis remap='I'>geometry_return</emphasis> with the actual changes
it is willing to make, including an appropriate <emphasis remap='I'>request_mode</emphasis> mask, and returns
<function>XtGeometryAlmost</function>.
If a bit in <emphasis remap='I'>geometry_return-&gt;request_mode</emphasis> is zero,
the geometry manager agrees not to change the corresponding value
if <emphasis remap='I'>geometry_return</emphasis> is used immediately
in a new request.
If a bit is 1,
the geometry manager does change that element to the corresponding
value in <emphasis remap='I'>geometry_return</emphasis>.
More bits may be set in <emphasis remap='I'>geometry_return-&gt;request_mode</emphasis>
than in the original request if
the geometry manager intends to change other fields should the
child accept the compromise.
</para>

<para>
When
<function>XtGeometryAlmost</function>
is returned,
the widget must decide if the compromise suggested in <emphasis remap='I'>geometry_return</emphasis>
is acceptable.
If it is, the widget must not change its geometry directly;
rather, it must make another call to
<xref linkend='XtMakeGeometryRequest' xrefstyle='select: title'/>.
</para>

<para>
If the next geometry request from this child uses the
<emphasis remap='I'>geometry_return</emphasis> values filled in by the geometry manager with an
<function>XtGeometryAlmost</function>
return and if there have been no intervening geometry requests on
either its parent or any of its other children,
the geometry manager must grant the request, if possible.
That is, if the child asks immediately with the returned geometry,
it should get an answer of
<function>XtGeometryYes</function>.
However,
dynamic behavior in
the user's window manager may affect the final outcome.
</para>

<para>
To return
<function>XtGeometryYes</function>,
the geometry manager frequently rearranges the position of other managed
children by calling
<xref linkend='XtMoveWidget' xrefstyle='select: title'/>.
However, a few geometry managers may sometimes change the
size of other managed children by calling
<xref linkend='XtResizeWidget' xrefstyle='select: title'/>
or
<xref linkend='XtConfigureWidget' xrefstyle='select: title'/>.
If
<function>XtCWQueryOnly</function>
is specified,
the geometry manager must return data describing
how it would react to this geometry
request without actually moving or resizing any widgets.
</para>

<para>
Geometry managers must not assume that the <emphasis remap='I'>request</emphasis>
and <emphasis remap='I'>geometry_return</emphasis> arguments point to independent storage.
The caller is permitted to use the same field for both,
and the geometry manager must allocate its own temporary storage,
if necessary.
</para>
</sect1>

<sect1 id="Widget_Placement_and_Sizing">
<title>Widget Placement and Sizing</title>
<para>
To move a sibling widget of the child making the geometry request,
the parent uses
<xref linkend='XtMoveWidget' xrefstyle='select: title'/>.
</para>

<funcsynopsis id='XtMoveWidget'>
<funcprototype>
<funcdef>void <function>XtMoveWidget</function></funcdef>
   <paramdef>Widget <parameter>w</parameter></paramdef>
   <paramdef>Position <parameter>x</parameter></paramdef>
   <paramdef>Position <parameter>y</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>w</emphasis>
    </term>
    <listitem>
      <para>
Specifies the widget.  Must be of class RectObj or any subclass thereof.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>x</emphasis>
    </term>
    <listitem>
     <para></para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>y</emphasis>
    </term>
    <listitem>
      <para>
Specify the new widget x and y coordinates.
    </para>
  </listitem>
  </varlistentry>
</variablelist>

<para>
The
<xref linkend='XtMoveWidget' xrefstyle='select: title'/>
function returns immediately if the specified geometry fields
are the same as the old values.
Otherwise,
<xref linkend='XtMoveWidget' xrefstyle='select: title'/>
writes the new <emphasis remap='I'>x</emphasis> and <emphasis remap='I'>y</emphasis> values into the object
and, if the object is a widget and is realized, issues an Xlib
<function>XMoveWindow</function>
call on the widget's window.
</para>

<para>
To resize a sibling widget of the child making the geometry request,
the parent uses
<xref linkend='XtResizeWidget' xrefstyle='select: title'/>.
</para>

<funcsynopsis id='XtResizeWidget'>
<funcprototype>
<funcdef>void <function>XtResizeWidget</function></funcdef>
   <paramdef>Widget <parameter>w</parameter></paramdef>
   <paramdef>Dimension <parameter>width</parameter></paramdef>
   <paramdef>Dimension <parameter>height</parameter></paramdef>
   <paramdef>Dimension <parameter>border_width</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>w</emphasis>
    </term>
    <listitem>
      <para>
Specifies the widget.  Must be of class RectObj or any subclass thereof.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>width</emphasis>
    </term>
    <listitem>
     <para></para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>height</emphasis>
    </term>
    <listitem>
     <para></para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>border_width</emphasis>
    </term>
    <listitem>
      <para>
Specify the new widget size.
    </para>
  </listitem>
  </varlistentry>
</variablelist>

<para>
The
<xref linkend='XtResizeWidget' xrefstyle='select: title'/>
function returns immediately if the specified geometry fields
are the same as the old values.
Otherwise,
<xref linkend='XtResizeWidget' xrefstyle='select: title'/>
writes the new <emphasis remap='I'>width</emphasis>, <emphasis remap='I'>height</emphasis>, and <emphasis remap='I'>border_width</emphasis> values into
the object and, if the object is a widget and is realized, issues an
<function>XConfigureWindow</function>
call on the widget's window.
</para>

<para>
If the new width or height is different from the old values,
<xref linkend='XtResizeWidget' xrefstyle='select: title'/>
calls the object's resize procedure to notify it of the size change.
</para>

<para>
To move and resize the sibling widget of the child making the geometry request,
the parent uses
<xref linkend='XtConfigureWidget' xrefstyle='select: title'/>.
</para>

<funcsynopsis id='XtConfigureWidget'>
<funcprototype>
<funcdef>void <function>XtConfigureWidget</function></funcdef>
   <paramdef>Widget <parameter>w</parameter></paramdef>
   <paramdef>Position <parameter>x</parameter></paramdef>
   <paramdef>Position <parameter>y</parameter></paramdef>
   <paramdef>Dimension <parameter>width</parameter></paramdef>
   <paramdef>Dimension <parameter>height</parameter></paramdef>
   <paramdef>Dimension <parameter>border_width</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>w</emphasis>
    </term>
    <listitem>
      <para>
Specifies the widget.  Must be of class RectObj or any subclass thereof.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>x</emphasis>
    </term>
    <listitem>
     <para></para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>y</emphasis>
    </term>
    <listitem>
      <para>
Specify the new widget x and y coordinates.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>width</emphasis>
    </term>
    <listitem>
     <para></para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>height</emphasis>
    </term>
    <listitem>
     <para></para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>border_width</emphasis>
    </term>
    <listitem>
      <para>
Specify the new widget size.
    </para>
  </listitem>
  </varlistentry>
</variablelist>

<para>
The
<xref linkend='XtConfigureWidget' xrefstyle='select: title'/>
function returns immediately if the specified new geometry fields
are all equal to the current values.
Otherwise,
<xref linkend='XtConfigureWidget' xrefstyle='select: title'/>
writes the new <emphasis remap='I'>x</emphasis>, <emphasis remap='I'>y</emphasis>, <emphasis remap='I'>width</emphasis>, <emphasis remap='I'>height</emphasis>,
and <emphasis remap='I'>border_width</emphasis> values
into the object and, if the object is a widget and is realized, makes an Xlib
<function>XConfigureWindow</function>
call on the widget's window.
</para>

<para>
If the new width or height is different from its old value,
<xref linkend='XtConfigureWidget' xrefstyle='select: title'/>
calls the object's resize procedure to notify it of the size change;
otherwise, it simply returns.
</para>

<para>
To resize a child widget that already has the new values of its width,
height, and border width, the parent uses
<xref linkend='XtResizeWindow' xrefstyle='select: title'/>.
</para>

<funcsynopsis id='XtResizeWindow'>
<funcprototype>
<funcdef>void <function>XtResizeWindow</function></funcdef>
   <paramdef>Widget <parameter>w</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>w</emphasis>
    </term>
    <listitem>
      <para>
Specifies the widget.  Must be of class Core or any subclass thereof.
    </para>
  </listitem>
  </varlistentry>
</variablelist>

<para>
The
<xref linkend='XtResizeWindow' xrefstyle='select: title'/>
function calls the
<function>XConfigureWindow</function>
Xlib function to make the window of the specified widget match its width,
height, and border width.
This request is done unconditionally because there is no
inexpensive way to tell if these
values match the current values.
Note that the widget's resize procedure is not called.
</para>

<para>
There are very few times to use
<xref linkend='XtResizeWindow' xrefstyle='select: title'/>;
instead, the parent should use
<xref linkend='XtResizeWidget' xrefstyle='select: title'/>.
</para>
</sect1>

<sect1 id="Preferred_Geometry">
<title>Preferred Geometry</title>
<para>
Some parents may be willing to adjust their layouts to accommodate the
preferred geometries of their children.
They can use
<xref linkend='XtQueryGeometry' xrefstyle='select: title'/>
to obtain the preferred geometry
and, as they see fit, can use or ignore any portion of the response.
</para>

<para>
To query a child widget's preferred geometry, use
<xref linkend='XtQueryGeometry' xrefstyle='select: title'/>.
</para>

<funcsynopsis id='XtQueryGeometry'>
<funcprototype>
<funcdef>XtGeometryResult <function>XtQueryGeometry</function></funcdef>
   <paramdef>Widget <parameter>w</parameter></paramdef>
   <paramdef>XtWidgetGeometry *<parameter>intended</parameter></paramdef>
   <paramdef>XtWidgetGeometry *<parameter>preferred_return</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>w</emphasis>
    </term>
    <listitem>
      <para>
Specifies the widget.  Must be of class RectObj or any subclass thereof.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>intended</emphasis>
    </term>
    <listitem>
      <para>
Specifies the new geometry the parent plans to give to the child, or
NULL.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>preferred_return</emphasis>
    </term>
    <listitem>
      <para>
Returns the child widget's preferred geometry.
    </para>
  </listitem>
  </varlistentry>
</variablelist>

<para>
To discover a child's preferred geometry,
the child's parent stores the new
geometry in the corresponding fields of
the intended structure, sets the corresponding bits in <emphasis remap='I'>intended.request_mode</emphasis>,
and calls
<xref linkend='XtQueryGeometry' xrefstyle='select: title'/>.
The parent should set only those fields that are important to it so
that the child can determine whether it may be able to attempt changes to
other fields.
</para>

<para>
<xref linkend='XtQueryGeometry' xrefstyle='select: title'/>
clears all bits in the <emphasis remap='I'>preferred_return-&gt;request_mode</emphasis>
field and checks the
<emphasis remap='I'>query_geometry</emphasis> field of the specified widget's class record.
If <emphasis remap='I'>query_geometry</emphasis> is not NULL,
<xref linkend='XtQueryGeometry' xrefstyle='select: title'/>
calls the query_geometry procedure and passes as arguments the
specified widget, <emphasis remap='I'>intended</emphasis>, and <emphasis remap='I'>preferred_return</emphasis> structures.
If the <emphasis remap='I'>intended</emphasis> argument is NULL,
<xref linkend='XtQueryGeometry' xrefstyle='select: title'/>
replaces it with a pointer to an
<function>XtWidgetGeometry</function>
structure with <emphasis remap='I'>request_mode</emphasis> equal to zero before calling the
query_geometry procedure.
</para>

<note>
<para>
If
<xref linkend='XtQueryGeometry' xrefstyle='select: title'/>
is called from within a geometry_manager
procedure for the widget that issued
<xref linkend='XtMakeGeometryRequest' xrefstyle='select: title'/>
or
<xref linkend='XtMakeResizeRequest' xrefstyle='select: title'/>,
the results
are not guaranteed to be consistent with the requested changes.  The
change request passed to the geometry manager takes precedence over
the preferred geometry.
</para>
</note>

<para>
The query_geometry procedure pointer is of type
<xref linkend='XtGeometryHandler' xrefstyle='select: title'/>.
</para>

<funcsynopsis id='_XtGeometryHandler'>
<funcprototype>
<funcdef>typedef XtGeometryResult <function>(*XtGeometryHandler)</function></funcdef>
   <paramdef>Widget <parameter>w</parameter></paramdef>
   <paramdef>XtWidgetGeometry *<parameter>request</parameter></paramdef>
   <paramdef>XtWidgetGeometry *<parameter>preferred_return</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>w</emphasis>
    </term>
    <listitem>
      <para>
Passes the child widget whose preferred geometry is required.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>request</emphasis>
    </term>
    <listitem>
      <para>
Passes the geometry changes that the parent plans to make.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>preferred_return</emphasis>
    </term>
    <listitem>
      <para>
Passes a structure in which the child returns its preferred geometry.
    </para>
  </listitem>
  </varlistentry>
</variablelist>

<para>
The query_geometry procedure is expected to examine the bits set in
<emphasis remap='I'>request-&gt;request_mode</emphasis>, evaluate the preferred geometry of the widget,
and store the result in <emphasis remap='I'>preferred_return</emphasis>
(setting the bits in <emphasis remap='I'>preferred_return-&gt;request_mode</emphasis> corresponding
to those geometry fields that it cares about).
If the proposed geometry change is acceptable without modification,
the query_geometry procedure should return
<function>XtGeometryYes</function>.
If at least one field in <emphasis remap='I'>preferred_return</emphasis>
with a bit set in <emphasis remap='I'>preferred_return-&gt;request_mode</emphasis>
is different
from the corresponding field in <emphasis remap='I'>request</emphasis>
or if a bit was set in <emphasis remap='I'>preferred_return-&gt;request_mode</emphasis>
that was not set in the request,
the query_geometry procedure should return
<function>XtGeometryAlmost</function>.
If the preferred geometry is identical to the current geometry,
the query_geometry procedure should return
<function>XtGeometryNo</function>.
</para>

<note><para>
The query_geometry procedure may assume
that no
<xref linkend='XtMakeResizeRequest' xrefstyle='select: title'/>
or
<xref linkend='XtMakeGeometryRequest' xrefstyle='select: title'/>
is in progress
for the specified widget; that is, it is not required to construct
a reply consistent with the requested geometry if such a request
were actually outstanding.
</para></note>

<para>
After calling the query_geometry procedure
or if the <emphasis remap='I'>query_geometry</emphasis> field is NULL,
<xref linkend='XtQueryGeometry' xrefstyle='select: title'/>
examines all the unset bits in <emphasis remap='I'>preferred_return-&gt;request_mode</emphasis>
and sets the corresponding fields in <emphasis remap='I'>preferred_return</emphasis>
to the current values from the widget instance.
If
<function>CWStackMode</function>
is not set,
the <emphasis remap='I'>stack_mode</emphasis> field is set to
<function>XtSMDontChange</function>.
<xref linkend='XtQueryGeometry' xrefstyle='select: title'/>
returns the value returned by the query_geometry procedure or
<function>XtGeometryYes</function>
if the <emphasis remap='I'>query_geometry</emphasis> field is NULL.
</para>

<para>
Therefore, the caller can interpret a return of
<function>XtGeometryYes</function>
as not needing to evaluate the contents of the reply and, more important,
not needing to modify its layout plans.
A return of
<function>XtGeometryAlmost</function>
means either that both the parent and the child expressed interest
in at least one common field and the child's preference does not match
the parent's intentions or that the child expressed interest in a field that
the parent might need to consider.
A return value of
<function>XtGeometryNo</function>
means that both the parent and the child expressed interest in a field and
that the child suggests that the field's current value in the widget instance
is its preferred value.
In addition, whether or not the caller ignores the return value or the
reply mask, it is guaranteed that the <emphasis remap='I'>preferred_return</emphasis> structure contains complete
geometry information for the child.
</para>

<para>
Parents are expected to call
<xref linkend='XtQueryGeometry' xrefstyle='select: title'/>
in their layout routine and wherever else the information is significant
after change_managed has been called.
The first time it is invoked,
the changed_managed procedure may assume that the child's current geometry
is its preferred geometry.
Thus, the child is still responsible for storing values
into its own geometry during its initialize procedure.
</para>
</sect1>

<sect1 id="Size_Change_Management_The_resize_Procedure">
<title>Size Change Management: The resize Procedure</title>
<para>
A child can be resized by its parent at any time.
Widgets usually need to know when they have changed size
so that they can lay out their displayed data again to match the new size.
When a parent resizes a child, it calls
<xref linkend='XtResizeWidget' xrefstyle='select: title'/>,
which updates the geometry fields in the widget,
configures the window if the widget is realized,
and calls the child's resize procedure to notify the child.
The resize procedure pointer is of type
<xref linkend='XtWidgetProc' xrefstyle='select: title'/>.
</para>

<para>
If a class need not recalculate anything when a widget is resized,
it can specify NULL for the <emphasis remap='I'>resize</emphasis> field in its class record.
This is an unusual case and should occur only for widgets
with very trivial display semantics.
The resize procedure takes a widget as its only argument.
The <emphasis remap='I'>x</emphasis>, <emphasis remap='I'>y</emphasis>, <emphasis remap='I'>width</emphasis>, <emphasis remap='I'>height</emphasis>,
and <emphasis remap='I'>border_width</emphasis> fields of the widget contain the new values.
The resize procedure should recalculate the layout of internal data
as needed.
(For example, a centered Label in a window that changes size
should recalculate the starting position of the text.)
The widget must obey resize as a command and must not treat it as a request.
A widget must not issue an
<xref linkend='XtMakeGeometryRequest' xrefstyle='select: title'/>
or
<xref linkend='XtMakeResizeRequest' xrefstyle='select: title'/>
call from its resize procedure.
</para>
</sect1>
</chapter>