xref: /xsrc/external/mit/libXaw/dist/specs/CH1.xml

<chapter id='Athena_Widgets_and_The_Intrinsics'>
<title>Athena Widgets and The Intrinsics</title>
<para>
The X Toolkit is made up of two distinct pieces, the Xt Intrinsics and a
widget set.  The Athena widget set is a sample implementation of a
widget set built upon the Intrinsics.  In the X Toolkit, a widget is the
combination of an X window or subwindow and its associated input and
output semantics.
</para>
<para>
Because the Intrinsics provide the same basic functionality to all widget
sets it may be possible to use widgets from the Athena widget set with
other widget sets based upon the Intrinsics.  Since widget sets may also
implement private protocols, all functionality may not be available when
mixing and matching widget sets.  For information about the Intrinsics, see
the <olink targetdoc='intrinsics' targetptr='intrinsics'
><citetitle>X Toolkit Intrinsics - C Language Interface</citetitle></olink>.
</para>
<para>
The Athena widget set is a library package layered on top of the Intrinsics
and Xlib that provides a set of user interface tools sufficient to build
a wide variety of applications.  This layer extends the basic
abstractions provided by X and provides the next layer of functionality
primarily by supplying a cohesive set of sample widgets.  Although the
Intrinsics are a Consortium standard, there is no standard widget set.
</para>

<para>
To the extent possible, the Intrinsics are "policy-free".  The application
environment and widget set, not the Intrinsics, define, implement, and
enforce:
</para>

<itemizedlist>
  <listitem><para>Policy</para></listitem>
  <listitem><para>Consistency</para></listitem>
  <listitem><para>Style</para></listitem>
</itemizedlist>

<para>
Each individual widget implementation defines its own policy.  The X Toolkit
design allows for, but does not necessarily encourage, the free mixing
of radically differing widget implementations.
</para>

<sect1 id='Introduction_to_the_X_Toolkit'>
<title>Introduction to the X Toolkit</title>
<para>
<!-- .LP -->
<!-- .XS -->
<!-- 	Introduction to the X Toolkit -->
<!-- .XE -->
<indexterm significance="preferred"><primary>introduction</primary></indexterm>
The X Toolkit provides tools that simplify the design of
application user interfaces in the X Window System programming environment.
It assists application programmers by providing a set of common
underlying user-interface functions.  It also lets widget programmers
modify existing widgets, by subclassing, or add new widgets.  By using
the X Toolkit in their applications, programmers can present a similar
user interface across applications to all workstation users.
</para>
<para>
<!-- .LP -->
The X Toolkit consists of:
</para>
<itemizedlist>
  <listitem>
    <para>
A set of Intrinsics functions for building widgets
    </para>
  </listitem>
  <listitem>
    <para>
An architectural model for constructing widgets
    </para>
  </listitem>
  <listitem>
    <para>
A widget set for application programming
    </para>
  </listitem>
</itemizedlist>
<para>
<!-- .LP -->
While the majority of the Intrinsics functions are intended
for the widget programmer,
a subset of the Intrinsics functions are to be used by application programmers
(see <olink targetdoc='intrinsics' targetptr='intrinsics'
><citetitle>X Toolkit Intrinsics - C Language Interface</citetitle></olink>).
The architectural model lets the widget programmer design new widgets
by using the Intrinsics and by combining other widgets.
The application interface layers built on top of the X Toolkit include a
coordinated set of widgets and composition policies.
Some of these widgets and policies are specific to a single
application domain, and others are common to a variety of
applications.
</para>
<para>
<!-- .LP -->
The remainder of this chapter discusses the X Toolkit and Athena widget set:
</para>
<itemizedlist>
  <listitem>
    <para>
Terminology
    </para>
  </listitem>
  <listitem>
    <para>
Model
    </para>
  </listitem>
  <listitem>
    <para>
Conventions used in this manual
    </para>
  </listitem>
  <listitem>
    <para>
Format of the Widget Reference Chapters
    </para>
  </listitem>
</itemizedlist>
</sect1>
<sect1 id="Terminology">
<title>Terminology</title>
<!-- .LP -->
<!-- .XS -->
<!-- 	Terminology -->
<!-- .XE -->
<para>
<!-- .LP -->
In addition to the terms already defined for X programming (see
<olink targetdoc='libX11' targetptr='glossary'
><citetitle>Xlib - C Language Interface</citetitle></olink>),
the following terms are specific to the Intrinsics and Athena widget set
and used throughout this document.
</para>
<glosslist>
<glossentry>
  <glossterm>Application programmer</glossterm>
<indexterm significance="preferred"><primary>application programmer</primary></indexterm>
  <glossdef>
    <para>
A programmer who uses the X Toolkit to produce an application user interface.
    </para>
  </glossdef>
</glossentry>
<glossentry>
  <glossterm>Child</glossterm>
<indexterm significance="preferred"><primary>child</primary></indexterm>
  <glossdef>
    <para>
A widget that is contained within another "parent" widget.
    </para>
  </glossdef>
</glossentry>
<glossentry>
  <glossterm>Class</glossterm>
<indexterm significance="preferred"><primary>class</primary></indexterm>
  <glossdef>
    <para>
The general group to which a specific object belongs.
    </para>
  </glossdef>
</glossentry>
<glossentry>
  <glossterm>Client</glossterm>
<indexterm significance="preferred"><primary>client</primary></indexterm>
  <glossdef>
    <para>
A function that uses a widget in an application or for composing
other widgets.
    </para>
  </glossdef>
</glossentry>
<glossentry>
  <glossterm>FullName</glossterm>
<indexterm significance="preferred"><primary>FullName</primary></indexterm>
  <glossdef>
    <para>
The name of a widget instance appended to the full name of its parent.
    </para>
  </glossdef>
</glossentry>
<glossentry>
  <glossterm>Instance</glossterm>
<indexterm significance="preferred"><primary>instance</primary></indexterm>
  <glossdef>
    <para>
A specific widget object as opposed to a general widget class.
    </para>
  </glossdef>
</glossentry>
<glossentry>
  <glossterm>Method</glossterm>
<indexterm significance="preferred"><primary>method</primary></indexterm>
  <glossdef>
    <para>
A function or procedure implemented by a widget class.
    </para>
  </glossdef>
</glossentry>
<glossentry>
  <glossterm>Name</glossterm>
<indexterm significance="preferred"><primary>name</primary><secondary>widget</secondary></indexterm>
  <glossdef>
    <para>
The name that is specific to an instance of a widget for a given client.
This name is specified at creation time and cannot be modified.
    </para>
  </glossdef>
</glossentry>
<glossentry>
  <glossterm>Object</glossterm>
<indexterm significance="preferred"><primary>object</primary></indexterm>
  <glossdef>
    <para>
A data abstraction consisting of private data and private and public
functions that operate on the private data.
Users of the abstraction can interact with the object only through calls
to the object's public functions.
In the X Toolkit,
some of the object's public functions are called directly by the application,
while others are called indirectly when the application calls the common
Intrinsics functions.
In general, if a function is common to all widgets,
an application uses a single Intrinsics function to invoke the function for all
types of widgets.
If a function is unique to a single widget type,
the widget exports the function.
    </para>
  </glossdef>
</glossentry>
<glossentry>
  <glossterm>Parent</glossterm>
<indexterm significance="preferred"><primary>parent</primary></indexterm>
  <glossdef>
    <para>
A widget that contains at least one other ("child") widget.
A parent widget is also known as a composite widget.
    </para>
  </glossdef>
</glossentry>
<glossentry>
  <glossterm>Resource</glossterm>
<indexterm significance="preferred"><primary>resource</primary></indexterm>
  <glossdef>
    <para>
A named piece of data in a widget that can be set by a client,
by an application, or by user defaults.
    </para>
  </glossdef>
</glossentry>
<glossentry>
  <glossterm>Superclass</glossterm>
<indexterm significance="preferred"><primary>superclass</primary></indexterm>
  <glossdef>
    <para>
A larger class of which a specific class is a member.
All members of a class are also members of the superclass.
    </para>
  </glossdef>
</glossentry>
<glossentry>
  <glossterm>User</glossterm>
<indexterm significance="preferred"><primary>user</primary></indexterm>
  <glossdef>
    <para>
A person interacting with a workstation.
    </para>
  </glossdef>
</glossentry>
<glossentry>
  <glossterm>Widget</glossterm>
<indexterm significance="preferred"><primary>widget</primary></indexterm>
  <glossdef>
    <para>
An object providing a user-interface abstraction (for example, a Scrollbar
widget).
    </para>
  </glossdef>
</glossentry>
<glossentry>
  <glossterm>Widget class</glossterm>
<indexterm significance="preferred"><primary>widget class</primary></indexterm>
  <glossdef>
    <para>
The general group to which a specific widget belongs,
otherwise known as the type of the widget.
    </para>
  </glossdef>
</glossentry>
<glossentry>
  <glossterm>Widget programmer</glossterm>
<indexterm significance="preferred"><primary>widget programmer</primary></indexterm>
  <glossdef>
    <para>
A programmer who adds new widgets to the X Toolkit.
    </para>
  </glossdef>
</glossentry>
</glosslist>
</sect1>
<sect1 id="Underlying_Model">
<title>Underlying Model</title>
<para>
<!-- .LP -->
<!-- .XS -->
<!-- 	Underlying Model -->
<!-- .XE -->
<indexterm significance="preferred"><primary>underlying model</primary></indexterm>
The underlying architectural model is based on the following premises:
<!-- .KS -->
</para>
<variablelist><?dbfo list-presentation="blocks"?>
<varlistentry>
  <term>Widgets are X windows</term>
  <listitem>
    <para>
Every user-interface widget is associated with an X window.
The X window ID for a widget is readily available from the widget.
Standard Xlib calls can be used by widgets for many of their input and
output operations.
<!-- .KE -->
<!-- .KS -->
    </para>
  </listitem>
</varlistentry>
<varlistentry>
  <term>Information hiding</term>
  <listitem>
    <para>
The data for every widget is private to the widget and its subclasses.
That is, the data is neither directly accessible
nor visible outside of the module implementing the widget.
All program interaction with the widget is performed by a set of operations
(methods) that are defined for the widget.
<!-- .KE -->
<!-- .KS -->
    </para>
  </listitem>
</varlistentry>
<varlistentry>
  <term>Widget semantics and widget layout geometry</term>
  <listitem>
    <para>
Widget semantics are clearly separated from widget layout geometry.
Widgets are concerned with implementing specific user-interface
semantics.  They have little control over issues such as their size or
placement relative to other widget peers.  Mechanisms are provided for
associating geometric managers with widgets and for widgets to make
suggestions about their own geometry.
<!-- .KE -->
    </para>
  </listitem>
</varlistentry>
</variablelist>
</sect1>
<sect1 id="Conventions_Used_in_this_Manual">
<title>Conventions Used in this Manual</title>
<itemizedlist>
  <listitem>
    <para>
<indexterm significance="preferred"><primary>conventions</primary><secondary>used in manual</secondary></indexterm>
All resources available to the widgets are listed with each widget.  Many
of these are available to more than one widget class due to the object
oriented nature of the Intrinsics.  The new resources for each widget are
listed in bold text, and the inherited resources are listed in plain text.
    </para>
  </listitem>
  <listitem>
    <para>
Global symbols are printed in <function>bold</function> and can be function names,
symbols defined in include files, or structure names.  Arguments are
printed in <emphasis remap='I'>italics</emphasis>.
    </para>
  </listitem>
  <listitem>
    <para>
Each function is introduced by a general discussion that distinguishes
it from other functions.  The function declaration itself follows, and
each argument is specifically explained.  General discussion of the
function, if any is required, follows the arguments.  Where
applicable, the last paragraph of the explanation lists the return values
of the function.
    </para>
  </listitem>
  <listitem>
    <para>
To eliminate any ambiguity between those arguments that you pass and
those that a function returns to you, the explanations for all
arguments that you pass start with the word <emphasis remap='I'>specifies</emphasis> or, in the
case of multiple arguments, the word <emphasis remap='I'>specify</emphasis>. The explanations
for all arguments that are returned to you start with the word
<emphasis remap='I'>returns</emphasis> or, in the case of multiple arguments, the word
<emphasis remap='I'>return</emphasis>.  The explanations for all arguments that you can pass
and are returned start with the words <emphasis remap='I'>specifies and returns</emphasis>.
    </para>
  </listitem>
  <listitem>
    <para>
Any pointer to a structure that is used to return a value is
designated as such by the <emphasis remap='I'>_return</emphasis> suffix as part of its name.
All other pointers passed to these functions are used for reading
only.  A few arguments use pointers to structures that are used for
both input and output and are indicated by using the <emphasis remap='I'>_in_out</emphasis>
suffix.
<indexterm significance="preferred"><primary>_return</primary></indexterm>
<indexterm significance="preferred"><primary>_in_out</primary></indexterm>
    </para>
  </listitem>
</itemizedlist>
</sect1>
<sect1 id="Format_of_the_Widget_Reference_Chapters">
<title>Format of the Widget Reference Chapters</title>
<para>
<!-- .LP -->
<indexterm significance="preferred"><primary>conventions</primary><secondary>chapter format</secondary></indexterm>
<indexterm significance="preferred"><primary>chapter format</primary></indexterm>
The majority of this document is a reference guide for the Athena
widget set.  Chapters three through six give the programmer all
information necessary to use the widgets.  The layout of the chapters
follows a specific pattern to allow the programmer to easily find the
desired information.
</para>
<para>
<!-- .LP -->
The first few pages of every chapter give an overview of the widgets
in that section.  Widgets are grouped into chapters by functionality.
<itemizedlist>
  <listitem><para><xref linkend='Simple_Widgets'/></para></listitem>
  <listitem><para><xref linkend='Menus'/></para></listitem>
  <listitem><para><xref linkend='Text_Widgets'/></para></listitem>
  <listitem><para><xref linkend='Composite_and_Constraint_Widgets'/></para></listitem>
</itemizedlist>
</para>
<para>
<!-- .LP -->
Following the introduction will be a description of each widget in that
chapter.  When no functional grouping is obvious the widgets are listed
in alphabetical order, such as in chapters three and six.
</para>
<para>
<!-- .LP -->
The first section of each widget's description is a table that
contains general information about this widget class.  Here is the
table for the Box widget, and an explanation of all the entries.
<literallayout class="monospaced">
<!-- .TA 2.0i -->
<!-- .ta 2.0i -->
<!-- .sp -->
Application Header file	&lt;X11/Xaw/Box.h&gt;
Class Header file	&lt;X11/Xaw/BoxP.h&gt;
Class		boxWidgetClass
Class Name	Box
Superclass	Composite
<!-- .sp -->
</literallayout>
<variablelist>
  <varlistentry>
    <term>
      <function>Application Header File</function>
    </term>
    <listitem>
      <para>
<indexterm significance="preferred"><primary>application header file</primary></indexterm>
This file must be included when an application uses this widget.
It usually contains the class definition, and some resource macros.
This is often called the <quote>public</quote> header file.
<indexterm significance="preferred"><primary>class header file</primary></indexterm>
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <function>Class Header File</function>
    </term>
    <listitem>
      <para>
This file will only be used by widget programmers.  It will need to be
included by any widget that subclasses this widget.  This is often
called the <quote>private</quote> header file.
<indexterm significance="preferred"><primary>class</primary></indexterm>
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <function>Class</function>
    </term>
    <listitem>
      <para>
This is the widget class of this widget.  This global symbol is passed to
<function>XtCreateWidget</function> so that the Intrinsics will know which type of widget
to create.
<indexterm significance="preferred"><primary>class name</primary></indexterm>
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <function>Class Name</function>
    </term>
    <listitem>
      <para>
This is the resource name of this class.  This name can be used in
a resource file to match any widget of this class.
<indexterm><primary>superclass</primary></indexterm>
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <function>Superclass</function>
    </term>
    <listitem>
      <para>
This is the superclass that this widget class is descended from.  If
you understand how the superclass works it will allow you to more quickly
understand what this widget does, since much of its functionality may be
inherited from its superclass.
<!-- .sp -->
    </para>
  </listitem>
  </varlistentry>
</variablelist>
</para>
<para>
<!-- .LP -->
After this table follows a general description of the default behavior of
this widget, as seen by the user.  In many cases this functionality
may be overridden by the application programmer, or by the user.
</para>
<para>
<!-- .LP -->
The next section is a table showing the
name, class, type and default value of each resource that is available
to this widget.  There is also a column containing notes describing
special restrictions placed upon individual resources.
<indexterm significance="preferred"><primary>notes</primary></indexterm>
<indexterm significance="preferred"><primary>A, note</primary></indexterm>
<indexterm significance="preferred"><primary>D, note</primary></indexterm>
<indexterm significance="preferred"><primary>C, note</primary></indexterm>
<indexterm significance="preferred"><primary>R, note</primary></indexterm>
<variablelist>
  <varlistentry>
    <term>
      A
    </term>
    <listitem>
      <para>
This resource may be automatically adjusted when another
resource is changed.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      C
    </term>
    <listitem>
      <para>
This resource is only settable at widget creation time, and may not
be modified with <xref linkend='XtSetValues' xrefstyle='select: title'/>.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      D
    </term>
    <listitem>
      <para>
Do not modify this resource.  While setting this resource will
work, it can cause unexpected behavior.  When this symbol appears
there is another, preferred, interface provided by the X Toolkit.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      R
    </term>
    <listitem>
      <para>
This resource is READ-ONLY, and may not be modified.
    </para>
  </listitem>
  </varlistentry>
</variablelist>
</para>
<para>
<!-- .LP -->
After the resource table is a detailed description of every resource
available to that widget.  Many of these are redundant, but printing
them with each widget saves page flipping.  The names of the resources
that are inherited are printed in plain text, while the names of the
resources that are new to this class are printed in <function>bold</function>.
If you have already read the description of the superclass you need
only pay attention to the resources printed in bold.
</para>
<para>
<!-- .LP -->
For each composite widget there is a section on layout semantics that
follows the resource description.  This section will describe the
effect of constraint resources on the layout of the children, as well
as a general description of where it prefers to place its children.
</para>
<para>
<!-- .LP -->
Descriptions of default translations and action routines come next, for
widgets to which they apply.  The last item in each widget's
documentation is the description of all convenience routines provided by
the widget.
</para>
</sect1>
<sect1 id="Input_Focus">
<title>Input Focus</title>
<!-- .XS -->
<!-- 	Input Focus -->
<!-- .XE -->
<indexterm significance="preferred"><primary>input focus</primary></indexterm>
<indexterm significance="preferred"><primary>input</primary></indexterm>
<indexterm significance="preferred"><primary>XtNinput</primary></indexterm>
<para>
<!-- .LP -->
The Intrinsics define a resource on all Shell widgets that interact with
the window manager called <function>input</function>.  This resource requests the
assistance of window manager in acquiring the input focus.  The
resource defaults to <function>False</function> in the Intrinsics, but is redefined to
default to <function>True</function> when an application is using the Athena widget
set.  An application programmer may override this default and set the
resource back to <function>False</function> if the application does not need the window
manager to give it the input focus.  See the
<olink targetdoc='intrinsics' targetptr='Shell_Widgets'
><citetitle>X Toolkit Intrinsics - C Language Interface</citetitle></olink> for details
on the <emphasis remap='I'>input</emphasis> resource.

</para>
</sect1>
</chapter>