Athena Widget Set — C Language Interface

X Window System

X Version 11, Release 6.4

Chris D. Peterson
formerly MIT X Consortium

X Window System is a trademark of X Consortium, Inc.

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Copyright © 1985, 1986, 1987, 1988, 1989, 1991 Digital Equipment Corporation, Maynard, Massachusetts.

Permission to use, copy, modify and distribute this documentation for any purpose and without fee is hereby granted, provided that the above copyright notice appears in all copies and that both that copyright notice and this permission notice appear in supporting documentation, and that the name of Digital not be used in in advertising or publicity pertaining to distribution of the software without specific, written prior permission. Digital makes no representations about the suitability of the software described herein for any purpose. It is provided ‘‘as is’’ without express or implied warranty.

Acknowledgments

Many thanks go to Ralph Swick (Project Athena / Digital) who has contributed much time and effort to this widget set. Previous versions of the widget set are largely due to his time and effort. Many of the improvements that I have been able to make are because he provided a solid foundation to build upon. While much of the effort has been Ralph’s, many other people have contributed to the code.

While not much remains of the X10 toolkit, many of the ideas for this widget set come from that original version. The design and implementation of the X10 toolkit were done by:

I have used the formatting ideas, and some of the words from previous versions of this document. The X11R3 Athena widget document was written by:

Putting this manual together was a major task in and of itself. I would like to thank Ralph Swick, Donna Converse, and Jim Fulton for taking the time to help convert my technical knowledge into legible text. A special thanks to Jean Diaz (O’Reilly and Associates) for spending nearly a month with me working out all the annoying little details.

Chris D. Peterson
MIT X Consortium 1989

The R5 edition of this document has been edited by the research staff of the MIT X Consortium, with significant contributions by Jim Fulton (NCD).

Donna Converse
MIT X Consortium 1991

The R6 edition of this document has been edited to reflect changes brought about by research staff of the Omron Corporation, with special recognition to Li Yuhong, Seiji Kuwari, and Hiroshi Kuribayashi for the X11R5/contrib/lib/Xaw internationalization that inspired this version.

Frank Sheeran
Omron Corporation 1994

Chapter 1

Athena Widgets and The Intrinsics

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.

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 X Toolkit Intrinsics — C Language Interface.

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.

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

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.

1.1. Introduction to the X Toolkit

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.

The X Toolkit consists of:

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 X Toolkit Intrinsics — C Language Interface). 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.

The remainder of this chapter discusses the X Toolkit and Athena widget set:

1.2. Terminology

In addition to the terms already defined for X programming (see Xlib — C Language X Interface), the following terms are specific to the Intrinsics and Athena widget set and used throughout this document.

Application programmer

Child

Class

Client

FullName

Instance

Method

Name

Object

Parent

Resource

Superclass

User

Widget

Widget class

Widget programmer

1.3. Underlying Model

The underlying architectural model is based on the following premises:

1.4. Conventions Used in this Manual

1.5. Format of the Widget Reference Chapters

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.

The first few pages of every chapter give an overview of the widgets in that section. Widgets are grouped into chapters by functionality.

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.

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.

Application Header file<X11/Xaw/Box.h>

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.

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.

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 bold. If you have already read the description of the superclass you need only pay attention to the resources printed in bold.

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.

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.

1.6. Input FocusThe Intrinsics define a resource on all Shell widgets thatinteract with the window manager called input. Thisresource requests the assistance of window manager inacquiring the input focus. The resource defaults to Falsein the Intrinsics, but is redefined to default to True whenan application is using the Athena widget set. Anapplication programmer may override this default and set theresource back to False if the application does not need thewindow manager to give it the input focus. See the XToolkit Intrinsics — C Language Interface for details on theinput resource.

Chapter 2

Using Widgets

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).

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.

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 X Toolkit Intrinsics — C Language Interface.

2.1. Setting the Locale

If it is desirable that the application take advantage of internationalization (i18n), you must establish locale with XtSetLanguageProc before XtDisplayInitialize or XtAppInitialize is called. For full details, please refer to the document X Toolkit Intrinsics — C Language Interface, section 2.2. However, the following simplest-case call is sufficient in many or most applications.

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.

2.2. Initializing the Toolkit

You must call a toolkit initialization function before invoking any other toolkit routines (besides locale setting, above). XtAppInitialize 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.
Widget XtAppInitialize(app_context_return, application_class, options, num_options,

application_class

fallback_resources

This function will remove the command line arguments that the toolkit reads from argc_in_out, and argv_in_out. 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.

2.3. Creating a Widget

Creating a widget is a three-step process. First, the widget instance is allocated, and various instance-specific attributes are set by using XtCreateWidget. Second, the widget’s parent is informed of the new child by using XtManageChild. Finally, X windows are created for the parent and all its children by using XtRealizeWidget and specifying the top-most widget. The first two steps can be combined by using XtCreateManagedWidget. In addition, XtRealizeWidget is automatically called when the child becomes managed if the parent is already realized.

To allocate, initialize, and manage a widget, use XtCreateManagedWidget.
Widget XtCreateManagedWidget(name, widget_class, parent, args, num_args)
String name;
WidgetClass widget_class;
Widget parent;
ArgList args;
Cardinal num_args;

widget_class

When a widget instance is successfully created, the widget identifier is returned to the application. If an error is encountered, the XtError routine is invoked to inform the user of the error.

For further information, see X Toolkit Intrinsics — C Language Interface.

2.4. Common ResourcesAlthough a widget can have unique arguments that itunderstands, all widgets have common arguments that providesome regularity of operation. The common arguments allowarbitrary widgets to be managed by higher-level componentswithout regard for the individual widget type. Widgets willignore any argument that they do not understand.The following resources are retrieved from the argument listor from the resource database by all of the Athena widgets:The following additional resources are retrieved from theargument list or from the resource database by many of theAthena widgets:2.5. Resource ConversionsMost resources in the Athena widget set have a converterregistered that will translate the string in a resource fileto the correct internal representation. While some areobvious (string to integer, for example), others needspecific mention of the allowable values. Three generalconverters are described here:• Cursor• Pixel• BitmapMany widgets have defined special converters that apply onlyto that widget. When these occur, the documentation sectionfor that widget will describe the converter.2.5.1. Cursor Conversion

The value for the cursorName resource is specified in the resource database as a string, and is of the following forms:

2.5.2. Pixel Conversion

The string-to-pixel converter takes any name that is acceptable to XParseColor (see Xlib — C Language X Interface). In addition this routine understands the special toolkit symbols ‘XtDefaultForeground’ and ‘XtDefaultBackground’, described in X Toolkit Intrinsics — C Language Interface. In short the acceptable pixel names are:

2.5.3. Bitmap Conversion

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 bitmapFilePath resource--class BitmapFilePath. 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 bitmapFilePath resource is global to the application, and may not be specified differently for each widget that wishes to convert a cursor to bitmap. In addition to the directories specified in the bitmapFilePath resource a default directory is searched. When using POSIX the default directory is /usr/include/X11/bitmaps.

2.6. Realizing a Widget

The XtRealizeWidget function performs two tasks:

void XtRealizeWidget(w)
Widget w;

For further information about this function, see the X Toolkit Intrinsics — C Language Interface.

2.7. Processing Events

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 XtAppMainLoop.
void XtAppMainLoop(app_context)
XtAppContext app_context;

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 X Toolkit Intrinsics — C Language Interface.

2.8. Standard Widget Manipulation FunctionsAfter a widget has been created, a client can interact withthat widget by calling one of the standard widgetmanipulation routines provided by the Intrinsics, or awidget class-specific manipulation routine.The Intrinsics provide generic routines to give theapplication programmer access to a set of standard widgetfunctions. The common widget routines let an application orcomposite widget perform the following operations on widgetswithout requiring explicit knowledge of the widget type.• Control the mapping of widget windows• Destroy a widget instance• Obtain an argument value• Set an argument value2.8.1. Mapping Widgets

By default, widget windows are mapped (made viewable) automatically by XtRealizeWidget. This behavior can be disabled by using XtSetMappedWhenManaged, making the client responsible for calling XtMapWidget to make the widget viewable.
void XtSetMappedWhenManaged(w, map_when_managed)
Widget w;
Boolean map_when_managed;

map_when_managed

The definition for XtMapWidget is:
void XtMapWidget(w)
Widget w;

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 XtCreateWidget) and then use XtManageChildren 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 ‘‘screen flash’’.
void XtManageChildren(children, num_children)
WidgetList children;
Cardinal num_children;

num_children

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.

For further information about these functions, see the X Toolkit Intrinsics — C Language Interface.

2.8.2. Destroying Widgets

To destroy a widget instance of any type, use XtDestroyWidget.
void XtDestroyWidget(w)
Widget w;

XtDestroyWidget destroys the widget and recursively destroys any children that it may have, including the windows created by its children. After calling XtDestroyWidget, no further references should be made to the widget or any children that the destroyed widget may have had.

2.8.3. Retrieving Widget Resource Values

To retrieve the current value of a resource attribute associated with a widget instance, use XtGetValues.
void XtGetValues(w, args, num_args)
Widget w;
ArgList args;
Cardinal num_args;

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 ArgList contains a pointer to this storage (e.g. x and y must be allocated as Position). For further information, see the X Toolkit Intrinsics — C Language Interface.

2.8.4. Modifying Widget Resource Values

To modify the current value of a resource attribute associated with a widget instance, use XtSetValues.
void XtSetValues(w, args, num_args)
Widget w;
ArgList args;
Cardinal num_args;

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 XtSetValues request is ignored.

For further information about these functions, see the X Toolkit Intrinsics — C Language Interface.

Note

The argument list entry for XtGetValues specifies the address to which the caller wants the value copied. The argument list entry for XtSetValues, 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.

2.9. Using the Client Callback Interface

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:
void CallbackProc(w, client_data, call_data)
Widget w;
XtPointer client_data;
XtPointer call_data;

client_data

Callbacks can be registered either by creating an argument containing the callback list described below or by using the special convenience routines XtAddCallback and XtAddCallbacks. When the widget is created, a pointer to a list of callback procedure and data pairs can be passed in the argument list to XtCreateWidget. The list is of type XtCallbackList:

typedef struct {

The callback list must be allocated and initialized before calling XtCreateWidget. 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.

The second method for registering callbacks is to use XtAddCallback after the widget has been created.
void XtAddCallback(w, callback_name, callback, client_data)
Widget w;
String callback_name;
XtCallbackProc callback;
XtPointer client_data;

callback_name

client_data

XtAddCallback adds the specified callback to the list for the named widget.

All widgets provide a callback list named destroyCallback 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 call_data argument is unused for destroy callbacks.

2.10. Programming Considerations

This section provides some guidelines on how to set up an application program that uses the X Toolkit.

2.10.1. Writing Applications

When writing an application that uses the X Toolkit, you should make sure that your application performs the following:

2.10.2. Changing Resource Values

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.

2.10.2.1. Specifying Resources

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.

Defaults

The resource specification has two colon-separated parts, a name, and a value. The value is a string whose format is dependent on the resource specified by name. Name is constructed by appending a resource name to a full widget name.

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:

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:

The root of all application widget trees is the widget returned by XtAppInitialize. 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 (argv[0]) or the name of the application specified using the standard -name command line option supported by the Intrinsics.

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.

xman.form.button1.label:Testing

An exclamation point (!) in the first column of a line indicates that the rest of the line should be treated as a comment.

Final Words

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:

For a complete explanation of the rules of precedence, and other specific topics see X Toolkit Intrinsics — C Language Interface and Xlib — C Language X Interface.

2.10.2.2. Creating Argument Lists

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 XtNresource name. For example, the symbol for ‘‘foreground’’ is XtNforeground. For further information, see the X Toolkit Intrinsics — C Language Interface.

Argument are specified by using the following structure:

typedef struct {

The first approach is to statically initialize the argument list. For example:

static Arg arglist[] = {

This approach is convenient for lists that do not need to be computed at runtime and makes adding or deleting new elements easy. The XtNumber macro is used to compute the number of elements in the argument list, preventing simple programming errors:

The second approach is to use the XtSetArg macro. For example:

Arg arglist[10];
XtSetArg(arglist[1], XtNwidth, 400);
XtSetArg(arglist[2], XtNheight, 300);

To make it easier to insert and delete entries, you also can use a variable index:

Arg arglist[10];
Cardinal i=0;
XtSetArg(arglist[i], XtNwidth, 400); i++;
XtSetArg(arglist[i], XtNheight, 300); i++;

The i variable can then be used as the argument list count in the widget create function. In this example, XtNumber would return 10, not 2, and therefore is not useful.

Note

You should not use auto-increment or auto-decrement within the first argument to XtSetArg. As it is currently implemented, XtSetArg is a macro that dereferences the first argument twice.

The third approach is to individually set the elements of the argument list array:

Arg arglist[10];
arglist[0].name = XtNwidth;
arglist[0].value = (XtArgVal) 400;
arglist[1].name = XtNheight;
arglist[1].value = (XtArgVal) 300;

Note that in this example, as in the previous example, XtNumber would return 10, not 2, and therefore would not be useful.

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:

static Arg arglist[] = {

In this example, XtNumber can be used, as in the first approach, for easier code maintenance.

2.11. Example ProgramsThe best way to understand how to use any programminglibrary is by trying some simple examples. A collection ofexample programs that introduces each of the widgets in thatAthena widget set, as well as many important toolkitprogramming concepts, is available in the X11R6 release asdistributed by the X Consortium. It can be found in thedistribution directory contrib/examples/mit/Xaw, but seeyour site administrator for the exact location of thesefiles on your system. See the README file from thatdirectory for a guide to the examples.

Chapter 3

Simple Widgets

Each of these widgets performs a specific user interface function. They are simple because they cannot have widget children—they may only be used as leaves of the widget tree. These widgets display information or take user input.

3.1. Command WidgetApplication header file<X11/Xaw/Command.h>Class header file <X11/Xaw/CommandP.h>Class commandWidgetClassClass Name CommandSuperclass LabelThe Command widget is an area, often rectangular, thatcontains text or a graphical image. Command widgets areoften referred to as ‘‘push buttons.’’ When the pointer isover a Command widget, the widget becomes highlighted bydrawing a rectangle around its perimeter. This highlightingindicates that the widget is ready for selection. Whenmouse button 1 is pressed, the Command widget indicates thatit has been selected by reversing its foreground andbackground colors. When the mouse button is released, theCommand widget’s notify action is invoked, calling allfunctions on its callback list. If the pointer is moved offof the widget before the pointer button is released, thewidget reverts to its normal foreground and backgroundcolors, and releasing the pointer button has no effect.This behavior allows the user to cancel an action.3.1.1. Resources

When creating a Command widget instance, the following resources are retrieved from the argument list or from the resource database:

ancestorSensitive

backgroundPixmap