Volume 6A: Motif Programming Manual

there would be no way to insert a tab character.) To traverse the tab groups in reverse, the SHIFT key is used with the

TAB key. Keyboard traversal wraps from the last item to the first item, both within a tab group and between tab

groups.

Although keyboard traversal is not completely controlled by manager widgets, they do play a pivotal role in

implementing it. A manager widget is typically initialized as a tab group; its primitive widget children are members of

the tab group. The Text and List widgets are exceptions to this rule. These widgets are set up as their own tab groups,

so that keyboard traversal can be used to move among the text in a Text widget or the items in a List widget. Within a

tab group, there is no sense of a manager−within−manager structure. The widget hierarchy is flattened out so that it

appears to the user that all of the controls in a window are at the same level.

Keyboard traversal only works if each widget in an interface cooperates. If a PushButton has the keyboard focus and

the user presses the TAB key, the internals of the PushButton widget are responsible for directing the focus to the next

tab group. Manager widgets play a key role in keyboard traversal because they are responsible for the keyboard events

that take place within gadgets. If an event occurs within a PushButton gadget, its manager parent is responsible for

directing the input focus to the next tab group.

Although the whole process of keyboard traversal may seem complex and difficult, it is automated by the Motif

toolkit and does not require application intervention. However, the toolkit does provide mechanisms that allow you to

control keyboard navigation. There are resources that allow you to specify widgets that are tab groups, widgets that

are in tab groups, and widgets that do not participate in keyboard navigation. There are also functions that allow you

to specify explicitly the direction of keyboard traversal. Fortunately, such fine−tuning is rarely necessary.

4.4 Putting Together a Complete Application

Managers and primitive widgets provide the basic tools with which you can build a graphical user interface from the

ground up. Motif also provides several components that address the large−scale organization of an application. The

specialized MainWindow manager widget is intended to be used as the organizing frame for an application. Motif also

provides different types of menus and dialog boxes that can be used to organize application functionality.

Since an application is always used in conjuction with a window manager, we need to discuss the role played by the

window manager. In the course of this discussion, we also need to take a closer look at shell widgets, since they

provide the communication link between an application and the window manager.

Both pixmaps and colors play an important role in a graphical user interface. Motif provides routines that cache

pixmaps so that they can be reused throughout an application. The three−dimensional appearance of Motif

components is implemented using a variety of color resources. It is important to understand these resources so that the

3D shadows are an effective part of the user interface.

4.4.1 The Main Window

Every application is different. A word processor, paint program, or spreadsheet typically has a single main work area,

with controls taking on a peripheral role, perhaps in PulldownMenus. More sophisticated programs, on the other hand,

may have several main work areas. For example, an electronic mail program may have a work area in which the user

reviews and selects from a list of incoming messages, another where she reads and responds to messages, and yet

another where she issues commands to organize, delete, or otherwise affect groups of messages. Still other

applications, such as data−entry programs, don't really have a separate work area. The work area is really just a

collection of controls, such as CheckBoxes and text entry areas, that are filled in by the user.

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It is quite conceivable that an application could provide multiple windows for performing different tasks. For

example, an order entry program might use one window for looking up a customer record, another for checking stock

on hand, and yet another for entering the current order. Motif allows for the creation of multiple top−level application

windows, as well as transient dialog boxes that ask for additional information or confirmation before carrying out a

command.

Nonetheless, every application has at least one main window. The main window is the most visible window in an

application. It is the first window the user sees and also the place where the user interacts with most application

functionality. No matter how small or large an application may be, there needs to be a focal point that ties it all

together. As a program grows more complex, the main window may grow more abstract and perform fewer functions,

but it always exists. In a sophisticated application, the main window is transformed into a hub where the user starts,

finishes, and returns again and again as she goes from one function to the next.

The Motif Style Guide suggests a particular layout for the main window. Applications should use this layout unless

they have a compelling reason not to. The recommended layout is shown in the figure.

Recommended layout for a main window

A main window should have a menu bar across the top, with the work area immediately below it. The work area

usually contains the main interface object of the application. For example, a paint or draw application might provide a

DrawingArea widget as a canvas, an electronic mail application might provide a ScrolledList of message summaries

from which the user can make selections, and a Text editor might place a Text widget in the work area. An application

work area might require a custom widget or a non−widget−based X window instead.

The work area can have both horizontal and vertical scrollbars allowing the user to view its entire contents if they are

too large to be displayed all at once. The main window can also contain an optional command area below the work

area, where the user can enter typed commands. This area is most helpful for porting character−based applications to a

Motif GUI, but it can be useful for other applications as well. At the bottom of the main window is an optional

message area. This area should be used for status and informational messages only, not for error messages or any

other type of message that requires a response from the user.

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