Motif/Lesstif Application Development

A tutorial designed to help you build your own GUI.
Getting and Installing Motif/Lesstif

A Motif development license can be had from Red Hat software (http://www.redhat.com/) or the Open Group (http://www.opengroup.org/desktop/motif/). If you have to pay for the development license, I strongly recommend you use Lesstif and find a commercial workstation with a Motif run-time license already installed. Odds are, you can tweak any errant code without needing to purchase Motif. If you have a spare machine on which to install Solaris for the Intel platform, Sun now makes Solaris available for non-commercial use for the cost of the media (about $10 US); this includes a run-time license for Motif and the headers needed for development. It is fairly easy to do your development on Linux/Lesstif, then make a quick build under Solaris/Motif to check compatibility.

Remember, though, Lesstif is an implementation of Motif version 1.2 with limited support for Motif 2.0, while the commercial implementation of Motif 2.1 has already been released. The good news is the vast majority of systems are still using Motif 1.2.

Lesstif can be downloaded from a number of places, beginning with http://www.hungryprogrammers.org/. Binaries are available for Linux (and some other UNIX flavors) as RPMs or gzipped tar files from the site and its mirrors. Installing Lesstif on my Red Hat-based workstation was as simple as typing:

rpm -i lesstif.rpm

You don't need the development RPM unless you plan on contributing to the Lesstif project.

For most commercial UNIX systems, the developer will not need to do anything extra to start developing using Motif; for example, Sun ships the Motif headers and libraries with Solaris. If you choose a commercial Motif license for Linux, you will need to follow the steps outlined in the package. Getting things rolling on Slackware or some other non-RPM-based system is rather trivial. The libXm files should end up in the /usr/X11R6/lib directory (or /usr/dt/lib on Solaris), and the headers should be placed in their own directory (named /Xm) off the /X11 include directory, e.g., /usr/X11R6/include/Xm or /usr/dt/include/Xm.

X Components

Figure 1. Accessing X with Motif

Access to the X Window System in a Motif application is accomplished primarily through three libraries: the X library (commonly referred to as Xlib) which provides the most primitive interface, the X Toolkit (Xt) upon which Motif is built and Motif (see Figure 1). A book covering Xt, or at least the Motif Programming Manual, would be a good investment if you become serious about GUI development. Many libraries choose to build on Xt rather than X, so it is reasonable to expect X and Xt to be consistent across UNIX flavors and available on any end-user configuration.

The X library functions are typically prefixed with “X”, and the X toolkit widgets and functions are prefixed with “Xt”. Although the toolkit is used fairly heavily within a Motif application, the need to access X library routines is rare. Symbols provided by Motif (functions, constants and variables) are prefixed with “Xm”.

The X server via the window manager is responsible for interacting with the video hardware and dispatching messages and events to the applications. It is important to note applications running under X are implemented using an event-driven paradigm. The programs generally spend their time waiting to receive messages that indicate such events as mouse movement, key presses, or exposed windows—more on this later.

Graphic Primitives

The graphic components used to build an X/Motif application are called widgets. Some simple widgets are a push button, a radio button and a text field; more-involved widgets might be a file selection dialog or an HTML widget. Many graphic components are composites of widgets coupled within a routine or C++ class. You could spend your career developing GUIs without ever learning how to create a custom widget. It is best to avoid writing custom widgets until you are very comfortable with the X/Motif environment; even then, you should have good reasons for not using more conventional techniques. The Motif widget libraries have been implemented in a very object-oriented fashion (especially for something written entirely in C). If this sort of thing interests you, I strongly encourage a study of the widget libraries (refer to the Lesstif source). Many widgets are available that implement functionality not addressed by the Motif library.

A number of generic routines can be used to create and alter instances of widgets (e.g., XtCreateManagedWidget); in addition, widgets typically make some specific routines available (e.g., XmCreateScrolledText). The run-time behavior of a widget is controlled through resources; that is, variables specific to a single instance of the widget which determine aspects of its behavior such as position, color, button labels, etc.

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