This book introduces the fundamentals of Motif programming and addreses wider issues concerning the X Window system. The aim of this book is to provide a practical introduction to writing Motif programs. The key principles of Motif programming are always supported by example programs.
The X Window system is very large and this book does not attempt to detail every aspect of either X or Motif. This book is not intended to be a complete reference on the subject.
The book is organised into logical parts, it begins by introducing the X Window system and Motif and goes on to study individual components in detail in specific Chapters. In the remainder of this Chapter we concentrate on why Motif and related areas are important and give a brief history of the development of Motif.
There are many reasons and advantages to programming in X/Motif. A few of these are listed below:
The X Window system, or simply X, is very large. It has been through many different versions since its conception although things are now becoming fairly standardised and established.
This book does not attempt to cover all of the X system. We will only look at important parts of the system. Indeed we only study important parts of Motif which is itself a component (albeit a large and significant one) of X. We will where necessary introduce components of X that are not part of Motif. These other components will always be treated as if they are to be used with Motif.
Other important concepts relating to more general Graphical User Interface (GUI) design and programming will be studied. In most cases this is directly in relation to the Motif programming model. However, Motif was designed to adhere to standard GUI design approaches and has guidelines defined in the Motif Style Guide (Chapter 20,[Ope93]).
X provides functionality via a vast set of subroutine libraries. These may be called from a variety of high level languages.
They are most readily called from C programs as this is the language in which most of X is actually implemented in. We will only give C program examples in the main body of text. Appendix A gives details how to convert these examples into C++ and, more generally, write X/Motif applications in this language. Full program listings of both C and C++ are available from the online support and reference material [Mar96].
Readers should not be too worried about programming in C. We will not need to get heavily involved in C. Basically we will just be calling X/Motif functions and setting variables and data structures from our C programs. The ANSI C programming conventions are assumed in all examples.
In order to distinguish between program code and other text in this book the following fonts are used:
We have already used the notation of X/Motif. For convenience throughout this book, a reference to X is taken to mean the X Window System. We refer to Motif whilst strictly speaking the full title is OSF/Motif where OSF stands for the Open Software Foundation the original developers of Motif.
Before we study Motif in detail it is worth considering why we need GUIs and how they can be effectively designed and used.
GUIs provide an easy means of data entry and modification. They should provide an attractive and easy to use interface between human and machine. So easy in fact that a non-computer literate person could use the system.
GUI's provide a better means of communication than cumbersome text-based interfaces. Typically, GUIs provide such facilities by means of:
Although GUIs provide some very powerful advantages, there are a couple drawbacks to the GUI approach:
The subject of Graphical User Interface design is large. Indeed it is a major topic in Computer Science in its own right. Consequently, we could devote the rest of the book to this topic. However many standard GUI design rules are prescribed by Motif. Many of these rules are prescribed automatically, whilst others are strongly suggested in the Motif Style Guide (Chapter 20,[Ope93]). In general it is the low level appearance and operation of specific objects (Buttons, Menus etc.) that are automatically facilitated by Motif. The higher level organisation of these objects is left to the control of the application developer. Some perhaps are fairly obvious, though not always strictly adhered to, rules of thumb for GUI design include:
The Motif Style Guide (Chapter 20,[Ope93]) is a valuable source of information in relation to GUI design. Also the online reference material ([Mar96]) addresses further details on GUI design.
This Section briefy surveys the important stages in the development of GUIs leading the X/Motif approach to GUI design and programming. Once X began to establish itself as one of the prime systems for window programming some issues still remained unresolved until recently, these are also briefly addressed.
Computers first became commercially available in the 1950s. However, they were very large and expensive. They were also hard to program with very little thought was given to human computer interaction. By the 1960s very basic inroads into ease of computer use were being made with the development of more reliable operating systems. This was made possible as computers became smaller in size and more powerful in terms of processing ability. The first seeds of user interaction appeared in the form of early text editors during this period.
The start of the development of GUIs can be traced back to the early 1970's to Alan Kay's research group at Xerox's Palo Alto Research Centre. Two important projects were undertaken there:
The first commercial exploitation of the Xerox work was realised in the early 1980s by Apple, firstly with Lisa and then the Macintosh series of computers. The Apple GUI proved very successful and popular and by the late 1980s many operating systems had adopted the GUI approach. UNIX vendors such as Sun (with SunView) and Dec (with DEC Windows) and Microsoft with Windows for the PC are examples.
There was one problem with the above developments. Every manufacturer had its own proprietary windowing system. These were all entirely different and different systems could not easily communicate with each other. It had been common to have networks of the same computers for some time and it was relatively easy to get machines of the same type in a network configuration to talk to each other.
The X Window system arose out of this very real need. The X system was designed to be platform independent and network-based. With X the programmer can write a single application in a single language and run this program on different machines with little or no modification. Moreover, applications can actually run programs on one computer and have the results displayed on another (or several) computer's terminal. The computer can be a similar model or an entirely different one altogether. The possibilities are endless.
Following the creation of the X Window system, two primary high level X interface toolkits came to prominence:
Open Look was designed to support the X Window platform yet still maintain compliance with Sun's older native SunView Window system. Open Look had a slightly different design philosophy to Motif. Indeed for many years Sun claimed that Open Look was superior to Motif. At the time Sun were the substantial market leader vendor of UNIX platforms and therefore had a large influence on such matters. However, recently Sun decided to cease support of Open Look and adopt Motif.
Motif was based on IBM's Common User Access (CUA) guidelines as were both Microsoft Windows and OS/2. Consequently, the visual appearance and mode of operation, the so called look and feel , of Motif is similar to that of Microsoft Windows and OS/2. This was a deliberate strategy since there is sound business sense in profiting from an open system. More importantly, however, the predominance of Microsoft Windows in the PC market means that an interface that appears to the user to behave in a similar fashion to Microsoft Windows would be a logical choice in migrating (PC) applications to UNIX. It is probably a mixture of these factors that has led to Sun's decision to stop the development of Open Look and adopt Motif for Sun Workstations.
Following Sun's decision to support Motif, the Common Open Software Environment (COSE) united the major UNIX producers including Sun, DEC, IBM, Hewlett-Packard and UNIX System Laboratories. This has had a significant impact on the endorsement of Motif since it is now the standard choice for UNIX and general cross-platform GUI development. COSE has also prescribed choices of other X libraries concerned with 3D graphics (PEX) and Image extension (XIE) which are closely coupled to Motif.
Motif has undergone four major revisions since its conception. Motif 1.0 is now quite old and should probably be avoided as there has been significant upgrades to Motif and the underlying X system in later Motif versions. Motif 1.1 was the next major release but this releases does not support some useful later features, such as drag and drop. However, many applications can still run under Motif 1.1. Motif 1.2 has been available since 1993 and is based on Release 5 of the Xlib and Xt specifications (X11R5). This version of Motif should be in common circulation now.
The latest version of Motif is version 2.0 and it was released in late 1994 as was the latest release of X11 (X11R6). Motif 2.0 provides some significant enhancements and many bug fixes. However, Motif 2.0 is not yet being shipped by the major UNIX vendors. The main reason is that most UNIX vendors made a decision to support a new Common Desktop Envirnoment (see Section 1.5.2 below) system, CDE 1.0, which uses Motif 1.2 and is not binary compatible with Motif 2.0. It is likely that these companies will not now deliver Motif 2.0 but wait to support the convergence of both products with the newer releases of Motif (2.1) and CDE (1.1). It is expected that both these will become available sometime in 1997.
Even though there have been four major revisions to Motif there have been several minor revisions to Motif. These were mainly fix bugs (sometimes a few hundred at a time !!). However different vendors do not always keep to consistent minor version release numbers.
The subset of Motif addressed in this book has remained more or less untouched by the developments in Motif 2.0. Where there are differences these are highlighted in the text. The major differences that concern us here are the support of additional widgets (Chapter 6 and C++ binding (Appendix A). Chapter 21 discusses the key features of Motif 2.0. The new features of Motif 2.0 are generally concerned with advanced uses of Motif, and are not within the defined scope of this text. All examples in this book have been tested extensively on Motif 1.2 and X11R5. There should be no problem in running these examples under Motif 2.0 or X11R6.
In using and writing Motif programs you will inevitably be exposed to key parts of your computer. You will have to write Motif programs in a particlar computer language -- usually C or C++. In writing and running Motif applications you will need to interact with the host operating system. You may also need to suitably equip your operating to run or display Motif applications. In conjuction with the operating system, there will be a windowing environment that controls how windows are displayed and managed in general. This section introduces these issues and explains how you configure your system to run Motif applications.
X Window is designed to be platform independent. Provided that machines which are connected to a network and are suitably equipped with software to run X Window, running applications across any kind of network is possible.
For Unix systems X/Motif is now the only practical window system available. Unix machines will usually be already configured to run some version of X. For users of PCs and Macintosh computers, the standard window environment is Microsoft Windows or the Macintosh Window Interface respectively. For users of these machines there are two options to set up X Window:
Linux is available for both PC and Macintosh (Power PC Macs only). Linux basically converts the host machine into a Unix environment. X/Motif libraries are available for Linux at a small additional cost. For further details on Linux consult the following URLs:
There are a few other commercial packages available that run Unix/X Window environments on a PC and Macintosh.
Packages for the PC that allow this include SunSoft Inc.'s SolarNet PC-X 1.1, Hummingbird Communications Ltd. eXceed 5 for Windows, Network Computing Devices Inc.'s PC-Xware 3.0 and Walker Richer and Quinn Inc.'s Reflection Suite for Windows 5.0.
Package available to allow a Macintosh to become an X Server include Apple's MacX, Intercon's Planet X, Netmanage/AGE's XoftWare, Tenon XTen and White Pine's eXodus.
A free X server for PCs and Macintosh exists called MI/X.
The WWW site URL:http://www.rahul.net/kenton/xsites.html contains links to almost all the above systems.
Note that minimum configurations of many computers in terms of processor speed and/or memory are unlikely to be adequate to support X Window.
Built on top of the operating system is the windowing environment. This environment controls how windows are displayed and how events invoked by mouse selection, keystrokes etc. are processed. The general term for the housekeeping of windows is window management and further details on this will be discussed in Section 3.2. X window toolkits, such as Motif and Open Look, generally provide two key components: the window manager and the toolkit libraries.
The window manager basically defines the look and feel of a particular toolkit. However, with ever increasing windowing needs, the basic window manager and related system and common application needs have grown into a desktop environment providing a whole suite of tools including a window manager . The unification of the Unix and X Window providers with COSE has led to the vendors developing a unified desktop for Unix systems -- the Common Desktop Environment (CDE) [Add94g, Add94a, Add94e, Add94f, Add94c, Add94d, Add94b]. The CDE is built on top of Motif.
The CDE was designed to provide end users with a consistent graphical user interface across workstations and PCs, and software developers with a single set of programming interfaces for platforms that support the X Window System and Motif.
The CDE core components include:
Section 3.3 addresses the CDE from a user's perspective.
This books assumes a knowledge of ANSI/ISO C. All program examples are written in C. C++ is also a popular language for writing X Window programs. C++ actually supports ANSI/ISO C, so some minor modifications are all that is required to convert the C examples provided in this text to C++ (Appendix A). Both C and C++ example programs are available in the online reference material ([Mar96]). Motif 2.0 (Chapter 21) actually provides C++ support built in.
In order to be most productive in writing Motif it is advisable that you should have at your disposal standard C program developments tools (such as good compilers, editors, debugging tools etc). Section 5.5 discusses compilation issues further.
Throughout the development of X/Motif some key companies and consortia have been repsonsible for key aspects of the system. We briefly summarise these contibutions in this Section. Another key aspect to the development of Motif is the prescribed uniformity of Motif applications. The Motif Style Guide is the main reference to Motif application development.
The Open Software Foundation consortium provides many services and is not solely concerned with X Window related matters. The OSF licenses Motif, offers training courses, testing and certification of software intended for commercial use.
The X Consortium distributes the X System and manuals at a minimal cost (basically the cost of distribution media and shipping). Motif is built on top of the X System.
The Open Group was formed in February, 1996 by the consolidation of the two leading open systems consortia, X/Open Company Ltd. and the Open Software Foundation (OSF). Under the Open Group umbrella, OSF and X/Open work together to deliver technology innovations and wide-scale adoption of open systems specifications. From the beginning of 1997 the Open Group will have responsibility for the X Window System transferred from the X Consortium.
For further information, the OSF, X Consortium and the Open Group can be contacted at the following addresses:
Open Software Foundation, 11 Cambridge Center Cambridge MA 02142. Tel
(USA): 617/621-8700. Email: info@osf.org WWW:
X Consortium Inc., One Memorial Drive PO BOX 546 Cambridge MA 02142-0004. Tel
(USA):617/374-1000. WWW:
Open Group, 11 Cambridge Center, Cambridge, MA 02142:
Tel
(USA): 617/621-7300. Email: info@opengroup.org WWW:
http://www.osf.org/
http://www.x.org/
http://www.opengroup.org/
The Common Open Software Environment (COSE) was formed when the major UNIX producers, including Sun, DEC, IBM, Hewlett-Packard and UNIX system Laboratories, decided to unite and attempt to standardise UNIX implementations worldwide in 1993. The remit of COSE is to define standard cross-platform UNIX systems incorporating application program interfaces, windows interfacing, desktop environments, graphics, multimedia, system management, support for distributed computing and large scale data management. The standardisation of a Common Desktop Environment (CDE) for UNIX resulted in the adoption of Motif for this purpose.
As such, the OSF, Open Group, and COSE can be regraded as the elders of Motif and future releases of Motif will be determined by them.
In late 1995, The OSF announced the formal signing of the Joint Development agreement for the further enhancement and evolution of the Common Desktop Environment and OSF/Motif under the OSF Prestructured Technology (PST) development process.
The Motif Style Guide[Ope93] can be regarded as the Bible for Motif Application developers. Along with a Motif Reference Manual [Mar96, Hel94b] and a programming text book (hopefully this text), the Motif Style Guide provides an invaluable source of information.
The Motif Style Guide provides a set of guidelines that provides a framework for the behaviour of Motif application developers, GUI developers, widget developers and window managers. The basic idea is that all Motif applications that adhere to the prescribed style will maintain a high level of consistency. Also, since Motif follows CUA guidelines, Motif applications will be similar to Microsoft Windows applications in terms of appearance and user operation. For developers of commercial applications, the adoption of Motif style is critical.
Many standard GUI issues are integrated into a Motif Widget default behaviour. Therefore, these defaults should only be modified with great care and consideration for such implications. Other aspects of style are left to the developer. The Motif Style Guide only suggests certain standard operations.
As has been mentioned, the Motif Style Guide has a greater scope than just the Motif application developer (the intended audience of this text). Chapter 20 summarises many important issues relating to the application developer. Where appropriate, specific style considerations are mentioned elsewhere in this text.