Using Xlib With Motif

Overview

Xlib may be viewed as an “assembly language” for X. Physically, Xlib is a library of C functions, many of which translate directly into one or more protocol requests. Like a program written in assembly language, an Xlib program contains many lines of code, each of which has minimal effect. For this reason, most programmers use C instead of assembly and Motif instead of Xlib.

There are, however, times when one needs to use Xlib calls in a Motif program. While Motif provides widgets that directly support higher-order interface objects, such as menus, it does not provide functions for lower-order operations, such as drawing a line. Instead, the program must call Xlib functions to draw within the window of a Motif widget.

This chapter does not present a complete view of Xlib — that would require a book of its own. Instead, it provides a basic understanding of Xlib, including a detailed look at how the server displays images. It then presents the XmDrawingArea widget, a Motif widget that gives the programmer a “canvas” in which to place Xlib drawings. The chapter concludes with an example of XmDrawingArea in use, a “doodle” program.