Volume 6A: Motif Programming Manual

This resource setting causes each Label widget to have a foreground color of red, regardless of the name of the widget

(and provided that the resource value is not hard−coded for the widget). See Volume Four, X Toolkit Intrinsics

Programming Manual, for a discussion of appropriate widget names and further details on resource specification

syntax.

3.3.6 Event Handling for Widgets

Once we have created and configured the widgets for an application, they must be hooked up to application functions

via callback resources. Before we can talk about callback resources and callback functions, we need to discuss events

and event handling. In one sense, the essence of X programming is the handling of asynchronous events. Events can

occur in any order, in any window, as the user moves the pointer, switches between the mouse and the keyboard,

moves and resizes windows, and invokes functions available through user interface components. X handles events by

dispatching them to the appropriate application and to the separate windows that make up each application.

Xlib provides many low−level functions for handling events. In special cases, which are described later in this book,

you may need to dip down to this level to handle events. However, Xt simplifies event handling by having widgets

handle many events for you, without any application interaction. For example, widgets know how to redraw

themselves, so they respond automatically to WExpose events, which are generated when one window is covered up

by another ...