Widgets can be sensitive or insensitive; insensitive widgets
do not respond to input. (On other platforms, this is
termed "ghosted" or "inactive").
gtk_widget_set_sensitive()
(Figure 25)
changes a widget's sensitivity.
By default sensitivity is set to TRUE. A widget is only "really"
sensitive if all its parents are sensitive; that is,
you can make an entire container full of widgets
(in)sensitive by setting the sensitivity of the
container. The "real" sensitivity of a widget,
including its parent's state, can be tested with the
GTK_WIDGET_IS_SENSITIVE()
macro. The sensitivity of the widget itself, which only
matters if the widget's parent is sensitive, can be
queried using
GTK_WIDGET_SENSITIVE(). These are in Figure 26.
