2. The BulletinBoard Class

geo_matrix_createXmGeoCreateProcThere is one and only one clue in a BulletinBoard subclass that indicates that this class wants to use the GeoUtils - the geo_matrix_create method in the BulletinBoard class part (see BulletinBP.h). If this member is not NULL, the GeoUtils are activated for this subclass. The prototype for this method looks like:

typedef XmGeoMatrix (*XmGeoCreateProc)(Widget composite,
                                       Widget instigator,
                                       XtWidgetGeometry *desired);

The composite widget is (obviously) the BulletinBoard subclass. The instigator is used in the geometry_manager and query_geometry methods, as is the desired geometry (more on the use of those later).