This is an event signal, initially emitted when the connected widget becomes fully visible on screen. Every widget can capture expose events; they are even synthesized for widgets that don't have a GdkWindow.

Expose events are also generated when a widget has been partially or fully covered by another widget, and is re-exposed. These events trigger a redraw internally; a GdkWindow that is not currently exposed is not currently drawn, and the same applies to any unexposed area of a window.

Following suit, the most likely reason to connect to an "expose-event" signal is that you have a drawing function in the callback.

See also: "event", GtkDrawingArea, GdkWindow, and the numerous GTK and GDK drawing functions filed under 'Misc'.

Callback function