Client Events

Client events are an arbitrary chunk of data sent from one application to another. However, there are some conventional "messages" that can be sent, mostly defined in the Inter-Client Communication Conventions Manual (ICCCM). The ICCCM is free with the X Window System distribution from the Open Group. Client events are mostly used for communication between applications and the window manager. (The Xlib event being wrapped is called ClientMessage, so look for ClientMessage in the ICCCM.) An important ClientMessage event is sent from the window manager to applications, asking for windows to be deleted. However, GDK converts these events to a GdkEventAny with type GDK_DELETE, so a GdkEventClient will not be received. Some events involved in drag-and-drop are also ClientMessage events, but GDK translates these to GdkEventDND, so a GdkEventClient will not be received for them either. GdkEventClient will only be received if some other client sends your application an unconventional message GDK and GTK+ are not prepared to understand. Most of the common messages are nicely wrapped in a high-level interface.

Just for reference, here is the event:

typedef struct _GdkEventClient GdkEventClient;

struct _GdkEventClient
{
  GdkEventType type;
  GdkWindow *window;
  gint8 send_event;
  GdkAtom message_type;
  gushort data_format;
  union {
    char b[20];
    short s[10];
    long l[5];
  } data;
};

The union at the end is used to hold the contents of the message. send_event is always TRUE, since this event is always sent from one client to another and does not come from the X server.