8.2 Event Processing

This section describes what an event type is and what an event structure contains, reviews how the event queue stores events and how a program reads events from it, and summarizes all the routines that can be used to get events.

8.2.1 The Event Structures

An event is implemented as a packet of information stored in a structure. The simplest event structure is shown in Example 8-1.

Example 8-1. The XAnyEvent structure

typedef struct {
    int type;        /* The type of event */
    unsigned long serial;    /* # of last request processed by server */
    Bool send_event;    /* True if sent from a SendEvent request */
    Display *display;    /* Display the event was read from */
    Window window;    /* Window that receives event */
} XAnyEvent;

There are 30 different event structures. Virtually all of them have the members shown in the XAnyEvent structure. Most of the event structures also contain various additional members that provide useful information for clients. The first member of every event structure, type, indicates the type of event. We will come back to the type in 8.2.2 Event Types and XEvent Union. The serial member identifies the last protocol request processed by the server, for use in debugging. The send_event flag indicates whether this event was sent from the server (False) or from another client (True). Other clients can send events with XSendEvent(), as described in 8.4 Sending Events.

Many of the event structures also have a display member or a root member or both. The display member ...

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