To receive KeymapNotify events, set the KeymapStateMask bit in the event-mask attribute of the window. The X server generates this event immediately after every EnterNotify and FocusIn event.
The structure for this event type contains:
/* generated on EnterWindow and FocusIn when KeymapState selected */
typedef struct {
int type; /* KeymapNotify */
unsigned long serial; /* # of last request processed by server */
Bool send_event; /* true if this came from a SendEvent request */
Display *display; /* Display the event was read from */
Window window;
char key_vector[32];
} XKeymapEvent;
The window member is not used but is present to aid some toolkits. The key_vector member is set to the bit vector of the keyboard. Each bit set to 1 indicates that the corresponding key is currently pressed. The vector is represented as 32 bytes. Byte N (from 0) contains the bits for keys 8N to 8N + 7 with the least-significant bit in the byte representing key 8N.