Xkb events are selected using an event mask, much the same as normal core X events are selected. However, unlike selecting core X events, where you must specify the selection status (on or off) for all possible event types whenever you wish to change the selection criteria for any one event, Xkb allows you to restrict the specification to only the event types you wish to change. This means that you do not need to remember the event selection values for all possible types each time you want to change one of them.
Many Xkb event types are generated under several different
circumstances. When selecting to receive an Xkb event, you may specify
either that you want it delivered under all circumstances, or that you
want it delivered only for a subset of the possible circumstances.
You can also deselect an event type that was previously selected for, using the same granularity.
Xkb provides two functions to select and deselect delivery of Xkb events. XkbSelectEvents allows you to select or deselect delivery of more than one Xkb event type at once. Events selected using XkbSelectEvents are delivered to your program under all circumstances that generate the events. To restrict delivery of an event to a subset of the conditions under which it occurs, use XkbSelectEventDetails. XkbSelectEventDetails only allows you to change the selection conditions for a single event at a time, but it provides a means of fine-tuning the conditions under which the event is delivered.
To select or deselect for a specific Xkb event and optionally place conditions on when events of that type are reported to your client, use XkbSelectEventDetails. This allows you to exercise a finer granularity of control over delivery of Xkb events with XkbSelectEvents.
While XkbSelectEvents allows multiple events to be
selected, XkbSelectEventDetails changes the selection criteria for a
single type of Xkb event. The interpretation of the bits_to_change and
values_for_bits masks depends on the event type in question.
XkbSelectEventDetails changes the Xkb event selection mask for the keyboard specified by device_spec and the Xkb event specified by event_type. To turn on event selection for an event detail, set the bit for the detail in the bits_to_change parameter and set the corresponding bit in the values_for_bits parameter. To turn off event detail selection for a detail, set the bit for the detail in the bits_to_change parameter and do not set the corresponding bit in the values_for_bits parameter.
If an invalid event type is specified, a BadValue protocol error results. If a bit is not set in the bits_to_change parameter, but the corresponding bit is set in the values_for_bits parameter, a BadMatch protocol error results. If an undefined bit is set in either the bits_to_change or the values_for_bits parameter, a BadValue protocol error results.
For each type of Xkb event, the legal event details that you can specify in the XkbSelectEventDetails request are listed in the chapters that describe each event in detail.
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