Enabling and Disabling Input Devices

Opening Extended Input Devices

In order to access input devices through the input extension, clients must request that the server open those devices. To open an extended input device, use XOpenDevice.

XDevice *XOpenDevice(display, device_id)
      Display *display;
      XID      device_id;

The XOpenDevice function makes an input device accessible to a client through input extension protocol requests. If successful, it returns a pointer to an XDevice structure.

XOpenDevice can generate a BadDevice error.

The XDevice structure contains:

typedef struct {
        XID              device_id;
        int              num_classes;
        XInputClassInfo *classes;
} XDevice;

The classes field is a pointer to an array of XInputClassInfo structures. Each element of this array contains an event type base for a class of input supported by this device.

The num_classes field indicates the number of elements in the classes array.

The XInputClassInfo structure contains:

typedef struct {
        unsigned char input_class;
        unsigned char event_type_base;
} XInputClassInfo;

The input_class field identifies one class of input supported by the device. Defined types include KeyClass, ButtonClass, ValuatorClass, ProximityClass, FeedbackClass, FocusClass, and OtherClass. The event_type_base identifies the event type of the first event in that class.

The information contained in the XInputClassInfo structure is used by macros to obtain the event classes that clients use in making XSelectExtensionEvent requests. Currently defined macros include DeviceKeyPress, DeviceKeyRelease, DeviceButtonPress, DeviceButtonRelese, DeviceMotionNotify, DeviceFocusIn, DeviceFocusOut, ProximityIn, ProximityOut, DeviceStateNotify, DeviceMappingNotify, ChangeDeviceNotify, DevicePointerMotionHint, DeviceButton1Motion, DeviceButton2Motion, DeviceButton3Motion, DeviceButton4Motion, DeviceButton5Motion, DeviceButtonMotion, DeviceOwnerGrabButton, DeviceButtonPressGrab, and NoExtensionEvent.

To obtain the proper event class for a particular device, one of the above macros is invoked using the XDevice structure for that device. For example,

DeviceKeyPress (*device, type, eventclass);

returns the DeviceKeyPress event type and the eventclass for DeviceKeyPress events from the specified device. This eventclass can then be used in an XSelectExtensionEvent request to ask the server to send DeviceKeyPress events from this device. When one of these events is received via XNextEvent, the type can be used for comparison with the type of the event.

Closing Input Devices

Before terminating, clients that have opened input devices through the input extension should close them. To close an extension input device, use XCloseDevice.

XCloseDevice(display, device)
      Display *display;
      XDevice *device;

The XCloseDevice function makes an input device inaccessible to a client through input extension protocol requests. Any active grabs that the client has on the device are released. Any event selections that the client has are deleted, as well as any passive grabs. If the requesting client is the last client accessing the device, the server will disable all access by X to the device.

XCloseDevice can generate a BadDevice error.