Some server implementations may make all input devices available at the time the server is initialized. Others may wait until requested by a client to access an input device. In the latter case, it is possible that an input device will be listed as available at one time but not at another.
For each input device available to the server, the XListInputDevices request returns an XDeviceInfo structure. That structure contains a pointer to a list of structures, each of which contains information about one class of input supported by the device.
The XDeviceInfo structure is defined as follows:
typedef struct _XDeviceInfo
{
XID id;
Atom type;
char *name;
int num_classes;
int use;
XAnyClassPtr inputclassinfo;
} XDeviceInfo;
The id is a number in the range 0-128 that uniquely identifies the device. It is assigned to the device when it is initialized by the server.
The type field is of type Atom and indicates the nature of the device.
The name field contains a pointer to a null-terminated string that corresponds to one of the defined device types. The name will correspond to one of the following strings (defined in the header file XI.h:
XI_MOUSE XI_TABLET XI_KEYBOARD XI_TOUCHSCREEN XI_TOUCHPAD XI_BUTTONBOX XI_BARCODE XI_TRACKBALL XI_QUADRATURE XI_ID_MODULE XI_ONE_KNOB XI_NINE_KNOB XI_KNOB_BOX XI_SPACEBALL XI_DATAGLOVE XI_EYETRACKER XI_CURSORKEYS XI_FOOTMOUSE
These names may be directly compared with the name field of the XDeviceInfo structure, or used in an XInternAtom request to return an atom that can be compared with the type field of the XDeviceInfo structure.
The num_classes field is a number in the range 0-255 that specifies the number of input classes supported by the device for which information is returned by ListInputDevices. Some input classes, such as class Focus and class Proximity do not have any information to be returned by ListInputDevices.
The use field specifies how the device is currently being used. If the value is IsXKeyboard, the device is currently being used as the X keyboard. If the value is IsXPointer, the device is currently being used as the X pointer. If the value is IsXExtensionDevice, the device is available for use as an extension device.
The inputclassinfo field contains a pointer to the first input-class specific data. The first two fields are common to all classes.
The class field is a number in the range 0-255. It uniquely identifies the class of input for which information is returned. Currently defined classes are KeyClass, ButtonClass, and ValuatorClass.
The length field is a number in the range 0- 255. It specifies the number of bytes of data that are contained in this input class. The length includes the class and length fields.
The XKeyInfo structure describes the characteristics of the keys on the device. It is defined as follows:
typedef struct _XKeyInfo {
XID class;
int length;
unsigned short min_keycode;
unsigned short max_keycode;
unsigned short num_keys;
} XKeyInfo;
min_keycode is of type KEYCODE. It specifies the minimum keycode that the device will report. The minimum keycode will not be smaller than 8.
max_keycode is of type KEYCODE. It specifies the maximum keycode that the device will report. The maximum keycode will not be larger than 255.
num_keys specifies the number of keys that the device has.
The XButtonInfo structure defines the characteristics of the buttons on the device. It is defined as follows:
typedef struct _XButtonInfo {
XID class;
int length;
short num_buttons;
} XButtonInfo;
num_buttons specifies the number of buttons that the device has.
The XValuatorInfo structure defines the characteristics of the valuators on the device. It is defined as follows:
typedef struct _XValuatorInfo {
XID class;
int length;
unsigned char num_axes;
unsigned char mode;
unsigned long motion_buffer;
XAxisInfoPtr axes;
} XValuatorInfo;
num_axes contains the number of axes the device supports. mode is a constant that has one of the following values: Absolute or Relative. Some devices allow the mode to be changed dynamically via the SetDeviceMode request.
motion_buffer_size is a cardinal number that specifies the number of elements that can be contained in the motion history buffer for the device.
The axes field contains a pointer to an XAxisInfo structure.
The XAxisInfo structure is defined as follows:
typedef struct _XAxisInfo {
int resolution;
int min_value;
int max_value;
} XAxisInfo;
The resolution contains a number in counts/meter.
The min_val field contains a number that specifies the minimum value the device reports for this axis. For devices whose mode is Relative, the min_val field will contain 0.
The max_val field contains a number that specifies the maximum value the device reports for this axis. For devices whose mode is Relative, the max_val field will contain 0.
To free the XDeviceInfo array created by XListInputDevices, use XFreeDeviceList.