Input Devices

Description

In addition to the normal keyboard and mouse input devices, GTK+ also contains support for extended input devices. In particular, this support is targeted at graphics tablets. Graphics tablets typically return sub-pixel positioning information and possibly information about the pressure and tilt of the stylus. Under X, the support for extended devices is done through the XInput extension.

Because handling extended input devices may involve considerable overhead, they need to be turned on for each GdkWindow individually using gdk_input_set_extension_events(). (Or, more typically, for GtkWidgets, using gtk_widget_set_extension_events()). As an additional complication, depending on the support from the windowing system, its possible that a normal mouse cursor will not be displayed for a particular extension device. If an application does not want to deal with displaying a cursor itself, it can ask only to get extension events from devices that will display a cursor, by passing the GDK_EXTENSION_EVENTS_CURSOR value to gdk_input_set_extension_events(). Otherwise, the application must retrieve the device information using gdk_devices_list(), check the has_cursor field, and, if it is FALSE, draw a cursor itself when it receives motion events.

Each pointing device is assigned a unique integer ID; events from a particular device can be identified by the deviceid field in the event structure. The events generated by pointer devices have also been extended to contain pressure, xtilt and ytilt fields which contain the extended information reported as additional valuators from the device. The pressure field is a a double value ranging from 0.0 to 1.0, while the tilt fields are double values ranging from -1.0 to 1.0. (With -1.0 representing the maximum tilt to the left or up, and 1.0 representing the maximum tilt to the right or down.)

One additional field in each event is the source field, which contains an enumeration value describing the type of device; this currently can be one of GDK_SOURCE_MOUSE, GDK_SOURCE_PEN, GDK_SOURCE_ERASER, or GDK_SOURCE_CURSOR. This field is present to allow simple applications to (for instance) delete when they detect eraser devices without having to keep track of complicated per-device settings.

Various aspects of each device may be configured. The easiest way of creating a GUI to allow the user to configure such a device is to use the GtkInputDialog widget in GTK+. However, even when using this widget, application writers will need to directly query and set the configuration parameters in order to save the state between invocations of the application. The configuration of devices is queried using gdk_devices_list(). Each device must be activated using gdk_device_set_mode(), which also controls whether the device's range is mapped to the entire screen or to a single window. The mapping of the valuators of the device onto the predefined valuator types is set using gdk_device_set_axis_use(). And the source type for each device can be set with gdk_device_set_source().

Devices may also have associated keys or macro buttons. Such keys can be globally set to map into normal X keyboard events. The mapping is set using gdk_device_set_key().

The interfaces in this section will most likely be considerably modified in the future to accomodate devices that may have different sets of additional valuators than the pressure xtilt and ytilt.

Details

struct GdkDevice
{
  GObject parent_instance;
  /* All fields are read-only */
	  
  gchar *name;
  GdkInputSource source;
  GdkInputMode mode;
  gboolean has_cursor;	     /* TRUE if the X pointer follows device motion */
	  
  gint num_axes;
  GdkDeviceAxis *axes;
	  
  gint num_keys;
  GdkDeviceKey *keys;
};

typedef enum
{
  GDK_SOURCE_MOUSE,
  GDK_SOURCE_PEN,
  GDK_SOURCE_ERASER,
  GDK_SOURCE_CURSOR
} GdkInputSource;

typedef enum
{
  GDK_MODE_DISABLED,
  GDK_MODE_SCREEN,
  GDK_MODE_WINDOW
} GdkInputMode;

struct GdkDeviceKey
{
  guint keyval;
  GdkModifierType modifiers;
};

struct GdkDeviceAxis
{
  GdkAxisUse use;
  gdouble    min;
  gdouble    max;
};

typedef enum
{
  GDK_AXIS_IGNORE,
  GDK_AXIS_X,
  GDK_AXIS_Y,
  GDK_AXIS_PRESSURE,
  GDK_AXIS_XTILT,
  GDK_AXIS_YTILT,
  GDK_AXIS_WHEEL,
  GDK_AXIS_LAST
} GdkAxisUse;

GList*      gdk_devices_list                (void);

void        gdk_device_set_source           (GdkDevice *device,
                                             GdkInputSource source);

gboolean    gdk_device_set_mode             (GdkDevice *device,
                                             GdkInputMode mode);

void        gdk_device_set_key              (GdkDevice *device,
                                             guint index,
                                             guint keyval,
                                             GdkModifierType modifiers);

void        gdk_device_set_axis_use         (GdkDevice *device,
                                             guint index,
                                             GdkAxisUse use);

GdkDevice*  gdk_device_get_core_pointer     (void);

void        gdk_device_get_state            (GdkDevice *device,
                                             GdkWindow *window,
                                             gdouble *axes,
                                             GdkModifierType *mask);

gboolean    gdk_device_get_history          (GdkDevice *device,
                                             GdkWindow *window,
                                             guint32 start,
                                             guint32 stop,
                                             GdkTimeCoord ***events,
                                             gint *n_events);

void        gdk_device_free_history         (GdkTimeCoord **events,
                                             gint n_events);

struct GdkTimeCoord
{
  guint32 time;
  gdouble axes[GDK_MAX_TIMECOORD_AXES];
};

gboolean    gdk_device_get_axis             (GdkDevice *device,
                                             gdouble *axes,
                                             GdkAxisUse use,
                                             gdouble *value);

void        gdk_input_set_extension_events  (GdkWindow *window,
                                             gint mask,
                                             GdkExtensionMode mode);

typedef enum
{
  GDK_EXTENSION_EVENTS_NONE,
  GDK_EXTENSION_EVENTS_ALL,
  GDK_EXTENSION_EVENTS_CURSOR
} GdkExtensionMode;