Events

## Events Events — Functions for handling events from the window system |

## Synopsis

    #include <gdk/gdk.h>

    enum        GdkEventType;
    enum        GdkEventMask;
    #define     GDK_CURRENT_TIME
    #define     GDK_PRIORITY_EVENTS
    #define     GDK_PRIORITY_REDRAW

    gboolean    gdk_events_pending              (void);
    GdkEvent*   gdk_event_peek                  (void);
    GdkEvent*   gdk_event_get                   (void);
    GdkEvent*   gdk_event_get_graphics_expose   (GdkWindow *window);
    void        gdk_event_put                   (GdkEvent *event);
    GdkEvent*   gdk_event_new                   (GdkEventType type);
    GdkEvent*   gdk_event_copy                  (GdkEvent *event);
    void        gdk_event_free                  (GdkEvent *event);
    guint32     gdk_event_get_time              (GdkEvent *event);
    gboolean    gdk_event_get_state             (GdkEvent *event,
                                                 GdkModifierType *state);
    gboolean    gdk_event_get_axis              (GdkEvent *event,
                                                 GdkAxisUse axis_use,
                                                 gdouble *value);
    gboolean    gdk_event_get_coords            (GdkEvent *event,
                                                 gdouble *x_win,
                                                 gdouble *y_win);
    gboolean    gdk_event_get_root_coords       (GdkEvent *event,
                                                 gdouble *x_root,
                                                 gdouble *y_root);

    void        gdk_event_handler_set           (GdkEventFunc func,
                                                 gpointer data,
                                                 GDestroyNotify notify);
    void        (*GdkEventFunc)                 (GdkEvent *event,
                                                 gpointer data);

    gboolean    gdk_event_send_client_message   (GdkEvent *event,
                                                 GdkNativeWindow winid);
    gboolean    gdk_event_send_client_message_for_display
                                                (GdkDisplay *display,
                                                 GdkEvent *event,
                                                 GdkNativeWindow winid);
    void        gdk_event_send_clientmessage_toall
                                                (GdkEvent *event);
    void        gdk_add_client_message_filter   (GdkAtom message_type,
                                                 GdkFilterFunc func,
                                                 gpointer data);

    gboolean    gdk_get_show_events             (void);
    void        gdk_set_show_events             (gboolean show_events);
    void        gdk_event_set_screen            (GdkEvent *event,
                                                 GdkScreen *screen);
    GdkScreen*  gdk_event_get_screen            (GdkEvent *event);

    gboolean    gdk_setting_get                 (const gchar *name,
                                                 GValue *value);

## Description

This section describes functions dealing with events from the window system.

In GTK+ applications the events are handled automatically in `gtk_main_do_event()` and passed on to the appropriate widgets, so these functions are rarely needed. Though some of the fields in the Event Structures are useful.

## Details

### enum GdkEventType

    typedef enum
    {
      GDK_NOTHING		= -1,
      GDK_DELETE		= 0,
      GDK_DESTROY		= 1,
      GDK_EXPOSE		= 2,
      GDK_MOTION_NOTIFY	= 3,
      GDK_BUTTON_PRESS	= 4,
      GDK_2BUTTON_PRESS	= 5,
      GDK_3BUTTON_PRESS	= 6,
      GDK_BUTTON_RELEASE	= 7,
      GDK_KEY_PRESS		= 8,
      GDK_KEY_RELEASE	= 9,
      GDK_ENTER_NOTIFY	= 10,
      GDK_LEAVE_NOTIFY	= 11,
      GDK_FOCUS_CHANGE	= 12,
      GDK_CONFIGURE		= 13,
      GDK_MAP		= 14,
      GDK_UNMAP		= 15,
      GDK_PROPERTY_NOTIFY	= 16,
      GDK_SELECTION_CLEAR	= 17,
      GDK_SELECTION_REQUEST = 18,
      GDK_SELECTION_NOTIFY	= 19,
      GDK_PROXIMITY_IN	= 20,
      GDK_PROXIMITY_OUT	= 21,
      GDK_DRAG_ENTER        = 22,
      GDK_DRAG_LEAVE        = 23,
      GDK_DRAG_MOTION       = 24,
      GDK_DRAG_STATUS       = 25,
      GDK_DROP_START        = 26,
      GDK_DROP_FINISHED     = 27,
      GDK_CLIENT_EVENT	= 28,
      GDK_VISIBILITY_NOTIFY = 29,
      GDK_NO_EXPOSE		= 30,
      GDK_SCROLL            = 31,
      GDK_WINDOW_STATE      = 32,
      GDK_SETTING           = 33
    } GdkEventType;

Specifies the type of the event.

Do not confuse these events with the signals that GTK+ widgets emit. Although many of these events result in corresponding signals being emitted, the events are often transformed or filtered along the way.

`GDK_NOTHING` | a special code to indicate a null event.
`GDK_DELETE` | the window manager has requested that the toplevel window be hidden or destroyed, usually when the user clicks on a special icon in the title bar.
`GDK_DESTROY` | the window has been destroyed.
`GDK_EXPOSE` | all or part of the window has become visible and needs to be redrawn.
`GDK_MOTION_NOTIFY` | the pointer (usually a mouse) has moved.
`GDK_BUTTON_PRESS` | a mouse button has been pressed.
`GDK_2BUTTON_PRESS` | a mouse button has been double-clicked (clicked twice within a short period of time). Note that each click also generates a `GDK_BUTTON_PRESS` event.
`GDK_3BUTTON_PRESS` | a mouse button has been clicked 3 times in a short period of time. Note that each click also generates a `GDK_BUTTON_PRESS` event.
`GDK_BUTTON_RELEASE` | a mouse button has been released.
`GDK_KEY_PRESS` | a key has been pressed.
`GDK_KEY_RELEASE` | a key has been released.
`GDK_ENTER_NOTIFY` | the pointer has entered the window.
`GDK_LEAVE_NOTIFY` | the pointer has left the window.
`GDK_FOCUS_CHANGE` | the keyboard focus has entered or left the window.
`GDK_CONFIGURE` | the size, position or stacking order of the window has changed. Note that GTK+ discards these events for `GDK_WINDOW_CHILD` windows.
`GDK_MAP` | the window has been mapped.
`GDK_UNMAP` | the window has been unmapped.
`GDK_PROPERTY_NOTIFY` | a property on the window has been changed or deleted.
`GDK_SELECTION_CLEAR` | the application has lost ownership of a selection.
`GDK_SELECTION_REQUEST` | another application has requested a selection.
`GDK_SELECTION_NOTIFY` | a selection has been received.
`GDK_PROXIMITY_IN` | an input device has moved into contact with a sensing surface (e.g. a touchscreen or graphics tablet).
`GDK_PROXIMITY_OUT` | an input device has moved out of contact with a sensing surface.
`GDK_DRAG_ENTER` | the mouse has entered the window while a drag is in progress.
`GDK_DRAG_LEAVE` | the mouse has left the window while a drag is in progress.
`GDK_DRAG_MOTION` | the mouse has moved in the window while a drag is in progress.
`GDK_DRAG_STATUS` | the status of the drag operation initiated by the window has changed.
`GDK_DROP_START` | a drop operation onto the window has started.
`GDK_DROP_FINISHED` | the drop operation initiated by the window has completed.
`GDK_CLIENT_EVENT` | a message has been received from another application.
`GDK_VISIBILITY_NOTIFY` | the window visibility status has changed.
`GDK_NO_EXPOSE` | indicates that the source region was completely available when parts of a drawable were copied. This is not very useful.
`GDK_SCROLL` |
`GDK_WINDOW_STATE` |
`GDK_SETTING` |

### enum GdkEventMask

    typedef enum
    {
      GDK_EXPOSURE_MASK		= 1 << 1,
      GDK_POINTER_MOTION_MASK	= 1 << 2,
      GDK_POINTER_MOTION_HINT_MASK	= 1 << 3,
      GDK_BUTTON_MOTION_MASK	= 1 << 4,
      GDK_BUTTON1_MOTION_MASK	= 1 << 5,
      GDK_BUTTON2_MOTION_MASK	= 1 << 6,
      GDK_BUTTON3_MOTION_MASK	= 1 << 7,
      GDK_BUTTON_PRESS_MASK		= 1 << 8,
      GDK_BUTTON_RELEASE_MASK	= 1 << 9,
      GDK_KEY_PRESS_MASK		= 1 << 10,
      GDK_KEY_RELEASE_MASK		= 1 << 11,
      GDK_ENTER_NOTIFY_MASK		= 1 << 12,
      GDK_LEAVE_NOTIFY_MASK		= 1 << 13,
      GDK_FOCUS_CHANGE_MASK		= 1 << 14,
      GDK_STRUCTURE_MASK		= 1 << 15,
      GDK_PROPERTY_CHANGE_MASK	= 1 << 16,
      GDK_VISIBILITY_NOTIFY_MASK	= 1 << 17,
      GDK_PROXIMITY_IN_MASK		= 1 << 18,
      GDK_PROXIMITY_OUT_MASK	= 1 << 19,
      GDK_SUBSTRUCTURE_MASK		= 1 << 20,
      GDK_SCROLL_MASK               = 1 << 21,
      GDK_ALL_EVENTS_MASK		= 0x3FFFFE
    } GdkEventMask;

A set of bit-flags to indicate which events a window is to receive. Most of these masks map onto one or more of the GdkEventType event types above.

`GDK_POINTER_MOTION_HINT_MASK` is a special mask which is used to reduce the number of `GDK_MOTION_NOTIFY` events received. Normally a `GDK_MOTION_NOTIFY` event is received each time the mouse moves. However, if the application spends a lot of time processing the event (updating the display, for example), it can easily lag behind the position of the mouse. When using the `GDK_POINTER_MOTION_HINT_MASK` the server will only send a single `GDK_MOTION_NOTIFY` event (which is marked as a hint) until the application asks for more, by calling `gdk_window_get_pointer()`.

`GDK_EXPOSURE_MASK` |
`GDK_POINTER_MOTION_MASK` |
`GDK_POINTER_MOTION_HINT_MASK` |
`GDK_BUTTON_MOTION_MASK` |
`GDK_BUTTON1_MOTION_MASK` |
`GDK_BUTTON2_MOTION_MASK` |
`GDK_BUTTON3_MOTION_MASK` |
`GDK_BUTTON_PRESS_MASK` |
`GDK_BUTTON_RELEASE_MASK` |
`GDK_KEY_PRESS_MASK` |
`GDK_KEY_RELEASE_MASK` |
`GDK_ENTER_NOTIFY_MASK` |
`GDK_LEAVE_NOTIFY_MASK` |
`GDK_FOCUS_CHANGE_MASK` |
`GDK_STRUCTURE_MASK` |
`GDK_PROPERTY_CHANGE_MASK` |
`GDK_VISIBILITY_NOTIFY_MASK` |
`GDK_PROXIMITY_IN_MASK` |
`GDK_PROXIMITY_OUT_MASK` |
`GDK_SUBSTRUCTURE_MASK` |
`GDK_SCROLL_MASK` |
`GDK_ALL_EVENTS_MASK` | the combination of all the above event masks.

### GDK_CURRENT_TIME

    #define GDK_CURRENT_TIME     0L

Represents the current time, and can be used anywhere a time is expected.

### GDK_PRIORITY_EVENTS

    #define     GDK_PRIORITY_EVENTS

This is the priority that events from the X server are given in the GLib Main Loop.

### GDK_PRIORITY_REDRAW

    #define GDK_PRIORITY_REDRAW     (G_PRIORITY_HIGH_IDLE + 20)

This is the priority that the idle handler processing window updates is given in the GLib Main Loop.

### gdk_events_pending ()

    gboolean    gdk_events_pending              (void);

Checks if any events are ready to be processed for any display.

Returns : | `TRUE` if any events are pending.

### gdk_event_peek ()

    GdkEvent*   gdk_event_peek                  (void);

If there is an event waiting in the event queue of some open display, returns a copy of it. See `gdk_display_peek_event()`.

Returns : | a copy of the first GdkEvent on some event queue, or `NULL` if no events are in any queues. The returned GdkEvent should be freed with `gdk_event_free()`.

### gdk_event_get ()

    GdkEvent*   gdk_event_get                   (void);

Checks all open displays for a GdkEvent to process,to be processed on, fetching events from the windowing system if necessary. See `gdk_display_get_event()`.

Returns : | the next GdkEvent to be processed, or `NULL` if no events are pending. The returned GdkEvent should be freed with `gdk_event_free()`.

### gdk_event_get_graphics_expose ()

    GdkEvent*   gdk_event_get_graphics_expose   (GdkWindow *window);

Waits for a GraphicsExpose or NoExpose event from the X server. This is used in the GtkText and GtkCList widgets in GTK+ to make sure any GraphicsExpose events are handled before the widget is scrolled.

`window` : | the GdkWindow to wait for the events for.
Returns : | a GdkEventExpose if a GraphicsExpose was received, or `NULL` if a NoExpose event was received.

### gdk_event_put ()

    void        gdk_event_put                   (GdkEvent *event);

Appends a copy of the given event onto the front of the event queue for event->any.window's display, or the default event queue if event->any.window is `NULL`. See `gdk_display_put_event()`.

`event` : | a GdkEvent.

### gdk_event_new ()

    GdkEvent*   gdk_event_new                   (GdkEventType type);

Creates a new event of the given type. All fields are set to 0.

`type` : | a GdkEventType
Returns : | a newly-allocated GdkEvent. The returned GdkEvent should be freed with `gdk_event_free()`.

Since 2.2

### gdk_event_copy ()

    GdkEvent*   gdk_event_copy                  (GdkEvent *event);

Copies a GdkEvent, copying or incrementing the reference count of the resources associated with it (e.g. GdkWindow's and strings).

`event` : | a GdkEvent
Returns : | a copy of `event`. The returned GdkEvent should be freed with `gdk_event_free()`.

### gdk_event_free ()

    void        gdk_event_free                  (GdkEvent *event);

Frees a GdkEvent, freeing or decrementing any resources associated with it. Note that this function should only be called with events returned from functions such as `gdk_event_peek()`, `gdk_event_get()`, `gdk_event_get_graphics_expose()` and `gdk_event_copy()`.

`event` : | a GdkEvent.

### gdk_event_get_time ()

    guint32     gdk_event_get_time              (GdkEvent *event);

Returns the time stamp from `event`, if there is one; otherwise returns GDK_CURRENT_TIME. If `event` is `NULL`, returns GDK_CURRENT_TIME.

`event` : | a GdkEvent
Returns : | time stamp field from `event`

### gdk_event_get_state ()

    gboolean    gdk_event_get_state             (GdkEvent *event,
                                                 GdkModifierType *state);

If the event contains a "state" field, puts that field in `state`. Otherwise stores an empty state (0). Returns `TRUE` if there was a state field in the event. `event` may be `NULL`, in which case it's treated as if the event had no state field.

`event` : | a GdkEvent or NULL
`state` : | return location for state
Returns : | `TRUE` if there was a state field in the event

### gdk_event_get_axis ()

    gboolean    gdk_event_get_axis              (GdkEvent *event,
                                                 GdkAxisUse axis_use,
                                                 gdouble *value);

Extract the axis value for a particular axis use from an event structure.

`event` : | a GdkEvent
`axis_use` : | the axis use to look for
`value` : | location to store the value found
Returns : | `TRUE` if the specified axis was found, otherwise `FALSE`

### gdk_event_get_coords ()

    gboolean    gdk_event_get_coords            (GdkEvent *event,
                                                 gdouble *x_win,
                                                 gdouble *y_win);

Extract the event window relative x/y coordinates from an event.

`event` : | a GdkEvent
`x_win` : | location to put event window x coordinate
`y_win` : | location to put event window y coordinate
Returns : | `TRUE` if the event delivered event window coordinates

### gdk_event_get_root_coords ()

    gboolean    gdk_event_get_root_coords       (GdkEvent *event,
                                                 gdouble *x_root,
                                                 gdouble *y_root);

Extract the root window relative x/y coordinates from an event.

`event` : | a GdkEvent
`x_root` : | location to put root window x coordinate
`y_root` : | location to put root window y coordinate
Returns : | `TRUE` if the event delivered root window coordinates

### gdk_event_handler_set ()

    void        gdk_event_handler_set           (GdkEventFunc func,
                                                 gpointer data,
                                                 GDestroyNotify notify);

Sets the function to call to handle all events from GDK.

Note that GTK+ uses this to install its own event handler, so it is usually not useful for GTK+ applications. (Although an application can call this function then call `gtk_main_do_event()` to pass events to GTK+.)

`func` : | the function to call to handle events from GDK.
`data` : | user data to pass to the function.
`notify` : | the function to call when the handler function is removed, i.e. when `gdk_event_handler_set()` is called with another event handler.

### GdkEventFunc ()

    void        (*GdkEventFunc)                 (GdkEvent *event,
                                                 gpointer data);

Specifies the type of function passed to `gdk_event_handler_set()` to handle all GDK events.

`event` : | the GdkEvent to process.
`data` : | user data set when the event handler was installed with `gdk_event_handler_set()`.

### gdk_event_send_client_message ()

    gboolean    gdk_event_send_client_message   (GdkEvent *event,
                                                 GdkNativeWindow winid);

Sends an X ClientMessage event to a given window (which must be on the default GdkDisplay.) This could be used for communicating between different applications, though the amount of data is limited to 20 bytes.

`event` : | the GdkEvent to send, which should be a GdkEventClient.
`winid` : | the window to send the X ClientMessage event to.
Returns : | non-zero on success.

### gdk_event_send_client_message_for_display ()

    gboolean    gdk_event_send_client_message_for_display
                                                (GdkDisplay *display,
                                                 GdkEvent *event,
                                                 GdkNativeWindow winid);

On X11, sends an X ClientMessage event to a given window. On Windows, sends a message registered with the name GDK_WIN32_CLIENT_MESSAGE.

This could be used for communicating between different applications, though the amount of data is limited to 20 bytes on X11, and to just four bytes on Windows.

`display` : | the GdkDisplay for the window where the message is to be sent.
`event` : | the GdkEvent to send, which should be a GdkEventClient.
`winid` : | the window to send the client message to.
Returns : | non-zero on success.

Since 2.2

### gdk_event_send_clientmessage_toall ()

    void        gdk_event_send_clientmessage_toall
                                                (GdkEvent *event);

Sends an X ClientMessage event to all toplevel windows on the default GdkScreen.

Toplevel windows are determined by checking for the WM_STATE property, as described in the Inter-Client Communication Conventions Manual (ICCCM). If no windows are found with the WM_STATE property set, the message is sent to all children of the root window.

`event` : | the GdkEvent to send, which should be a GdkEventClient.

### gdk_add_client_message_filter ()

    void        gdk_add_client_message_filter   (GdkAtom message_type,
                                                 GdkFilterFunc func,
                                                 gpointer data);

Adds a filter to the default display to be called when X ClientMessage events are received. See `gdk_display_add_client_message_filter()`.

`message_type` : | the type of ClientMessage events to receive. This will be checked against the `message_type` field of the XClientMessage event struct.
`func` : | the function to call to process the event.
`data` : | user data to pass to `func`.

### gdk_get_show_events ()

    gboolean    gdk_get_show_events             (void);

Gets whether event debugging output is enabled.

Returns : | `TRUE` if event debugging output is enabled.

### gdk_set_show_events ()

    void        gdk_set_show_events             (gboolean show_events);

Sets whether a trace of received events is output. Note that GTK+ must be compiled with debugging (that is, configured using the `--enable-debug` option) to use this option.

`show_events` : | `TRUE` to output event debugging information.

### gdk_event_set_screen ()

    void        gdk_event_set_screen            (GdkEvent *event,
                                                 GdkScreen *screen);

Sets the screen for `event` to `screen`. The event must have been allocated by GTK+, for instance, by `gdk_event_copy()`.

`event` : | a GdkEvent
`screen` : | a GdkScreen

Since 2.2

### gdk_event_get_screen ()

    GdkScreen*  gdk_event_get_screen            (GdkEvent *event);

Returns the screen for the event. The screen is typically the screen for `event->any.window`, but for events such as mouse events, it is the screen where the the pointer was when the event occurs - that is, the screen which has the root window to which `event->motion.x_root` and `event->motion.y_root` are relative.

`event` : | a GdkEvent
Returns : | the screen for the event

Since 2.2

### gdk_setting_get ()

    gboolean    gdk_setting_get                 (const gchar *name,
                                                 GValue *value);

Obtains a desktop-wide setting, such as the double-click time, for the default screen. See `gdk_screen_get_setting()`.

`name` : | the name of the setting.
`value` : | location to store the value of the setting.
Returns : | : `TRUE` if the setting existed and a value was stored in `value`, `FALSE` otherwise.

## See Also

Event Structures | The structs used for each type of event.