Events

Events — Functions for handling events from the window system

Types and Values

Includes

#include <gdk/gdk.h>

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.

Functions

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);

gdk_event_get_graphics_expose has been deprecated since version 2.18 and should not be used in newly-written code.

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.

Parameters

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 (const 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().

Parameters

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.

Parameters

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 (const GdkEvent *event);

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

Parameters

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() and gdk_event_new().

Parameters

event

a GdkEvent.

 

gdk_event_get_time ()

guint32
gdk_event_get_time (const 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.

Parameters

event

a GdkEvent

 

Returns

time stamp field from event


gdk_event_get_state ()

gboolean
gdk_event_get_state (const 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.

Parameters

event

a GdkEvent or NULL

 

state

return location for state.

[out]

Returns

TRUE if there was a state field in the event


gdk_event_get_axis ()

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

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

Parameters

event

a GdkEvent

 

axis_use

the axis use to look for

 

value

location to store the value found.

[out]

Returns

TRUE if the specified axis was found, otherwise FALSE


gdk_event_get_coords ()

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

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

Parameters

event

a GdkEvent

 

x_win

location to put event window x coordinate.

[out]

y_win

location to put event window y coordinate.

[out]

Returns

TRUE if the event delivered event window coordinates


gdk_event_get_root_coords ()

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

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

Parameters

event

a GdkEvent

 

x_root

location to put root window x coordinate.

[out]

y_root

location to put root window y coordinate.

[out]

Returns

TRUE if the event delivered root window coordinates


gdk_event_request_motions ()

void
gdk_event_request_motions (const GdkEventMotion *event);

Request more motion notifies if event is a motion notify hint event. This function should be used instead of gdk_window_get_pointer() to request further motion notifies, because it also works for extension events where motion notifies are provided for devices other than the core pointer. Coordinate extraction, processing and requesting more motion events from a GDK_MOTION_NOTIFY event usually works like this:

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{ 
  /* motion_event handler */
  x = motion_event->x;
  y = motion_event->y;
  /* handle (x,y) motion */
  gdk_event_request_motions (motion_event); /* handles is_hint events */
}

Parameters

event

a valid GdkEvent

 

Since: 2.12


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+.)

Parameters

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.

Parameters

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.

Parameters

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.

Parameters

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.

Parameters

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().

Parameters

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.

Parameters

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().

Parameters

event

a GdkEvent

 

screen

a GdkScreen

 

Since: 2.2


gdk_event_get_screen ()

GdkScreen *
gdk_event_get_screen (const 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 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.

Parameters

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().

Parameters

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.

Types and Values

enum 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.

Members

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

the scroll wheel was turned

 

GDK_WINDOW_STATE

the state of a window has changed. See GdkWindowState for the possible window states

 

GDK_SETTING

a setting has been modified.

 

GDK_OWNER_CHANGE

the owner of a selection has changed. This event type was added in 2.6

 

GDK_GRAB_BROKEN

a pointer or keyboard grab was broken. This event type was added in 2.8.

 

GDK_DAMAGE

the content of the window has been changed. This event type was added in 2.14.

 

GDK_EVENT_LAST

marks the end of the GdkEventType enumeration. Added in 2.18

 

enum 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 lag behind the position of the mouse. When using GDK_POINTER_MOTION_HINT_MASK, fewer GDK_MOTION_NOTIFY events will be sent, some of which are marked as a hint (the is_hint member is TRUE). To receive more motion events after a motion hint event, the application needs to asks for more, by calling gdk_event_request_motions().

Members

GDK_EXPOSURE_MASK

receive expose events

 

GDK_POINTER_MOTION_MASK

receive all pointer motion events

 

GDK_POINTER_MOTION_HINT_MASK

see the explanation above

 

GDK_BUTTON_MOTION_MASK

receive pointer motion events while any button is pressed

 

GDK_BUTTON1_MOTION_MASK

receive pointer motion events while 1 button is pressed

 

GDK_BUTTON2_MOTION_MASK

receive pointer motion events while 2 button is pressed

 

GDK_BUTTON3_MOTION_MASK

receive pointer motion events while 3 button is pressed

 

GDK_BUTTON_PRESS_MASK

receive button press events

 

GDK_BUTTON_RELEASE_MASK

receive button release events

 

GDK_KEY_PRESS_MASK

receive key press events

 

GDK_KEY_RELEASE_MASK

receive key release events

 

GDK_ENTER_NOTIFY_MASK

receive window enter events

 

GDK_LEAVE_NOTIFY_MASK

receive window leave events

 

GDK_FOCUS_CHANGE_MASK

receive focus change events

 

GDK_STRUCTURE_MASK

receive events about window configuration change

 

GDK_PROPERTY_CHANGE_MASK

receive property change events

 

GDK_VISIBILITY_NOTIFY_MASK

receive visibility change events

 

GDK_PROXIMITY_IN_MASK

receive proximity in events

 

GDK_PROXIMITY_OUT_MASK

receive proximity out events

 

GDK_SUBSTRUCTURE_MASK

receive events about window configuration changes of child windows

 

GDK_SCROLL_MASK

receive scroll events

 

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.

See Also

Event Structures

The structs used for each type of event.