gtk2/docs/reference/gdk/tmpl/events.sgml

<!-- ##### SECTION Title ##### -->
Events

<!-- ##### SECTION Short_Description ##### -->
functions for handling events from the window system.

<!-- ##### SECTION Long_Description ##### -->
<para>
This section describes functions dealing with events from the window system.
</para>
<para>
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
<link linkend="gdk-Event-Structures">Event Structures</link> are useful.
</para>

<!-- ##### SECTION See_Also ##### -->
<para>
<variablelist>
<varlistentry>
<term><link linkend="gdk-Event-Structures">Event Structures</link></term>
<listitem><para>
The structs used for each type of event.
</para></listitem>
</varlistentry>
</variablelist>
</para>

<!-- ##### ENUM GdkEventType ##### -->
<para>
Specifies the type of the event.
</para>
<para>
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.
</para>

@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.

<!-- ##### ENUM GdkEventMask ##### -->
<para>
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.
</para>
<para>
%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 %GDK_MOTION_NOTIFY
events when the application asks for them, by calling gdk_window_get_pointer().
</para>

@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_ALL_EVENTS_MASK: the combination of all the above event masks.

<!-- ##### MACRO GDK_CURRENT_TIME ##### -->
<para>
Represents the current time, and can be used anywhere a time is expected.
</para>



<!-- ##### MACRO GDK_PRIORITY_EVENTS ##### -->
<para>
This is the priority that events from the X server are given in the
<link linkend="glib-The-Main-Event-Loop">GLib Main Loop</link>.
</para>



<!-- ##### FUNCTION gdk_events_pending ##### -->
<para>
Checks if any events are waiting to be processed.
</para>

@Returns: TRUE if any events are pending.


<!-- ##### FUNCTION gdk_event_peek ##### -->
<para>
Gets a copy of the first #GdkEvent in the event queue.
(Note that this function will not get more events from the X server.
It only checks the events that have already been moved to the GDK event queue.)
</para>

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


<!-- ##### FUNCTION gdk_event_get ##### -->
<para>
Gets the next #GdkEvent to be processed, fetching events from the X server if
necessary.
</para>

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


<!-- ##### FUNCTION gdk_event_get_graphics_expose ##### -->
<para>
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.
</para>

@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.


<!-- ##### FUNCTION gdk_event_put ##### -->
<para>
Appends a copy of the given event onto the front of the event queue.
</para>

@event: a #GdkEvent.


<!-- ##### FUNCTION gdk_event_copy ##### -->
<para>
Copies a #GdkEvent, copying or incrementing the reference count of the
resources associated with it (e.g. #GdkWindow's and strings).
</para>

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


<!-- ##### FUNCTION gdk_event_free ##### -->
<para>
Frees a #GdkEvent, freeing or decrementing any resources associated with it.
Note that this function should only be called with events returned from
gdk_event_peek(), gdk_event_get(), gdk_event_get_graphics_expose() and
gdk_event_copy().
</para>

@event: a #GdkEvent.


<!-- ##### FUNCTION gdk_event_get_time ##### -->
<para>
Gets the timestamp from a #GdkEvent.
</para>

@event: a #GdkEvent.
@Returns: the timestamp from @event, or #GDK_CURRENT_TIME if the event has
no timestamp.


<!-- ##### FUNCTION gdk_event_handler_set ##### -->
<para>
Sets the function to call to handle all events from GDK.
</para>
<para>
Note that GTK+ uses this to install its own event handler, so it is probably
not useful for GTK+ applications.
</para>

@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.


<!-- ##### USER_FUNCTION GdkEventFunc ##### -->
<para>
Specifies the type of function passed to gdk_event_handler_set() to handle
all GDK events.
</para>

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


<!-- ##### FUNCTION gdk_event_send_client_message ##### -->
<para>
Sends an X ClientMessage event to a given window.
</para>
<para>
This could be used for communicating between different applications,
though the amount of data is limited to 20 bytes.
</para>

@event: the #GdkEvent to send, which should be a #GdkEventClient.
@xid: the window to send the X ClientMessage event to.
@Returns: non-zero on success.


<!-- ##### FUNCTION gdk_event_send_clientmessage_toall ##### -->
<para>
Sends an X ClientMessage event to all toplevel windows.
</para>
<para>
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.
</para>

@event: the #GdkEvent to send, which should be a #GdkEventClient.


<!-- ##### FUNCTION gdk_add_client_message_filter ##### -->
<para>
Adds a filter to be called when X ClientMessage events are received.
</para>

@message_type: the type of ClientMessage events to receive. This will be
checked against the <structfield>message_type</structfield> field of the
XClientMessage event struct.
@func: the function to call to process the event.
@data: user data to pass to @func.


<!-- ##### FUNCTION gdk_get_show_events ##### -->
<para>
Returns non-zero if event debugging output is enabled.
</para>

@Returns: non-zero if event debugging output is enabled.


<!-- ##### FUNCTION gdk_set_show_events ##### -->
<para>
Sets whether event debugging information is output.
Note that GTK+ must be compiled with debugging enabled, i.e. using the
'--enable-debug' configure option.
</para>

@show_events: TRUE to output event debugging information.