Commit 09bb109f authored by Philip Withnall's avatar Philip Withnall

docs: Expand input handling documentation to cover event masks

Also try and clarify a few things about event propagation. Move
input-handling.xml into gtk-doc’s expand_content_files variable so it
automatically links to widget documentation. Add links from
gtk_widget_add_events() and friends to the new documentation.

https://bugzilla.gnome.org/show_bug.cgi?id=744054
parent 668d5d86
......@@ -174,6 +174,7 @@ expand_content_files = \
drawing-model.xml \
getting_started.xml \
glossary.xml \
input-handling.xml \
migrating-2to3.xml \
migrating-checklist.sgml \
migrating-unique-GtkApplication.xml \
......
......@@ -25,7 +25,7 @@
<xi:include href="resources.sgml" />
<xi:include href="xml/question_index.sgml" />
<xi:include href="drawing-model.xml" />
<xi:include href="input-handling.xml" />
<xi:include href="xml/input-handling.xml" />
</part>
......
......@@ -87,56 +87,143 @@
</para>
</refsect2>
<refsect2>
<refsect2 id="event-propagation">
<title>Event propagation</title>
<para>
When GTK+ receives an event, it determines the target widget that
it is directed to. Unless grabs are involved, this is done by finding
the widget to which the window of the event belongs.
For widgets which have a #GdkWindow set, events are received from the
windowing system and passed to gtk_main_do_event(). See its documentation
for details of what it does: compression of enter/leave events,
identification of the widget receiving the event, pushing the event onto a
stack for gtk_get_current_event(), and propagating the event to the
widget.
</para>
<para>
The event is then propagated from the toplevel window down to the
target widget. In this phase, which is known as the “capture” phase,
gestures that are attached with GTK_PHASE_CAPTURE get a chance
to react to the event.
When a GDK backend produces an input event, it is tied to a #GdkDevice and
a #GdkWindow, which in turn represents a windowing system surface in the
backend. If a widget has grabbed the current input device, or all input
devices, the event is propagated to that #GtkWidget. Otherwise, it is
propagated to the the #GtkWidget which called gtk_widget_register_window()
on the #GdkWindow receiving the event.
</para>
<para>
Grabs are implemented for each input device, and globally. A grab for a
specific input device (gtk_device_grab_add()), is sent events in
preference to a global grab (gtk_grab_add()). Input grabs only have effect
within the #GtkWindowGroup containing the #GtkWidget which registered the
event’s #GdkWindow. If this #GtkWidget is a child of the grab widget, the
event is propagated to the child — this is the basis for propagating
events within modal dialogs.
</para>
<para>
An event is propagated to a widget using gtk_propagate_event().
Propagation differs between event types: key events (%GDK_KEY_PRESS,
%GDK_KEY_RELEASE) are delivered to the top-level #GtkWindow; other events
are propagated down and up the widget hierarchy in three phases (see
#GtkPropagationPhase).
</para>
<para>
For key events, the top-level window’s default #GtkWindow::key-press-event
and #GtkWindow::key-release-event signal handlers handle mnemonics and
accelerators first. Other key presses are then passed to
gtk_window_propagate_key_event() which propagates the event upwards from
the window’s current focus widget (gtk_window_get_focus()) to the
top-level.
</para>
<para>
For other events, in the first phase (the “capture” phase) the event is
delivered to each widget from the top-most (for example, the top-level
#GtkWindow or grab widget) down to the target #GtkWidget.
<link linkend="event-controllers-and-gestures">Gestures</link> that are
attached with %GTK_PHASE_CAPTURE get a chance to react to the event.
</para>
<para>
After the “capture” phase, the widget that was intended to be the
destination of the event will let run gestures attached to it with
GTK_PHASE_TARGET. This is known as the “target” phase, and does only
happen on that widget.
destination of the event will run gestures attached to it with
%GTK_PHASE_TARGET. This is known as the “target” phase, and only
happens on that widget.
</para>
<para>
Next, the appropriate event signal is emitted for the event in question,
e.g. “motion-notify-event”. Handling these signals was the primary
way to handle input in GTK+ widgets before gestures were introduced.
The signals are emitted from the target widget up to the toplevel,
until a signal handler indicates that it has handled the event, by
returning GDK_EVENT_STOP.
Next, the #GtkWidget::event signal is emitted, then the appropriate signal
for the event in question, for example #GtkWidget::motion-notify-event.
Handling these signals was the primary way to handle input in GTK+ widgets
before gestures were introduced. If the widget is realized, the
#GtkWidget::event-after signal is emitted. The signals are emitted from
the target widget up to the top-level, as part of the “bubble” phase.
</para>
<para>
The default handlers for the event signals send the event
to gestures that are attached with GTK_PHASE_BUBBLE. Therefore,
to gestures that are attached with %GTK_PHASE_BUBBLE. Therefore,
gestures in the “bubble” phase are only used if the widget does
not have its own event handlers, or takes care to chain up to the
default GtkWidget handlers.
default #GtkWidget handlers.
</para>
<para>
Anytime during the propagation phase, a widget may indicate that a
Events are not delivered to a widget which is insensitive or unmapped.
</para>
<para>
Any time during the propagation phase, a widget may indicate that a
received event was consumed and propagation should therefore be stopped.
In traditional event handlers, this is hinted by returning GDK_EVENT_STOP,
if gestures are used, this may happen when the widget tells the gesture
In traditional event handlers, this is hinted by returning %GDK_EVENT_STOP.
If gestures are used, this may happen when the widget tells the gesture
to claim the event touch sequence (or the pointer events) for its own. See the
"gesture states" section below to know more of the latter.
</para>
</refsect2>
<refsect2 id="event-masks">
<title>Event masks</title>
<para>
Each widget instance has a basic event mask and another per input device,
which determine the types of input event it receives. Each event mask set
on a widget is added to the corresponding (basic or per-device) event mask
for the widget’s #GdkWindow, and all child #GdkWindows.
</para>
<para>
If a widget is windowless (gtk_widget_get_has_window() returns %FALSE) and
an application wants to receive custom events on it, it must be placed
inside a #GtkEventBox to receive the events, and an appropriate event mask
must be set on the box. When implementing a widget, use a %GDK_INPUT_ONLY
#GdkWindow to receive the events instead.
</para>
<para>
Filtering events against event masks happens inside #GdkWindow, which
exposes event masks to the windowing system to reduce the number of events
GDK receives from it. On receiving an event, it is filtered against the
#GdkWindow’s mask for the input device, if set. Otherwise, it is filtered
against the #GdkWindow’s basic event mask.
</para>
<para>
This means that widgets must add to the event mask for each event type
they expect to receive, using gtk_widget_set_events() or
gtk_widget_add_events() to preserve the existing mask. Widgets which are
aware of floating devices should use gtk_widget_set_device_events() or
gtk_widget_add_device_events(), and must explicitly enable the device
using gtk_widget_set_device_enabled(). See the #GdkDeviceManager
documentation for more information.
</para>
<para>
All standard widgets set the event mask for all events they expect to
receive, and it is not necessary to modify this. Masks should be set when
implementing a new widget.
</para>
</refsect2>
<refsect2>
<title>Touch events</title>
......@@ -209,7 +296,7 @@
<!-- mnemonics, accelerators, bindings -->
</refsect2>
<refsect2>
<refsect2 id="event-controllers-and-gestures">
<title>Event controllers and gestures</title>
<para>
......
......@@ -372,6 +372,9 @@ typedef enum
* Most of these masks map onto one or more of the #GdkEventType event types
* above.
*
* See the [input handling overview][chap-input-handling] for details of
* [event masks][event-masks] and [event propagation][event-propagation].
*
* %GDK_POINTER_MOTION_HINT_MASK is deprecated. It is a special mask
* to reduce the number of %GDK_MOTION_NOTIFY events received. When using
* %GDK_POINTER_MOTION_HINT_MASK, fewer %GDK_MOTION_NOTIFY events will
......
......@@ -5425,6 +5425,8 @@ gdk_window_withdraw (GdkWindow *window)
* including #GDK_BUTTON_PRESS_MASK means the window should report button
* press events. The event mask is the bitwise OR of values from the
* #GdkEventMask enumeration.
*
* See the [input handling overview][event-masks] for details.
**/
void
gdk_window_set_events (GdkWindow *window,
......@@ -5495,6 +5497,8 @@ gdk_window_get_events (GdkWindow *window)
* press events. The event mask is the bitwise OR of values from the
* #GdkEventMask enumeration.
*
* See the [input handling overview][event-masks] for details.
*
* Since: 3.0
**/
void
......
......@@ -11301,7 +11301,8 @@ gtk_widget_add_events_internal (GtkWidget *widget,
* @events: an event mask, see #GdkEventMask
*
* Adds the events in the bitfield @events to the event mask for
* @widget. See gtk_widget_set_events() for details.
* @widget. See gtk_widget_set_events() and the
* [input handling overview][event-masks] for details.
**/
void
gtk_widget_add_events (GtkWidget *widget,
......@@ -11534,9 +11535,8 @@ gtk_widget_get_settings (GtkWidget *widget)
* gtk_widget_get_events:
* @widget: a #GtkWidget
*
* Returns the event mask for the widget (a bitfield containing flags
* from the #GdkEventMask enumeration). These are the events that the widget
* will receive.
* Returns the event mask (see #GdkEventMask) for the widget. These are the
* events that the widget will receive.
*
* Note: Internally, the widget event mask will be the logical OR of the event
* mask set through gtk_widget_set_events() or gtk_widget_add_events(), and the
......
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