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GtkGesture

GtkGesture — Base class for gestures

Properties

guint n-points Read / Write / Construct Only
GdkWindow * window Read / Write

Types and Values

Object Hierarchy

    GObject
    ╰── GtkEventController
        ╰── GtkGesture
            ├── GtkGestureSingle
            ├── GtkGestureRotate
            ╰── GtkGestureZoom

Includes

#include <gtk/gtk.h>

Description

GtkGesture is the base object for gesture recognition, although this object is quite generalized to serve as a base for multi-touch gestures, it is suitable to implement single-touch and pointer-based gestures (using the special NULL GdkEventSequence value for these).

The number of touches that a GtkGesture need to be recognized is controlled by the “n-points” property, if a gesture is keeping track of less or more than that number of sequences, it won't check wether the gesture is recognized.

As soon as the gesture has the expected number of touches, the gesture will run the “check” signal regularly on input events until the gesture is recognized, the criteria to consider a gesture as "recognized" is left to GtkGesture subclasses.

A recognized gesture will then emit the following signals:

  • “begin” when the gesture is recognized.

  • A number of “update”, whenever an input event is processed.

  • “end” when the gesture is no longer recognized.

Event propagation

In order to receive events, a gesture needs to either set a propagation phase through gtk_event_controller_set_propagation_phase(), or feed those manually through gtk_event_controller_handle_event().

In the capture phase, events are propagated from the toplevel down to the target widget, and gestures that are attached to containers above the widget get a chance to interact with the event before it reaches the target.

After the capture phase, GTK+ emits the traditional “button-press-event”, “button-release-event”, “touch-event”, etc signals. Gestures with the GTK_PHASE_TARGET phase are fed events from the default “event” handlers.

In the bubble phase, events are propagated up from the target widget to the toplevel, and gestures that are attached to containers above the widget get a chance to interact with events that have not been handled yet.

States of a sequence

Whenever input interaction happens, a single event may trigger a cascade of GtkGestures, both across the parents of the widget receiving the event and in parallel within an individual widget. It is a responsibility of the widgets using those gestures to set the state of touch sequences accordingly in order to enable cooperation of gestures around the GdkEventSequences triggering those.

Within a widget, gestures can be grouped through gtk_gesture_group(), grouped gestures synchronize the state of sequences, so calling gtk_gesture_set_sequence_state() on one will effectively propagate the state throughout the group.

By default, all sequences start out in the GTK_EVENT_SEQUENCE_NONE state, sequences in this state trigger the gesture event handler, but event propagation will continue unstopped by gestures.

If a sequence enters into the GTK_EVENT_SEQUENCE_DENIED state, the gesture group will effectively ignore the sequence, letting events go unstopped through the gesture, but the "slot" will still remain occupied while the touch is active.

If a sequence enters in the GTK_EVENT_SEQUENCE_CLAIMED state, the gesture group will grab all interaction on the sequence, by:

  • Setting the same sequence to GTK_EVENT_SEQUENCE_DENIED on every other gesture group within the widget, and every gesture on parent widgets in the propagation chain.

  • calling “cancel” on every gesture in widgets underneath in the propagation chain.

  • Stopping event propagation after the gesture group handles the event.

Note: if a sequence is set early to GTK_EVENT_SEQUENCE_CLAIMED on GDK_TOUCH_BEGIN/GDK_BUTTON_PRESS (so those events are captured before reaching the event widget, this implies GTK_PHASE_CAPTURE), one similar event will emulated if the sequence changes to GTK_EVENT_SEQUENCE_DENIED. This way event coherence is preserved before event propagation is unstopped again.

Sequence states can't be changed freely, see gtk_gesture_set_sequence_state() to know about the possible lifetimes of a GdkEventSequence.

Touchpad gestures

On the platforms that support it, GtkGesture will handle transparently touchpad gesture events. The only precautions users of GtkGesture should do to enable this support are:

Functions

gtk_gesture_get_device ()

GdkDevice *
gtk_gesture_get_device (GtkGesture *gesture);

Returns the master GdkDevice that is currently operating on gesture , or NULL if the gesture is not being interacted.

Parameters

gesture

a GtkGesture

 

Returns

a GdkDevice, or NULL.

[nullable][transfer none]

Since: 3.14


gtk_gesture_get_window ()

GdkWindow *
gtk_gesture_get_window (GtkGesture *gesture);

Returns the user-defined window that receives the events handled by gesture . See gtk_gesture_set_window() for more information.

Parameters

gesture

a GtkGesture

 

Returns

the user defined window, or NULL if none.

[nullable][transfer none]

Since: 3.14


gtk_gesture_set_window ()

void
gtk_gesture_set_window (GtkGesture *gesture,
                        GdkWindow *window);

Sets a specific window to receive events about, so gesture will effectively handle only events targeting window , or a child of it. window must pertain to gtk_event_controller_get_widget().

Parameters

gesture

a GtkGesture

 

window

a GdkWindow, or NULL.

[allow-none]

Since: 3.14


gtk_gesture_is_active ()

gboolean
gtk_gesture_is_active (GtkGesture *gesture);

Returns TRUE if the gesture is currently active. A gesture is active meanwhile there are touch sequences interacting with it.

Parameters

gesture

a GtkGesture

 

Returns

TRUE if gesture is active

Since: 3.14


gtk_gesture_is_recognized ()

gboolean
gtk_gesture_is_recognized (GtkGesture *gesture);

Returns TRUE if the gesture is currently recognized. A gesture is recognized if there are as many interacting touch sequences as required by gesture , and “check” returned TRUE for the sequences being currently interpreted.

Parameters

gesture

a GtkGesture

 

Returns

TRUE if gesture is recognized

Since: 3.14


gtk_gesture_get_sequence_state ()

GtkEventSequenceState
gtk_gesture_get_sequence_state (GtkGesture *gesture,
                                GdkEventSequence *sequence);

Returns the sequence state, as seen by gesture .

Parameters

gesture

a GtkGesture

 

sequence

a GdkEventSequence

 

Returns

The sequence state in gesture

Since: 3.14


gtk_gesture_set_sequence_state ()

gboolean
gtk_gesture_set_sequence_state (GtkGesture *gesture,
                                GdkEventSequence *sequence,
                                GtkEventSequenceState state);

Sets the state of sequence in gesture . Sequences start in state GTK_EVENT_SEQUENCE_NONE, and whenever they change state, they can never go back to that state. Likewise, sequences in state GTK_EVENT_SEQUENCE_DENIED cannot turn back to a not denied state. With these rules, the lifetime of an event sequence is constrained to the next four:

  • None

  • None → Denied

  • None → Claimed

  • None → Claimed → Denied

Note: Due to event handling ordering, it may be unsafe to set the state on another gesture within a “begin” signal handler, as the callback might be executed before the other gesture knows about the sequence. A safe way to perform this could be:

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static void
first_gesture_begin_cb (GtkGesture       *first_gesture,
                        GdkEventSequence *sequence,
                        gpointer          user_data)
{
  gtk_gesture_set_sequence_state (first_gesture, sequence, GTK_EVENT_SEQUENCE_ACCEPTED);
  gtk_gesture_set_sequence_state (second_gesture, sequence, GTK_EVENT_SEQUENCE_DENIED);
}

static void
second_gesture_begin_cb (GtkGesture       *second_gesture,
                         GdkEventSequence *sequence,
                         gpointer          user_data)
{
  if (gtk_gesture_get_sequence_state (first_gesture, sequence) == GTK_EVENT_SEQUENCE_ACCEPTED)
    gtk_gesture_set_sequence_state (second_gesture, sequence, GTK_EVENT_SEQUENCE_DENIED);
}

If both gestures are in the same group, just set the state on the gesture emitting the event, the sequence will be already be initialized to the group's global state when the second gesture processes the event.

Parameters

gesture

a GtkGesture

 

sequence

a GdkEventSequence

 

state

the sequence state

 

Returns

TRUE if sequence is handled by gesture , and the state is changed successfully

Since: 3.14


gtk_gesture_set_state ()

gboolean
gtk_gesture_set_state (GtkGesture *gesture,
                       GtkEventSequenceState state);

Sets the state of all sequences that gesture is currently interacting with. See gtk_gesture_set_sequence_state() for more details on sequence states.

Parameters

gesture

a GtkGesture

 

state

the sequence state

 

Returns

TRUE if the state of at least one sequence was changed successfully

Since: 3.14


gtk_gesture_get_sequences ()

GList *
gtk_gesture_get_sequences (GtkGesture *gesture);

Returns the list of GdkEventSequences currently being interpreted by gesture .

Parameters

gesture

a GtkGesture

 

Returns

A list of GdkEventSequences, the list elements are owned by GTK+ and must not be freed or modified, the list itself must be deleted through g_list_free().

[transfer container][element-type GdkEventSequence]

Since: 3.14


gtk_gesture_handles_sequence ()

gboolean
gtk_gesture_handles_sequence (GtkGesture *gesture,
                              GdkEventSequence *sequence);

Returns TRUE if gesture is currently handling events corresponding to sequence .

Parameters

gesture

a GtkGesture

 

sequence

a GdkEventSequence

 

Returns

TRUE if gesture is handling sequence

Since: 3.14


gtk_gesture_get_last_updated_sequence ()

GdkEventSequence *
gtk_gesture_get_last_updated_sequence (GtkGesture *gesture);

Returns the GdkEventSequence that was last updated on gesture .

Parameters

gesture

a GtkGesture

 

Returns

The last updated sequence.

[transfer none][nullable]

Since: 3.14


gtk_gesture_get_last_event ()

const GdkEvent *
gtk_gesture_get_last_event (GtkGesture *gesture,
                            GdkEventSequence *sequence);

Returns the last event that was processed for sequence .

Note that the returned pointer is only valid as long as the sequence is still interpreted by the gesture . If in doubt, you should make a copy of the event.

Parameters

gesture

a GtkGesture

 

sequence

a GdkEventSequence

 

Returns

The last event from sequence .

[transfer none][nullable]


gtk_gesture_get_point ()

gboolean
gtk_gesture_get_point (GtkGesture *gesture,
                       GdkEventSequence *sequence,
                       gdouble *x,
                       gdouble *y);

If sequence is currently being interpreted by gesture , this function returns TRUE and fills in x and y with the last coordinates stored for that event sequence. The coordinates are always relative to the widget allocation.

Parameters

gesture

a GtkGesture

 

sequence

a GdkEventSequence, or NULL for pointer events.

[allow-none]

x

return location for X axis of the sequence coordinates.

[out][allow-none]

y

return location for Y axis of the sequence coordinates.

[out][allow-none]

Returns

TRUE if sequence is currently interpreted

Since: 3.14


gtk_gesture_get_bounding_box ()

gboolean
gtk_gesture_get_bounding_box (GtkGesture *gesture,
                              GdkRectangle *rect);

If there are touch sequences being currently handled by gesture , this function returns TRUE and fills in rect with the bounding box containing all active touches. Otherwise, FALSE will be returned.

Note: This function will yield unexpected results on touchpad gestures. Since there is no correlation between physical and pixel distances, these will look as if constrained in an infinitely small area, rect width and height will thus be 0 regardless of the number of touchpoints.

Parameters

gesture

a GtkGesture

 

rect

bounding box containing all active touches.

[out]

Returns

TRUE if there are active touches, FALSE otherwise

Since: 3.14


gtk_gesture_get_bounding_box_center ()

gboolean
gtk_gesture_get_bounding_box_center (GtkGesture *gesture,
                                     gdouble *x,
                                     gdouble *y);

If there are touch sequences being currently handled by gesture , this function returns TRUE and fills in x and y with the center of the bounding box containing all active touches. Otherwise, FALSE will be returned.

Parameters

gesture

a GtkGesture

 

x

X coordinate for the bounding box center.

[out]

y

Y coordinate for the bounding box center.

[out]

Returns

FALSE if no active touches are present, TRUE otherwise

Since: 3.14


gtk_gesture_group ()

void
gtk_gesture_group (GtkGesture *group_gesture,
                   GtkGesture *gesture);

Adds gesture to the same group than group_gesture . Gestures are by default isolated in their own groups.

When gestures are grouped, the state of GdkEventSequences is kept in sync for all of those, so calling gtk_gesture_set_sequence_state(), on one will transfer the same value to the others.

Groups also perform an "implicit grabbing" of sequences, if a GdkEventSequence state is set to GTK_EVENT_SEQUENCE_CLAIMED on one group, every other gesture group attached to the same GtkWidget will switch the state for that sequence to GTK_EVENT_SEQUENCE_DENIED.

Parameters

gesture

a GtkGesture

 

group_gesture

GtkGesture to group gesture with

 

Since: 3.14


gtk_gesture_ungroup ()

void
gtk_gesture_ungroup (GtkGesture *gesture);

Separates gesture into an isolated group.

Parameters

gesture

a GtkGesture

 

Since: 3.14


gtk_gesture_get_group ()

GList *
gtk_gesture_get_group (GtkGesture *gesture);

Returns all gestures in the group of gesture

Parameters

gesture

a GtkGesture

 

Returns

The list of GtkGestures, free with g_list_free().

[element-type GtkGesture][transfer container]

Since: 3.14


gtk_gesture_is_grouped_with ()

gboolean
gtk_gesture_is_grouped_with (GtkGesture *gesture,
                             GtkGesture *other);

Returns TRUE if both gestures pertain to the same group.

Parameters

gesture

a GtkGesture

 

other

another GtkGesture

 

Returns

whether the gestures are grouped

Since: 3.14

Types and Values

GtkGesture

typedef struct _GtkGesture GtkGesture;

enum GtkEventSequenceState

Describes the state of a GdkEventSequence in a GtkGesture.

Members

GTK_EVENT_SEQUENCE_NONE

The sequence is handled, but not grabbed.

 

GTK_EVENT_SEQUENCE_CLAIMED

The sequence is handled and grabbed.

 

GTK_EVENT_SEQUENCE_DENIED

The sequence is denied.

 

Since: 3.14

Property Details

The “n-points” property

  “n-points”                 guint

The number of touch points that trigger recognition on this gesture,

Flags: Read / Write / Construct Only

Allowed values: >= 1

Default value: 1

Since: 3.14


The “window” property

  “window”                   GdkWindow *

If non-NULL, the gesture will only listen for events that happen on this GdkWindow, or a child of it.

Flags: Read / Write

Since: 3.14

Signal Details

The “begin” signal

void
user_function (GtkGesture       *gesture,
               GdkEventSequence *sequence,
               gpointer          user_data)

This signal is emitted when the gesture is recognized. This means the number of touch sequences matches “n-points”, and the “check” handler(s) returned TRUE.

Note: These conditions may also happen when an extra touch (eg. a third touch on a 2-touches gesture) is lifted, in that situation sequence won't pertain to the current set of active touches, so don't rely on this being true.

Parameters

gesture

the object which received the signal

 

sequence

the GdkEventSequence that made the gesture to be recognized

 

user_data

user data set when the signal handler was connected.

 

Flags: Run Last

Since: 3.14


The “cancel” signal

void
user_function (GtkGesture       *gesture,
               GdkEventSequence *sequence,
               gpointer          user_data)

This signal is emitted whenever a sequence is cancelled. This usually happens on active touches when gtk_event_controller_reset() is called on gesture (manually, due to grabs...), or the individual sequence was claimed by parent widgets' controllers (see gtk_gesture_set_sequence_state()).

gesture must forget everything about sequence as a reaction to this signal.

Parameters

gesture

the object which received the signal

 

sequence

the GdkEventSequence that was cancelled

 

user_data

user data set when the signal handler was connected.

 

Flags: Run Last

Since: 3.14


The “end” signal

void
user_function (GtkGesture       *gesture,
               GdkEventSequence *sequence,
               gpointer          user_data)

This signal is emitted when gesture either stopped recognizing the event sequences as something to be handled (the “check” handler returned FALSE), or the number of touch sequences became higher or lower than “n-points”.

Note: sequence might not pertain to the group of sequences that were previously triggering recognition on gesture (ie. a just pressed touch sequence that exceeds “n-points”). This situation may be detected by checking through gtk_gesture_handles_sequence().

Parameters

gesture

the object which received the signal

 

sequence

the GdkEventSequence that made gesture recognition to finish

 

user_data

user data set when the signal handler was connected.

 

Flags: Run Last

Since: 3.14


The “sequence-state-changed” signal

void
user_function (GtkGesture           *gesture,
               GdkEventSequence     *sequence,
               GtkEventSequenceState state,
               gpointer              user_data)

This signal is emitted whenever a sequence state changes. See gtk_gesture_set_sequence_state() to know more about the expectable sequence lifetimes.

Parameters

gesture

the object which received the signal

 

sequence

the GdkEventSequence that was cancelled

 

state

the new sequence state

 

user_data

user data set when the signal handler was connected.

 

Flags: Run Last

Since: 3.14


The “update” signal

void
user_function (GtkGesture       *gesture,
               GdkEventSequence *sequence,
               gpointer          user_data)

This signal is emitted whenever an event is handled while the gesture is recognized. sequence is guaranteed to pertain to the set of active touches.

Parameters

gesture

the object which received the signal

 

sequence

the GdkEventSequence that was updated

 

user_data

user data set when the signal handler was connected.

 

Flags: Run Last

Since: 3.14

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