Gtk.Gesture
Description: Reference for Gtk.Gesture

### Class

# GtkGesture

#### Description [src]

    abstract class Gtk.Gesture : Gtk.EventController {
      /* No available fields */
    }

`GtkGesture` is the base class for gesture recognition.

Although `GtkGesture` 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 `GtkGesture:n-points` property, if a gesture is keeping track of less or more than that number of sequences, it won’t check whether the gesture is recognized.

As soon as the gesture has the expected number of touches, it will check regularly if it is recognized, the criteria to consider a gesture as “recognized” is left to `GtkGesture` subclasses.

A recognized gesture will then emit the following signals:

- `GtkGesture::begin` when the gesture is recognized.
- `GtkGesture::update`, whenever an input event is processed.
- `GtkGesture::end` when the gesture is no longer recognized.

## Event propagation

In order to receive events, a gesture needs to set a propagation phase through `gtk_event_controller_set_propagation_phase()`.

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.

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 `GtkGesture`s, 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 `GdkEventSequence`s 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.
- Emitting `GtkGesture::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 be 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:

- If the gesture has `GTK_PHASE_NONE`, ensuring events of type `GDK_TOUCHPAD_SWIPE` and `GDK_TOUCHPAD_PINCH` are handled by the `GtkGesture`

#### Ancestors

- GtkEventController
- GObject

#### Descendants

- GtkGestureRotate
- GtkGestureSingle
- GtkGestureZoom

#### Instance methods

###### gtk_gesture_get_bounding_box

If there are touch sequences being currently handled by `gesture`, returns `TRUE` and fills in `rect` with the bounding box containing all active touches.

###### gtk_gesture_get_bounding_box_center

If there are touch sequences being currently handled by `gesture`, returns `TRUE` and fills in `x` and `y` with the center of the bounding box containing all active touches.

###### gtk_gesture_get_device

Returns the logical `GdkDevice` that is currently operating on `gesture`.

###### gtk_gesture_get_group

Returns all gestures in the group of `gesture`.

###### gtk_gesture_get_last_event

Returns the last event that was processed for `sequence`.

###### gtk_gesture_get_last_updated_sequence

Returns the `GdkEventSequence` that was last updated on `gesture`.

###### gtk_gesture_get_point

If `sequence` is currently being interpreted by `gesture`, returns `TRUE` and fills in `x` and `y` with the last coordinates stored for that event sequence.

###### gtk_gesture_get_sequence_state

Returns the `sequence` state, as seen by `gesture`.

###### gtk_gesture_get_sequences

Returns the list of `GdkEventSequences` currently being interpreted by `gesture`.

###### gtk_gesture_group

Adds `gesture` to the same group than `group_gesture`.

###### gtk_gesture_handles_sequence

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

###### gtk_gesture_is_active

Returns `TRUE` if the gesture is currently active.

###### gtk_gesture_is_grouped_with

Returns `TRUE` if both gestures pertain to the same group.

###### gtk_gesture_is_recognized

Returns `TRUE` if the gesture is currently recognized.

###### gtk_gesture_set_sequence_state

Sets the state of `sequence` in `gesture`.

###### gtk_gesture_set_state

Sets the state of all sequences that `gesture` is currently interacting with.

###### gtk_gesture_ungroup

Separates `gesture` into an isolated group.

##### Methods inherited from GtkEventController (13)

###### gtk_event_controller_get_current_event

Returns the event that is currently being handled by the controller.

###### gtk_event_controller_get_current_event_device

Returns the device of the event that is currently being handled by the controller.

###### gtk_event_controller_get_current_event_state

Returns the modifier state of the event that is currently being handled by the controller.

###### gtk_event_controller_get_current_event_time

Returns the timestamp of the event that is currently being handled by the controller.

###### gtk_event_controller_get_name

Gets the name of `controller`.

###### gtk_event_controller_get_propagation_limit

Gets the propagation limit of the event controller.

###### gtk_event_controller_get_propagation_phase

Gets the propagation phase at which `controller` handles events.

###### gtk_event_controller_get_widget

Returns the `GtkWidget` this controller relates to.

###### gtk_event_controller_reset

Resets the `controller` to a clean state.

###### gtk_event_controller_set_name

Sets a name on the controller that can be used for debugging.

###### gtk_event_controller_set_propagation_limit

Sets the event propagation limit on the event controller.

###### gtk_event_controller_set_propagation_phase

Sets the propagation phase at which a controller handles events.

###### gtk_event_controller_set_static_name

Sets a name on the controller that can be used for debugging.

Available since: 4.8

##### Methods inherited from GObject (43)

Please see GObject for a full list of methods.

#### Properties

###### Gtk.Gesture:n-points

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

##### Properties inherited from GtkEventController (4)

###### Gtk.EventController:name

The name for this controller, typically used for debugging purposes.

###### Gtk.EventController:propagation-limit

The limit for which events this controller will handle.

###### Gtk.EventController:propagation-phase

The propagation phase at which this controller will handle events.

###### Gtk.EventController:widget

The widget receiving the `GdkEvents` that the controller will handle.

#### Signals

###### Gtk.Gesture::begin

Emitted when the gesture is recognized.

###### Gtk.Gesture::cancel

Emitted whenever a sequence is cancelled.

###### Gtk.Gesture::end

Emitted when `gesture` either stopped recognizing the event sequences as something to be handled, or the number of touch sequences became higher or lower than `GtkGesture:n-points`.

###### Gtk.Gesture::sequence-state-changed

Emitted whenever a sequence state changes.

###### Gtk.Gesture::update

Emitted whenever an event is handled while the gesture is recognized.

##### Signals inherited from GObject (1)

###### GObject.Object::notify

The notify signal is emitted on an object when one of its properties has its value set through g_object_set_property(), g_object_set(), et al.

#### Class structure

    struct GtkGestureClass {
      /* no available fields */
    }

No description available.