Gesture

Object Hierarchy:

Description:

[ CCode ( type_id = "gtk_gesture_get_type ()" ) ]
public abstract class Gesture : EventController

`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 [property@Gtk.Gesture: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:

[signal@Gtk.Gesture:GtkGesture:begin] when the gesture is recognized.
[signal@Gtk.Gesture:GtkGesture:update], whenever an input event is processed.
[signal@Gtk.Gesture: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 [method@Gtk.EventController.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 [method@Gtk.Gesture.group]. Grouped gestures synchronize the state of sequences, so calling [ method@Gtk.Gesture.set_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 [signal@Gtk.Gesture: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 [method@Gtk.Gesture.set_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`

All known sub-classes:

Namespace: Gtk

Package: gtk4

Content:

Properties:

public uint n_points { get; construct; }
The number of touch points that trigger recognition on this gesture.

Creation methods:

protected Gesture ()

Methods:

public bool get_bounding_box (out Rectangle rect)
If there are touch sequences being currently handled by this, returns true and fills in rect with the bounding box containing all active touches.
public bool get_bounding_box_center (out double x, out double y)
If there are touch sequences being currently handled by this, returns true and fills in x and y with the center of the bounding box containing all active touches.
public unowned Device? get_device ()
Returns the logical `GdkDevice` that is currently operating on this.
public List<unowned Gesture> get_group ()
Returns all gestures in the group of this
public unowned Event? get_last_event (EventSequence? sequence)
Returns the last event that was processed for sequence.
public unowned EventSequence? get_last_updated_sequence ()
Returns the `GdkEventSequence` that was last updated on this.
public bool get_point (EventSequence? sequence, out double x = null, out double y = null)
If sequence is currently being interpreted by this, returns true and fills in x and y with the last coordinates stored for that event sequence.
public EventSequenceState get_sequence_state (EventSequence sequence)
Returns the sequence state, as seen by this.
public List<unowned EventSequence> get_sequences ()
Returns the list of `GdkEventSequences` currently being interpreted by this.
public void group (Gesture gesture)
Adds gesture to the same group than this.
public bool handles_sequence (EventSequence? sequence)
Returns true if this is currently handling events corresponding to sequence.
public bool is_active ()
Returns true if the gesture is currently active.
public bool is_grouped_with (Gesture other)
Returns true if both gestures pertain to the same group.
public bool is_recognized ()
Returns true if the gesture is currently recognized.
public bool set_sequence_state (EventSequence sequence, EventSequenceState state)
Sets the state of sequence in this .
public bool set_state (EventSequenceState state)
Sets the state of all sequences that this is currently interacting with.
public void ungroup ()
Separates this into an isolated group.

Signals:

public signal void begin (EventSequence? sequence)
Emitted when the gesture is recognized.
public signal void cancel (EventSequence? sequence)
Emitted whenever a sequence is cancelled.
public signal void end (EventSequence? sequence)
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 [property@Gtk.
public signal void sequence_state_changed (EventSequence? sequence, EventSequenceState state)
Emitted whenever a sequence state changes.
public signal void update (EventSequence? sequence)
Emitted whenever an event is handled while the gesture is recognized.

Inherited Members:

All known members inherited from class Gtk.EventController

All known members inherited from class GLib.Object