Gesture

class Gesture(**properties: Any)

Superclasses: EventController, Object

Subclasses: GestureRotate, GestureSingle, GestureZoom

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 None 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 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:

begin when the gesture is recognized.
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 set a propagation phase through 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 group. Grouped gestures synchronize the state of sequences, so calling set_state on one will effectively propagate the state throughout the group.

By default, all sequences start out in the 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 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 CLAIMED state, the gesture group will grab all interaction on the sequence, by:

Setting the same sequence to DENIED on every other gesture group within the widget, and every gesture on parent widgets in the propagation chain.
Emitting 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 CLAIMED on %GDK_TOUCH_BEGIN/%GDK_BUTTON_PRESS (so those events are captured before reaching the event widget, this implies CAPTURE), one similar event will be emulated if the sequence changes to DENIED. This way event coherence is preserved before event propagation is unstopped again.

Sequence states can’t be changed freely. See 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 NONE, ensuring events of type %GDK_TOUCHPAD_SWIPE and %GDK_TOUCHPAD_PINCH are handled by the GtkGesture

Methods

class Gesture

get_bounding_box() → tuple[bool, Rectangle]

If there are touch sequences being currently handled by gesture, 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.

get_bounding_box_center() → tuple[bool, float, float]

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.

Otherwise, False will be returned.

get_device() → Device | None

Returns the logical GdkDevice that is currently operating on gesture.

This returns None if the gesture is not being interacted.

get_group() → list[Gesture]: Returns all gestures in the group of gesture

get_last_event(sequence: EventSequence | None = None) → Event | None

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:: sequence – a GdkEventSequence

get_last_updated_sequence() → EventSequence | None: Returns the GdkEventSequence that was last updated on gesture.

get_point(sequence: EventSequence | None = None) → tuple[bool, float, float]

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.

The coordinates are always relative to the widget allocation.

Parameters:: sequence – a GdkEventSequence, or None for pointer events

get_sequence_state(sequence: EventSequence) → EventSequenceState

Returns the sequence state, as seen by gesture.

Parameters:: sequence – a GdkEventSequence

get_sequences() → list[EventSequence]: Returns the list of GdkEventSequences currently being interpreted by gesture.

group(gesture: Gesture) → None

Adds gesture to the same group than group_gesture.

Gestures are by default isolated in their own groups.

Both gestures must have been added to the same widget before they can be grouped.

When gestures are grouped, the state of GdkEventSequences is kept in sync for all of those, so calling 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 CLAIMED on one group, every other gesture group attached to the same GtkWidget will switch the state for that sequence to DENIED.

Parameters:: gesture – a GtkGesture

handles_sequence(sequence: EventSequence | None = None) → bool

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

Parameters:: sequence – a GdkEventSequence

is_active() → bool

Returns True if the gesture is currently active.

A gesture is active while there are touch sequences interacting with it.

is_grouped_with(other: Gesture) → bool

Returns True if both gestures pertain to the same group.

Parameters:: other – another GtkGesture

is_recognized() → bool

Returns True if the gesture is currently recognized.

A gesture is recognized if there are as many interacting touch sequences as required by gesture.

set_sequence_state(sequence: EventSequence, state: EventSequenceState) → bool

Sets the state of sequence in gesture.

Sequences start in state NONE, and whenever they change state, they can never go back to that state. Likewise, sequences in state 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:

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_CLAIMED);
  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_CLAIMED)
    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.

Deprecated since version 4.10.: Use set_state

Parameters:

sequence – a GdkEventSequence
state – the sequence state

set_state(state: EventSequenceState) → bool

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

None
None → Denied
None → Claimed
None → Claimed → Denied

static void
first_gesture_begin_cb (GtkGesture       *first_gesture,
                        GdkEventSequence *sequence,
                        gpointer          user_data)
{
  gtk_gesture_set_state (first_gesture, GTK_EVENT_SEQUENCE_CLAIMED);
  gtk_gesture_set_state (second_gesture, 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_CLAIMED)
    gtk_gesture_set_state (second_gesture, GTK_EVENT_SEQUENCE_DENIED);
}

Parameters:: state – the sequence state

ungroup() → None: Separates gesture into an isolated group.

Properties

class Gesture

props.n_points: int: The number of touch points that trigger recognition on this gesture.

Signals

class Gesture.signals

begin(sequence: EventSequence | None = None) → None

Emitted when the gesture is recognized.

This means the number of touch sequences matches n_points.

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:: sequence – the GdkEventSequence that made the gesture to be recognized

cancel(sequence: EventSequence | None = None) → None

Emitted whenever a sequence is cancelled.

This usually happens on active touches when reset is called on gesture (manually, due to grabs…), or the individual sequence was claimed by parent widgets’ controllers (see set_sequence_state).

gesture must forget everything about sequence as in response to this signal.

Parameters:: sequence – the GdkEventSequence that was cancelled

end(sequence: EventSequence | None = None) → None

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 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 handles_sequence.

Parameters:: sequence – the GdkEventSequence that made gesture recognition to finish

sequence_state_changed(sequence: EventSequence | None, state: EventSequenceState) → None

Emitted whenever a sequence state changes.

See set_sequence_state to know more about the expectable sequence lifetimes.

Parameters:

sequence – the GdkEventSequence that was cancelled
state – the new sequence state

update(sequence: EventSequence | None = None) → None

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

sequence is guaranteed to pertain to the set of active touches.

Parameters:: sequence – the GdkEventSequence that was updated