Struct gtk4::Gesture

#[repr(transparent)]
pub struct Gesture { /* private fields */ }

Gesture is the base class for gesture recognition.

Although Gesture 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 gdk::EventSequence value for these).

The number of touches that a Gesture 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 Gesture 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 EventControllerExt::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 Gestures, 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 gdk::EventSequences triggering those.

Within a widget, gestures can be grouped through GestureExt::group_with(). Grouped gestures synchronize the state of sequences, so calling GestureExt::set_state() on one will effectively propagate the state throughout the group.

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

• Setting the same sequence to EventSequenceState::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 EventSequenceState::Claimed on GDK_TOUCH_BEGIN/GDK_BUTTON_PRESS (so those events are captured before reaching the event widget, this implies PropagationPhase::Capture), one similar event will be emulated if the sequence changes to EventSequenceState::Denied. This way event coherence is preserved before event propagation is unstopped again.

Sequence states can’t be changed freely. See GestureExt::set_state() to know about the possible lifetimes of a gdk::EventSequence.

Touchpad gestures

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

• If the gesture has PropagationPhase::None, ensuring events of type GDK_TOUCHPAD_SWIPE and GDK_TOUCHPAD_PINCH are handled by the Gesture

This is an Abstract Base Class, you cannot instantiate it.

Properties

n-points

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

Readable | Writeable | Construct Only

EventController

name

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

Readable | Writeable

propagation-limit

The limit for which events this controller will handle.

Readable | Writeable

propagation-phase

The propagation phase at which this controller will handle events.

Readable | Writeable

widget

The widget receiving the GdkEvents that the controller will handle.

Readable

Signals

begin

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.

cancel

Emitted whenever a sequence is cancelled.

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

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

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 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 GestureExt::handles_sequence().

sequence-state-changed

Emitted whenever a sequence state changes.

See GestureExt::set_sequence_state() to know more about the expectable sequence lifetimes.

update

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

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

Implements

GestureExt, EventControllerExt, glib::ObjectExt

Implementations

impl Gesture

pub const NONE: Option<&'static Gesture> = None

Trait Implementations

impl Clone for Gesture

fn clone(&self) -> Self

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for Gesture

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Display for Gesture

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl HasParamSpec for Gesture

type ParamSpec = ParamSpecObject

type SetValue = Gesture

Preferred value to be used as setter for the associated ParamSpec.

type BuilderFn = fn(_: &str) -> ParamSpecObjectBuilder<'_, Gesture>

fn param_spec_builder() -> Self::BuilderFn

impl Hash for Gesture

fn hash<H>(&self, state: &mut H)where H: Hasher,

Feeds this value into the given Hasher.

fn hash_slice<H>(data: &[Self], state: &mut H)where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher.

impl Ord for Gesture

fn cmp(&self, other: &Self) -> Ordering

This method returns an Ordering between self and other.

fn max(self, other: Self) -> Selfwhere Self: Sized,

Compares and returns the maximum of two values.

fn min(self, other: Self) -> Selfwhere Self: Sized,

Compares and returns the minimum of two values.

fn clamp(self, min: Self, max: Self) -> Selfwhere Self: Sized + PartialOrd<Self>,

Restrict a value to a certain interval.

impl ParentClassIs for Gesture

type Parent = EventController

impl<OT: ObjectType> PartialEq<OT> for Gesture

fn eq(&self, other: &OT) -> bool

This method tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

This method tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl<OT: ObjectType> PartialOrd<OT> for Gesture

fn partial_cmp(&self, other: &OT) -> Option<Ordering>

This method returns an ordering between self and other values if one exists.

fn lt(&self, other: &Rhs) -> bool

This method tests less than (for self and other) and is used by the < operator.

fn le(&self, other: &Rhs) -> bool

This method tests less than or equal to (for self and other) and is used by the <= operator.

fn gt(&self, other: &Rhs) -> bool

This method tests greater than (for self and other) and is used by the > operator.

fn ge(&self, other: &Rhs) -> bool

This method tests greater than or equal to (for self and other) and is used by the >= operator.

impl StaticType for Gesture

fn static_type() -> Type

Returns the type identifier of Self.

impl Eq for Gesture

impl IsA<EventController> for Gesture

impl IsA<Gesture> for DragSource

impl IsA<Gesture> for GestureClick

impl IsA<Gesture> for GestureDrag

impl IsA<Gesture> for GestureLongPress

impl IsA<Gesture> for GesturePan

impl IsA<Gesture> for GestureRotate

impl IsA<Gesture> for GestureSingle

impl IsA<Gesture> for GestureStylus

impl IsA<Gesture> for GestureSwipe

impl IsA<Gesture> for GestureZoom