Gnome::Gtk4::Gesture

Table of Contents
Description
Event propagation
States of a sequence
Touchpad gestures
Class initialization
new
:native-object
Methods
get-bounding-box
get-bounding-box-center
get-device
get-group
get-last-event
get-last-updated-sequence
get-point
get-sequence-state
get-sequences
group
handles-sequence
is-active
is-grouped-with
is-recognized
set-sequence-state
set-state
ungroup
Signals
begin
cancel
end
sequence-state-changed
update

Description

Gnome::Gtk4::Gesture is the base class for gesture recognition.

Although Gnome::Gtk4::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 undefined Gnome::Gdk4::N-EventSequence value for these).

The number of touches that a Gnome::Gtk4::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 Gnome::Gtk4::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 .set-propagation-phase() in class Gnome::Gtk4::EventController.

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 Gnome::Gtk4::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 Gnome::Gdk4::N-EventSequences 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 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 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 .set-state() to know about the possible lifetimes of a Gnome::Gdk4::N-EventSequence.

Touchpad gestures

On the platforms that support it, Gnome::Gtk4::Gesture will handle transparently touchpad gesture events. The only precautions users of Gnome::Gtk4::Gesture 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 Gnome::Gtk4::Gesture

Class initialization

new

:native-object

Create an object using a native object from elsewhere. See also Gnome::N::TopLevelSupportClass.

multi method new ( N-Object :$native-object! )

Methods

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.

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.

method get-bounding-box ( N-Object $rect --> Bool )

$rect; bounding box containing all active touches.

Return value; True if there are active touches, False otherwise.

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.

Otherwise, False will be returned.

method get-bounding-box-center ( Num() $x, Num() $y --> Bool )

$x; (transfer ownership: full) X coordinate for the bounding box center.
$y; (transfer ownership: full) Y coordinate for the bounding box center.

Return value; False if no active touches are present, True otherwise.

get-device

Returns the logical Gnome::Gdk4::Device that is currently operating on $gesture.

This returns undefined if the gesture is not being interacted.

method get-device (--> N-Object )

Return value; a Gnome::Gdk4::Device.

get-group

Returns all gestures in the group of $gesture

method get-group (--> N-List )

Return value; The list of Gnome::Gtk4::Gestures, free with g_list_free().

get-last-event

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.

method get-last-event ( N-Object $sequence --> N-Object )

$sequence; a Gnome::Gdk4::N-EventSequence

Return value; The last event from $sequence.

get-last-updated-sequence

Returns the Gnome::Gdk4::N-EventSequence that was last updated on $gesture.

method get-last-updated-sequence (--> N-Object )

Return value; The last updated sequence.

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.

The coordinates are always relative to the widget allocation.

method get-point ( N-Object $sequence, Num() $x, Num() $y --> Bool )

$sequence; a Gnome::Gdk4::N-EventSequence, or undefined for pointer events
$x; (transfer ownership: full) return location for X axis of the sequence coordinates.
$y; (transfer ownership: full) return location for Y axis of the sequence coordinates.

Return value; True if $sequence is currently interpreted.

get-sequence-state

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

method get-sequence-state ( N-Object $sequence --> GtkEventSequenceState )

$sequence; a Gnome::Gdk4::N-EventSequence

Return value; The sequence state in $gesture.

get-sequences

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

method get-sequences (--> N-List )

Return value; A list of Gnome::Gdk4::N-EventSequence, the list elements are owned by GTK and must not be freed or modified, the list itself must be deleted through g_list_free().

group

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 Gnome::Gdk4::N-EventSequence state is set to GTK_EVENT_SEQUENCE_CLAIMED on one group, every other gesture group attached to the same Gnome::Gtk4::Widget will switch the state for that sequence to GTK_EVENT_SEQUENCE_DENIED.

method group ( N-Object() $gesture )

$gesture; a Gnome::Gtk4::Gesture.

handles-sequence

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

method handles-sequence ( N-Object $sequence --> Bool )

$sequence; a Gnome::Gdk4::N-EventSequence

Return value; True if $gesture is handling $sequence, False otherwise.

is-active

Returns True if the gesture is currently active.

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

method is-active (--> Bool )

Return value; True if gesture is active.

is-grouped-with

Returns True if both gestures pertain to the same group.

method is-grouped-with ( N-Object() $other --> Bool )

$other; another Gnome::Gtk4::Gesture.

Return value; whether the gestures are grouped.

is-recognized

Returns True if the gesture is currently recognized.

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

method is-recognized (--> Bool )

Return value; True if gesture is recognized.

set-sequence-state

Note: The native version of this routine is deprecated in gtk4-lib() since version 4.10.

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:

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.

method set-sequence-state ( N-Object $sequence, GtkEventSequenceState $state --> Bool )

$sequence; a Gnome::Gdk4::N-EventSequence
$state; the sequence state.

Return value; True if $sequence is handled by $gesture, and the state is changed successfully.

set-state

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

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

method set-state ( GtkEventSequenceState $state --> Bool )

$state; the sequence state.

Return value; True if the state of at least one sequence was changed successfully.

ungroup

Separates $gesture into an isolated group.

method ungroup ( )

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.

method handler (
   $sequence,
  Int :$_handle_id,
  N-GObject :$_native-object,
  Gnome::Gtk4::Gesture :$_widget,
  *C<user>-options
)

$sequence; the Gnome::Gdk4::N-EventSequence that made the gesture to be recognized.
$_handle_id; The registered event handler id.
$_native-object; The native object provided by the Raku object which registered this event. This a native Gnome::Gtk4::Gesture object.
$_widget; The object which registered the signal. User code may have left the object going out of scope.
user-options; A list of named arguments provided at the .register-signal() method from Gnome::GObject::Object.

cancel

Emitted whenever a sequence is cancelled.

This usually happens on active touches when .reset() in class Gnome::Gtk4::EventController 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.

method handler (
   $sequence,
  Int :$_handle_id,
  N-GObject :$_native-object,
  Gnome::Gtk4::Gesture :$_widget,
  *C<user>-options
)

$sequence; the Gnome::Gdk4::N-EventSequence that was cancelled.
$_handle_id; The registered event handler id.
$_native-object; The native object provided by the Raku object which registered this event. This a native Gnome::Gtk4::Gesture object.
$_widget; The object which registered the signal. User code may have left the object going out of scope.
user-options; A list of named arguments provided at the .register-signal() method from Gnome::GObject::Object.

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 .handles-sequence().

method handler (
   $sequence,
  Int :$_handle_id,
  N-GObject :$_native-object,
  Gnome::Gtk4::Gesture :$_widget,
  *C<user>-options
)

$sequence; the Gnome::Gdk4::N-EventSequence that made gesture recognition to finish.
$_handle_id; The registered event handler id.
$_native-object; The native object provided by the Raku object which registered this event. This a native Gnome::Gtk4::Gesture object.
$_widget; The object which registered the signal. User code may have left the object going out of scope.
user-options; A list of named arguments provided at the .register-signal() method from Gnome::GObject::Object.

sequence-state-changed

Emitted whenever a sequence state changes.

See .set-sequence-state() to know more about the expectable sequence lifetimes.

method handler (
   $sequence,
   $state,
  Int :$_handle_id,
  N-GObject :$_native-object,
  Gnome::Gtk4::Gesture :$_widget,
  *C<user>-options
)

$sequence; the Gnome::Gdk4::N-EventSequence that was cancelled.
$state; the new sequence state.
$_handle_id; The registered event handler id.
$_native-object; The native object provided by the Raku object which registered this event. This a native Gnome::Gtk4::Gesture object.
$_widget; The object which registered the signal. User code may have left the object going out of scope.
user-options; A list of named arguments provided at the .register-signal() method from Gnome::GObject::Object.

update

Emitted whenever an event is handled while the gesture is recognized. $sequence is guaranteed to pertain to the set of active touches.

method handler (
   $sequence,
  Int :$_handle_id,
  N-GObject :$_native-object,
  Gnome::Gtk4::Gesture :$_widget,
  *C<user>-options
)

$sequence; the Gnome::Gdk4::N-EventSequence that was updated.
$_handle_id; The registered event handler id.
$_native-object; The native object provided by the Raku object which registered this event. This a native Gnome::Gtk4::Gesture object.
$_widget; The object which registered the signal. User code may have left the object going out of scope.
user-options; A list of named arguments provided at the .register-signal() method from Gnome::GObject::Object.