Although gtk.gesture.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 null gdk.event_sequence.EventSequence
value for these).
The number of touches that a gtk.gesture.Gesture 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 gtk.gesture.Gesture subclasses.
A recognized gesture will then emit the following signals:
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.
Whenever input interaction happens, a single event may trigger a cascade
of gtk.gesture.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.event_sequence.EventSequences triggering those.
Within a widget, gestures can be grouped through gtk.gesture.Gesture.group.
Grouped gestures synchronize the state of sequences, so calling
gtk.gesture.Gesture.setState on one will effectively propagate
the state throughout the group.
By default, all sequences start out in the gtk.types.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 gtk.types.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.
Setting the same sequence to gtk.types.EventSequenceState.Denied on every other
gesture group within the widget, and every gesture on parent widgets
in the propagation chain.
On the platforms that support it, gtk.gesture.Gesture will handle transparently
touchpad gesture events. The only precautions users of gtk.gesture.Gesture should
do to enable this support are:
gtk.gesture.Gesture is the base class for gesture recognition.
Although gtk.gesture.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 null gdk.event_sequence.EventSequence value for these).
The number of touches that a gtk.gesture.Gesture 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 gtk.gesture.Gesture subclasses.
A recognized gesture will then emit the following signals:
Event propagation
In order to receive events, a gesture needs to set a propagation phase through gtk.event_controller.EventController.setPropagationPhase.
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 gtk.gesture.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.event_sequence.EventSequences triggering those.
Within a widget, gestures can be grouped through gtk.gesture.Gesture.group. Grouped gestures synchronize the state of sequences, so calling gtk.gesture.Gesture.setState on one will effectively propagate the state throughout the group.
By default, all sequences start out in the gtk.types.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 gtk.types.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 gtk.types.EventSequenceState.Claimed state, the gesture group will grab all interaction on the sequence, by:
Note: if a sequence is set early to gtk.types.EventSequenceState.Claimed on gdk.types.EventType.TouchBegin/gdk.types.EventType.ButtonPress (so those events are captured before reaching the event widget, this implies gtk.types.PropagationPhase.Capture), one similar event will be emulated if the sequence changes to gtk.types.EventSequenceState.Denied. This way event coherence is preserved before event propagation is unstopped again.
Sequence states can't be changed freely. See gtk.gesture.Gesture.setState to know about the possible lifetimes of a gdk.event_sequence.EventSequence.
Touchpad gestures
On the platforms that support it, gtk.gesture.Gesture will handle transparently touchpad gesture events. The only precautions users of gtk.gesture.Gesture should do to enable this support are: