Class Gesture

java.lang.Object
org.javagi.base.ProxyInstance
org.gnome.gobject.TypeInstance
org.gnome.gobject.GObject
org.gnome.gtk.EventController
org.gnome.gtk.Gesture
All Implemented Interfaces:
Proxy
Direct Known Subclasses:
Gesture.Gesture$Impl, GestureRotate, GestureSingle, GestureZoom
@Generated("org.javagi.JavaGI") public abstract class Gesture extends EventController

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 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:

  • Gtk.Gesture::begin when the gesture is recognized.
  • Gtk.Gesture::update, whenever an input event is processed.
  • Gtk.Gesture::end when the gesture is no longer recognized.

Event propagation

In order to receive events, a gesture needs to set a propagation phase through EventController.setPropagationPhase(PropagationPhase).

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 GtkGestures, 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 GdkEventSequences triggering those.

Within a widget, gestures can be grouped through group(Gesture). Grouped gestures synchronize the state of sequences, so calling setState(EventSequenceState) 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 Gtk.Gesture::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 EventType.TOUCH_BEGIN/EventType.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 setState(EventSequenceState) 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:

  • Constructor Details

    • Gesture

      public Gesture(MemorySegment address)
      Create a Gesture instance for the provided memory address.
      Parameters:
      address - the memory address of the native object

    • Gesture

      public Gesture()
      Create a new Gesture.

  • Method Details

    • getType

      public static @Nullable Type getType()
      Get the GType of the Gesture class.
      Returns:
      the GType

    • getMemoryLayout

      public static MemoryLayout getMemoryLayout()
      The memory layout of the native struct.
      Returns:
      the memory layout

    • asParent

      protected Gesture asParent()
      Return this instance as if it were its parent type. Comparable to the Java super keyword, but ensures the parent typeclass is also used in native code.
      Overrides:
      asParent in class EventController
      Returns:
      the instance as if it were its parent type

    • getBoundingBox

      public boolean getBoundingBox(Rectangle rect)

      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.

      Parameters:
      rect - bounding box containing all active touches.
      Returns:
      true if there are active touches, false otherwise

    • getBoundingBoxCenter

      public boolean getBoundingBoxCenter(Out<Double> x, Out<Double> y)

      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.

      Parameters:
      x - X coordinate for the bounding box center
      y - Y coordinate for the bounding box center
      Returns:
      false if no active touches are present, true otherwise

    • getDevice

      public @Nullable Device getDevice()

      Returns the logical GdkDevice that is currently operating on gesture.

      This returns null if the gesture is not being interacted.

      Returns:
      a GdkDevice

    • getGroup

      public List<Gesture> getGroup()
      Returns all gestures in the group of this Gesture
      Returns:
      The list of GtkGestures, free with g_list_free()

    • getLastEvent

      public @Nullable Event getLastEvent(@Nullable EventSequence sequence)

      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
      Returns:
      The last event from sequence

    • getLastUpdatedSequence

      public @Nullable EventSequence getLastUpdatedSequence()
      Returns the GdkEventSequence that was last updated on gesture.
      Returns:
      The last updated sequence

    • getPoint

      public boolean getPoint(@Nullable EventSequence sequence, @Nullable Out<Double> x, @Nullable Out<Double> y)

      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 null for pointer events
      x - return location for X axis of the sequence coordinates
      y - return location for Y axis of the sequence coordinates
      Returns:
      true if sequence is currently interpreted

    • getSequenceState

      public EventSequenceState getSequenceState(EventSequence sequence)
      Returns the sequence state, as seen by gesture.
      Parameters:
      sequence - a GdkEventSequence
      Returns:
      The sequence state in this Gesture

    • getSequences

      public List<EventSequence> getSequences()
      Returns the list of GdkEventSequences currently being interpreted by gesture.
      Returns:
      A list of GdkEventSequence, 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

      public void group(Gesture gesture)

      Adds gesture to the same group than groupGesture.

      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 setSequenceState(EventSequence, EventSequenceState), 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 EventSequenceState.CLAIMED on one group, every other gesture group attached to the same GtkWidget will switch the state for that sequence to EventSequenceState.DENIED.

      Parameters:
      gesture - a GtkGesture

    • handlesSequence

      public boolean handlesSequence(@Nullable EventSequence sequence)
      Returns true if this Gesture is currently handling events corresponding to sequence.
      Parameters:
      sequence - a GdkEventSequence
      Returns:
      true if this Gesture is handling sequence, false otherwise

    • isActive

      public boolean isActive()

      Returns true if the gesture is currently active.

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

      Returns:
      true if gesture is active

    • isGroupedWith

      public boolean isGroupedWith(Gesture other)
      Returns true if both gestures pertain to the same group.
      Parameters:
      other - another GtkGesture
      Returns:
      whether the gestures are grouped

    • isRecognized

      public boolean isRecognized()

      Returns true if the gesture is currently recognized.

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

      Returns:
      true if gesture is recognized

    • setSequenceState

      @Deprecated public boolean setSequenceState(EventSequence sequence, EventSequenceState state)
      Deprecated.
      Use setState(EventSequenceState)

      Sets the state of sequence in gesture.

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

      Parameters:
      sequence - a GdkEventSequence
      state - the sequence state
      Returns:
      true if sequence is handled by gesture, and the state is changed successfully

    • setState

      public boolean setState(EventSequenceState state)

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

      Sequences start in state EventSequenceState.NONE, and whenever they change state, they can never go back to that state. Likewise, sequences in state EventSequenceState.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 Gtk.Gesture::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_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);
}

      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.

      Parameters:
      state - the sequence state
      Returns:
      true if the state of at least one sequence was changed successfully

    • ungroup

      public void ungroup()
      Separates this Gesture into an isolated group.

    • onBegin

      public SignalConnection<Gesture.BeginCallback> onBegin(Gesture.BeginCallback handler)

      Emitted when the gesture is recognized.

      This means the number of touch sequences matches Gtk.Gesture: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:
      handler - the signal handler
      Returns:
      a signal handler ID to keep track of the signal connection
      See Also:

    • emitBegin

      public void emitBegin(@Nullable EventSequence sequence)
      Emits the "begin" signal. See onBegin(Gesture.BeginCallback).

    • onCancel

      public SignalConnection<Gesture.CancelCallback> onCancel(Gesture.CancelCallback handler)

      Emitted whenever a sequence is cancelled.

      This usually happens on active touches when EventController.reset() is called on gesture (manually, due to grabs...), or the individual sequence was claimed by parent widgets' controllers (see setSequenceState(EventSequence, EventSequenceState)).

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

      Parameters:
      handler - the signal handler
      Returns:
      a signal handler ID to keep track of the signal connection
      See Also:

    • emitCancel

      public void emitCancel(@Nullable EventSequence sequence)
      Emits the "cancel" signal. See onCancel(Gesture.CancelCallback).

    • onEnd

      public SignalConnection<Gesture.EndCallback> onEnd(Gesture.EndCallback handler)

      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 Gtk.Gesture: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 Gtk.Gesture:n-points). This situation may be detected by checking through handlesSequence(EventSequence).

      Parameters:
      handler - the signal handler
      Returns:
      a signal handler ID to keep track of the signal connection
      See Also:

    • emitEnd

      public void emitEnd(@Nullable EventSequence sequence)
      Emits the "end" signal. See onEnd(Gesture.EndCallback).

    • onSequenceStateChanged

      public SignalConnection<Gesture.SequenceStateChangedCallback> onSequenceStateChanged(Gesture.SequenceStateChangedCallback handler)

      Emitted whenever a sequence state changes.

      See setSequenceState(EventSequence, EventSequenceState) to know more about the expectable sequence lifetimes.

      Parameters:
      handler - the signal handler
      Returns:
      a signal handler ID to keep track of the signal connection
      See Also:

    • emitSequenceStateChanged

      public void emitSequenceStateChanged(@Nullable EventSequence sequence, EventSequenceState state)
      Emits the "sequence-state-changed" signal. See onSequenceStateChanged(Gesture.SequenceStateChangedCallback).

    • onUpdate

      public SignalConnection<Gesture.UpdateCallback> onUpdate(Gesture.UpdateCallback handler)

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

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

      Parameters:
      handler - the signal handler
      Returns:
      a signal handler ID to keep track of the signal connection
      See Also:

    • emitUpdate

      public void emitUpdate(@Nullable EventSequence sequence)
      Emits the "update" signal. See onUpdate(Gesture.UpdateCallback).