[libhandy] swipe-tracker: Add begin-swipe signal

[Adrien Plazas <aplazas src gnome org>]

commit 58a6ac89ab81a2e99e1606ac64b9013c1d19100f
Author: Alexander Mikhaylenko <alexm gnome org>
Date:   Sat Jun 20 16:48:58 2020 +0500

    swipe-tracker: Add begin-swipe signal
    
    This will replace HdySwipeable's signal and at the same time allow
    swipeables to connect to it instead of overriding begin_swipe() there,
    making it clear the 2 classes are closely related and are only meant to be
    used together.
    
    Signed-off-by: Alexander Mikhaylenko <alexm gnome org>

 src/hdy-swipe-tracker-private.h |  4 ++++
 src/hdy-swipe-tracker.c         | 42 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 46 insertions(+)
---
diff --git a/src/hdy-swipe-tracker-private.h b/src/hdy-swipe-tracker-private.h
index ee4891dd..8d364a0d 100644
--- a/src/hdy-swipe-tracker-private.h
+++ b/src/hdy-swipe-tracker-private.h
@@ -38,4 +38,8 @@ void             hdy_swipe_tracker_set_allow_mouse_drag (HdySwipeTracker *self,
 void             hdy_swipe_tracker_shift_position (HdySwipeTracker *self,
                                                    gdouble          delta);
 
+void             hdy_swipe_tracker_emit_begin_swipe (HdySwipeTracker        *self,
+                                                     HdyNavigationDirection  direction,
+                                                     gboolean                direct);
+
 G_END_DECLS
diff --git a/src/hdy-swipe-tracker.c b/src/hdy-swipe-tracker.c
index 6895cb0c..f704ac73 100644
--- a/src/hdy-swipe-tracker.c
+++ b/src/hdy-swipe-tracker.c
@@ -90,6 +90,13 @@ enum {
 
 static GParamSpec *props[LAST_PROP];
 
+enum {
+  SIGNAL_BEGIN_SWIPE,
+  SIGNAL_LAST_SIGNAL,
+};
+
+static guint signals[SIGNAL_LAST_SIGNAL];
+
 static void
 reset (HdySwipeTracker *self)
 {
@@ -117,6 +124,7 @@ gesture_prepare (HdySwipeTracker        *self,
     return;
 
   hdy_swipeable_begin_swipe (self->swipeable, direction, TRUE);
+  hdy_swipe_tracker_emit_begin_swipe (self, direction, TRUE);
 
   self->initial_progress = hdy_swipeable_get_progress (self->swipeable);
   self->progress = self->initial_progress;
@@ -739,6 +747,30 @@ hdy_swipe_tracker_class_init (HdySwipeTrackerClass *klass)
                                     "orientation");
 
   g_object_class_install_properties (object_class, LAST_PROP, props);
+
+  /**
+   * HdySwipeTracker::begin-swipe:
+   * @self: The #HdySwipeTracker instance
+   * @direction: The direction of the swipe
+   * @direct: %TRUE if the swipe is directly triggered by a gesture,
+   *   %FALSE if it's triggered via a #HdySwipeGroup
+   *
+   * This signal is emitted when a possible swipe is detected.
+   *
+   * The @direction value can be used to restrict the swipe to a certain
+   * direction.
+   *
+   * Since: 1.0
+   */
+  signals[SIGNAL_BEGIN_SWIPE] =
+    g_signal_new ("begin-swipe",
+                  G_TYPE_FROM_CLASS (klass),
+                  G_SIGNAL_RUN_FIRST,
+                  0,
+                  NULL, NULL, NULL,
+                  G_TYPE_NONE,
+                  2,
+                  HDY_TYPE_NAVIGATION_DIRECTION, G_TYPE_BOOLEAN);
 }
 
 static void
@@ -944,3 +976,13 @@ hdy_swipe_tracker_shift_position (HdySwipeTracker *self,
   self->progress += delta;
   self->initial_progress += delta;
 }
+
+void
+hdy_swipe_tracker_emit_begin_swipe (HdySwipeTracker        *self,
+                                    HdyNavigationDirection  direction,
+                                    gboolean                direct)
+{
+  g_return_if_fail (HDY_IS_SWIPE_TRACKER (self));
+
+  g_signal_emit (self, signals[SIGNAL_BEGIN_SWIPE], 0, direction, direct);
+}