scrolledwindow: Handle directional cancellation if there is a single scroll direction

A pan gesture is optionally attached if there is only one scrolling direction, the pan
gesture orientation is changed so movements tangential to the scroll direction get
scrolling cancelled (The pan gesture is automatically denied when that happens, and
that state change spreads to the others gestures in the group). If the pan direction
happens in the expected directions, no cancellation happens, and scrolling eventually
takes place.

1 files changed, 36 insertions, 2 deletions

diff --git a/gtk/gtkscrolledwindow.c b/gtk/gtkscrolledwindow.c
index 65061d4ffc..e5fe575cf2 100644
--- a/gtk/gtkscrolledwindow.c
+++ b/gtk/gtkscrolledwindow.c
@@ -149,9 +149,13 @@ struct _GtkScrolledWindowPrivate
   gint     min_content_height;
 
   /* Kinetic scrolling */
-  GtkGesture *drag_gesture;
-  GtkGesture *swipe_gesture;
   GtkGesture *long_press_gesture;
+  GtkGesture *swipe_gesture;
+
+  /* These two gestures are mutually exclusive */
+  GtkGesture *drag_gesture;
+  GtkGesture *pan_gesture;
+
   gdouble drag_start_x;
   gdouble drag_start_y;
 
@@ -718,6 +722,30 @@ scrolled_window_long_press_cancelled_cb (GtkScrolledWindow *scrolled_window,
 }
 
 static void
+gtk_scrolled_window_check_attach_pan_gesture (GtkScrolledWindow *sw)
+{
+  GtkScrolledWindowPrivate *priv = sw->priv;
+
+  if (priv->kinetic_scrolling &&
+      ((priv->hscrollbar_visible && !priv->vscrollbar_visible) ||
+       (!priv->hscrollbar_visible && priv->vscrollbar_visible)))
+    {
+      GtkPanOrientation orientation;
+
+      if (priv->hscrollbar_visible)
+        orientation = GTK_PAN_ORIENTATION_HORIZONTAL;
+      else
+        orientation = GTK_PAN_ORIENTATION_VERTICAL;
+
+      gtk_gesture_pan_set_orientation (GTK_GESTURE_PAN (priv->pan_gesture),
+                                       orientation);
+      gtk_gesture_attach (priv->pan_gesture, GTK_PHASE_CAPTURE);
+    }
+  else
+    gtk_gesture_detach (priv->pan_gesture);
+}
+
+static void
 gtk_scrolled_window_init (GtkScrolledWindow *scrolled_window)
 {
   GtkWidget *widget = GTK_WIDGET (scrolled_window);
@@ -755,6 +783,10 @@ gtk_scrolled_window_init (GtkScrolledWindow *scrolled_window)
                             G_CALLBACK (scrolled_window_drag_end_cb),
                             scrolled_window);
 
+  priv->pan_gesture = gtk_gesture_pan_new (widget, GTK_PAN_ORIENTATION_VERTICAL);
+  gtk_gesture_group (priv->pan_gesture, priv->drag_gesture);
+  gtk_gesture_single_set_button (GTK_GESTURE_SINGLE (priv->pan_gesture), 1);
+
   priv->swipe_gesture = gtk_gesture_swipe_new (widget);
   gtk_gesture_group (priv->swipe_gesture, priv->drag_gesture);
   gtk_gesture_single_set_button (GTK_GESTURE_SINGLE (priv->swipe_gesture), 1);
@@ -1244,6 +1276,7 @@ gtk_scrolled_window_set_kinetic_scrolling (GtkScrolledWindow *scrolled_window,
     return;
 
   priv->kinetic_scrolling = kinetic_scrolling;
+  gtk_scrolled_window_check_attach_pan_gesture (scrolled_window);
 
   if (priv->kinetic_scrolling)
     {
@@ -2289,6 +2322,7 @@ gtk_scrolled_window_size_allocate (GtkWidget     *widget,
     }
 
   _gtk_scrolled_window_allocate_overshoot_window (scrolled_window);
+  gtk_scrolled_window_check_attach_pan_gesture (scrolled_window);
 }
 
 static gboolean