[gtk+] gtkscrolledwindow: Fold kinetic deceleration handling into scroll_event()

[Carlos Garnacho <carlosg src gnome org>]

commit 8599f209c1a0c766429429275027284491ded7ac
Author: Carlos Garnacho <carlosg gnome org>
Date:   Wed Aug 19 18:45:50 2015 +0200

    gtkscrolledwindow: Fold kinetic deceleration handling into scroll_event()
    
    In order to play along with child widgets that use scroll events for anything
    else than scrolling, it will be better to do this in the bubble phase, so
    the child widget has an opportunity to GDK_EVENT_STOP the event before we
    trigger kinetic scrolling.
    
    This of course won't work for widgets that choose to reimplement scroll event
    handling themselves, they should be smart at resorting to GtkScrolledWindow's
    scroll event handling.
    
    This fixes kinetic scrolling kicking in too pervasively on widgets that eg.
    implement zoom on scroll events.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=753495

 gtk/gtkscrolledwindow.c |   56 ++++++++++++++++++++++------------------------
 1 files changed, 27 insertions(+), 29 deletions(-)
---
diff --git a/gtk/gtkscrolledwindow.c b/gtk/gtkscrolledwindow.c
index 1c85362..d28b126 100644
--- a/gtk/gtkscrolledwindow.c
+++ b/gtk/gtkscrolledwindow.c
@@ -1229,33 +1229,6 @@ captured_event_cb (GtkWidget *widget,
   priv = sw->priv;
   source_device = gdk_event_get_source_device (event);
 
-  if (event->type == GDK_SCROLL)
-    {
-      gdouble dx, dy, vel_x, vel_y;
-
-      /* The libinput driver may generate a final event with dx=dy=0
-       * after scrolling finished, start kinetic scrolling when this
-       * happens.
-       */
-      gtk_scrolled_window_cancel_deceleration (sw);
-      gdk_event_get_scroll_deltas (event, &dx, &dy);
-
-      if (priv->scroll_device != source_device)
-        {
-          priv->scroll_device = source_device;
-          scroll_history_reset (sw);
-        }
-
-      scroll_history_push (sw, &event->scroll);
-
-      if (event->scroll.direction == GDK_SCROLL_SMOOTH &&
-          dx == 0 && dy == 0 &&
-          scroll_history_finish (sw, &vel_x, &vel_y))
-        gtk_scrolled_window_decelerate (sw, vel_x, vel_y);
-
-      return GDK_EVENT_PROPAGATE;
-    }
-
   if (!priv->use_indicators)
     return GDK_EVENT_PROPAGATE;
 
@@ -3107,7 +3080,8 @@ gtk_scrolled_window_scroll_event (GtkWidget      *widget,
   gdouble delta_x;
   gdouble delta_y;
   GdkScrollDirection direction;
-  gboolean shifted;
+  gboolean shifted, start_deceleration = FALSE;
+  GdkDevice *source_device;
 
   shifted = (event->state & GDK_SHIFT_MASK) != 0;
 
@@ -3115,9 +3089,18 @@ gtk_scrolled_window_scroll_event (GtkWidget      *widget,
   priv = scrolled_window->priv;
 
   gtk_scrolled_window_invalidate_overshoot (scrolled_window);
+  source_device = gdk_event_get_source_device ((GdkEvent *) event);
 
   if (gdk_event_get_scroll_deltas ((GdkEvent *) event, &delta_x, &delta_y))
     {
+      if (priv->scroll_device != source_device)
+        {
+          priv->scroll_device = source_device;
+          scroll_history_reset (scrolled_window);
+        }
+
+      scroll_history_push (scrolled_window, event);
+
       if (shifted)
         {
           gdouble delta;
@@ -3158,6 +3141,16 @@ gtk_scrolled_window_scroll_event (GtkWidget      *widget,
                                                      new_value);
           handled = TRUE;
         }
+
+      /* The libinput driver may generate a final event with dx=dy=0
+       * after scrolling finished, start kinetic scrolling when this
+       * happens.
+       */
+      if (delta_y == 0 && delta_x == 0)
+        {
+          handled = TRUE;
+          start_deceleration = TRUE;
+        }
     }
   else if (gdk_event_get_scroll_direction ((GdkEvent *)event, &direction))
     {
@@ -3197,6 +3190,8 @@ gtk_scrolled_window_scroll_event (GtkWidget      *widget,
 
   if (handled)
     {
+      gdouble vel_x, vel_y;
+
       gtk_scrolled_window_cancel_deceleration (scrolled_window);
       gtk_scrolled_window_invalidate_overshoot (scrolled_window);
 
@@ -3206,7 +3201,10 @@ gtk_scrolled_window_scroll_event (GtkWidget      *widget,
           priv->scroll_events_overshoot_id = 0;
         }
 
-      if (_gtk_scrolled_window_get_overshoot (scrolled_window, NULL, NULL))
+      if (start_deceleration &&
+          scroll_history_finish (scrolled_window, &vel_x, &vel_y))
+        gtk_scrolled_window_decelerate (scrolled_window, vel_x, vel_y);
+      else if (_gtk_scrolled_window_get_overshoot (scrolled_window, NULL, NULL))
         {
           priv->scroll_events_overshoot_id =
             gdk_threads_add_timeout (50, start_scroll_deceleration_cb, scrolled_window);