From 8599f209c1a0c766429429275027284491ded7ac Mon Sep 17 00:00:00 2001
From: Carlos Garnacho <carlosg@gnome.org>
Date: Wed, 19 Aug 2015 18:45:50 +0200
Subject: [PATCH] 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 file changed, 27 insertions(+), 29 deletions(-)

diff --git a/gtk/gtkscrolledwindow.c b/gtk/gtkscrolledwindow.c
index 1c8536266d..d28b126598 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);
-- 
2.30.2