[gimp] app: fix GimpControllerWheel for smooth scrolling events

[Michael Natterer <mitch src gnome org>]

commit 8b71d326597c7cde985392859d4083fac8bb1ebf
Author: Michael Natterer <mitch gimp org>
Date:   Sun Jul 15 13:56:44 2018 +0200

    app: fix GimpControllerWheel for smooth scrolling events
    
    gimp_controller_wheel_scroll(): attempt to translate smooth scroll
    deltas to GdkScrollDirection, controller events are always discrete
    steps.
    
    Works fine on X11, no idea how it behaves on other backends, please
    check and report.

 app/widgets/gimpcontrollerwheel.c | 30 +++++++++++++++++++++++++++---
 1 file changed, 27 insertions(+), 3 deletions(-)
---
diff --git a/app/widgets/gimpcontrollerwheel.c b/app/widgets/gimpcontrollerwheel.c
index 473bb6e8ce..a91f6a802f 100644
--- a/app/widgets/gimpcontrollerwheel.c
+++ b/app/widgets/gimpcontrollerwheel.c
@@ -260,18 +260,42 @@ gboolean
 gimp_controller_wheel_scroll (GimpControllerWheel  *wheel,
                               const GdkEventScroll *sevent)
 {
-  gint i;
+  GdkScrollDirection direction;
+  GdkModifierType    state;
+  gint               i;
 
   g_return_val_if_fail (GIMP_IS_CONTROLLER_WHEEL (wheel), FALSE);
   g_return_val_if_fail (sevent != NULL, FALSE);
 
+  gdk_event_get_state ((const GdkEvent *) sevent, &state);
+
+  if (! gdk_event_get_scroll_direction ((const GdkEvent *) sevent, &direction))
+    {
+      gdouble dx = 0.0;
+      gdouble dy = 0.0;
+
+      if (! gdk_event_get_scroll_deltas ((const GdkEvent *) sevent, &dx, &dy))
+        return FALSE;
+
+      if (dy <= -1.0)
+        direction = GDK_SCROLL_UP;
+      else if (dy >= 1.0)
+        direction = GDK_SCROLL_DOWN;
+      else if (dx <= -1.0)
+        direction = GDK_SCROLL_LEFT;
+      else if (dx >= 1.0)
+        direction = GDK_SCROLL_RIGHT;
+      else
+        return FALSE;
+    }
+
   /*  start with the last event because the last ones in the
    *  up,down,left,right groups have the most keyboard modifiers
    */
   for (i = G_N_ELEMENTS (wheel_events) - 1; i >= 0; i--)
     {
-      if (wheel_events[i].direction == sevent->direction &&
-          (wheel_events[i].modifiers & sevent->state) ==
+      if (wheel_events[i].direction == direction &&
+          (wheel_events[i].modifiers & state) ==
           wheel_events[i].modifiers)
         {
           GimpControllerEvent         controller_event;