[libchamplain] view: Accumulate smooth scroll dy in order to trigger zoom

[Jiří Techet <jiritechet src gnome org>]

commit d3964299fe4ef1c79df54f687301ce34eaae7b2f
Author: Jiří Techet <techet gmail com>
Date:   Mon Nov 30 23:13:56 2015 +0100

    view: Accumulate smooth scroll dy in order to trigger zoom
    
    The way scroll is triggered is somewhat unreliable, it is better
    to accumulate the scroll value, until enough delta is accumulated
    to trigger a "tick" (1 scroll unit is equivalent to one traditional
    scroll event).
    
    Based on patch from Carlos Garnacho.

 champlain/champlain-view.c |   42 +++++++++++++++++++++++++++++++++++-------
 1 files changed, 35 insertions(+), 7 deletions(-)
---
diff --git a/champlain/champlain-view.c b/champlain/champlain-view.c
index 8d0bcb1..363e3b1 100644
--- a/champlain/champlain-view.c
+++ b/champlain/champlain-view.c
@@ -191,6 +191,7 @@ struct _ChamplainViewPrivate
   gint tiles_loading;
   
   guint redraw_timeout;
+  guint zoom_timeout;
   
   ClutterAnimationMode goto_mode;
   guint goto_duration;
@@ -214,6 +215,7 @@ struct _ChamplainViewPrivate
   gdouble focus_lat;
   gdouble focus_lon;
   gboolean zoom_started;
+  gdouble accumulated_scroll_dy;
 
   ChamplainBoundingBox *world_bbox;
 };
@@ -389,6 +391,21 @@ panning_completed (G_GNUC_UNUSED ChamplainKineticScrollView *scroll,
 
 
 static gboolean
+zoom_timeout_cb (gpointer data)
+{
+  DEBUG_LOG ()
+
+  ChamplainView *view = data;
+  ChamplainViewPrivate *priv = view->priv;
+
+  priv->accumulated_scroll_dy = 0;
+  priv->zoom_timeout = 0;
+
+  return FALSE;
+}
+
+
+static gboolean
 scroll_event (G_GNUC_UNUSED ClutterActor *actor,
     ClutterScrollEvent *event,
     ChamplainView *view)
@@ -406,18 +423,23 @@ scroll_event (G_GNUC_UNUSED ClutterActor *actor,
   else if (event->direction == CLUTTER_SCROLL_SMOOTH)
     {
       gdouble dx, dy;
+      gint steps;
 
       clutter_event_get_scroll_delta ((ClutterEvent *)event, &dx, &dy);
 
-      /* Use a threshhold value to avoid jitter */
-      if (fabs(dy) < 0.75)
-        return FALSE;
-
+      priv->accumulated_scroll_dy += dy;
+      /* add some small value to avoid missing step for values like 0.999999 */
       if (dy > 0)
-        zoom_level = priv->zoom_level - 1;
+        steps = (int) (priv->accumulated_scroll_dy + 0.01);
       else
-        zoom_level = priv->zoom_level + 1;
-  }
+        steps = (int) (priv->accumulated_scroll_dy - 0.01);
+      zoom_level = priv->zoom_level - steps;
+      priv->accumulated_scroll_dy -= steps;
+
+      if (priv->zoom_timeout != 0)
+        g_source_remove (priv->zoom_timeout);
+      priv->zoom_timeout = g_timeout_add (1000, zoom_timeout_cb, view);
+    }
 
   return view_set_zoom_level_at (view, zoom_level, TRUE, event->x, event->y);
 }
@@ -682,6 +704,12 @@ champlain_view_dispose (GObject *object)
       priv->zoom_actor_timeout = 0;
     }
 
+  if (priv->zoom_timeout != 0)
+    {
+      g_source_remove (priv->zoom_timeout);
+      priv->zoom_timeout = 0;
+    }
+
   if (priv->tile_map != NULL)
     {
       g_hash_table_destroy (priv->tile_map);