month-view: allow changing months with scrolling

It is very natural and intuitive to try and change the current date
by scrolling. The current implementation of the Month view, however,
blatantly ignores scroll events.

Fix that by hearing to the scrolling events and changing the month
when the scroll is enough.

src/gcal-month-view.c

@@ -31,7 +31,7 @@
 
 #include <math.h>
 
-#define LINE_WIDTH 0.5
+#define LINE_WIDTH      0.5
 
 typedef struct
 {
@@ -83,6 +83,9 @@ typedef struct
   /* The cell hovered during Drag and Drop */
   gint            dnd_cell;
 
+  /* Storage for the accumulated scrolling */
+  gdouble         scroll_value;
+
   /* property */
   icaltimetype   *date;
   GcalManager    *manager;
@@ -967,6 +970,29 @@ cancel_dnd_from_overflow_popover (GtkWidget *popover)
   return FALSE;
 }
 
+static gboolean
+gcal_month_view_scroll_event (GtkWidget      *widget,
+                              GdkEventScroll *scroll_event)
+{
+  GcalMonthView *self = GCAL_MONTH_VIEW (widget);
+  GcalMonthViewPrivate *priv = gcal_month_view_get_instance_private (self);
+
+  /*
+   * If we accumulated enough scrolling, change the month. Otherwise, we'd scroll
+   * waaay too fast.
+   */
+  if (should_change_date_for_scroll (&priv->scroll_value, scroll_event))
+    {
+      priv->date->month += priv->scroll_value > 0 ? 1 : -1;
+      *priv->date = icaltime_normalize (*priv->date);
+      priv->scroll_value = 0;
+
+      g_object_notify (G_OBJECT (widget), "active-date");
+    }
+
+  return GDK_EVENT_STOP;
+}
+
 static void
 add_new_event_button_cb (GtkWidget *button,
                          gpointer   user_data)
@@ -1014,6 +1040,7 @@ gcal_month_view_class_init (GcalMonthViewClass *klass)
   widget_class->drag_motion = gcal_month_view_drag_motion;
   widget_class->drag_drop = gcal_month_view_drag_drop;
   widget_class->drag_leave = gcal_month_view_drag_leave;
+  widget_class->scroll_event = gcal_month_view_scroll_event;
 
   subscriber_view_class = GCAL_SUBSCRIBER_VIEW_CLASS (klass);
   subscriber_view_class->get_child_cell = gcal_month_view_get_child_cell;
@@ -1198,7 +1225,9 @@ gcal_month_view_realize (GtkWidget *widget)
                             GDK_POINTER_MOTION_HINT_MASK |
                             GDK_POINTER_MOTION_MASK |
                             GDK_ENTER_NOTIFY_MASK |
-                            GDK_LEAVE_NOTIFY_MASK);
+                            GDK_LEAVE_NOTIFY_MASK |
+                            GDK_SCROLL_MASK |
+                            GDK_SMOOTH_SCROLL_MASK);
   attributes_mask = GDK_WA_X | GDK_WA_Y;
 
   priv->event_window = gdk_window_new (parent_window,

src/gcal-utils.c

@@ -63,6 +63,8 @@ month_item[12] =
   MON_12
 };
 
+#define SCROLL_HARDNESS 10.0
+
 G_DEFINE_BOXED_TYPE (icaltimetype, icaltime, gcal_dup_icaltime, g_free)
 
 gint
@@ -844,3 +846,37 @@ get_alarm_trigger_minutes (GcalEvent          *event,
 
   return diff;
 }
+
+gboolean
+should_change_date_for_scroll (gdouble        *scroll_value,
+                               GdkEventScroll *scroll_event)
+{
+  gdouble delta_y;
+
+  switch (scroll_event->direction)
+    {
+    case GDK_SCROLL_DOWN:
+      *scroll_value = SCROLL_HARDNESS;
+      break;
+
+    case GDK_SCROLL_UP:
+      *scroll_value = -SCROLL_HARDNESS;
+      break;
+
+    case GDK_SCROLL_SMOOTH:
+      gdk_event_get_scroll_deltas ((GdkEvent*) scroll_event, NULL, &delta_y);
+      *scroll_value += delta_y;
+      break;
+
+    /* Ignore horizontal scrolling for now */
+    case GDK_SCROLL_LEFT:
+    case GDK_SCROLL_RIGHT:
+    default:
+      break;
+    }
+
+  if (*scroll_value <= -SCROLL_HARDNESS || *scroll_value >= SCROLL_HARDNESS)
+    return TRUE;
+
+  return FALSE;
+}

src/gcal-utils.h

@@ -123,4 +123,7 @@ gchar*          format_utc_offset                               (gint64
 gint            get_alarm_trigger_minutes                       (GcalEvent             *event,
                                                                  ECalComponentAlarm    *alarm);
 
+gboolean        should_change_date_for_scroll                   (gdouble               *scroll_value,
+                                                                 GdkEventScroll        *scroll_event);
+
 #endif // __GCAL_UTILS_H__