year-view: add hover effect to the navigator

The current implementation of the Year navigator gives
absolutely no clue that the days are actually selectable,
which may confuse some users.

A simple way to inform the user that the Year navigator
is actually interactive is the hovering effect.

Fix the lack of feedback by adding the hover effect to the
year navigator.

https://bugzilla.gnome.org/show_bug.cgi?id=762462

data/theme/gtk-styles.css

@@ -122,6 +122,11 @@ calendar-view.second-view-header {
     font-weight: bold;
 }
 
+.year-navigator:hover {
+    background-color: alpha(@theme_fg_color, 0.1);
+    border-radius: 2px;
+}
+
 .year-navigator.with-events {
     background-color: @theme_fg_color;
     border-radius: 3px;

src/gcal-year-view.c

@@ -34,6 +34,7 @@ typedef struct
   /* month span from 0 to 11 */
   gint start_day, start_month;
   gint end_day, end_month;
+  gint hovered_day, hovered_month;
 } ButtonData;
 
 typedef struct
@@ -729,6 +730,27 @@ draw_month_grid (GcalYearView *year_view,
       box_padding_top = (box_side - layout_height) / 2 > 0 ? (box_side - layout_height) / 2 : 0;
       box_padding_start = (box_side - layout_width) / 2 > 0 ? (box_side - layout_width) / 2 : 0;
 
+      /* Draw the hover background */
+      if (year_view->selected_data->hovered_day == j &&
+          year_view->selected_data->hovered_month == month_nr)
+        {
+          gint hover_x, hover_y;
+
+          hover_x = box_side * column + x + sw * box_padding_start / 2.0 - year_view->k * box_side - 2.0;
+          hover_y = box_side * (row + 1) + y + box_padding_top - 1.0;
+
+          gtk_style_context_set_state (context, state_flags | GTK_STATE_FLAG_PRELIGHT);
+
+          gtk_render_background (context,
+                                 cr,
+                                 hover_x,
+                                 hover_y,
+                                 box_side - box_padding_start / 2.0,
+                                 box_side);
+
+          gtk_style_context_set_state (context, state_flags);
+        }
+
       selected_day = FALSE;
       if (year_view->selected_data->start_day != 0)
         {
@@ -1054,25 +1076,43 @@ navigator_motion_notify_cb (GcalYearView   *year_view,
   gint day, month;
   gboolean is_title = FALSE;
 
-  if (!year_view->button_pressed)
+  if (calculate_day_month_for_coord (year_view, event->x, event->y, &day, &month, &is_title))
-    return FALSE;
+    {
+      if (year_view->button_pressed)
+        {
+          /* Cancel the hover when selecting a date range */
+          year_view->selected_data->hovered_day = -1;
+          year_view->selected_data->hovered_month = -1;
 
-  if (!calculate_day_month_for_coord (year_view, event->x, event->y, &day, &month, &is_title))
+          if (is_title)
-    goto fail;
+            day = g_date_get_days_in_month (month + 1, year_view->date->year);
 
-  if (is_title)
+          year_view->selected_data->end_day = day;
-    day = g_date_get_days_in_month (month + 1, year_view->date->year);
+          year_view->selected_data->end_month = month;
+          gtk_widget_queue_draw (widget);
 
-  year_view->selected_data->end_day = day;
+          return GDK_EVENT_STOP;
-  year_view->selected_data->end_month = month;
+        }
-  gtk_widget_queue_draw (widget);
+      else
-  return TRUE;
+        {
+          /* We only deal with the hover effect when the button is not pressed */
+          year_view->selected_data->hovered_day = day;
+          year_view->selected_data->hovered_month = month;
+          gtk_widget_queue_draw (widget);
 
-fail:
+          return GDK_EVENT_PROPAGATE;
-  year_view->selected_data->end_day = year_view->selected_data->start_day;
+        }
-  year_view->selected_data->end_month = year_view->selected_data->start_month;
+    }
-  gtk_widget_queue_draw (widget);
+  else
-  return TRUE;
+    {
+      /* Reset the end day */
+      year_view->selected_data->end_day = year_view->selected_data->start_day;
+      year_view->selected_data->end_month = year_view->selected_data->start_month;
+
+      gtk_widget_queue_draw (widget);
+
+      return GDK_EVENT_STOP;
+    }
 }
 
 static void