--- bug4119/panel-plugin/datetime.c	2008/05/28 21:33:20	1.1
+++ bug4119/panel-plugin/datetime.c	2008/05/29 12:06:16
@@ -39,6 +39,15 @@
 #define USE_GTK_TOOLTIP_API     GTK_CHECK_VERSION(2,12,0)
 
 #define DATETIME_MAX_STRLEN 256
+
+/*
+ * Compute the difference a-b between two GTimeVal structs.
+ * Returns the result as a gdouble in milliseconds.
+ */
+#define DATETIME_DIFFTIME_MILLISECONDS(a, b) \
+  ((gdouble) ((a).tv_sec  - (b).tv_sec ) * 1000.0 + \
+   (gdouble) ((a).tv_usec - (b).tv_usec) / 1000.0)
+
 /*
  * Get date/time string
  */
@@ -72,7 +81,7 @@
     .tm_hour  = 0,
     .tm_mday  = 1,
     .tm_mon   = 0,
-    .tm_year  = 0,
+    .tm_year  = 100,
     .tm_wday  = 0,
     .tm_yday  = 0,
     .tm_isdst = 0
@@ -106,6 +115,8 @@
   gchar *utf8str;
   struct tm *current;
   t_datetime *datetime;
+  GTimeVal next_update_time;  /* time of next update */
+  guint update_interval;      /* milliseconds to next update */
 
   if (data == NULL)
   {
@@ -114,6 +125,12 @@
 
   datetime = (t_datetime*)data;
 
+  /* stop timer */
+  if (datetime->timeout_id)
+  {
+    g_source_remove(datetime->timeout_id);
+  }
+
   g_get_current_time(&timeval);
   current = localtime((time_t *)&timeval.tv_sec);
   if (datetime->date_format != NULL && GTK_IS_LABEL(datetime->date_label))
@@ -180,6 +197,21 @@
       break;
   }
 
+  /*
+   * Compute the time to the next update and start the timer.
+   * The calculation finds the next larger integral multiple of the given update interval.
+   * This results in the next update occurring on the second or minute
+   * when the update interval is 1 or 60 seconds, respectively.
+   */
+  if (datetime->update_interval == 1)
+    next_update_time.tv_sec = timeval.tv_sec + 1; /* this branch is an optimization */
+  else
+    next_update_time.tv_sec = timeval.tv_sec +
+                              datetime->update_interval - timeval.tv_sec % datetime->update_interval;
+  next_update_time.tv_usec = 0;
+  update_interval = DATETIME_DIFFTIME_MILLISECONDS(next_update_time, timeval);
+  datetime->timeout_id = g_timeout_add(update_interval, datetime_update, datetime);
+
   return TRUE;
 }
 
@@ -450,19 +482,14 @@
       gtk_widget_show(GTK_WIDGET(datetime->time_label));
   }
 
-  if (datetime->timeout_id)
-  {
-    g_source_remove(datetime->timeout_id);
-  }
-
   if (datetime_format_has_seconds(datetime->date_format) ||
       datetime_format_has_seconds(datetime->time_format))
   {
-    datetime->timeout_id = g_timeout_add(1000, datetime_update, datetime);
+    datetime->update_interval = 1;
   }
   else
   {
-    datetime->timeout_id = g_timeout_add(10000, datetime_update, datetime);
+    datetime->update_interval = 60;
   }
 }
 
@@ -616,6 +643,7 @@
   gtk_widget_show_all(datetime->button);
 
   /* set date and time labels */
+  datetime->timeout_id = 0;
   datetime_update(datetime);
 
   return datetime;
--- bug4119/panel-plugin/datetime.h	2008/05/29 09:03:23	1.1
+++ bug4119/panel-plugin/datetime.h	2008/05/29 10:49:20
@@ -46,6 +46,7 @@
   GtkWidget *date_label;
   GtkWidget *time_label;
   GtkTooltips *tips;
+  guint update_interval;  /* time between updates in seconds */
   guint timeout_id;
 
   /* settings */