[gnome-control-center] display: Remove duplicate non-ATSC/NTSC rates from the list

[Bastien Nocera <hadess src gnome org>]

commit 529b29cae97aba55dcfa6faa07f5fde2ce2afb09
Author: Bastien Nocera <hadess hadess net>
Date:   Wed Mar 16 19:01:41 2016 +0100

    display: Remove duplicate non-ATSC/NTSC rates from the list
    
    When a mode has 2 very close refresh rates such as 59.94Hz and 60Hz,
    most of the time, we'll want the 59.94Hz version.
    
    Hide the "PC" 60Hz version and only show the 59.94Hz version in those
    cases, and mark the frequency as "60Hz (ATSC)" so that those
    knowledgeable know that it's really 59.94Hz, and doesn't confuse those
    who expect rates to be multiple of 30Hz or 25Hz.
    
    See also https://en.wikipedia.org/wiki/NTSC#Lines_and_refresh_rate
    
    Note that we also do this for half and double that rate, eg. close to
    ~30Hz and ~120Hz.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=655041

 panels/display/cc-display-panel.c |   87 +++++++++++++++++++++++++++++++++++--
 1 files changed, 83 insertions(+), 4 deletions(-)
---
diff --git a/panels/display/cc-display-panel.c b/panels/display/cc-display-panel.c
index 4b59839..93d701a 100644
--- a/panels/display/cc-display-panel.c
+++ b/panels/display/cc-display-panel.c
@@ -1697,6 +1697,42 @@ list_box_item (const gchar *title,
   return row;
 }
 
+static gboolean
+is_atsc_duplicate_freq (GnomeRRMode *mode,
+                        GnomeRRMode *next_mode)
+{
+  double freq, next_freq;
+  gboolean ret;
+
+  if (next_mode == NULL)
+    return FALSE;
+
+  freq = gnome_rr_mode_get_freq_f (mode);
+  next_freq = gnome_rr_mode_get_freq_f (next_mode);
+
+  ret = fabs (freq - (next_freq / 1000.0 * 1001.0)) < 0.01;
+
+  if (ret)
+    g_debug ("Next frequency %f is the NTSC variant of %f",
+             next_freq, freq);
+
+  return ret;
+}
+
+static int
+sort_frequencies (gconstpointer a, gconstpointer b)
+{
+  GnomeRRMode *mode_a = (GnomeRRMode *) a;
+  GnomeRRMode *mode_b = (GnomeRRMode *) b;
+
+  /* Highest to lowest */
+  if (gnome_rr_mode_get_freq_f (mode_a) > gnome_rr_mode_get_freq_f (mode_b))
+    return -1;
+  if (gnome_rr_mode_get_freq_f (mode_a) < gnome_rr_mode_get_freq_f (mode_b))
+    return 1;
+  return 0;
+}
+
 static void
 setup_frequency_combo_box (CcDisplayPanel *panel,
                            GnomeRRMode    *resolution_mode)
@@ -1707,8 +1743,9 @@ setup_frequency_combo_box (CcDisplayPanel *panel,
   GtkTreeModel *model;
   GtkTreeIter iter;
   gchar *res;
-  GSList *l;
+  GSList *l, *frequencies;
   guint i;
+  gboolean prev_dup;
 
   current_output = gnome_rr_screen_get_output_by_name (priv->screen,
                                                        gnome_rr_output_info_get_name (priv->current_output));
@@ -1719,10 +1756,50 @@ setup_frequency_combo_box (CcDisplayPanel *panel,
 
   i = 0;
   res = make_resolution_string (resolution_mode);
-  for (l = g_hash_table_lookup (priv->res_freqs, res); l != NULL; l = l->next)
+  frequencies = g_slist_copy (g_hash_table_lookup (priv->res_freqs, res));
+  g_free (res);
+  frequencies = g_slist_sort (frequencies, sort_frequencies);
+  prev_dup = FALSE;
+
+  /* Look for 59.94Hz, and if it exists, remove the 60Hz option
+   * in favour of this NTSC/ATSC frequency.
+   * 60Hz is a "PC" frequency, 59.94Hz is a holdover
+   * from NTSC:
+   * https://en.wikipedia.org/wiki/NTSC#Lines_and_refresh_rate
+   *
+   * We also want to handle this for ~30Hz and ~120Hz */
+  for (l = frequencies; l != NULL; l = l->next)
     {
       GnomeRRMode *mode = l->data;
-      gchar *freq = g_strdup_printf ("%d Hz", gnome_rr_mode_get_freq (mode));
+      GnomeRRMode *next_mode;
+      gchar *freq;
+      gboolean dup;
+
+      if (l->next != NULL)
+        next_mode = l->next->data;
+      else
+        next_mode = NULL;
+
+      dup = is_atsc_duplicate_freq (mode, next_mode);
+      if (dup && mode != current_mode)
+        {
+          prev_dup = TRUE;
+          continue;
+        }
+
+      if (prev_dup)
+        {
+          /* translators: example string is "60 Hz (NTSC)"
+           * NTSC is https://en.wikipedia.org/wiki/NTSC */
+          freq = g_strdup_printf (_("%d Hz (NTSC)"),
+                                  (int) (roundf (gnome_rr_mode_get_freq_f (mode))));
+        }
+      else
+        {
+          /* translators: example string is "60 Hz" */
+          freq = g_strdup_printf (_("%d Hz"), gnome_rr_mode_get_freq (mode));
+        }
+
       gtk_list_store_insert_with_values (GTK_LIST_STORE (model), &iter,
                                          -1, 0, freq, 1, mode, -1);
       g_free (freq);
@@ -1730,9 +1807,11 @@ setup_frequency_combo_box (CcDisplayPanel *panel,
       if (mode == current_mode)
         gtk_combo_box_set_active_iter (GTK_COMBO_BOX (priv->freq_combo), &iter);
 
+      prev_dup = dup;
       i++;
     }
-  g_free (res);
+
+  g_slist_free (frequencies);
 
   if (i < 2)
     {