From c573523c4de8445d2579d094658c0e3c0142a374 Mon Sep 17 00:00:00 2001
From: "Owen W. Taylor" <otaylor@fishsoup.net>
Date: Tue, 3 May 2011 13:04:01 -0400
Subject: [PATCH] Filter mirrored monitors from the monitors list

For the purposes of window placement or arranging window manager or
plugin controls, screens that are just mirrors of other screens should
be ignored, so filter them out of the monitors list.

https://bugzilla.gnome.org/show_bug.cgi?id=649299
---
 src/core/screen.c | 39 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 39 insertions(+)

diff --git a/src/core/screen.c b/src/core/screen.c
index cbfcdb8f2..4f73b9de2 100644
--- a/src/core/screen.c
+++ b/src/core/screen.c
@@ -349,6 +349,43 @@ set_wm_icon_size_hint (MetaScreen *screen)
 #undef N_VALS
 }
 
+/* The list of monitors reported by the windowing system might include
+ * mirrored monitors with identical bounds. Since mirrored monitors
+ * shouldn't be treated as separate monitors for most purposes, we
+ * filter them out here. (We ignore the possibility of partially
+ * overlapping monitors because they are rare and it's hard to come
+ * up with any sensible interpretation.)
+ */
+static void
+filter_mirrored_monitors (MetaScreen *screen)
+{
+  int i, j;
+
+  /* Currently always true and simplifies things */
+  g_assert (screen->primary_monitor_index == 0);
+
+  for (i = 1; i < screen->n_monitor_infos; i++)
+    {
+      /* In case we've filtered previous monitors */
+      screen->monitor_infos[i].number = i;
+
+      for (j = 0; j < i; j++)
+        {
+          if (meta_rectangle_equal (&screen->monitor_infos[i].rect,
+                                    &screen->monitor_infos[j].rect))
+            {
+              memmove (&screen->monitor_infos[i],
+                       &screen->monitor_infos[i + 1],
+                       (screen->n_monitor_infos - i - 1) * sizeof (MetaMonitorInfo));
+              screen->n_monitor_infos--;
+              i--;
+
+              continue;
+            }
+        }
+    }
+}
+
 static void
 reload_monitor_infos (MetaScreen *screen)
 {
@@ -538,6 +575,8 @@ reload_monitor_infos (MetaScreen *screen)
       screen->monitor_infos[0].rect = screen->rect;
     }
 
+  filter_mirrored_monitors (screen);
+
   g_assert (screen->n_monitor_infos > 0);
   g_assert (screen->monitor_infos != NULL);
 }