diff -r 000000000000 -r 6474c204b198 widget/gtk/nsScreenGtk.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/widget/gtk/nsScreenGtk.cpp	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,156 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsScreenGtk.h"
+
+#include <gdk/gdk.h>
+#ifdef MOZ_X11
+#include <gdk/gdkx.h>
+#include <X11/Xatom.h>
+#endif
+#include <gtk/gtk.h>
+
+nsScreenGtk :: nsScreenGtk (  )
+  : mScreenNum(0),
+    mRect(0, 0, 0, 0),
+    mAvailRect(0, 0, 0, 0)
+{
+}
+
+
+nsScreenGtk :: ~nsScreenGtk()
+{
+}
+
+
+NS_IMETHODIMP
+nsScreenGtk :: GetRect(int32_t *outLeft, int32_t *outTop, int32_t *outWidth, int32_t *outHeight)
+{
+  *outLeft = mRect.x;
+  *outTop = mRect.y;
+  *outWidth = mRect.width;
+  *outHeight = mRect.height;
+
+  return NS_OK;
+  
+} // GetRect
+
+
+NS_IMETHODIMP
+nsScreenGtk :: GetAvailRect(int32_t *outLeft, int32_t *outTop, int32_t *outWidth, int32_t *outHeight)
+{
+  *outLeft = mAvailRect.x;
+  *outTop = mAvailRect.y;
+  *outWidth = mAvailRect.width;
+  *outHeight = mAvailRect.height;
+
+  return NS_OK;
+  
+} // GetAvailRect
+
+
+NS_IMETHODIMP 
+nsScreenGtk :: GetPixelDepth(int32_t *aPixelDepth)
+{
+  GdkVisual * visual = gdk_screen_get_system_visual(gdk_screen_get_default());
+  *aPixelDepth = gdk_visual_get_depth(visual);
+
+  return NS_OK;
+
+} // GetPixelDepth
+
+
+NS_IMETHODIMP 
+nsScreenGtk :: GetColorDepth(int32_t *aColorDepth)
+{
+  return GetPixelDepth ( aColorDepth );
+
+} // GetColorDepth
+
+
+void
+nsScreenGtk :: Init (GdkWindow *aRootWindow)
+{
+  // We listen for configure events on the root window to pick up
+  // changes to this rect.  We could listen for "size_changed" signals
+  // on the default screen to do this, except that doesn't work with
+  // versions of GDK predating the GdkScreen object.  See bug 256646.
+  mAvailRect = mRect = nsIntRect(0, 0, gdk_screen_width(), gdk_screen_height());
+
+#ifdef MOZ_X11
+  // We need to account for the taskbar, etc in the available rect.
+  // See http://freedesktop.org/Standards/wm-spec/index.html#id2767771
+
+  // XXX do we care about _NET_WM_STRUT_PARTIAL?  That will
+  // add much more complexity to the code here (our screen
+  // could have a non-rectangular shape), but should
+  // lead to greater accuracy.
+
+  long *workareas;
+  GdkAtom type_returned;
+  int format_returned;
+  int length_returned;
+
+  GdkAtom cardinal_atom = gdk_x11_xatom_to_atom(XA_CARDINAL);
+
+  gdk_error_trap_push();
+
+  // gdk_property_get uses (length + 3) / 4, hence G_MAXLONG - 3 here.
+  if (!gdk_property_get(aRootWindow,
+                        gdk_atom_intern ("_NET_WORKAREA", FALSE),
+                        cardinal_atom,
+                        0, G_MAXLONG - 3, FALSE,
+                        &type_returned,
+                        &format_returned,
+                        &length_returned,
+                        (guchar **) &workareas)) {
+    // This window manager doesn't support the freedesktop standard.
+    // Nothing we can do about it, so assume full screen size.
+    return;
+  }
+
+  // Flush the X queue to catch errors now.
+  gdk_flush();
+
+  if (!gdk_error_trap_pop() &&
+      type_returned == cardinal_atom &&
+      length_returned && (length_returned % 4) == 0 &&
+      format_returned == 32) {
+    int num_items = length_returned / sizeof(long);
+
+    for (int i = 0; i < num_items; i += 4) {
+      nsIntRect workarea(workareas[i],     workareas[i + 1],
+                         workareas[i + 2], workareas[i + 3]);
+      if (!mRect.Contains(workarea)) {
+        // Note that we hit this when processing screen size changes,
+        // since we'll get the configure event before the toolbars have
+        // been moved.  We'll end up cleaning this up when we get the
+        // change notification to the _NET_WORKAREA property.  However,
+        // we still want to listen to both, so we'll handle changes
+        // properly for desktop environments that don't set the
+        // _NET_WORKAREA property.
+        NS_WARNING("Invalid bounds");
+        continue;
+      }
+
+      mAvailRect.IntersectRect(mAvailRect, workarea);
+    }
+  }
+  g_free (workareas);
+#endif
+}
+
+#ifdef MOZ_X11
+void
+nsScreenGtk :: Init (XineramaScreenInfo *aScreenInfo)
+{
+  nsIntRect xineRect(aScreenInfo->x_org, aScreenInfo->y_org,
+                     aScreenInfo->width, aScreenInfo->height);
+
+  mScreenNum = aScreenInfo->screen_number;
+
+  mAvailRect = mRect = xineRect;
+}
+#endif