Implement side-by-side tiling

When dragging a window over a screen edge and dropping it there,
maximize it vertically and scale it horizontally to cover the
corresponding half of the current monitor.

Whenever a "hot area" which triggers this behavior is entered, an
indication of window's target size is displayed after a short delay
to avoid distraction when moving a window between monitors.

https://bugzilla.gnome.org/show_bug.cgi?id=606260

src/include/tile-preview.h

@@ -0,0 +1,39 @@
+/* -*- mode: C; c-file-style: "gnu"; indent-tabs-mode: nil; -*- */
+
+/* Meta tile preview */
+
+/*
+ * Copyright (C) 2010 Florian Müllner
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of the
+ * License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
+ * 02111-1307, USA.
+ */
+#ifndef META_TILE_PREVIEW_H
+#define META_TILE_PREVIEW_H
+
+#include "boxes.h"
+
+typedef struct _MetaTilePreview MetaTilePreview;
+
+MetaTilePreview   *meta_tile_preview_new    (int                screen_number,
+                                             gboolean           composited);
+void               meta_tile_preview_free   (MetaTilePreview   *preview);
+void               meta_tile_preview_show   (MetaTilePreview   *preview,
+                                             MetaRectangle     *rect);
+void               meta_tile_preview_hide   (MetaTilePreview   *preview);
+Window             meta_tile_preview_get_xwindow (MetaTilePreview   *preview,
+                                                  gulong            *create_serial);
+
+#endif /* META_TILE_PREVIEW_H */