Change Themes tab layout and add wallpaper behind preview.

Wox/Helper/WallpaperPathRetrieval.cs

@@ -0,0 +1,48 @@
+using System;
+using System.Linq;
+using System.Runtime.InteropServices;
+using System.Text;
+using System.Windows.Media;
+using Microsoft.Win32;
+
+namespace Wox.Helper
+{
+    public static class WallpaperPathRetrieval
+    {
+        [DllImport("user32.dll", CharSet = CharSet.Unicode)]
+        private static extern Int32 SystemParametersInfo(UInt32 action,
+            Int32 uParam, StringBuilder vParam, UInt32 winIni);
+        private static readonly UInt32 SPI_GETDESKWALLPAPER = 0x73;
+        private static int MAX_PATH = 260;
+
+        public static string GetWallpaperPath()
+        {
+            var wallpaper = new StringBuilder(MAX_PATH);
+            SystemParametersInfo(SPI_GETDESKWALLPAPER, MAX_PATH, wallpaper, 0);
+
+            var str = wallpaper.ToString();
+            if (string.IsNullOrEmpty(str))
+                return null;
+
+            return str;
+        }
+
+        public static Color GetWallpaperColor()
+        {
+            RegistryKey key = Registry.CurrentUser.OpenSubKey("Control Panel\\Colors", true);
+            var result = key.GetValue(@"Background", null);
+            if (result != null && result is string)
+            {
+                try
+                {
+                    var parts = result.ToString().Trim().Split(new char[] {' '}, 3).Select(byte.Parse).ToList();
+                    return Color.FromRgb(parts[0], parts[1], parts[2]);
+                }
+                catch
+                {
+                }
+            }
+            return Colors.Transparent;
+        }
+    }
+}