Pasted

public static class WindowHelper
{
    // https://code.google.com/p/zscreen/source/browse/trunk/ZScreenLib/Global/GraphicsCore.cs?r=1349
 
    /// <summary>
    /// Get real window size, no matter whether Win XP, Win Vista, 7 or 8.
    /// </summary>
    public static Rectangle GetWindowRectangle(IntPtr handle)
    {
        if (Environment.OSVersion.Version.Major < 6)
        {
            return GetWindowRect(handle);
        }
        else
        {
            Rectangle rectangle;
            return DWMWA_EXTENDED_FRAME_BOUNDS(handle, out rectangle) ? rectangle : GetWindowRect(handle);
        }
    }
 
    [DllImport(@"dwmapi.dll")]
    private static extern int DwmGetWindowAttribute(IntPtr hwnd, int dwAttribute, out Rect pvAttribute, int cbAttribute);
 
    private enum Dwmwindowattribute
    {
        DwmwaExtendedFrameBounds = 9
    }
 
    [Serializable, StructLayout(LayoutKind.Sequential)]
    private struct Rect
    {
        // ReSharper disable MemberCanBePrivate.Local
        // ReSharper disable FieldCanBeMadeReadOnly.Local
        public int Left;
        public int Top;
        public int Right;
        public int Bottom;
        // ReSharper restore FieldCanBeMadeReadOnly.Local
        // ReSharper restore MemberCanBePrivate.Local
 
        public Rectangle ToRectangle()
        {
            return Rectangle.FromLTRB(Left, Top, Right, Bottom);
        }
    }
 
    private static bool DWMWA_EXTENDED_FRAME_BOUNDS(IntPtr handle, out Rectangle rectangle)
    {
        Rect rect;
        var result = DwmGetWindowAttribute(handle, (int)Dwmwindowattribute.DwmwaExtendedFrameBounds,
            out rect, Marshal.SizeOf(typeof(Rect)));
        rectangle = rect.ToRectangle();
        return result >= 0;
    }
 
    [DllImport(@"user32.dll")]
    [return: MarshalAs(UnmanagedType.Bool)]
    private static extern bool GetWindowRect(IntPtr hWnd, out Rect lpRect);
 
    private static Rectangle GetWindowRect(IntPtr handle)
    {
        Rect rect;
        GetWindowRect(handle, out rect);
        return rect.ToRectangle();
    }
}