Blurring the background of a semi-transparent form (like Aero glass)

If you want to use the Aero blur then you can use the DwmEnableBlurBehindWindow api. Here's an example derived Window that utilizes this.

public class BlurWindow : Window{    #region Constants    private const int WM_DWMCOMPOSITIONCHANGED = 0x031E;    private const int DWM_BB_ENABLE = 0x1;     #endregion //Constants    #region Structures    [StructLayout( LayoutKind.Sequential )]    private struct DWM_BLURBEHIND    {        public int dwFlags;        public bool fEnable;        public IntPtr hRgnBlur;        public bool fTransitionOnMaximized;    }    [StructLayout( LayoutKind.Sequential )]    private struct MARGINS    {        public int cxLeftWidth;        public int cxRightWidth;        public int cyTopHeight;        public int cyBottomHeight;    }     #endregion //Structures    #region APIs    [DllImport( "dwmapi.dll", PreserveSig = false )]    private static extern void DwmEnableBlurBehindWindow(IntPtr hwnd, ref DWM_BLURBEHIND blurBehind);    [DllImport( "dwmapi.dll" )]    private static extern int DwmExtendFrameIntoClientArea(IntPtr hWnd, ref MARGINS pMargins);    [DllImport( "dwmapi.dll", PreserveSig = false )]    private static extern bool DwmIsCompositionEnabled();     #endregion //APIs    #region Constructor    public BlurWindow()    {        this.WindowStyle = System.Windows.WindowStyle.None;        this.ResizeMode = System.Windows.ResizeMode.NoResize;        this.Background = Brushes.Transparent;    }     #endregion //Constructor    #region Base class overrides    protected override void OnSourceInitialized(EventArgs e)    {        base.OnSourceInitialized( e );        if ( Environment.OSVersion.Version.Major >= 6 )        {            var hwnd = new WindowInteropHelper( this ).Handle;            var hs = HwndSource.FromHwnd( hwnd );            hs.CompositionTarget.BackgroundColor = Colors.Transparent;            hs.AddHook( new HwndSourceHook( this.WndProc ) );            this.InitializeGlass( hwnd );        }    }     #endregion //Base class overrides    #region Methods    #region InitializeGlass    private void InitializeGlass(IntPtr hwnd)    {        if ( !DwmIsCompositionEnabled() )            return;        // fill the background with glass        var margins = new MARGINS();        margins.cxLeftWidth = margins.cxRightWidth = margins.cyBottomHeight = margins.cyTopHeight = -1;        DwmExtendFrameIntoClientArea( hwnd, ref margins );        // initialize blur for the window        DWM_BLURBEHIND bbh = new DWM_BLURBEHIND();        bbh.fEnable = true;        bbh.dwFlags = DWM_BB_ENABLE;        DwmEnableBlurBehindWindow( hwnd, ref bbh );    }    #endregion //InitializeGlass    #region WndProc    private IntPtr WndProc(IntPtr hwnd, int msg, IntPtr wParam, IntPtr lParam, ref bool handled)    {        if ( msg == WM_DWMCOMPOSITIONCHANGED )        {            this.InitializeGlass( hwnd );            handled = false;        }        return IntPtr.Zero;    }     #endregion //WndProc     #endregion //Methods}

And here's a snippet of using the BlurWindow.

var w = new BlurWindow();w.Width = 100;w.Height = 100;w.MouseLeftButtonDown += (s1, e1) => {    ((Window)s1).DragMove();    e1.Handled = true;};w.Background = new SolidColorBrush( Color.FromArgb( 75, 255, 0, 0 ) );w.Show();

I did something similar once but I didn't need the following:

1. I didn't need to move my form much.
2. No movement took place under my form.

What I did:

1. I used to minimize my form window for a moment (programmatically).
2. Form used to capture the image snip of it's size and at the same coordinates.
3. Set that image as it's background after applying the BlurBitmapEffect.

Not a great answer I presume, but I'm just writing what I did!

If you're interested in this approach this article will help you: http://www.codeproject.com/Articles/91487/Screen-Capture-in-WPF-WinForms-Application