How to create a semi transparent form in WPF - wpf

Question

I have to develop a semi-transparent form in WPF, but controls should not be transparent.
I have tried different things like setting opacity=0.5 but no result.
I know that AllowTransparency can be set to True only if WindowStyle set to None, but I need to show Border as well
UPDATE:
Pavlo Glazkov, What is your opinion for this solution
<Window x:Class="WpfApplication1.Window1"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="Window1" Height="300" Width="300" Opacity="1" AllowsTransparency="True" WindowStyle="None" Background="Transparent">
<Grid Background="Transparent">
<Border Margin="2,2,12,34" Name="border1" BorderBrush="Lavender" BorderThickness="5" CornerRadius="20,0,20,0"></Border>
<Button Height="23" Margin="93,101,110,0" Name="button1" VerticalAlignment="Top" Background="CadetBlue" Foreground="White">Hello WPF</Button>
<Button Height="24" Margin="0,8,20,0" Name="button2" VerticalAlignment="Top" HorizontalAlignment="Right" Width="21" Click="button2_Click">X</Button>
</Grid>
</Window>

Answer 1

First, you need to set AllowTransperency to True. Then, you can set the background of the window to a transparent (to desired extent) brush:
<Window x:Class="MyWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
WindowStyle="None"
AllowsTransparency="True"
Background="{DynamicResource WindowBackground}">
<Window.Resources>
<SolidColorBrush x:Key="WindowBackground"
Color="White"
Opacity="0.5"/>
</Window.Resources>
...
</Window>
Please note that AllowTransperency can be set to True only if WindowStyle set to None.
Update:
If you don't want to set WindowStyle to None and would like to keep standart border and window buttons there is an alternative that will work only on Windows Vista/7 with Windows Aero theme.
The trick is that you can extend the "Glass" area to the whole window using the following code:
public static class WindowUtils
{
/// <summary>
/// Extends the glass area into the client area of the window
/// </summary>
/// <param name="window">Window to extend the glass on.</param>
/// <param name="thikness">Thickness of border to extend.</param>
public static void ExtendGlass(this Window window, Thickness thikness) {
try {
int isGlassEnabled = 0;
Win32.DwmIsCompositionEnabled(ref isGlassEnabled);
if (Environment.OSVersion.Version.Major > 5 && isGlassEnabled > 0) {
// Get the window handle
var helper = new WindowInteropHelper(window);
var mainWindowSrc = HwndSource.FromHwnd(helper.Handle);
if (mainWindowSrc != null) {
if (mainWindowSrc.CompositionTarget != null) {
mainWindowSrc.CompositionTarget.BackgroundColor = Colors.Transparent;
}
// Get the dpi of the screen
System.Drawing.Graphics desktop =
System.Drawing.Graphics.FromHwnd(mainWindowSrc.Handle);
float dpiX = desktop.DpiX / 96;
float dpiY = desktop.DpiY / 96;
// Set Margins
var margins = new MARGINS {
cxLeftWidth = (int)(thikness.Left * dpiX),
cxRightWidth = (int)(thikness.Right * dpiX),
cyBottomHeight = (int)(thikness.Bottom * dpiY),
cyTopHeight = (int)(thikness.Top * dpiY)
};
window.Background = Brushes.Transparent;
Win32.DwmExtendFrameIntoClientArea(mainWindowSrc.Handle, ref margins);
}
}
else {
window.Background = SystemColors.WindowBrush;
}
}
catch (DllNotFoundException) {
}
}
}
public class Win32
{
[DllImport("dwmapi.dll")]
public static extern int DwmExtendFrameIntoClientArea(IntPtr hWnd, ref MARGINS pMarInset);
[DllImport("dwmapi.dll")]
public static extern int DwmIsCompositionEnabled(ref int en);
[DllImport("user32.dll")]
public static extern bool SetCursorPos(int X, int Y);
[DllImport("User32", EntryPoint = "ClientToScreen", SetLastError = true, ExactSpelling = true, CharSet = CharSet.Auto)]
public static extern int ClientToScreen(IntPtr hWnd, [In, Out] POINT pt);
}
[StructLayout(LayoutKind.Sequential)]
public struct MARGINS
{
public int cxLeftWidth;
public int cxRightWidth;
public int cyTopHeight;
public int cyBottomHeight;
}
[StructLayout(LayoutKind.Sequential)]
public class POINT
{
public int x = 0;
public int y = 0;
}
To extend the glass to the whole window you need to call the ExtendGlass extension method in a SizeChanged event handler of the window and pass a Thickness that covers whole window:
public MyWindow() {
InitializeComponent();
SizeChanged += OnSizeChanged;
}
private void OnSizeChanged(object sender, SizeChangedEventArgs e) {
double horisontalThickness = Width / 2;
double verticalThickness = Height / 2;
var glassThickness = new Thickness(horisontalThickness, verticalThickness, horisontalThickness, verticalThickness);
this.ExtendGlass(glassThickness);
}

Answer 2

You could try this, it will create a Glass Background for your Window (looks like the Vista and Windows7 transparency effect)
Here is some further explanation from Microsoft.