Drop Shadow On A Borderless WinForm

问题:

I'm trying to drop a shadow around the whole form just like the first picture, except that that is a WPF not a WinForm. now i want to drop the same shadow on a winform.

This is what i want..¬

Not this..¬

回答1:

In WinForms, you can just override the form's protected CreateParams property and add the CS_DROPSHADOW flag to the class styles. For example:

public class ShadowedForm : Form {
    protected override CreateParams CreateParams {
        get {
            const int CS_DROPSHADOW = 0x20000;
            CreateParams cp = base.CreateParams;
            cp.ClassStyle |= CS_DROPSHADOW;
            return cp;
        }
    }

    // ... other code ...
}

But, a couple of caveats…

1. This flag works only on top-level windows. In Win32-speak, that means overlapped and popup windows. It has no effect on child windows (e.g. controls). I thought I remembered hearing somewhere that this limitation had been removed from Windows 8, but I can't find a link confirming this and I don't have Windows 8 installed for testing purposes.

2. It is possible that the user has disabled this feature altogether. If so, you won't get drop shadows, no matter how you ask for them. That's by design. Your application should not try and override this request. You can determine whether drop shadows are enabled or disabled by P/Invoking the SystemParametersInfo function and passing the SPI_GETDROPSHADOW flag.

3. The Aero theme also adds shadows to top-level windows. This effect is separate and distinct from CS_DROPSHADOW, and works only when Aero is enabled. There's no way to turn it off and on for individual windows. Moreover, since the Aero theme has been removed from Windows 8, it won't ever have these shadows.

回答2:

Here's my C# implementation. It's similar to Al.Pertro's, but you'll notice that when you lose focus and regain focus, the shadow repaints itself.

I've also added code to allow mouse-dragging.

public partial class Form1 : Form
{
    [DllImport("Gdi32.dll", EntryPoint = "CreateRoundRectRgn")]
    private static extern IntPtr CreateRoundRectRgn
    (
        int nLeftRect, // x-coordinate of upper-left corner
        int nTopRect, // y-coordinate of upper-left corner
        int nRightRect, // x-coordinate of lower-right corner
        int nBottomRect, // y-coordinate of lower-right corner
        int nWidthEllipse, // height of ellipse
        int nHeightEllipse // width of ellipse
     );        

    [DllImport("dwmapi.dll")]
    public static extern int DwmExtendFrameIntoClientArea(IntPtr hWnd, ref MARGINS pMarInset);

    [DllImport("dwmapi.dll")]
    public static extern int DwmSetWindowAttribute(IntPtr hwnd, int attr, ref int attrValue, int attrSize);

    [DllImport("dwmapi.dll")]
    public static extern int DwmIsCompositionEnabled(ref int pfEnabled);

    private bool m_aeroEnabled;                     // variables for box shadow
    private const int CS_DROPSHADOW = 0x00020000;
    private const int WM_NCPAINT = 0x0085;
    private const int WM_ACTIVATEAPP = 0x001C;

    public struct MARGINS                           // struct for box shadow
    {
        public int leftWidth;
        public int rightWidth;
        public int topHeight;
        public int bottomHeight;
    }

    private const int WM_NCHITTEST = 0x84;          // variables for dragging the form
    private const int HTCLIENT = 0x1;
    private const int HTCAPTION = 0x2;

    protected override CreateParams CreateParams
    {
        get
        {
            m_aeroEnabled = CheckAeroEnabled();

            CreateParams cp = base.CreateParams;
            if (!m_aeroEnabled)
                cp.ClassStyle |= CS_DROPSHADOW;

            return cp;
        }
    }

    private bool CheckAeroEnabled()
    {
        if (Environment.OSVersion.Version.Major >= 6)
        {
            int enabled = 0;
            DwmIsCompositionEnabled(ref enabled);
            return (enabled == 1) ? true : false;
        }
        return false;
    }

    protected override void WndProc(ref Message m)
    {
        switch (m.Msg)
        {
            case WM_NCPAINT:                        // box shadow
                if (m_aeroEnabled)
                {
                    var v = 2;
                    DwmSetWindowAttribute(this.Handle, 2, ref v, 4);
                    MARGINS margins = new MARGINS()
                    {
                        bottomHeight = 1,
                        leftWidth = 1,
                        rightWidth = 1,
                        topHeight = 1
                    };
                    DwmExtendFrameIntoClientArea(this.Handle, ref margins);

                }
                break;
            default:
                break;
        }
        base.WndProc(ref m);

        if (m.Msg == WM_NCHITTEST && (int)m.Result == HTCLIENT)     // drag the form
            m.Result = (IntPtr)HTCAPTION;

    }

    public Form1()
    {
        m_aeroEnabled = false;

        this.FormBorderStyle = FormBorderStyle.None;

        InitializeComponent();
    }
}

回答3:

Humm ,,, Just past the code and you will get the windows 7 Drop Shadow like this >>> http://marcin.floryan.pl/wp-content/uploads/2010/08/WPF-Window-native-shadow.png

Imports System.Runtime.InteropServices

Public Class IMSS_SplashScreen
    Private aeroEnabled As Boolean
    Protected Overrides ReadOnly Property CreateParams() As CreateParams
        Get
            CheckAeroEnabled()
            Dim cp As CreateParams = MyBase.CreateParams
            If Not aeroEnabled Then
                cp.ClassStyle = cp.ClassStyle Or NativeConstants.CS_DROPSHADOW
                Return cp
            Else
                Return cp
            End If
        End Get
    End Property
    Protected Overrides Sub WndProc(ByRef m As Message)
        Select Case m.Msg
            Case NativeConstants.WM_NCPAINT
                Dim val = 2
                If aeroEnabled Then
                    NativeMethods.DwmSetWindowAttribute(Handle, 2, val, 4)
                    Dim bla As New NativeStructs.MARGINS()
                    With bla
                        .bottomHeight = 1
                        .leftWidth = 1
                        .rightWidth = 1
                        .topHeight = 1
                    End With
                    NativeMethods.DwmExtendFrameIntoClientArea(Handle, bla)
                End If
                Exit Select
        End Select
        MyBase.WndProc(m)
    End Sub
    Private Sub CheckAeroEnabled()
        If Environment.OSVersion.Version.Major >= 6 Then
            Dim enabled As Integer = 0
            Dim response As Integer = NativeMethods.DwmIsCompositionEnabled(enabled)
            aeroEnabled = (enabled = 1)
        Else
            aeroEnabled = False
        End If
    End Sub
End Class
Public Class NativeStructs
    Public Structure MARGINS
        Public leftWidth As Integer
        Public rightWidth As Integer
        Public topHeight As Integer
        Public bottomHeight As Integer
    End Structure
End Class
Public Class NativeMethods
    <DllImport("dwmapi")> _
    Public Shared Function DwmExtendFrameIntoClientArea(ByVal hWnd As IntPtr, ByRef pMarInset As NativeStructs.MARGINS) As Integer
    End Function
    <DllImport("dwmapi")> _
    Friend Shared Function DwmSetWindowAttribute(ByVal hwnd As IntPtr, ByVal attr As Integer, ByRef attrValue As Integer, ByVal attrSize As Integer) As Integer
    End Function
    <DllImport("dwmapi.dll")> _
    Public Shared Function DwmIsCompositionEnabled(ByRef pfEnabled As Integer) As Integer
    End Function
End Class
Public Class NativeConstants
    Public Const CS_DROPSHADOW As Integer = &H20000
    Public Const WM_NCPAINT As Integer = &H85
End Class

回答4:

As far as I know, there is no direct way of doing this in WinForms.

Instead, you can follow this step by step:

1) Create an image having the desired drop shadow using photoshop or any other tool.
2) Use this image as background image of your form.
3) Set FormBorderStyle property of the form to None.
4) You are done!
5) Note: Make sure to save the image in proper format(such as png) so that the drop shadow effect could work.