Тень у "Form"

#region Shadow

private const int WM_NCHITTEST = 0x84;
private const int HTCLIENT = 0x1;
private const int HTCAPTION = 0x2;
private bool m_aeroEnabled;
private const int CS_DROPSHADOW = 0x00020000;
private const int WM_NCPAINT = 0x0085;
private const int WM_ACTIVATEAPP = 0x001C;

[System.Runtime.InteropServices.DllImport("dwmapi.dll")]
public static extern int DwmExtendFrameIntoClientArea(IntPtr hWnd, ref MARGINS pMarInset);
[System.Runtime.InteropServices.DllImport("dwmapi.dll")]
public static extern int DwmSetWindowAttribute(IntPtr hwnd, int attr, ref int attrValue, int attrSize);
[System.Runtime.InteropServices.DllImport("dwmapi.dll")]

public static extern int DwmIsCompositionEnabled(ref int pfEnabled);
[System.Runtime.InteropServices.DllImport("Gdi32.dll", EntryPoint = "CreateRoundRectRgn")]
private static extern IntPtr CreateRoundRectRgn(
    Int32 nLeftRect, Int32 nTopRect, Int32 nRightRect, Int32 nBottomRect, Int32 nWidthEllipse, Int32 nHeightEllipse);

public struct MARGINS
{
    public int leftWidth;
    public int rightWidth;
    public int topHeight;
    public int bottomHeight;
}
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 e)
{
    switch (e.Msg)
    {
        case WM_NCPAINT:
            if (m_aeroEnabled)
            {
                var v = 2;
                DwmSetWindowAttribute(this.Handle, 2, ref v, 4);
                MARGINS margins = new MARGINS()
                {
                    bottomHeight = 1,
                    leftWidth = 0,
                    rightWidth = 0,
                    topHeight = 0
                };
                DwmExtendFrameIntoClientArea(this.Handle, ref margins);
            }
            break;

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

#endregion