Visual Basic

Protected Overrides Sub OnPaint(ByVal e As System.Windows.Forms.PaintEventArgs)
    MyBase.OnPaint(e)

    'Painting starts here...
    e.Graphics.FillEllipse(Brushes.CadetBlue, Me.ClientRectangle)
    'Painting done

End Sub

Protected Overrides Sub OnPaint(ByVal e As System.Windows.Forms.PaintEventArgs)
    MyBase.OnPaint(e)

    'Graphics of a bitmap to paint on instead of e.Graphics
    Dim bmp As New Bitmap(Me.Width, Me.Height, Imaging.PixelFormat.Format32bppPArgb)
    Dim g As Graphics = Graphics.FromImage(bmp)

    'Painting starts here...
    'Use g instead of e.GRaphics
    g.FillEllipse(Brushes.CadetBlue, Me.ClientRectangle)
    ''Painting done

    'Get rid of bmp graphics
    g.Dispose()

    'Assuming that Opacity is a Single from 0 to 1
    If Me.Opacity = 1 Then
         'Opacity = 100%, so just draw bmp
         e.Graphics.DrawImageUnscaled(bmp, 0, 0)
    Else 'Opacity less than 100%
        'Attributes for the bmp
        Dim attrib As New Imaging.ImageAttributes
        'ColorMatrix for the transparency of the bmp
        Dim colorm As New Imaging.ColorMatrix
        'Set the Opacity of the colormatrix
        colorm.Matrix33 = Opacity
        'Set the colormatrix of the attributes
        attrib.SetColorMatrix(colorm)

        'Draw the bmp on e.Graphics with the right opacity
        e.Graphics.DrawImage(bmp, New Rectangle(0, 0, bmp.Width, bmp.Height), 0, 0, bmp.Width, bmp.Height, GraphicsUnit.Pixel, attrib)

        'Get rid of the attributes
        attrib.Dispose()
    End If

    'Get rid of the bitmap
    bmp.Dispose
End Sub