绘制同心圆或圆环

        Dim i, X0, Y0 As Integer
        Dim Ox As New Bitmap(Me.Width, Me.Height) '创建位图，用窗体的大小
        Dim Kos As Graphics = Graphics.FromImage(Ox) '根据位图创建Graphics，这个是gdi+的封装
        Dim pen1 As New Pen(Color.Black, 3) '声明画笔，黑色，3像素宽度
        Dim Vs As RectangleF '声明矩形，用来绘制在指定位置和大小
        X0 = Me.Width / 2  '定义圆心坐标于窗体的中心(x0,y0)
        Y0 = Me.Height / 2
        Kos.SmoothingMode = Drawing2D.SmoothingMode.HighQuality '开启抗锯齿。
        For i = 50 To 150 Step 10 '将此处的10变为1可以绘出圆环
            pen1.Color = Color.FromArgb(255, 250 - i, i, i)  '改变画笔颜色
            ' Llo.Color = Color.FromArgb(255, 128, 128, 128)
            Vs.X = X0 - i 'x坐标
            Vs.Y = Y0 - i 'Y坐标
            Vs.Width = i * 2 '宽度
            Vs.Height = i * 2 '高度
            Kos.DrawEllipse(pen1, Vs) '绘制园
        Next
        Me.BackgroundImage = Ox '将位图做为窗体的背景图