What does exactly 'Invalidate' method of controls do?

Try the following code:

VB Code:

Private Sub Form1_MouseDown(ByVal sender As Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles MyBase.MouseDown
        Static Dim secondclick As Boolean
        Static mousepos1, mousepos2 As Point
        If e.Button = MouseButtons.Left Then
            Dim  g As Graphics = Me.CreateGraphics
            If secondclick = False Then
                Me.Refresh() ' comment this line and try the next line to note the difference.
                ' Me.Invalidate()
                mousepos1 = New Point(e.X, e.Y)
                secondclick = True
            Else
                mousepos2 = New Point(e.X, e.Y)
                secondclick = False
                g.DrawLine(New Pen(Color.Black, 1), mousepos1.X, mousepos1.Y, mousepos2.X, mousepos2.Y)
          End If
            g.DrawLine(New Pen(Color.Black, 1), e.X, e.Y - 5, e.X, e.Y + 5)
            g.DrawLine(New Pen(Color.Black, 1), e.X - 5, e.Y, e.X + 5, e.Y)
            g.Dispose()
        End If
End Sub

How can you describe this difference between Refresh and Invalidate? Doesn't Refresh call Invalidate?

Me.Invalidate() forces a Re-Paint

Quote:

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Originally posted by dynamic_sysop
Me.Invalidate() forces a Re-Paint

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Refresh: Forces the control to invalidate its client area and immediately redraw itself and any child controls.

Invalidate: Invalidates a specific region of the control (adds it to the control's update region, which is the area that will be repainted at the next paint operation) and causes a paint message to be sent to the control.

I think i am getting close to the difference but it is not still clear.