Private Class Line
        Implements GraphicsItem
 
        '...
 
        Private ps As PointF
        Private pe As PointF
 
        '...
 
        Public Function IsOnLine(ByVal p As PointF) As Boolean
            Dim l1 As Single = Math.Sqrt((p.X - ps.X) ^ 2 + (p.Y - ps.Y) ^ 2)
            Dim l2 As Single = Math.Sqrt((p.X - pe.X) ^ 2 + (p.Y - pe.Y) ^ 2)
            Dim l3 As Single = Math.Sqrt((ps.X - pe.X) ^ 2 + (ps.Y - pe.Y) ^ 2)
            Select Case True
                Case l1 <= l3 AndAlso l2 <= l3
                    Return Math.Abs(l3 - l1 - l2) <= 0.05
                Case l2 <= l1 AndAlso l3 <= l1
                    Return Math.Abs(l1 - l2 - l3) <= 0.05
                Case Else
                    Return Math.Abs(l2 - l1 - l3) <= 0.05
            End Select
        End Function
 
        '...
 
    End Class

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