' See if we are over a grab handle.
Private Sub Form_MouseDown(Button As Integer, Shift As _
    Integer, X As Single, Y As Single)
Dim i As Integer
Dim dx As Single
Dim dy As Single

    For i = 1 To m_NumPoints
        If Abs(m_PointX(i) - X) < HANDLE_HALF_WIDTH And _
           Abs(m_PointY(i) - Y) < HANDLE_HALF_WIDTH _
        Then
            ' We are over this grab handle.
            ' Start dragging.
            m_DraggingHandle = i
            Exit For
        End If
    Next i
End Sub

' Move the drag handle.
Private Sub Form_MouseMove(Button As Integer, Shift As _
    Integer, X As Single, Y As Single)
    ' Do nothing if we are not dragging.
    If m_DraggingHandle = 0 Then Exit Sub

    ' Move the handle.
    m_PointX(m_DraggingHandle) = X
    m_PointY(m_DraggingHandle) = Y

    ' Redraw.
    Refresh
End Sub

' Stop dragging.
Private Sub Form_MouseUp(Button As Integer, Shift As _
    Integer, X As Single, Y As Single)
    m_DraggingHandle = 0
End Sub