.NET 4.x Обработка нажатия кнопки мыши в зависимости от условия - Visual Basic .NET

Формулировка задачи:

Здраствуйте! У меня есть проект, в котором я использую сетку. Мне нужно рисовать точки только места, где оси пересекаются.Эти точки рисоват с помощью мыши.Мышь не следует делать в пустые коробки! Как запретить мыши не рисует в пустых коробках? Пожалуйста, если кто-нибудь может мне помочь.Простите меня для плохой русский язык!

Private Sub picTest_MouseDown(ByVal sender As Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles picTest.MouseDown  

Dim hstep As Double = picTest.Width / 12  
Dim vstep As Double = picTest.Height / 12  
  
Dim myPen As New Pen(Color.Red, 3)  
Dim g As Graphics = Graphics.FromImage(gBitmap)  
  
picAG.Refresh()  
  
If e.Button = System.Windows.Forms.MouseButtons.Left Then  
points.Add(e.Location) ' add point on left click  
For i As Integer = 0 To points.Count - 1  
g.DrawRectangle(myPen, points(i).X - 2, points(i).Y - 2, 5, 5)  
Next  

End If  

If (NewPolygon IsNot Nothing) Then  
If (e.Button = MouseButtons.Right) Then  
gBitmap = Nothing  
' Finish this polygon.  
If (NewPolygon.Count > 0) Then Polygons.Add(NewPolygon)  
NewPolygon = Nothing  
picTest.Image = gBitmap  
  
Else  
' Add a point to this polygon.  
If (NewPolygon(NewPolygon.Count - 1) <> e.Location) Then  
  
Dim i As Integer  
For i = 0 To 12  
NewPolygon.Add(New Point(e.X, e.Y )'Here I think to use'hstep,vstep and i',but I don`t know how to do ?!  
picTest.Image = gBitmap  
  
Next i  
End If  
End If  
  
Else  
' Start a new polygon.  
NewPolygon = New List(Of Point)()  
NewPolygon.Add(e.Location)  
NewPoint = (e.Location)  
End If  

' Redraw.  
picTest.Invalidate()  
  
'Dispose of objects  
myPen.Dispose()  
g.Dispose()  
  
Private Sub picTest_MouseMove(ByVal sender As Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles picTest.MouseMove  
  
If (NewPolygon Is Nothing) Then Exit Sub  
NewPoint = e.Location  
' Redraw.  
picTest.Invalidate()  
End Sub  
  
Private Sub picTest_Paint(ByVal sender As System.Object, ByVal e As System.Windows.Forms.PaintEventArgs) Handles picTest.Paint  
Dim g As Graphics = e.Graphics  
Dim myPen As New Pen(Color.Red, 2)  
  
If (NewPolygon IsNot Nothing) Then  
  
' Draw the new polygon.  
If (NewPolygon.Count > 1) Then  
e.Graphics.DrawLines(myPen, NewPolygon.ToArray())  

For i As Integer = 0 To points.Count - 1  
e.Graphics.FillEllipse(Brushes.Green, points(i).X - 2, points(i).Y - 2, 5, 5)  
Next  
  
End If  
  
End If  

Dim hstep As Double = picTest.Width / 12  
Dim vstep As Double = picTest.Height / 12  
  
'Draw horizontal Line  
Dim X As Single = hstep  
For i As Integer = 0 To hstep  
  
g.DrawLine(New Pen(Color.Black, 2), New Point(X, 0), New Point(X, Height))  
X += hstep  
Next i  
  
Dim Y As Single = vstep  
For i As Integer = 0 To vstep  
  
'Draw Vertical Line  
g.DrawLine(New Pen(Color.Black, 2), New Point(0, Y), New Point(Width, Y))  
Y += vstep  
Next i  
  
End Sub

Решение задачи: «.NET 4.x Обработка нажатия кнопки мыши в зависимости от условия»

textual
                            Листинг программы 
                        

                            Private Sub Form6_Load(sender As System.Object, e As System.EventArgs) Handles MyBase.Load
'…
    PictureBox1.Cursor = Cursors.Hand
End Sub
Private Sub PictureBox1_MouseDown(sender As System.Object, e As System.Windows.Forms.MouseEventArgs) Handles PictureBox1.MouseDown
    If e.Button = Windows.Forms.MouseButtons.Left Then
        Dim x As Integer = (Math.Round(e.X / sd)) * sd
        Dim y As Integer = (Math.Round(e.Y / sd)) * sd
        If points.Count > 0 Then
            If x < points(points.Count - 1).X Then
                isDown = False
                Exit Sub
            ElseIf x = points(points.Count - 1).X Then
                points.RemoveAt(points.Count - 1)
            End If
        End If
        points.Add(New Point(x, y))
        isDown = True
    End If
    PictureBox1.Invalidate()
End Sub
                        