Private Declare Sub ClipCursor Lib "user32" (ByVal RectPointer As IntPtr)
 
Private Structure RECT
        Public left As Integer
        Public top As Integer
        Public right As Integer
        Public bottom As Integer
    End Structure
 
Private Sub Button3_Click(ByVal sender As System.Object, ByVal e As _
  System.EventArgs) Handles Button3.Click
        Button3.Tag = Not CBool(Button3.Tag)
 
        If CBool(Button3.Tag) Then
            Dim Re As Rectangle = Button3.RectangleToScreen(New Rectangle( _
              Button3.Location, Button3.Size))
            Dim R As New RECT
            R.left = Re.X
            R.top = Re.Y
            R.right = Re.Width
            R.bottom = Re.Height
            ClipCursor(VarPtr(R))
        Else
            ClipCursor(New IntPtr(0&))
        End If
    End Sub
 
    Private Function VarPtr(ByVal o As Object) As IntPtr
        Return GCHandle.Alloc(o, GCHandleType.Pinned).AddrOfPinnedObject()
        'Return GCHandle.ToIntPtr(GCHandle.Alloc(o))
    End Function