GetActiveWindow（）并不总是返回活动窗口吗？

Control.MouseButtons

GetActiveWindow()

        Private Declare Auto Function GetActiveWindow Lib \"user32.dll\" () As IntPtr

        Public Sub GetMouseState(ByRef x As Integer, ByRef y As Integer, ByRef lButton As Boolean)
            Dim p As Point = Parent.PointToClient(Windows.Forms.Cursor.Position)
            x = p.X
            y = p.Y
            lButton = _
                (Control.MouseButtons And MouseButtons.Left) = MouseButtons.Left AndAlso _
                 Parent.Handle = GetActiveWindow()
        End Sub

Parent

Form

    Dim down As Boolean
    Game.GetMouseState(0, 0, down)
    If down Then g.Clear(Color.Red)

    Dim mouseX, mouseY As Integer, mouseDown As Boolean
    Game.GetMouseState(mouseX, mouseY, mouseDown)

    If mouseDown Then
        Dim mouseLocation As New PointF(mouseX - Game.Width \\ 2, mouseY - Game.Height \\ 2)

        centerParticle.MoveTowards(mouseLocation, centerParticle.Location)
    End If