How to use the nanogui.Alignment.Middle function in nanogui

b.setFlags(Button.Flags.ToggleButton)

        def change_cb(state):
            print("Toggle button state: %s" % str(state))
        b.setChangeCallback(change_cb)

        Label(window, "Radio buttons", "sans-bold")
        b = Button(window, "Radio button 1")
        b.setFlags(Button.Flags.RadioButton)
        b = Button(window, "Radio button 2")
        b.setFlags(Button.Flags.RadioButton)

        Label(window, "A tool palette", "sans-bold")
        tools = Widget(window)
        tools.setLayout(BoxLayout(Orientation.Horizontal,
                                  Alignment.Middle, 0, 6))

        ToolButton(tools, entypo.ICON_CLOUD)
        ToolButton(tools, entypo.ICON_CONTROLLER_FAST_FORWARD)
        ToolButton(tools, entypo.ICON_COMPASS)
        ToolButton(tools, entypo.ICON_INSTALL)

        Label(window, "Popup buttons", "sans-bold")
        popupBtn = PopupButton(window, "Popup", entypo.ICON_EXPORT)
        popup = popupBtn.popup()
        popup.setLayout(GroupLayout())
        Label(popup, "Arbitrary widgets can be placed here")
        CheckBox(popup, "A check box")
        # popup right
        popupBtn = PopupButton(popup, "Recursive popup", entypo.ICON_FLASH)
        popupRight = popupBtn.popup()
        popupRight.setLayout(GroupLayout())

def __init__(self):
        super(TestApp, self).__init__((800, 600), "NanoGUI Test", False)

        window = Window(self, "GLCanvas Demo")
        window.setPosition((15, 15))
        window.setLayout(GroupLayout())

        self.canvas = MyGLCanvas(window)
        self.canvas.setBackgroundColor(Color(0.5, 0.5, 0.5, 1.0))
        self.canvas.setSize((400, 400))

        self.canvas.rotation = [0.25, 0.5, 0.33]

        tools = Widget(window)
        tools.setLayout(BoxLayout(Orientation.Horizontal,
                                  Alignment.Middle, 0, 5))

        b0 = Button(tools, "Random Color")
        def cb0():
            self.canvas.setBackgroundColor(Color(random.random(), random.random(), random.random(), 1.0))
        b0.setCallback(cb0)

        b1 = Button(tools, "Random Rotation")
        def cb1():
            self.canvas.rotation = [random.random(), random.random(), random.random()]
        b1.setCallback(cb1)

        self.performLayout()

for i in range(100)]
                graphDyn.setValues(valuesDyn)
                counter += 1
                # We must invoke perform layout from the screen instance to keep everything in order.
                # This is essential when creating tabs dynamically.
                self.performLayout()
                # Ensure that the newly added header is visible on screen
                tabWidget.ensureTabVisible(index)

        tabWidget.setCallback(tab_cb)
        tabWidget.setActiveTab(0);

        window = Window(self, "Grid of small widgets")
        window.setPosition((425, 300))
        layout = GridLayout(Orientation.Horizontal, 2,
                            Alignment.Middle, 15, 5)
        layout.setColAlignment(
            [Alignment.Maximum, Alignment.Fill])
        layout.setSpacing(0, 10)
        window.setLayout(layout)

        Label(window, "Floating point :", "sans-bold")
        floatBox = TextBox(window)
        floatBox.setEditable(True)
        floatBox.setFixedSize((100, 20))
        floatBox.setValue("50")
        floatBox.setUnits("GiB")
        floatBox.setDefaultValue("0.0")
        floatBox.setFontSize(16)
        floatBox.setFormat("[-]?[0-9]*\\.?[0-9]+")

        Label(window, "Positive integer :", "sans-bold")

b.setFlags(Button.Flags.ToggleButton)

        def change_cb(state):
            print("Toggle button state: %s" % str(state))
        b.setChangeCallback(change_cb)

        Label(window, "Radio buttons", "sans-bold")
        b = Button(window, "Radio button 1")
        b.setFlags(Button.Flags.RadioButton)
        b = Button(window, "Radio button 2")
        b.setFlags(Button.Flags.RadioButton)

        Label(window, "A tool palette", "sans-bold")
        tools = Widget(window)
        tools.setLayout(BoxLayout(Orientation.Horizontal,
                                  Alignment.Middle, 0, 6))

        ToolButton(tools, entypo.ICON_CLOUD)
        ToolButton(tools, entypo.ICON_CONTROLLER_FAST_FORWARD)
        ToolButton(tools, entypo.ICON_COMPASS)
        ToolButton(tools, entypo.ICON_INSTALL)

        Label(window, "Popup buttons", "sans-bold")
        popupBtn = PopupButton(window, "Popup", entypo.ICON_EXPORT)
        popup = popupBtn.popup()
        popup.setLayout(GroupLayout())
        Label(popup, "Arbitrary widgets can be placed here")
        CheckBox(popup, "A check box")
        # popup right
        popupBtn = PopupButton(popup, "Recursive popup", entypo.ICON_FLASH)
        popupRight = popupBtn.popup()
        popupRight.setLayout(GroupLayout())

img_window.setPosition((710, 15))
        img_window.setLayout(GroupLayout())

        imgView = ImageView(img_window, icons[0][0])

        def cb(i):
            print("Selected item %i" % i)
            imgView.bindImage(icons[i][0])
        imgPanel.setCallback(cb)

        imgView.setGridThreshold(3)

        Label(window, "File dialog", "sans-bold")
        tools = Widget(window)
        tools.setLayout(BoxLayout(Orientation.Horizontal,
                                  Alignment.Middle, 0, 6))
        b = Button(tools, "Open")
        valid = [("png", "Portable Network Graphics"), ("txt", "Text file")]

        def cb():
            result = nanogui.file_dialog(valid, False)
            print("File dialog result = %s" % result)

        b.setCallback(cb)
        b = Button(tools, "Save")

        def cb():
            result = nanogui.file_dialog(valid, True)
            print("File dialog result = %s" % result)

        b.setCallback(cb)