Как расположить объекты. Kivy?

Здравстуйте. Подскажите, как расположить объекты в следующем порядке:

1. Форма ввода
2. Радио кнопки все в одну строку
3. Кнопка. И выровнять все по центру окна.

from kivy.app import App
from kivy.uix.widget import Widget
from kivy.lang import Builder

Builder.load_file('test.kv')

class MyLayout(Widget):
    pass

class TestApp(App):
    def build(self):
        return MyLayout()
if __name__ == '__main__':
    TestApp().run()

    <MyLayout>
    GridLayout:
        cols:8
        size: self.minimum_size
        Label:
            id: laba1
            text: "a1"
            font_size:20
            size_hint: None, None
            size: self.texture_size
        CheckBox:
            group: "toppings"
            on_active: root.checkbox_click(self, self.active, "a1")
            size_hint: None, None
            size: laba1.height, laba1.height
        Label:
            id: laba2
            text: "a2"
            font_size:20
            size_hint: None, None
            size: self.texture_size
        CheckBox:
            group: "toppings"
            on_active: root.checkbox_click(self, self.active, "a2")
            size_hint: None, None
            size: laba2.height, laba2.height
        Label:
            id: laba3
            text: "a3"
            font_size:20
            size_hint: None, None
            size: self.texture_size
        CheckBox:
            group: "toppings"
            on_active: root.checkbox_click(self, self.active, "a3")
            size_hint: None, None
            size: laba3.height, laba3.height
        Label:
            id: laba4
            text: "a4"
            font_size:20
            size_hint: None, None
            size: self.texture_size
        CheckBox:
            group: "toppings"
            on_active: root.checkbox_click(self, self.active, "a4")
            size_hint: None, None
            size: laba4.height, laba4.height
    BoxLayout:
        Button:
            text:"Test"
            size_hint: (.32, .3)
            pos_hint: {"x":.10, "top":.5}
        TextInput:
            size_hint: (.32, .3)
            pos_hint: {"x":.10, "top":.5}