layout2

from kivy.app import runTouchApp
from kivy.lang import Builder

runTouchApp(Builder.load_string ('''
StackLayout:
    ActionBar:
        background_color: [1,1,1,0]
        ActionView:
            use_separator: True
            ActionPrevious:
                with_previous: True
                on_release: app.home()

    AnchorLayout:
        id: al
        anchor_x: 'center'
        anchor_y: 'center'
        canvas:
            Color:
                rgba: 1,0,0,1
            Rectangle:
                pos: al.pos
                size: al.size
        Widget:
            id: preview
            size: 112,112
            size_hint: None,None
            canvas:
                Color:
                    rgba: 0,1,0,1
                Rectangle:
                    pos: preview.pos
                    size: preview.size
'''))