How to use several splitters in Kivy?

Question

I'd like to use two splitters in a single screen, so that the user can have either one of the 3 parts to fill the whole screen (but leaving a bit for the splitters to be shown).

I've tried doing it (see code below), but when I shrink part 3 to the minimum and then enlarge part 1 as much as I can, part 3 disappears, which is not the desired behavior (I'd like it to be symmetrical to all 3 parts).

Does anyone have an idea?

BoxLayout:
id: all
min_view_size: sp(30)
strip_size: sp(13)

Splitter:
    sizable_from: 'right'
    strip_size: all.strip_size
    max_size: all.width - (all.min_view_size + all.strip_size)*2
    min_size: all.min_view_size + all.strip_size

    Label:
        text: '1'

Splitter:
    sizable_from: 'right'
    strip_size: all.strip_size
    max_size: all.width - (all.min_view_size + self.strip_size)*2
    min_size: all.min_view_size + self.strip_size

    Label:
        text: '2'

BoxLayout:
    max_size: all.width - (all.min_view_size + all.strip_size)*2
    min_size: all.min_view_size
    Label:
        text: '3'

Answer 1

After some tweaking, here is a working example for 2 horizontal splitters, so the parts between them have a minimum size:

BoxLayout:
    id: all
    min_view_size: sp(30)
    strip_size: sp(13)

Splitter:
    id: splitter1
    sizable_from: 'right'
    strip_size: all.strip_size
    max_size: all.width - (all.min_view_size + all.strip_size)*2
    min_size: all.min_view_size + all.strip_size

    Label:
        text: '1'

Splitter:
    id: splitter2
    sizable_from: 'right'
    strip_size: all.strip_size
    max_size: (all.width - splitter1.width) - (all.min_view_size + self.strip_size)
    min_size: all.min_view_size + self.strip_size

    Label:
        text: '2'

BoxLayout:
    Label:
        text: '3'

The trick was to have the min_size rule for the second splitter depend on the size of the first one.

EDIT:

And here it is with auto-orientation-adjustment when the window is narrow/wide:

BoxLayout:
    id: all
    min_view_size: sp(30)
    strip_size: sp(13)
    orientation: 'vertical' if self.width < self.height else 'horizontal'
    vertical: self.orientation == 'vertical'
    bigger_size: self.height if self.vertical else self.width
    default_part_size: (self.bigger_size - self.strip_size*2)/3

    # Reset part sizes when orientation changes
    on_vertical:
        if args[1]: (splitter1.height, splitter2.height) = (self.default_part_size, self.default_part_size)
        if not args[1]: (splitter1.width, splitter2.width) = (self.default_part_size, self.default_part_size)

Splitter:
    id: splitter1
    strip_size: all.strip_size
    max_size: all.bigger_size - (all.min_view_size + all.strip_size)*2
    min_size: all.min_view_size + all.strip_size
    sizable_from: 'bottom' if all.vertical else 'right'
    size_hint: (1, None) if all.vertical else (None, 1)
    size: (all.width, all.default_part_size) if all.vertical else (all.default_part_size, all.height)

    BoxLayout:
        Button:
            text: '1'

Splitter:
    id: splitter2
    strip_size: all.strip_size
    splitter1_bigger_size: splitter1.height if all.vertical else splitter1.width
    max_size: (all.bigger_size - self.splitter1_bigger_size) - (all.min_view_size + self.strip_size)
    min_size: all.min_view_size + self.strip_size
    sizable_from: 'bottom' if all.vertical else 'right'
    size_hint: (1, None) if all.vertical else (None, 1)
    size: (all.width, all.default_part_size) if all.vertical else (all.default_part_size, all.height)

    BoxLayout:    
        Button:
            text: '2'

BoxLayout:
    Button:
        text: '3'