Kivy Label that doesn't waste texture

ecolabel.py

'''
KivyのLabelはpaddingを設定するとその分だけtextureを大きくしてしまうのでそれへの対策。
'''
__all__ = ("EcoLabel", )

from kivy.properties import NumericProperty, ReferenceListProperty, OptionProperty
from kivy.lang import Builder
from kivy.clock import Clock
from kivy.uix.label import Label


Builder.load_string("""
<-EcoLabel>:
    canvas:
        Color:
            rgba: 1, 1, 1, 1
        Rectangle:
            group: "EcoLabel_rectangle"
            texture: self.texture
            size: self.texture_size
""")


class EcoLabel(Label):
    minimum_width = NumericProperty()
    minimum_height = NumericProperty()
    minimum_size = ReferenceListProperty(minimum_width, minimum_height)
    halign = OptionProperty("center", options=("left", "center", "right", ))
    valign = OptionProperty("center", options=("top", "center", "bottom", ))

    def on_kv_post(self, *args, **kwargs):
        super().on_kv_post(*args, **kwargs)
        self._rectangle_inst = self.canvas.get_group("EcoLabel_rectangle")[0]
        dont_make_the_texture_bigger_just_for_padding(self)
        dont_update_the_texture_when_halign_or_valign_changes(self)
        t = Clock.schedule_once(self._update_minimum_size, -1)
        self.bind(texture_size=t, padding=t)
        t = Clock.schedule_once(self._update_texture_position, -1)
        self.bind(texture_size=t, size=t, pos=t, padding=t, halign=t, valign=t)

    def _update_minimum_size(self, dt):
        w, h = self.texture_size
        left, top, right, bottom = self.padding
        self.minimum_width = w + left + right
        self.minimum_height = h + top + bottom

    def _update_texture_position(self, *args):
        x, y = self.pos
        w, h = self.size
        tw, th = self.texture_size
        left, top, right, bottom = self.padding
        match self.halign:
            case "center":
                tx = x + (w - tw) / 2.
            case "left":
                tx = x + left
            case _:
                tx = x + w - tw - right
        match self.valign:
            case "center":
                ty = y + (h - th) / 2.
            case "bottom":
                ty = y + bottom
            case _:
                ty = y + h - th - top
        self._rectangle_inst.pos = (tx, ty)


def dont_make_the_texture_bigger_just_for_padding(label: Label):
    label._label.options["padding"] = (0, ) * 4
    t = label._trigger_texture_update
    for name in ("padding_x", "padding_y", "padding", ):
        label.funbind(name, t, name)
    t()


def dont_update_the_texture_when_halign_or_valign_changes(label: Label):
    label._label.options.update(halign="center", valign="center")
    t = label._trigger_texture_update
    for name in ("halign", "valign", ):
        label.funbind(name, t, name)
    t()


def test():
    from textwrap import dedent

    from kivy.clock import Clock
    from kivy.lang import Builder
    from kivy.app import App

    class TestApp(App):
        def build(self):
            Clock.schedule_interval(self.print_texture_size, 3)
            return Builder.load_string(dedent("""
                BoxLayout:
                    orientation: "vertical"
                    padding: 20
                    spacing: 20
                    Label:
                        id: label
                        text: "XXX"
                        halign: "right"
                        padding: (20, 20)
                    EcoLabel:
                        id: ecolabel
                        text: "XXX"
                        halign: "right"
                        padding: (20, 20)
                """))

        def print_texture_size(self, dt):
            ids = self.root.ids
            print("")
            print("Label    texture size:", ids.label.texture_size)
            print("EcoLabel texture size:", ids.ecolabel.texture_size)

    TestApp().run()


if __name__ == "__main__":
    test()