CLabel.py

from kivy.uix.label import Label as K_Label
from kivy.properties import OptionProperty
from kivy.lang import Builder
from kivy.graphics import Rectangle, Color

class CLabel(K_Label):
	orientation = OptionProperty('horizontal', options=(
        'horizontal', 'vertical'))
	def __init__(self, *args, **kwargs):
		super(CLabel, self).__init__(*args, **kwargs)
		kv_style_file = 'label.kv'
		if kv_style_file not in Builder.files:
			Builder.load_file('label.kv')
	def draw_on_canvas(self):
		print 'proper', self.size, self.pos
		with self.canvas.before:
			Color(0, 1, 0)
			Rectangle(size=self.size,
			          pos=self.pos)
		self.text = "Changed"


if __name__ == '__main__':
	from kivy.app import App


	kv = '''
test:

<test@BoxLayout>:
	orientation: 'horizontal'
	BoxLayout:
		orientation: 'vertical'
		CLabel:
			id: vert_1
			orientation: 'vertical'
			text: 'Vertical Label'
		Button:
			text: "Change"
			size_hint_y: None
			height: "30dp"
			on_release: vert_1.draw_on_canvas()
	BoxLayout:
		orientation: 'vertical'
		CLabel:
			orientation: 'horizontal'
			text: 'Horizontal Label'
		CLabel:
			orientation: 'horizontal'
			text: 'Horizontal Label'



'''

	class TestLabel(App):
		def build(self):
			return Builder.load_string(kv)

	TestLabel().run()

label.kv

<CLabel>:
	canvas.before:
		PushMatrix
		Translate:
			xy: self.center_x, self.center_y
		Rotate:
			angle: 90 if self.orientation is 'vertical' else 0
			axis: 0, 0, 1
		Translate:
			xy: -self.center_x, -self.center_y
	canvas.after:
		PopMatrix