calling gl functions

inversecolor.py

from kivy.uix.widget import Widget
from kivy.graphics import Callback
from kivy.graphics.opengl import glBlendFunc, GL_ONE_MINUS_DST_COLOR, GL_ZERO


class InverseColor(Widget):
	
	def __init__(self, **kwargs):
		super(InverseColor, self).__init__(**kwargs)
		
		with self.canvas.before:
			Callback(self._enable)
		with self.canvas.after:
			Callback(self._disable, reset_context=True)
	
	def _enable(self, *_):
		glBlendFunc(GL_ONE_MINUS_DST_COLOR, GL_ZERO)
	
	def _disable(self, *_):
		pass