test.py

#!/usr/bin/env python
from kivy.app import App
from kivy.uix.widget import Widget
from kivy.properties import ObjectProperty

from kivy.graphics import Color, Line

class ArrowPointer(Widget):
    arrow_tip = ObjectProperty(None)

    def __init__(self, **kwargs):
        super(ArrowPointer, self).__init__(**kwargs)
        with self.canvas.after:
            Color (0, 0, 111)
            self.arrow_tip = Line()
        self.bind(pos=self._update_arrow_points)
        self._update_arrow_points(self, self.pos)

    def _update_arrow_points(self, object, pos):
        offset = 50
        x,y = pos
        self.arrow_tip.points = (x - offset, y - offset, x + offset, y + offset)
        print self.arrow_tip

class TestB(App):
    def build(self):
        return ArrowPointer()

if __name__ == '__main__':
    TestB().run()