code: def _prepare_draw(self, view=None):
          
  
          if self._changed['pos']:
              self.pos_buf.set_data(self._pos)
              self._changed['pos'] = False
  
          if self._changed['color']:
              self.color_buf.set_data(self._color)
              self._program.vert['color'] = self.color_buf
              self._changed['color'] = False
  
          return True
docs: This method is called immediately before each draw.
  
          The *view* argument indicates which view is about to be drawn.