Plots the volume and the control points.

def render(self, **kwargs):
        """ Plots the volume and the control points. """
        # Calling parent function
        super(VisVoxel, self).render(**kwargs)

        # Initialize a list to store VTK actors
        vtk_actors = []

        # Start plotting
        for plot in self._plots:
            # Plot control points
            if plot['type'] == 'ctrlpts' and self.vconf.display_ctrlpts:
                # Points as spheres
                pts = np.array(plot['ptsarr'], dtype=np.float)
                vtkpts = numpy_to_vtk(pts, deep=False, array_type=VTK_FLOAT)
                vtkpts.SetName(plot['name'])
                temp_actor = vtkh.create_actor_pts(pts=vtkpts, color=vtkh.create_color(plot['color']),
                                                   name=plot['name'], index=plot['idx'])
                vtk_actors.append(temp_actor)

            # Plot evaluated points
            if plot['type'] == 'evalpts' and self.vconf.display_evalpts:
                faces = np.array(plot['ptsarr'][1], dtype=np.float)
                filled = np.array(plot['ptsarr'][2], dtype=np.int)
                grid_filled = faces[filled == 1]
                temp_actor = vtkh.create_actor_hexahedron(grid=grid_filled, color=vtkh.create_color(plot['color']),
                                                          name=plot['name'], index=plot['idx'])
                vtk_actors.append(temp_actor)

        # Render actors
        return vtkh.create_render_window(vtk_actors, dict(KeyPressEvent=(self.vconf.keypress_callback, 1.0)),
                                         figure_size=self.vconf.figure_size)