def render_registration(self):
        '''
        Render pinned points on video frame as red rectangle.
        '''
        surface = self.get_surface()
        if self.canvas is None or self.df_canvas_corners.shape[0] == 0:
            return surface

        corners = self.df_canvas_corners.copy()
        corners['w'] = 1

        transform = self.canvas.shapes_to_canvas_transform
        canvas_corners = corners.values.dot(transform.T.values).T

        points_x = canvas_corners[0]
        points_y = canvas_corners[1]

        cairo_context = cairo.Context(surface)
        cairo_context.move_to(points_x[0], points_y[0])
        for x, y in zip(points_x[1:], points_y[1:]):
            cairo_context.line_to(x, y)
        cairo_context.line_to(points_x[0], points_y[0])
        cairo_context.set_source_rgb(1, 0, 0)
        cairo_context.stroke()
        return surface
Render pinned points on video frame as red rectangle.