Possible to implement env.render()?

[signalprime]

I have been playing around with implementing an updating chart with the gym.envs.classic_control.rendering object, as seen in https://github.com/openai/gym/blob/master/gym/envs/classic_control/pendulum.py

I added a variable 'self.data' to save the data, and

   def render(self, mode='human'):
        if self.viewer is None:
            print("Creating the rendering view:")
            self.viewer = rendering.Viewer(640, 480)
        fig = self.data.plot().get_figure()
        filename = './plot.png'
        fig.savefig(filename)
        plt.close('all')
        self.img = rendering.Image(filename, 640., 480.)
        self.imgtrans = rendering.Transform()
        self.img.add_attr(self.imgtrans)
        self.viewer.add_onetime(self.img)
        return self.viewer.render(return_rgb_array = mode =='rgb_array')

However only a white image window appears. The png file is fine, but it doesn't show in self.viewer. I've not been able to find much information on this. Any thoughts?