===== Rendering =====
  * Render an RNA molecule
<code>
set orthoscopic, on
bg_color white
set cartoon_ring_mode, 1
set cartoon_ring_transparency, 0.3
set cartoon_ring_color, green
color green
viewport 480, 480
ray
</code>

  * Make an animation for rotating molecule
<code>
cmd.movie.add_roll(2.0, axis='y', start=1)
set ray_trace_frames, 1
mpng snapshot/mov
</code>