Code review comment for lp:~alan-griffiths/mir/spike-making-render_surfaces-an-example

> I think that we could probably get rid of the DisplayBufferCompositorFactory,
> if we had the lone function on DisplayBuffer look something like:
> void render(mg::DisplayBuffer&, SceneElementList& list);

It is this sort of suggestion that ought to be addressed *before* we republish these interfaces.