Code review comment for lp:~kdub/mir/post-if-optimizable

> I thought that we were migrating the basic GL composition pass down into
> DisplayBuffer? So that if your scene is expressible exclusively in terms of a
> RenderableList then you can just dump it into render_and_post_update() and the
> DisplayBuffer will either GL or overlay?
>
> This would satisfy the ‘needs no negotiation’ criterion, and would seem to
> make the higher levels a little bit less complex?

So there's been a subtle shift since Renderable was reintroduced as it merged closer to the surface classes. Android can now know beforehand that it can reject the list (eg, if something is transformed to non-90degree).
The option to reject works nicely with mesa too, as mesa now does not have the burden of drawing with OpenGL, it can just reject, and the platform-independent GL compositor takes over.

So basically, the lp:~kdub/mir/overlay-gl-program branch just handles the quirky requirement that android has to draw the fallback with OpenGL. We do not require all the platforms to draw (just to reject), which is a bit nicer for the non-android DisplayBuffer implementations too.