Emacs: Ugly Redisplay Internals Hack
this article is very well written.
[Buttery Smooth Emacs By Daniel Colascione. At https://www.facebook.com/notes/daniel-colascione/buttery-smooth-emacs/10155313440066102 , accessed on 2016-11-30 ]
it discusses the internals of emacs's display engine, and shows how ancient it is. The English, as an essay, is also top notch.
but, by the way, i remember the author Daniel Colascione.