Custom "graphics" engine?

Is it possible/trivial to add a new graphics engine without recompiling the whole library? I'm kind of stuck as to what methods the "graphics" is expected to have as there's no base class that I can see.

The issue names no files or tests; start by locating the library's graphics engine entry point and determining the methods an engine is expected to provide. The work is complete only when the extension contract is clear and a new graphics engine can be added without recompiling the whole library.

Written by the indexing model from the issue text.