Most of this stuff exists, in various forms, in other libraries, but it has the major drawback of coming along with the rest of those libraries, which may or may not be what you want. Those libraries are also available in various languages, as long as those languages are C++; again, it may or may not be something you want.
For this reason, I decided to write the thinnest, smallest possible layer needed to write a canvas library; given its relative size, and the propensity for graphics libraries to have a pun in their name, I decided to call it Graphene.
This library provides types and their relative API; it does not deal with windowing system surfaces, drawing, scene graphs, or input. You are supposed to do that yourself, in your own canvas implementation, which is the whole point of writing the library in the first place.