When creating graphic libraries you most likely end up dealing with
points and rectangles. If you're particularly unlucky, you may end
up dealing with affine matrices and 2D transformations. If you're
writing a graphic library with 3D transformations, though, you are
going to hit the jackpot:  4x4 matrices, projections, transformations,
vectors, and quaternions.

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're supposed to do that yourself, in your own canvas
implementation, which is the whole point of writing the library in
the first place.