In accordance with federal law (http://n-gate.com/), I'm obligated to point out this Rust library, which does exactly this! https://github.com/gfx-rs/gfx. I worked on the second version of the API in 2014 and it's only gotten better since. The major thing this particular abstraction still doesn't solve is shaders: you need to write a shader per backend you support. Shader portability is a bit of a sticky problem.