Comment by riggsdk

BGFX (https://github.com/bkaradzic/bgfx) uses a different approach. You basically write your shader in a GLSL-like language but it's all just (either very clever or very horrible) macro expansions that handles all the platform differences. With that you get a very performant backend for OpenGL, WebGL, Vulkan, Metal, Direct3D 11 and 12 and Playstation. It's shader compiler program basically does minimal source level transformations before handing it over to the platforms' own shader compiler if available.