https://github.com/raysan5/raylib/blob/master/src/external/rlsw.h
rlsw v1.0 - An OpenGL 1.1-style software renderer implementation
rlsw is a custom OpenGL 1.1-style implementation on software, intended to provide all functionality available on rlgl.h library used by raylib, becoming a direct software rendering replacement for OpenGL 1.1 backend and allowing to run raylib on GPU-less devices when required.